WO1988006154A1

WO1988006154A1 - Polymetallic molecular systems with ferromagnetic properties

Info

Publication number: WO1988006154A1
Application number: PCT/FR1988/000080
Authority: WO
Inventors: Olivier Kahn; Pei Yu; Yves Journaux; Michel Verdaguer
Original assignee: Societe Nationale Elf Aquitaine; Centre National De La Recherche Scientifique (Cnrs
Priority date: 1987-02-13
Filing date: 1988-02-15
Publication date: 1988-08-25
Also published as: FI893796A0; FR2610927A1; FR2610927B1; JPH02502181A; EP0346368A1

Abstract

Molecular systems formed from ordered heterometallic chains containing A and B ions with different spins, connected by bis-bidentate ligands which, due to their substituent (s), are capable of creating a strong steric hindrance around the B ion, which has the weaker spin, or of establishing the interaction with the A ion of an adjacent chain.

Description

Polymetallic molecular systems with ferromagnetic properties.

The invention relates to polymetallic molecular systems, more especially heterometallic chains endowed in particular with permanent magnetization properties.

It also relates to a process for the synthesis of such systems and their applications in particular as ferro-magnets. One of the major challenges in the field of molecular materials lies in the synthesis of molecular systems with permanent magnetization below a certain critical temperature.

The work of the inventors in this field has led them to develop a strategy allowing them to synthesize molecular systems having this property of permanent magnetization at low temperature.

This strategy is based on the development of means making it possible to carry out strong anti-ferromagnetic interactions between different metal ions in one-dimensional systems and means making it possible to ensure ferromagnetic interactions between adjacent chains.

The molecular systems of the invention are characterized in that they are formed of ordered heterometallic chains in which the basic molecular unit corresponds to the formula ABL.xL 'in which - A and B are bivalent ions of different spins, A being chosen from Mn (II) whose spin is 5/2, Fe (II) from spin 2, Co (II) from spin 3/2 and B from Cu (II) and V (IV) as in VO ₂ , spin 1/2, L is a bisidental ligand obtained by deprotonation of the H ₄ L molecules of structure 1 or 2,

in which X represents O or S

R represents a group capable of creating a large steric hindrance around B and / or of establishing an interaction with an ion A of an adjacent chain, Y represents OH or NHR ', R' representing a hydrogen atom or a group R, the various R groups of the ligand being identical or different from each other,

- L 'corresponds to the solvent used for the preparation of these systems, generally water, and

- x represents the number of attached solvent molecules.

The group R is an organic group, preferably chosen from a phenyl group, phenyl substituted for example by an alkyl, alkoxy or amino group, these groups being linear, or a carboxyl, ester, ether, hydroxyl or halogen group. R can also represent an alkylene, alkoxy, branched or substituted amine group, with the exception of R representing a group -CH ₂ -CH (OH) -CH ₂ - when x is equal to at least 3. Advantageously, the steric bulk created by R around B leads to a gear system between two adjacent chains as shown schematically below.

such a structure ensures great stability of the crystal lattice which does not include the large holes which appear between the chains when the shortest interchain distances are of type A ... A and B ... B. With this structure, the shortest interchain distances between metal ions are of type A ... B, which creates a ferromagnetic interaction between adjacent chains. The alignment of the spins of all the A ions in the same direction, and of those of the B ions in the opposite direction, is also favored when using an R group, capable of establishing an interaction with a B ion of a adjacent chain, according to the diagram:

It will be noted that the intrachain distances AB, BA are identical when L presents the structure 1 and are different in the case where L presents the structure 2.

According to an aspect of great interest, the inventors have established that it is possible to increase the permanent magnetization properties of molecular systems of the type defined above by practically eliminating the molecules L 'of solvent, for example by pumping under empty.

The invention therefore preferably relates to the above molecular systems practically devoid of solvent molecules, in particular of water, more especially systems whose basic molecular units of the ordered heterometallic chains correspond to the formula ABL. The substituent R in the ligand L has the meanings given above and includes in particular the meanings - (CH ₂ ) ₃ and -CH ₂ -CH (OH) -CH ₂ -. Advantageously, the at least partial elimination of the water molecules from systems in which R represents for example a propylene group, optionally substituted, makes it possible to give them advantageous ferromagnetic properties or to improve them.

The bimetallic chains of the invention have, in the ground state, a structure of spins which can be symbolized by

The ions A and B are linked by ligands capable of promoting strong antiferromagnetic interactions between metal ions, which result from the deprotonation of the following molecules:

In preferred compounds, A represents manganese (II) ions and B represents copper (II) ions whose spins are 5/2 and 1/2 respectively. A preferred family among these compounds comprises oxamido bridging ligands in which R is a benzoato group.

