WO2007087434A2

WO2007087434A2 - Method for the production of copper and zinc mono-and bi-metallic imidazolates

Info

Publication number: WO2007087434A2
Application number: PCT/US2007/002177
Authority: WO
Inventors: David M. Schubert
Original assignee: U.S. Borax Inc.
Priority date: 2006-01-28
Filing date: 2007-01-26
Publication date: 2007-08-02
Also published as: WO2007087434A3

Abstract

Improved methods for preparing copper and zinc imidazolates, M(C3H3N2)2 (M = Zn, Cu), and their C-substituted derivatives, including copper and zinc 2-methyl-imidazolates, 2- ethylimidazolates and benzimidazolates, by reaction of a copper or zinc source with an imidazole-containing compound in aqueous media in the absence of base, and preferably in the presence of an acid. The invention also provides novel copper-zinc bimetallic imidazolates. The copper and zinc imidazolate compounds are useful as biocides and biostats and in coatings systems.

Description

METHOD FOR THE PRODUCTION OF COPPER AND ZINC MONO- AND BIMETALLIC IMIDAZOLATES

Cross Reference to Related Applications

[0001] This application claims the benefit under 35 USC 119(e) of U.S. Provisional

Applications No. 60/763,192, filed January 28, 2006, and No. 60/785,468, filed March 24, 2006, which are incorporated in their entirety herein by reference.

Field of the Invention

[0002] This invention relates to improved methods for preparing copper and zinc imidazolates, M(CaHaN₂^, and their C-substituted derivatives, where M = Cu or Zn. The invention also relates to novel copper-zinc bimetallic imidazolates.

Background

[0003] Imidazole, C3H4N2, (ImH) is a readily available heterocyclic organic compound (see Scheme 1). It is a moderate Brønsted base that readily accepts a proton to produce the imidazolium cation 03N₂Hs⁺ (Im^⁺), which is stabilized by electron derealization. Imidazole can also be deprotonated by stronger bases to form the imidazolate anion C3N2H3^", (IπT), which also displays electron derealization. It is the imidazolate anion, Im^", which is present in zinc and copper imidazolates.

ImH₂ ⁺ ImH Im^"

Scheme 1

[0004] Imidazole forms a variety of very stable metal complexes. Metal complexes based on imidazole have been known since the 19^th century and the imidazolate anion has been recognized as a constituent of some metal complexes since at least the 1920s. These metal complexes include a family of metal imϊdazolates of the type MIm₂, where M includes copper and zinc.

[0005] Copper and zinc form stable divalent cations, Cu²⁺ and Zn²⁺, in aqueous solution that readily form complexes with nitrogen-donor ligands, such as ammonia, amines, and a variety of nitrogen-containing heterocycles. In copper and zinc imidazolates of the MIm₂ type (also known as metal bis(imidazolates)), the Im^" anion coordinates through nitrogen to the formally divalent metal. The structures of these compounds contain infinite chains in which each exo-bidentate Im^~ anion links two metal atoms. Since each metal atom bonds with four Im^" anions, each metal atom lies at the intersection of two infinite chains, forming a three-dimensional network. In ZnIm₂, the zinc atom is tetrahedral, whereas in Culm₂ the copper atom may be square planar, pseudotetrahedral, or both, depending on the specific polymorph.

[0006] The structure of zinc imidazσlate was determined by a single crystal X-ray diffraction study and reported in 1980. Copper imidazolate occurs as at least five distinct polymorphs, each having the CuIm₂ composition, but exhibiting unique structural arrangements in the extended network. These polymorphs have different colors, two being described as blue and the other three as green, olive green, and pink. The structure of one of the blue polymorphs was elucidated by a single crystal X-ray diffraction study and reported in 1960. The structures of the remaining polymorphs, except for the pink one, were determined only recently by ab initio reduction of X-ray powder diffraction (XRD) data. The green polymorph and the more recently described blue polymorph of copper imidazolate are particularly relevant to our disclosure.

[0007] The most commonly cited procedure for preparation of metal imidazolates is that described by Wang and Bauman. This method involves the reaction of a metal salt with imidazole in water in the presence of a strong base, such as sodium hydroxide. This procedure for the preparation of zinc and copper and zinc imidazolate involves balanced Equations 1 and 2, respectively.

Zn(ClO₃)₂ + 2 ImH + 2 NaOH 3-ZnIm₂ + 2 NaClO₃ + H₂O Eq. 1

Cu(NO₃)₂ + 2 ImH + 2 NaOH =>- CuIm₂ + 2 NaNO₃ + H₂O Eq. 2 [0008] Brandys, et al. prepared copper imidazolate by adding a solution of copper sulfate to a solution of imidazole followed by addition of a sodium hydroxide solution. Another procedure described in the literature for preparation zinc imidazolate involves reacting zinc acetylacetonate with imidazole for 12 hours at 160 ⁰C. Cornilescu, et al. described another procedure for preparation of zinc imidazolate involving the reaction of zinc salts with the glyoxal-formaldehyde-ammonia condensate. Masciocchi, et al. recently reported a variety of methods for the selective preparation of the copper imidazolate polymorphs. It is notable that none of these methods employ acid catalysis.

[0009] . The known procedures for the preparation of copper and zinc imidazolates are either only practical for laboratory-scale preparation of small quantities of copper and zinc imidazolates or require separations of byproduct salts that presents a disadvantage for larger scale manufacture of these compounds. Separation of byproduct salts from the desired metal imidazolate products requires additional steps and equipment and leads to byproduct disposal problems.

Summary of the Invention

[0010] In one aspect, the invention provides a method for preparing a metal imidazolate compound comprising reacting a source of metal, said metal selected from the group consisting of copper, zinc and mixtures thereof, with an imidazole-containing compound, said reaction being carried out in aqueous media in the absence of a strong base, thereby forming a metal imidazolate compound.

[0011] In another aspect, the invention provides a copper-zinc bimetallic imidazolate compound having the formula CuαZnδ(C3N2R²R⁴R⁵)2(a+i) or

R²R⁴'⁵)2(α+ή) where R², R⁴ and R⁵ = hydrogen, halogen, alkyl, aryl, alkoxy, aryloxy, carboxyl, nitro, cyano or imidazole, and R⁴'⁵ is a substituted or unsubstituted carbon group which forms a cyclic alkyl or aryl ring with the carbons at the 4 and 5 positions of the imidazolate ring.

[0012] In another aspect, the invention provides a copper-zinc bimetallic imidazolate compound according to claim 22 having an amber, tan, or brown color and a chemical formula of CuaZnlnx_t and a characteristic X-ray diffraction pattern as follows:

[0013] In yet another aspect, the invention provides a method of controlling the growth of algae comprising applying to said algae or to a substrate or material wherein algae might grow, a biostatic or biocidal amount of metal ϊmidazolate comprising zinc imidazolate, copper imidazolate, copper-zinc bimetallic imidazolate or a combination thereof, wherein said imidazolates comprise unsubstituted imidazolate, benzimidazolate 2-methylimidazolate, 2-ethylimidazolate or a mixture thereof.

[0014] In still another aspect, the invention provides for the use of zinc and copper imidazolates and their C-substituted derivatives as a biocide or biostat or for controlling the growth of algae.

[0015] In still another aspect, the invention provides coating compositions comprising a copper, zinc or bimetallic copper-zinc imidazolate compound in an aqueous or oil-based coating system.

[0016] In still another aspect, the invention provides for use of copper, zinc or bimetallic copper-zinc imidazolate compounds in an aqueous or oil-based coating system. Detailed Description of the Invention

[0017] This invention provides improved methods for preparing copper and zinc imidazolates, M(CsH₃Na)₂ (M = Zn, Cu), and their C-substituted derivatives. These copper and zinc imidazolates and their derivatives are prepared by reaction of a suitable source of copper and/or zinc with a suitable source of imidazole, or a C-substituted derivative thereof, in aqueous media in the absence of base and preferably in the presence of an acid. The invention also provides novel copper-zinc bimetallic imidazolate compounds.

[0018] Copper and zinc imidazolates, M(C₃IHyNb)₂ (M = Zn, Cu), and their C- substituted derivatives have many potential industrial applications. These compounds are water insoluble, chemically and thermally stable, and display unusual physical and spectroscopic properties, including UV fluorescence. They have potential applications as heterogeneous catalysts, biostats, and epoxy curing agents (see U.S. Patent No. 6,506,494 which is incorporated herein by reference). As additives for paints and plastics these metal imidazolates may provide biostatic effects, including inhibition of algal and fungal growth as well as antifouling effects. They may also provide desirable optical properties, including both color and fluorescent effects, e.g. for use as pigments in paints and plastics. Furthermore, their useful optical properties can be modulated by changing substituents on the imidazole moiety, by changing the copper-zinc ratio in mixed metal imidazolates, or, in the case of copper imidazolates, by controlling polymorph formation using the methods provided herein. The synthetic methods described in this invention could be used to design nano- or meso-porous metal-organic frameworks, for use in applications including the storage of gases, such as hydrogen.

[0019] Suitable sources of copper and zinc may include as non-limiting examples copper oxide, zinc oxide, copper hydroxide carbonate and zinc borate . Suitable acids may include as non-limiting examples strong acids, such as HCl and H2SO4, and weak organic and inorganic acids, including acetic acid, citric acid, and boric acid. Suitable sources of imidazole may include as non-limiting examples imidazole, imidazolium borates, such as imidazolium nonaborate (see U.S. Patent No. 6,919,036 which is incorporated herein by reference), and the C-substituted derivatives of imidazole. Such C-substituted derivatives of imidazole may include for example aryl-substituted imidazoles, such as benzimidazole, and alkyl-substituted imidazoles, such as 2-methylimidazole and 2-ethylimidazole. Preparation of zinc imidazolates

[0020] It was unexpectedly found that zinc oxide reacts directly with imidazole in hot water to produce zinc imidazolate, Znlπ_2. However, this reaction is slow and does not proceed to completion even after several days of continuous reflux in water. However, even more unexpectedly, it has been discovered that this reaction is efficiently catalyzed by the presence of acids (Equation 3).

H₃O⁺

ZnO + 2 ImH =>- ZnIm₂ + H₂O Eq. 3

[0021] This is unexpected since the formation of the imidazolate anion contained in this compound would reasonably be expected to require the presence of a relatively strong Brønsted base rather than an acid. In fact, the presence of even weak acids readily converts imidazole in aqueous solution to the stable imidazolium cation, ImEb⁺ (Scheme 1), which would not be expected to serve as an intermediate in the formation of zinc imidazolate compounds. Indeed, published methods for the preparation of zinc imidazolate invariably involve the use of strong base, or in one case, a zinc salt having basic counterions, quite the opposite of the use of acid catalysis in the preparation of zinc imidazolate or its C-substituted derivatives as described herein. Using the methods of this invention, zinc imidazolate and its C-substituted derivatives can be prepared efficiently and nearly quantitatively in large quantities by employing an industrially practical method of reacting zinc oxide directly with imidazole in water in the presence of a catalytic amount of any of a variety of strong or weak acids.

[0022] According to the technique generally employed in the examples provided herein, zinc oxide is suspended in a hot aqueous solution containing a catalytic amount of an acid followed by addition of a stoichiometric amount or slight stoichiometric excess of imidazole or C-substituted imidazole. However, as a practical matter, these reagents can be combined in any order. Due to the formation of soluble metal salts in the presence of acids it has been observed that, in general, higher levels of acid catalyst resulted in lower yields per batch, and increasingly so for stronger acids. Thus, for single batch preparations, the acid catalyst should be added at a low level. For example, an acetic acid concentration of 0.5% by weight was found to be sufficient to bring about the rapid conversion of a mixture of zinc oxide and imidazole to zinc imidazolate in a relatively concentrated hot aqueous mixture of these reagents. In this case, the yield of zinc imidazolate is typically 80-90% by weight based on metal oxide. The effect of acid concentration on yield is less important when this reaction is carried out in closed loop multiple batch or continuous process, since the reaction filtrate is then recycled and higher yields are obtained in all subsequent batches and the eventual conversion of reactants to products is nearly quantitative. In this case a higher level of acid catalyst can be used, for example 1% by weight acetic acid, in order to provide a more robust process that does require precise measurement of acid concentrations for each batch cycle. It should be noted that the methods described herein involving closed-loop processes produce only water as the byproduct and are thus more economically and environmentally favorable than previously known processes.

[0023] The acid-catalyzed reaction to produce zinc imidazolate from zinc oxide and imidazole is rapid. Reaction times of 20-30 minutes were generally employed to insure complete reaction. However, this may not be necessary as it was found that the reaction is essentially complete in less than ten minutes. Such rapid reactions are readily amenable to continuous reaction processes and this reaction could likely be conducted using a one or two- stage continuous process.