Ligands of this type result from the tetradreprotonation of the molecule of formula:

in which Z represents a hydrogen atom, a hydroxy group or a substitution group such as alkyl or aryl. Among the alkyl groups, mention will be made of those of 1 to 10 carbon atoms, in particular the methyl, ethyl, propyl and butyl groups. Preferred aryl groups include phenyl, phenyl substituted, for example with an alkoxy, alkenyl, alkyl, amino, carboxyl, ester, ether, hydroxyl or halogen radical.

Advantageously, the compounds of this family have a ferromagnetic transition of at least 10ºK. These results show the advantage of the group R with a large size implemented according to the invention. Indeed, with known compounds in which R represents a group -CH ₂ -CH ₂ -COO instead of the group C ₆ H ₅ -COO, no ferro-magnetic transition is observed.

In another preferred family, the bridging ligand is a bisoxamato group which results from the tetradreprotonation of a molecule of formula:

The effect of the interaction created with the Mn (II) ions of an adjacent chain in the compounds of this family resulting from the bulk of R, also appears to be very important in terms of ferromagnetic properties. It is thus possible, using compounds in which R represents a benzyl group, to reach ferromagnetic transition values of the order of 5ºK, which was not suggested by the results obtained with compounds comprising a group R of small bulk . Thus, in the case where R represents a propylene group, the ferromagnetic transition only occurs if the compound is at least partially dehydrated.

The invention also relates to a process for the preparation of the molecular systems defined above.

The preparation of these systems includes the reaction of the ion B with the ligand molecule H ₄ L in a reaction medium L ′ in order to form the mononuclear complex of the ion B, followed by the polymerization of this complex, by reacting a salt of A in solution in L 'with the complex in solution, under conditions of slow diffusion of the salt of A. This gives very well formed single crystals or very stable crystalline powders.

The stage of formation of the mononuclear complex is preferably carried out in basic medium. For example, a strong base such as sodium hydroxide is used. The ion B is in the form of a salt soluble in the reaction solvent L '. The resulting solution is filtered and the complex is recovered, for example by vacuum evaporation. An additional vacuum pumping step makes it possible to eliminate, if desired, at least partially the solvent molecules.

The following reaction scheme illustrates two methods of obtaining these complexes.

depending on whether or not there is hydrolysis of the amide functions.

Ligand L is prepared according to conventional techniques.

To obtain oxamide ligands as defined above, one will advantageously proceed according to one of the following reaction schemes:

In the above formulas, T represents an alkyl radical, in particular ethyl, X represents a halogen atom, in particular chlorine, R is as defined above and THF denotes tetrahydrofuran.

The preparation of bisoxamide ligands can be carried out according to the following scheme.

The various reactions (a) to (e) are carried out at reflux.

Schemes (a), (c) and (d) apply more especially when the amine NH ₂ R is not aromatic and (c) and (e) in the case of aromatic amines.

By way of example, the reaction scheme (f) which can be used for the synthesis of dithiooxamide ligands is given below _:

The polymetallic systems of the invention have permanent magnetization, which gives them great interest as ferro-magnets. These systems also have the advantage of being soluble in polar solvents such as pyridine, which makes it possible to apply them to a substrate and to produce thin ferromagnetic layers with evaporation of the solvent.

In addition, these systems are remarkably transparent, even in the ferromagnetic phase. In addition, at the transition temperature, they exhibit a sudden change in the optical spectrum which allows them to be used in display systems.

These metal systems can also be used as catalysts, the catalytic activity being favored by the presence of two different metal ions in interaction. This activity can be specific thanks to their spin structure.

Other characteristics and advantages of the invention will appear in the examples which follow relating to the synthesis of metallic systems as defined above. EXAMPLE 1 Synthesis of chains with the basic motif

Mn Cu (o-phenylene bisoxamato). 1H ₂ O. This synthesis includes:

1) the preparation of the o-phenylene bis oxamide ligand,

2) the synthesis of the disodium Cu [o-phenylene bisoxamato] mononuclear compound,

3) the preparation of the final compound.

Step 1) is carried out according to the scheme (e) given above using as amine the o-phenylene diamine and as the oxalic derivative, diethyl oxalate chloride. 8 mmol of ethyl oxalate chloride at 0 ° C. are slowly poured into 40 ml of a solution of 4 mmol of o-phenylene diamine in THF. The mixture is allowed to return to room temperature. The precipitate formed is removed by filtration. The filtrate is evaporated to dryness, which gives an oil. The addition of water leads to colorless crystals of (1).