[0024] As demonstrated in Example 1, zinc imidazolate can be produced using a semi-continuous batch process. In this process, zinc imidazolate is prepared in individual batches in which the filtrate solution from each batches is recycled to the following batch, thus providing a closed loop process that does not generate waste. In this process a solution of 1% by weight acetic acid was employed as catalyst for the reaction. However, a wide variety of acids could be used. The product from each batch was found to be substantially pure zinc imidazolate by XRD analysis. Only the first batch contained a detectable trace amount of unreacted zinc oxide and subsequent batches appeared to pure crystalline phase products. The percentage yields from a series of closed loop reactions based on zinc oxide were 84.6%, 91.2%, 94.6%, 93.3, and 97.1%. The recovered yield is lower for the first batch first since some zinc remains in solution in the filtrate in the presence of acetic acid and imidazole. However, in subsequent batches the mother liquor is saturated with zinc and higher yields are obtained (average greater than 94.0% based on zinc oxide). Evaporation of the clear filtrate solution resulted in formation colorless crystals identified by single crystal X-ray diffraction as zinc diimidazole diacetate, Zn(η^! -CaH₄Na^Cn * -02CCHs)₂.

[0025] A variety of acids can be used to catalyze the reaction of zinc oxide with imidazole. These include strong acids, such as HCl and H₂SO₄, and weak organic and inorganic acids, including acetic acid, citric acid, and boric acid. In the case of boric acid we found that higher concentrations were needed to effectively catalyze this reaction. However, in a multi-batch or continuous process involving liquor recycle the use of boric acid catalyst is a practical option. It was also found that boric acid catalyst may be used in a latent form. For example, the zinc borate compound ZnO-3B₂θ₃-3H₂θ (known as an article of commerce as ZnO-3B₂θ₃*3.5H₂θ) reacts with imidazole in aqueous media to give zinc imidazolate quantitatively, as shown in Equation 4. Alternatively, imidazolium borates, such as imidazolium nonaborate, (ImH₂)₃B₉θ_t2(OH)₆, reacts with zinc oxide in aqueous media to produce zinc imidazolate, also quantitatively, as shown in Equation 5.

2ZnO-3B₂θ₃-3H₂O + 2 ImH + 4 H₂θ >- 2 ZnIm₂ + 6 B(OH)₃

Eq.4

2 (ImH₂)SB₉O₁₂(OH)₆ + 3 ZnO + 15 H₂O >- 3 ZnIm₂ + 18 B(OH)₃ Eq.

5

Methods for the preparation of selective polymorphs of copper imidazolate

[0026] Copper oxide can be reacted directly with imidazole in the absence of both acid and base as a synthetic method to prepare copper imidazolates. This uncatalyzed reaction of finely divided copper oxide with imidazole in hot aqueous media to produce copper imidazolate is more rapid than that of zinc oxide with imidazole at high slurry concentrations, requiring only about 30-60 minutes to proceed substantially to completion (Equation 6).

H₂O

CuO + 2 ImH >- green-CuIm₂ + H₂O Eq. 6

Δ, <l h

[0027] This reaction is also unexpected for the same reasons as explained above for zinc. When carried out in the absence of acid catalysts for relatively short reactions in boiling water, for example less than 24 hours, this reaction provides the green polymorph of copper imidazolate. This compound has an X-ray diffraction (XRD) pattern identical to that presented by Masciocchi et al. (see N. Masciocchi, S. Bruni, E. Caraiati, F. Cariati, S. Galli, and A. Sironi Inorg. Chem., 2001, 40, 5897-5905.) This green polymorph is converted to the blue polymorph of copper imidazolate by longer reactions times of several days duration in boiling water, as shown in Equation 7.

H₂O green-CuIni2 ^" blue-CuImz Eq. 7

Δ, days

[0028] This blue polymorph was also described by Masciocchi, et al. Although this blue copper imidazolate forms slowly in boiling water, the acid-catalyzed reaction of copper oxide with imidazole using the method of this invention provides this same blue polymorph of copper imidazolate directly with short reaction times (Equation 8).

H₃O⁺

CuO + 2 ImH >- blue-CuIm₂ + H₂O Eq. 8

Δ, <l h

H₃O⁺ green-CuIm2 ^- blue-Culm^ Eq. 9

Δ, <l h

[0029] As with zinc imidazolate, a variety of strong or weak acids may be used to catalyze the reaction of copper oxide with imidazole. As with the zinc system, higher acid concentrations lead to lower single batch yields of copper imidazolates. Thus, acid catalyst concentrations should be kept relatively for single batch preparations, but this is less important for multi-batch semi-continuous or continuous production of copper imidazolate. Furthermore, other sources of copper, such as copper hydroxide carbonate, Cu₂(OH)₂CO₃, can be employed as copper sources in the synthesis of copper imidazolates, as shown in Equation 10.

H₃O⁺

Cu₂(OH)₂CO₃ + 4 ImH >- 2 blue-CuIm₂ + 3 H₂O + CO₂ Eq. 10

Δ, <l h

Copper-zinc bimetallic imidazolate derivatives and methods for preparing same

[0030] It has also been discovered that reaction of a mixture of copper oxide and zinc oxide with imidazole produces not the expected mixture of copper imidazolate and zinc imidazolate, but rather novel bimetallic copper-zinc imidazolates. It has also been found that the acid catalysis methods described herein for the preparation of monometallic copper and zinc imidazolates are also applicable to the preparation of bimetallic copper-zinc imidazolates. Equation 11 expresses the general reaction that found useful for the preparation of copper- zinc bimetallic imidazolates having any desired copper to zinc ratio.

H₃O⁺ α CuO + 6 ZnO + 2(α+ό) ImH >- Cu₀ZnJm₂(O₊*,) + (a+b) H₂O Eq. 11

[0031] The resulting copper-zinc bimetallic imidazolates form a continuous solid solution series having a unique x-ray diffraction (XRD) pattern, indicating a novel crystal structure, over a broad composition range of copper-zinc ratios, from about 30% copper, 70% zinc to about 98% copper, 2% zinc. The XRD pattern and crystal structure of these compositions are distinctly different from pure zinc imidazolate or any of the pure copper imidazolate polymorphs. This solid solution series of compositions is represented as Cu_αZn₆(Im)₂(_α+i₎, where 0.3 < a < 0.98, a + b = 1, and Im is an imidazolate anion. At a > 0.98, the XRD pattern and crystal structure resemble the one of the blue polymorphs of pure copper imidazolate and at a less than approximately 0.3, the XRD pattern resembles pure zinc imidazolate.

[0032] These copper-zinc imidazolates possess chemical and physical properties that are different from the monometallic copper and zinc imidazolates. At low copper content, e.g. at a less than approximately 0.3 in the formula Cu_αZn6(Im)2(_σ+6)_;> bimetallic copper-zinc imidazolate resembles monometallic zinc imidazolate. However, with increasing copper content copper-zinc imidazolate becomes avocado green in color and displays a unique XRD pattern indicating a different and unique chemical structure. Bimetallic copper-zinc imidazolate remains green and unique by XRD up to high copper content, e.g. up to about α = 0.98.

[0033] For example, reaction of imidazole with a mixture of copper and zinc oxides containing 98% copper oxide and only 2% zinc oxide, in the presence of an acid catalyst such as a 1 % acetic acid solution, produces an avocado green colored copper-zinc imidazolate that displays an XRD pattern that is different from either zinc imidazolate or any of the copper imidazolate polymorphs. Microscopic examination of this product indicates that this is a single crystalline phase and elemental analysis confirms that it contain both copper and zinc in approximately the same ratio as the reactant mixture. Increasing the ratio of zinc oxide to copper oxide in the metal oxide reactant mixture, for example to 50% zinc oxide and 50% copper oxide, also produces a similar avocado green colored product. The XRD patterns for these bimetallic copper-zinc imidazolates are similar and change only slightly with changing proportions of copper and zinc until the reactant mixture contains about one third copper oxide, whereupon the XRD patterns begin to resemble that of pure zinc imidazolate. Also, when the copper oxide-zinc oxide reactant mixture contains significantly less than 2% zinc oxide, the product gives an XRD pattern resembling that of the blue polymorph of copper imidazolate.

[0034] A special case occurs in the copper-zinc bimetallic system when the copper- zinc molar ratio is approximately 2:1, respectively. It was found that mild hydrothermal treatment of a mixture of CuO, ZnO, and imidazole in an approximately 2:1 :6 mole ratio in aqueous media results in formation of a unique crystalline compound of composition Cu₂ZnIm₄. This compound, which exhibits a unique XRD pattern, presents itself as a brown powder, microscopic examination of which reveals amber colored tetragonal single crystals. The structure of this compound was determined by a single-crystal X-ray diffraction study and was found to contain tetrahedral zinc and square plane copper atoms linked together by coordination with the nitrogen atoms of imidazolate moieties. The zinc atoms are surrounded by four imidazolate nitrogen atoms, whereas the copper atoms are surrounded by only two imidazolate nitrogen atoms at trans position of the copper square planes. The other two trans positions of each copper square plane are occupied by copper atoms to form parallel linear one dimensional chains of copper atoms with Cu-Cu intermetallic distances of 3.16 A along the chains. Charge balance considerations indicate that the copper in this compound has been reduced from Cu(II) to Cu(I). This Cu(I) compound can also be prepared by mild hydrothermal treatment of the avocado green Cu₂ZnImS, descried above. Some quantities of Cu₂ZnIm₄ are formed in the stoichiometric reaction of CuO, ZnO, and imidazole (2:1:4 mole ratio, respectively) under mild hydrothermal conditions, but significantly higher yields are obtained when a 50% or greater molar excess of imidazole is present, suggesting that imidazole serves as the reductant for copper in this system, possibly involving CUaZnIm₆ as an intermediate. Method for the preparation of C-substituted copper, zinc, and copper-zinc imidazolate derivatives

ϊ[0035] The methods described above can be applied to the preparation of derivative zinc, copper and bimetallic copper-zinc imidazolates bearing a variety of substituents at the 2, 4, and 5 positions of the imidazole ring (see Figure 1).

Figure 1. C-substituted imidazoles

[0036] R², R⁴ and R⁵ in Figure 1 can be selected from a wide variety of substitution groups including hydrogen, halogen, alkyl, aryl, alkoxy, aryioxy, carboxyl, nitro, cyano, or other imidazole groups. Alternatively, R⁴ and R⁵ can be replaced with R⁴'⁵, a substituted or unsubstituted carbon group which forms a cyclic alkyl or aryl ring with the carbons at the 4 and 5 positions of the imidazolate ring.

¹ [0037J For example 2-methylimidazole and 2-ethylimidazole were shown to react with copper oxide or zinc oxide, or mixtures thereof, under essentially identical conditions as unsubstituted imidazole to give the corresponding alkyl-substituted products, M(2-Rϊm)₂ (M = Cu, Zn; R = Me, Et). Also, copper oxide or zinc oxide, or mixtures thereof, react with the 4,5-substituted imidazole known as benzimidazole, i.e. C₃H₂N₂C₄H₄ or C₃H₂N₂R⁴'⁵ (Figure 2), under acid-catalyzed conditions to produce the corresponding metal benzimidazolate products, i.e. M(C₃HN₂C-JiO₂ or M(C₃HN₂R⁴'⁵^, where M = Cu, Zn; R⁴'⁵ is a C₄H₄ carbon group which forms a benzene ring attached at the 4 and 5 positions of the imidazolate ring. Other cyclic rings could be similarly attached at the 4 and 5 positions of the imidazolate ring.

Figure 2. Benzimidazole [0038] Changing the C-substitution of metal imidazolates alters their physical properties in potentially useful ways. For example, for zinc imidazolates, changing the substitution at the 2-position from hydrogen to methyl or ethyl significantly enhances the UV fluorescence exhibited by these compounds. In the case of copper imidazoles, changing the imidazole C-substitutes can alter color. For example, copper benzimidazolate is brown. Copper imidazolate has been reported to display catalytic activity. Varying the C- substitution of metal imidazolates may provide a means of modulating or fine tuning the catalytic activity of these compounds.

Biostatic activity of copper and zinc imidazolates

[0039] Small quantities of zinc, and copper imidazolates were added to algae cultures, which were incubated along side cultures containing no additive. After incubation it was found that copper imidazolate acted as a biocide against algae and zinc imidazolates acted as a biostat against algal growth.