The addition of 10 ml of 32% ammonia to a solution of 2 mmol of (1) in 10 ml of THF gives a white precipitate of (2) which is washed with water and THF.

According to step (2), the disodium mononuclear compound (3) Cu (o-phenylene bisoxamato) is synthesized.

4H ₂ O as follows:

2 mmol of 2 and 8 mmol of NaOH are dissolved in 80 ml of water. A solution of 2 mmol of Cu (NO ₃ ) ₂ in 5 ml of water is slowly added. The resulting solution is filtered. Compound (3) is isolated in the form of a purple polycrystalline powder by evaporation of water.

According to step (3), the compound formed from Mn Cu units [o-phenylene bis oxamato]. 3H ₂ O is obtained by slow diffusion of an aqueous solution of Mn (C10 ₄ ) ₂ -6H ₂ O in an aqueous solution of (3), and is in the form of a blue-green polycrystalline powder. By light pumping under vacuum, this compound loses 2 water molecules and then has a ferromagnetic transition around 4º K.

EXAMPLE 2 Synthesis of chains with the basic motif Mn Cu [oxamido bis (2-benzoato)] - 1H ₂ O.

The operation is carried out according to the 3 steps of Example 1: 1) The oxamide bis (2-benzoic) ligand is obtained by pouring dropwise 2 mmol of the acid chloride oxalic in 30ml of a solution of 4 mmol of anthranilic acid in THF. The ligand precipitates; it is rinsed with water and dried under vacuum (4).

2) The disodium Cu (oxamido bis (2-benzoato)) monocule compound. 4H ₂ O is synthesized as follows: 2 mmol of

(4) and 8 mmol of NaOH are dissolved in 80 ml of water.

Then a solution of 2 mmol of

Cu (NO ₃ ) ₂ . 3H ₂ O in 5 ml of water. The resulting solution is filtered. The compound is isolated in the form of a red polycrystalline powder by slow evaporation of the water (5).

3) The final compound with the basic units Mn Cu [oxamido bis (2-benzoato)]. 1H ₂ O is obtained by slow diffusion of an aqueous solution of Mn (ClO ₄ ) ₂ . 6H ₂ O in an aqueous solution of (5) and drying under vacuum; it is in the form of a blue polycrystalline powder. It has a ferromagnetic transition of at least 15º K. EXAMPLE 3: Synthesis of chains with the basic motif

Mn Cu [1,3 propylene- bis oxamato] -1H ₂ O.

The procedure is as in Example 1, but replacing the o-phenylene diamine with 1-3 propylene diamine. A ferromagnetic transition of 3 º K is induced by the elimination of 4 molecules of the initial compound which has 5 of them.

EXAMPLE 4 Synthesis of chains with the basic motif Fe Cu [1,3 propylene bis oxamato] -1H ₂ O.

A synthesis analogous to that described in Example 3 by replacing Mn by Fe leads to the desired compound which has a ferromagnetic transition around 4º K. EXAMPLE 5 Synthesis of chains with the basic motif

Mn Cu [oxamido bis (2-methyl phenolato)] -2H ₂ O. This synthesis includes:

1 - the preparation of the oxamide bis (2-methylphenol) ligand

2 - synthesis of the mononuclear compound

Cu [oxamido bis (2-methyl phenolato)] disodium

3 - the preparation of the final compound.

1 - 10 mmoles of 2-methylamine phenol are dissolved in 50 ml of toluene. 5 mmol of diethyloxalate are added. After heating at reflux for 12 hours, the oxamide bis (2-methyl phenol) compound which has precipitated is filtered.

2 - 5 mmol of the compound described above and 20 mmol of NaOH are dissolved in 60 ml of methanol. 20 ml of a methanolic solution containing 5 mmol of cupric chloride are then poured. Filtered to remove NaCl. The filtrate is reduced and the disodium mononuclear Cu [oxamido bis (2-methyl phenolato)] compound is precipitated by adding ether.

3 - The final compound is obtained by slow diffusion of methanolic solutions containing manganese (II) perchlorate on the one hand and the copper (II) mononuclear compound on the other hand.