[0040] The antimicrobial properties of copper and zinc imidazolate were evaluated in aqueous solutions at 100 and 1,000 ppm concentrations against two species of blue-green algae. The results of these tests showed that both compounds exhibit algaestatic activity at concentrations of 100 ppm, the lowest level tested. Copper imidazolate also showed moderate algaecidal activity at 1 ,000 ppm. ^•

Examples

[0041] Example 1. Synthesis of zinc imidazolate by a semi-continuous process. The process involves preparing zinc imidazolate in subsequent batches in which the weak liquor from the proceeding batch is used in each following batch, resulting in no waste products. A small excess of imidazole is employed in the first batch and then stoichiometric amounts of imidazole are added in subsequent batches. Batch 1: A flask was charged with 80 g 1% aqueous acetic acid and 8.14 g (0.10 mole) zinc oxide. This mixture was brought to a boil and 14.0 g (0.206 mole) imidazole was added with stirring. After 30 minutes the mixture was filtered and the filtrate solution was returned to the original reaction flask. The solids recovered by filtration were washed with water and dried at 70 ⁰C, giving 16.9 g zinc imidazolate,

or 84.6% yield based on zinc oxide. Batch 2: To the filtrate solution recovered from batch 1 was added 10 g 1% acetic acid make-up solution and the solution was returned to a boil. To this solution was added 8.14 g (0.10 mole) zinc oxide and 13.62 g (0.20 mole) imidazole with stirring. After 30 minutes the mixture was filtered, the filtrate solution was returned to reaction flask, and the filtered solids were washed with water and dried at 70 ⁰C₅ giving 18.2 g zinc imidazolate, Zn(C₃H₃N₂)₂, or 91.2% yield based on zinc oxide. Subsequent batches: The procedure for batch 2 was repeated three more times, providing product weights of 18.9, 18.6, and 19.4 g, or 94.6%, 93.3, and 97.1% yields, respectively. The products were identified as substantially pure zinc imidazolate, Zn(C₃HsN₂)2_> by the characteristic X-ray diffraction pattern of this compound.

[0042] Example 2. Acetic acid-catalyzed batch synthesis of zinc imidazolate. To a hot stirred suspension of 25.0 g (0.307 mole) zinc oxide in 200 mL 0.5% aqueous acetic acid was added 42.7 g (0.627 mole) imidazole. The mixture was heated to a boil and maintained under reflux with stirring for 20 minutes. The solid product was separated by filtration, washed with water, and dried at 105 ⁰C, to give 57.72 g (94.2% yield) of white micrbcrystalline powder identified as zinc imidazolate, Zn(CsHsN₂)₂, by its characteristic X- ray diffraction pattern. No unreacted zinc oxide was detected in the product.

[0043] Example 3. Boric acid-catalyzed synthesis of zinc imidazolate. A flask was charged with 35.74 g (0.525 moles) imidazole, 30.915 g (0.50 moles) boric acid, and 200 mL water. The mixture was heated to 95 ⁰C and 20.35 g (0.25 mole) zinc oxide was added. The mixture was boiled for 10 minutes and the white solid product were separated by filtration, washed with water, and dried at 105 ⁰C. The resulting product was identified as zinc imidazolate, Zn(CsHsN₂^, by its characteristic XRD.

[0044] Example 4. Citric acid-catalyzed synthesis of zinc imidazolate. To a hot stirred suspension of 12.5 g (0.154 mole) zinc oxide in 100 mL 5% aqueous citric acid solution was added 21.3 g (0.313 mole) imidazole. The mixture was heated to a boil and maintained under reflux with stirring for 30 minutes. The solid product was separated by filtration, washed with water, and dried at 105 ⁰C, to give 25.04 g (82% yield) of white microcrystalline powder identified as zinc imidazolate, Zn(CsHsN₂)₂, by its characteristic X- ray diffraction pattern. No unreacted zinc oxide was detected in the product. [0045] Example 5. Preparation of zinc imidazolate from zinc borate. A flask was charged with 200 g water, 53.22 g (0.125 mole) zinc borate of composition 2Zn03B₂θ3^#3H2θ (note that this form of zinc borate is usually referred by the composition 2ZnO3B₂C>3^»3.5H₂0 as a commercial article). The resulting slurry was heated to 95 ⁰C and 35.74 g (0.525 mole) imidazole was added and the mixture was brought to a boil. After maintaining under reflux for 30 minute, the solid product was separated by filtration, washed with water, and dried at 105 ⁰C (8.55 g, 17% yield). The product was identified as zinc imidazolate, Zn(C₃H3N2)2, by its characteristic X-ray diffraction pattern and contained no detectable unreacted zinc borate or zinc oxide.

[0046] Example 6. Preparation of zinc imidazolate from imidazolium nonaborate.

To a stirred suspension of 4.07 g (0.050 mole) zinc oxide in 400 mL water at 95 ⁰C was added 61.06 g (0.102 mole) imidazolium nonaborate,

The mixture was heated to a boil and maintained under reflux for 30 minutes. The resulting solid product was separated by filtration, washed with water, and dried at 105 ⁰C (4.95 g, 50% yield). The product was identified as zinc imidazolate,

by its characteristic X-ray diffraction pattern. No detectable zinc borate or zinc oxide was present in the product.

[0047] Example 7. Synthesis of zinc 2-methylimidazolate. To a stirred suspension of and 4.07 g (0.050 mole) zinc oxide in 50 g 1% aqueous acetic acid solution at 95 ^PC was added 8.37 g (0.102 moles) 2-methylimidazole. The mixture was brought to a boil and maintained under reflux for 30 minutes. The resulting solid product was separated by filtration, washed with water, and dried at 105 ⁰C to give 10.80 g of a white microcrystalline powder product (95% yield). This product gave a unique X-ray diffraction pattern and contained no detectable unreacted zinc oxide.

[0048] Example 8. Synthesis of zinc 2-ethylimidazolate. To a stirred suspension of and 4.07 g (0.05 mole) zinc oxide in 50 g 1% aqueous acetic acid solution at 95 ⁰C was added 9.81 g (0.102 moles) 2-ethylimidazole. The mixture was brought to a boil and maintained under reflux for 30 minutes. The resulting solid product was separated by filtration, washed with water, and dried at 105 ⁰C to give 12.32 g of a white microcrystalline powder product (96% yield). This product gave a unique X-ray diffraction pattern and contained no detectable unreacted zinc oxide. [0049] Example 9. Synthesis of zinc benzimidazolate. To a stirred suspension of 4.07 g (0.050 mole) zinc oxide in 100 g 0.5% aqueous acetic acid was added 12.0 g (0.102 mole) benzimidazole. The mixture was brought to a boil and maintained under reflux for 40 minutes. The resulting solid product was separated filtration, washed with water, and dried at 105 ⁰C to give 13.79 g of a white microcrystalline powder product (92% yield). The product gave a unique X-ray diffraction pattern and contained no detectable unreacted zinc oxide.

[0050] Example 10. Synthesis of green copper imida∑olate from copper oxide. To a hot stirred suspension of 3.98 g (0.100 mole) copper oxide in 100 mL water was added 7.15 g (0.105 mole) imidazole. The mixture was maintained at 100 ⁰C with stirring for one hour. The resulting solid product was separated by filtration, washed with water, and dried in a 105 ⁰C oven to give 7.30 g of a forest green microcrystalline powder product (74% yield). The product exhibited a characteristic X-ray diffraction pattern of green copper imidazolate. A small amount of unreacted copper oxide was present in the product.

[0051] Example 11. Synthesis of blue copper imidazolate from copper oxide. To a hot stirred suspension of 3.98 g (0.05 mole) copper oxide in 100 mL 2.0% aqueous acetic acid was added 7.15 g (0.105 mole) imidazole. The mixture was maintained at 100 ⁰C with strong stirring for one hour, during which time the slurry viscosity increased significantly. The resulting solids were separated by filtration, washed with water, and dried in a 105 ⁰C oven to give a sky blue microcrystalline product having a filiform morphology (6.91 g, 70% yield). The product exhibited the characteristic X-ray diffraction pattern of blue copper imidazolate. A small amount of unreacted copper oxide was present in the product.

[0052] Example 12. Synthesis of blue copper imidazolate from copper hydroxide carbonate. To a hot stirred suspension of 5.53 g (0.025 mole) Cu₂(OH)₂CO₃ in 100 mL 2.0% aqueous acetic acid was added 7.15 g (0.105 mole) imidazole. The mixture was maintained at 100 ⁰C with strong stirring for one hour, during which time the slurry viscosity increased significantly. The resulting solid product was separated by filtration, washed with water, and dried in a 105 ⁰C oven. The sky blue microcrystalline product having a filiform morphology (5.31 g, 54% yield) exhibited the characteristic X-ray diffraction pattern of blue copper imidazolate. Some unreacted copper oxide was present in the product.

[0053] Example 13. Synthesis of copper 2-methylimidazolate. To a stirred slurry of

9.95 g (0.125 mole) copper oxide in 100 mL 2% aqueous acetic acid at 95 ⁰C was added 20.93 g (0.255 mole) 2-methylimϊdazole. The mixture was brought to a boil and maintained under reflux for one hour. The resulting slurry was filtered and the solids washed with water and dried at 105 ⁰C to give a green powder product (20.24 g, 72% yield). The product gave a unique X-ray diffraction pattern and was confirmed to have the composition of copper 2- methylimidazolate, Cu[C3H2N2(CH3)]2, by elemental analysis. A small amount of unreacted copper oxide was present in the product

[0054] Example 14. Synthesis of copper 2-ethylimidazolate. To a stirred slurry of

9.95 g (0.125 mole) copper oxide in 100 mL 2% aqueous acetic acid at 95 ⁰C was added 25.24 g (0.263 mole) 2-ethylimidazole. The mixture was brought to a boil and maintained under reflux for several hours. The resulting slurry was filtered and the solids washed with water and dried at 105 ⁰C to give a brown powder. The product (23.92 g, 75% yield) gave a unique X-ray diffraction pattern and was confirmed to have the composition of copper 2- ethylimidazolate,

by elemental analysis. Some unreacted copper oxide was present in the product.

[0055] Example 15. Synthesis of copper benzimidazolate. To a stirred suspension of

3.98 g (0.050 mole) copper oxide in 50 g 2% aqueous acetic acid at 95 ⁰C was added 12.05 g (0.102 mole) benzimidazole. This mixture was heated to a boil and maintained under reflux for one hour. The resulting solid product was separated by filtration, washed with water and dried at 105 ⁰C to give a brick red microcrystalline powder. This product (12.56 g, 84% yield) gave a unique X-ray diffraction pattern. Some unreacted copper oxide was present in the product.

[0056] Example 16. Synthesis of copper-zinc imidazolate containing approximately

25/75 mole ratio of copper to zinc. To a stirred suspension of 3.98 (0.050 mole) copper oxide and 12.21 g (0.150 mole) zinc oxide in 200 g 1% aqueous acetic acid at 95 ⁰C was added 28.59 g (0.420 mole) imidazole. The mixture was heated to a boil and maintained under reflux for 1.5 hours. The resulting solid product separated by filtration, washed with water, and dried at 105 ⁰C to give an avocado green microcrystalline product (35.36 g, 89% yield). This product gave a unique X-ray diffraction pattern and was found to have the approximate composition Cuo.₂sZno.7₅(C3H3N2)2 by elemental analysis. [0057] Example 17. Synthesis of copper-zinc imidazolate containing approximately

50/50 mole ratio of copper to zinc. To a stirred suspension of 9.54 (0.120 mole) copper oxide and 6.51 g (0.080 mole) zinc oxide in 200 g 1% aqueous acetic acid at 95 ⁰C was added 28.59 g (0.420 mole) imidazole. The mixture was heated to a boil and maintained under reflux for 1.5 hours. The resulting solid product separated by filtration, washed with water, and dried at 105 ⁰C to give an avocado green microcrystalline product (34.66 g, 87% yield). This product gave a unique X-ray diffraction pattern and was found to have the approximate composition Cuo.₅Zno.₅(C₃H₃N2)2 by elemental analysis.

[0058] Example 18. Synthesis of copper-zinc imidazolate containing approximately

80/20 mole ratio of copper to zinc. To a stirred suspension of 12.73 g (0.160 mole) copper oxide and 3.26 g (0.040 mole) zinc oxide in 200 g 1% aqueous acetic acid at 95 ⁰C was added 28.59 g (0.420 mole) imidazole. The mixture was heated to a boil and maintained under reflux for 1.5 hours. The resulting solid product separated by filtration, washed with water, and dried at 105 ⁰C to give an avocado green microcrystalline product (29.57 g, 75% yield). This product gave a unique X-ray diffraction pattern and was found to have the approximate composition Cuo.₈Zno_.2(C₃H3N2)2 by elemental analysis. The X-ray diffraction pattern is shown in Table 1.

Table 1

[0059] Example 19. Synthesis of copper-zinc imidazolate containing approximately

95/5 mole ratio of copper to zinc. To a stirred suspension of 15.11 (0.180 mole) copper oxide and 0.81 g (0.010 mole) zinc oxide in 200 g 1% aqueous acetic acid at 95 ⁰C was added 28.59 g (0.420 mole) imidazole. The mixture was heated to a boil and maintained under reflux for 1.5 hours. The resulting solid product separated by filtration, washed with water, and dried at 105 ⁰C to give an avocado green microcrystalline product (28.31 g, 72% yield). This product gave a unique X-ray diffraction pattern and was found to have the approximate composition Cuo.8Zno.2(C3H3N2)2 by elemental analysis.