EXAMPLE 6 Synthesis of chains with the basic motif Mn Cu [oxamido (2-benzoato, 3-propionato)]. H ₂ O. This synthesis comprises:

1) the preparation of the oxamido ligand (2-benzoic, 3-propionic) = H ₄ L;

2) the synthesis of the mononuclear compound Cu [oxamido (2-benzoato, 3-propionato)] disodium;

3) the preparation of the final compound. 1) 10 mmoles of anthranilic acid are dissolved in 40 ml of THF. 10 mmol of ethyloxalate chloride are then added and the mixture is heated at 40 ° C for 30 min. It is then evaporated to dryness, 40 ml of water are added and acidified with HCl, which leads to the precipitation of ethyl monobenzoic oxamate.

5 mmol of this compound are dissolved in 30 ml of methanol. 5 mmol of beta-alanine and 5 mmol of NaOH dissolved in 30 ml of methanol are slowly poured. It is heated to 50 ° C for 12 hours. One precipitates appears. It is evaporated to dryness and water is added to the residue, which then dissolves. H ₄ L precipitates when the solution is acidified with HCl.

2) 5 mmol of H ₄ L and 20 mmol of NaOH are dissolved in 60 ml of methanol. Then poured 20 ml of a methanolic solution of cupric chloride. Filtered to remove NaCl. The filtrate is reduced and Na ₂ (CuL) is precipitated by adding ether.

3) The final compound is obtained by slow diffusion of methanolic solutions of manganese perchlorate (II) on the one hand and of the mononuclear copper (II) compound prepared above on the other hand.

Claims

CLAIMS 1. Polymetallic molecular systems, characterized in that they are formed of ordered heterometallic chains in which the basic molecular unit corresponds to the formula ABL.xL 'in which

- A and B are bivalent ions with different spins, A being chosen from Mn (II) and Fe (III) whose spins are 5/2, Fe (II) of spin 2, Co (II) of spin 3 / 2 and B among Cu (II) and V (IV), of spins 1/2,

- L is a bis-bidente ligand obtained by deprotonation of H ₄ L of structure 1 or 2,

in which X represents O or S

R represents a group capable of creating a large steric bulk around B and / or of establishing an interaction with an ion A of an adjacent chain, Y represents OH or NHR ', R' representing a hydrogen atom or a group R, the various R groups of the ligand being identical or different from each other,

- x represents the number of attached solvent molecules.

2. Systems according to claim 1, characterized in that R is an organic group chosen from a phenyl group, phenyl substituted, for example by a alkyl, alkoxy or amino group, these groups being linear, a carboxyl, ester, ether, hydroxyl or halogen group, or an alkylene, alkoxy or amino radical, these groups being branched or substituted, with the exception of R representing a group -CH ₂ -CH (OH) -CH ₂ - when x is equal to at least 3.

3. Systems according to claim 1 or 2, characterized in that L is chosen from ligands which result from the deprotonation of the molecules corresponding to the following bridges:

4. Systems according to any one of claims 1 to 3, characterized in that A represents Mn (II) ions and B represents Cu (II) ions whose spin is 5/2 and 1/2 respectively.

5. Systems according to claim 4, characterized in that L represents an oxamido bridging ligand in which R is a benzoic acid group.

6. Systems according to claim 4, characterized in that L results from tetradeprotonation of the molecule of formula:

in which Z represents a hydrogen atom, a hydroxy group or a substitution group such as alkyl or aryl.

7. Systems according to claim 4, characterized in that R represents an alkyl radical of 1 to 10 carbon atoms, in particular methyl, ethyl, propyl and butyl groups, or an aryl radical such as the phenyl group, substituted phenyl for example by an alkyl, alkenyl, alkoxy, amino, carboxyl, ester, ether, hydroxyl or halogen radical.

8. Systems according to claim 4, characterized in that the bridging ligand is a bisoxamato group which results from the deprotonation of a molecule of formula:

wherein R is as defined in claim 1 or 7.

9. Systems according to any one of claims 1 to 8 characterized in that they are practically devoid of solvent molecules.

10. A method of synthesizing molecular systems according to claim 1, characterized in that it comprises the reaction of the ion B with the ligand molecule L in a reaction medium L 'in order to form the mononuclear complex of the ion B , followed by the polymerization of this complex, by reacting a salt of A in solution in L 'with the complex in solution, under conditions of slow diffusion of the salt of A.

11. Method according to claim 10, characterized in that the step of forming the mononuclear complex is carried out in basic medium, using the ion B in the form of a salt soluble in the reaction solvent L '.

12. Method according to any one of claims 10 or 11, characterized by the additional step of vacuum pumping to at least partially remove the solvent molecules.

13. Application of the molecular systems according to any one of claims 1 to 9 as ferro-magnets.

14. Application of the molecular systems according to any one of claims 1 to 9 as catalysts.

15. Application of molecular systems according to any one of claims 1 to 9 for the development of display systems.