[0060] Example 20. Procedure for assessing antimicrobial activity against blue- green algae. Two species of blue-green algae were used in these tests, Gloeocapsa sp 795 and Gloeocapsa alpicola 1598. The algae culture of Gloeocapsa sp 795 was grown on Allen's medium containing the following ingredients per liter of de-ionized water: 0.0375 g K₂HPO₄, 0.0375 g MgSO₄ -7H₂O₅ 0.020 g Na₂CO₃, 0.025 g CaCl₂-2H₂O, 0.085 g Na₂SiO₃, 1.2 g citric acid, and 1 mL trace element solution. The trace element solution contained the following ingredients per liter of de-ionized water: 97 mg FeCl₃-OH₂0, 41 mg MnCl₂»4H₂O, 5 mg ZnCl₂, 2 mg CoCl₂*2H₂O, and 4 mg Na₂MoO₄^H₂O. The algae culture of Gloeocapsa alpicola 1598 was grown on #N Bold medium, containing the following ingredients per liter of de-ionized water:^;0.75 g NaNO₃, 0.025 g CaCl₂ ^«2H₂O, 0.075 g MgSO₄-7H₂O, 0.075 g K₂HPO₄, 0.175 g KH₂PO₄, 0.025 g NaCl, 0.00015 mg vitamin B12, and 6 mL trace element solution. The media was autoclaved and the copper and zinc imidazolate test compounds were incorporated into media after sterilization. These test compounds were evaluated separately at two different levels: 100 ppm and 1,000 ppm. Negative controls had no test compounds incorporated into the medium. Each sample was inoculated with a 7 day growing algae culture to achieve a final concentration 1x10⁵ cfu/ml. Samples were incubated at 25 ° C for 21 days under a light-dark cycle of 12-12 hours. Two detection methods were used to evaluate algaecidal efficacy: visual observation/ranking and microbial plate counts on agar medium. Results generated by a visual observation/ranking method showed that each test compounds at both of the two levels were sufficient to inhibit visible growth of both species of algae (samples, containing the test compounds were clear, colorless solutions in contrast controls, which were green). The plate count method showed that zinc imidazolate at 100, and 1,000 ppm, and copper imidazolate at 100 ppm were biostatic, while copper imidazolate at 1,000 ppm provided a moderate biocidal effect with two log reduction in microbial populations.

[0061] Example 21: Preparation of green Cu_∑Znflm)^ Zinc oxide (8.14 g, 0.10 mole) and CuO (15.9 g, 0.20 mole) was suspended in 100 g of 1% aqueous acetic acid. This mixture was heated to 90 ⁰C and 42.0 g (0.62 mole) imidazole added. The mixture was then heated to a boil and maintained under reflux for 30 minutes. The resulting solids were separated by filtration, washed with water, and dried at 105 ⁰C to give a brilliant avocado green microcrystalline powder. Elemental analysis showed that this product had the approximate composition Cu₂Zn (Im)₆. The compound exhibited an X-ray diffraction pattern similar to other members of the Cu_aZn₆(hn)2(_β+6) series.

[0062] Example 22: Hydrothermal preparation at 120 ⁰C Cu_∑Znlntφ Zinc oxide

(0.81 g, 0.01 mole) and CuO (1.63 g, 0.02 moles) was mixed with 10 g of 1% aqueous acetic acid and 4.17 g (0.061 mole) imidazole. This mixture was heated at 120 ⁰C overnight in a thick- walled borosilicate glass pressure tube. A plug of consolidated brown powder formed on the bottom of the tube and numerous well-formed amber crystals ranging in size up to several tenths of a millimeter adhered to the walls of the tube above the consolidated solid. The material was removed from the tube, washed with water and dried at 105 ⁰C. Samples of the larger well-formed crystals were mechanically separated from the mixture and one crystal was used for single crystal structure determination, revealing a compound having linear -Cu- Cu- chains. A sufficient number of amber crystals were separated from the mixture and ground to a powder to obtain an X-ray powder diffraction pattern for this bulk material, which matched exactly with the pattern generated from the single-crystal X-ray data, confirming that single crystal used for structure determination was representative of the bulk material. The powder X-ray diffraction pattern obtained for the consolidated solids removed from the bottom of the tube also matched the pattern of the single crystals, showing this to be a microcrystalline form of the same material. This was also confirmed by microscopic examination of this material, where 0.98 > a >0.30.

70 [0063] Example 23: Hydrothermal preparation at 180 ⁰C of bulk samples ofCu₂ZnIni₄ containing linear copper chains. Zinc oxide (0.81 g, 0.01 mole) and CuO (1.63 g, 0.02 moles) was mixed with 10 g of 1% aqueous acetic acid and 4.17 g (0.061 mole) imidazole. This mixture was heated in a Teflon-lined stainless steel pressure vessel at 180 ⁰C for 48 hrs. The resulting solids were separated by filtration, washed with water, and dried at 105 ⁰C to give 5.24 g (88% yield based on metals) of an amber-brown microcrystalline powder. The X-ray diffraction pattern of this material was identical to the pattern exhibited by Cu₂ZnIiri₄ prepared according to Example 22, as well as the pattern generated from the single-crystal X-ray data obtained from a single amber crystal of Cu₂ZnIm₄ containing copper chains.

Table 2

[0064] The methods of this invention provide a practical process for the preparation and industrial scale manufacture of metal imidazolates, also known as metal bis(imidazolates), having potential technological importance. An advantage of the methods disclosed herein is the direct preparation of metal imidazolates from metal oxides under mild conditions with the elimination of waste byproducts, allowing for more practical and environmentally acceptable large-scale industrial manufacture. This novel process utilizes an unanticipated acid catalysis in a closed loop process to give metal imidazolates and no waster byproducts. Since copper imidazolate occurs as several polymorphs, a method for controlling the formation of some specific polymorphs of this compound is also provided. Furthermore, these methods can be used to prepare a series of novel copper-zinc bimetallic imidazolates having any desired copper to zinc ratio. In addition, these methods can also be applied to the preparation of a wide range of substituted derivatives of mono- and bi-metallic copper and zinc imidazolates. Furthermore, these compounds exhibit useful biostatic properties of commercial value. The metal imidazolates described herein are water insoluble, chemically and thermally stable, and display and range of attractive colors, making them of interest for use as pigments for paints and plastics. Metal imidazolates have also been shown to act as latent epoxy curing agents and also to display catalytic activity. The methods described herein can be used to modify metal imidazolates in ways that may be useful to modulate epoxy curing, biostatic, and catalytic activity.

[0065] Examples of the Use of Copper and Copper-Zinc Imidazolates as Color

Pigments in Coatings. Coatings were prepared by dispersing powdered metal imidazolates into an exterior gloss alkyd white tint base (PPG Olympic Premium Exterior Gloss Alkyd White 73710), as described in the following examples:

[0066] Example 24: Example of coatings preparation using copper-zinc imidazolate as Color Pigment. A pre- weighed amount (5.4 grams) of avocado green copper- zinc imidazolate, CUaZnIm₆ (see Examples 16-19 and 21), screened to -325 U.S. mesh, was dispersed into 200 grams of the white tint base. Dispersal was accomplished using a using a Dispermat high speed mixer running at 2,000 rpm for 10 minutes. Samples of the coating were prepared by drawing down with a drawdown bar onstandard drawdown sheets. The final dried coating samples were light green and had good gloss (Gloss: 60° gloss = 57.5; 85° sheen = 81.2; Lab color: L = 90.90, a = -0.64, b = 0.46) .

[0067] Example 25: Example of coatings preparation using copper imidazolate as

Color Pigment A pre- weighed amount (5.4 grams) of the brick red copper benzimidazolate, Cu(BzIm)₂, screened to -325 U.S. mesh, was dispersed into 200 grams of the white tint base. Dispersal was accomplished using a using a Dispermat high speed mixer running at 3,000 rpm for 10 minutes. Drawdowns were prepared on standard drawdown sheets the final dried coating samples were salmon color and had good gloss (60° gloss = 69.2, 85° sheen = 87.4; Lab color: L = 71.12, a = 14.83, b = 9.53).

[0068] Various changes and modifications of the invention can be made and to the extent that such changes and modifications incorporate the spirit of this invention, they are intended to be included within the scope of the appended claims. The patents cited herein are incorporated by reference in their entirety.

Claims

1. A method for preparing a metal imidazolate compound comprising of reacting a source of metal, said metal selected from the group consisting of copper, zinc and mixtures thereof, with an imidazole-containing compound, said reaction being carried out in aqueous media in the absence of a base, thereby forming a metal imidazolate compound.

2. The method of claim 1 wherein the imidazole-containing compound comprises imidazole, imidazolium borate, C-substituted derivatives of imidazole, or mixtures thereof.

3. The method of claim 2 wherein the C-substituted derivatives of imidazole comprise alkyl-substituted imidazole compounds and aryl-substituted imidazole compounds.

4. The method of claim 3 wherein the alkyl-substituted imidazole compounds comprise 2-methylimidazole or 2-ethylimidazole.

5. The method of claim 3 wherein the aryl-substituted imidazole compounds comprise benzimidazole.

6. The method of claim 1 wherein the. source of metal is zinc oxide, zinc borate, copper oxide, copper hydroxide carbonate, or a combination thereof.

7. The method of claim 1 wherein the reaction is carried out in the presence of an acid.

8. The method of claim 7 wherein the acid is a strong acid.

9. The method of claim 8 wherein the strong acid comprises hydrochloric acid, sulfuric acid or mixtures thereof.

10. The method of claim 7 wherein the acid is a weak acid.

11. The method of claim 10 wherein the weak acid comprises acetic acid, boric acid, citric acid or mixtures thereof.

12. The method of claim 1 wherein the metal imidazolate compound is a bimetallic copper-zinc imidazolate.

13. The method of claim 12 wherein the bimetallic copper-zinc imidazolate has a formula of CuαZni(Im)2(o+i) , wherein 0.3 < a < 0.98, a + b = \, and Im is an imidazolate anion.

14. The method of claim 13 wherein the imidazolate anion is a C-substituted imidazolate anion.

15. The method of claim 12 wherein the reaction is carried out at a temperature at or below about 100⁰C and the bimetallic copper-zinc imidazolate is a green copper-zinc imidazolate having a characteristic X-ray diffraction pattern as follows:

16. The method of claim 12 wherein the mole ratio of copper to zinc is about 2:1, and the reaction is carried out at a temperature above about 100⁰C, and the bimetallic copper-zinc imidazolate is an amber or tan colored copper-zinc imidazolate having a chemical formula of C^ZnIm₄.

17. The method of claim 16 wherein the bimetallic copper-zinc imidazolate has a characteristic X-ray diffraction pattern as follows:

18. The method of claim 1 wherein copper oxide is reacted with imidazole in hot aqueous media in the absence of acid catalyst for a period of less than 24 hours, thereby forming the green polymorph of copper imidazolate, green-Cu(C3N2H3)2.

19. The method of claim 1 wherein copper oxide is reacted with imidazole in hot aqueous media in the presence of acid catalyst, thereby forming the blue polymorph of copper imidazolate, MUe-Cu(CsN₂Hs)₂.

20. The method of claim 1 wherein zinc borate is reacted with imidazole, thereby forming zinc imidazolate, Zn(C₃N₂Hs)₂.

21. The method of claim 1 wherein zinc oxide is reacted with imidazolium borate, thereby forming zinc imidazolate, Zn(CsN₂Ha)₂.

22. A copper-zinc bimetallic imidazolate compound having the formula Cu_αZni(C₃N₂R²R⁴R⁵)_2(α+6) or

^where R²= ^R4 ^d R⁵ = hydrogen, alkyl, aryl, alkoxy, aryloxy, halogen, carboxyl, nitro, cyano or imidazole and R⁴'⁵ is a substituted or unsubstituted carbon group which forms a cyclic alkyl or aryl ring with the carbons at the 4 and 5 positions of the imidazolate ring.

23. A copper-zinc bimetallic imidazolate compound according to claim 22, wherein R², R⁴ and R⁵ are each selected from the group consisting of hydrogen, methyl and ethyl.

24. A copper-zinc bimetallic imidazolate compound according to claim 22 having the formula CuαZni(C3N2R²R^4>5)2(β+A) where C₃NIR²R⁴'⁵ is benzimidazolate, and a+b=l.

25. A copper-zinc bimetallic imidazolate compound according to claim 22 wherein 0.3 < a < 0.98, a + b = l, and the bimetallic copper-zinc imidazolate is a green copper-zinc imidazolate having a characteristic X-ray diffraction pattern as follows:

26. A copper-zinc bimetallic imidazolate compound according to claim 22 having an amber, tan, or brown color and a chemical formula of CuaZnlnu and a characteristic X-ray diffraction pattern as follows:

27. A method of controlling the growth of algae comprising applying to said algae or to a substrate or material wherein algae might grow, a biostatic or biocidal amount of metal imidazolate comprising zinc imidazolate, copper imidazolate, copper-zinc bimetallic imidazolate or a combination thereof, wherein said imidazolates comprise unsubstituted imidazolate, benzimidazolate 2-methylimidazolate, 2-ethylimidazolate or a mixture thereof.

28. A coatings composition comprising a copper, zinc or bimetallic copper-zinc imidazolate compound in an aqueous or oil-based coating system.