Three complexes are reported from the initial use of dimethylarsinic acid (Me2AsO2H) in Mn(III/IV... more Three complexes are reported from the initial use of dimethylarsinic acid (Me2AsO2H) in Mn(III/IV) cluster chemistry, [Mn4O4(O2AsMe2)6] (3; 2Mn(III), 2Mn(IV)), and [Mn16X4O8(O2CPh)16(Me2AsO2)24] (X = Ca(2+) (4) or Sr(2+) (5); 16Mn(III)). They were obtained from reactions with [Mn12O12(O2CR)16(H2O)4] (R = Me, Ph) either without (3) or with (4 and 5) the addition of X(2+) salts. Complex 3 contains a [Mn4O4](6+) cubane, whereas isostructural 4 and 5 contain a planar loop structure comprising four Mn4 asymmetric "butterfly" units linked by alternating anti,anti μ-O2AsMe2 and {X2(O2AsMe2)(O2CPh)2} units. Variable-temperature magnetic susceptibility (χM) data were collected on dried microcrystalline samples of 3-5 in the 5.0-300 K range in a 0.1 T (1000 G) direct-current (dc) magnetic field. Data for 3 were fit to the appropriate Van Vleck equation (using the [Formula: see text] = -2JŜi·Ŝj convention) for a cubane of virtual C2v symmetry, giving J33 = 0.0(1) cm(-1), J34 = -3.4(4) cm(-1), J44 = -9.8(2) cm(-1), and g = 1.99(1), where the Jij subscripts refer to the oxidation states of the interacting Mn atoms. The ground state thus consists of two coupled Mn(IV) and two essentially noninteracting Mn(III). For 4 and 5, low-lying excited states from the high nuclearity and weak couplings prevent fits of dc magnetization data, but in-phase alternating current susceptibility χ'MT data down to 1.8 K indicate them to possess S = 4 ground states, if considered single Mn16 units. If instead they are treated as tetramers of weakly coupled Mn4 units, then each of the latter has an S = 2 ground state. Complexes 4 and 5 also exhibit very weak out-of-phase χ″M signals characteristic of slow relaxation, and magnetization versus dc field scans on a single crystal of 4·15MeCN at T ≥ 0.04 K showed hysteresis loops but with unusual features suggesting the magnetization relaxation barrier consists of more than one contribution.
The use has been explored in Mn cluster chemistry of N(3)(-) or Cl(-) in combination with N-methy... more The use has been explored in Mn cluster chemistry of N(3)(-) or Cl(-) in combination with N-methyldiethanolamine (mdaH(2)) or triethanolamine (teaH(3)). The reactions of Mn(ClO(4))(2).6H(2)O, NEt(3), NaN(3), and either mdaH(2) or teaH(3) (1:2:1:2) in DMF/MeOH afford {[Na(MeOH)(3)][Mn(7)(N(3))(6)(mda)(6)]}(n) (1) and {Na[Mn(7)(N(3))(6)(teaH)(6)]}(n) (2), respectively, whereas the 2:1:1 reaction of MnCl(2).4H(2)O, mdaH(2), and NEt(3) in MeCN gives (NHEt(3))[Mn(7)Cl(6)(mda)(6)] (3). Similar reactions using NBu(n)(4)N(3) in place of NaN(3) gave (NHEt(3))[Mn(7)(N(3))(6)(mda)(6)] (4) and (NHEt(3))[Mn(7)(N(3))(6)(teaH)(6)] (5). The Mn(7) anions consist of a Mn(6) hexagon of alternating Mn(II) and Mn(III) ions surrounding a central Mn(II) ion. The remaining ligation is by six bridging and chelating mda(2-) or teaH(2-) groups, and either six terminal N(3)(-) (1, 2, 4, 5) or Cl(-) (3) ions. Each bridging mda(2-) or teaH(2-) ligand contains both mu- and mu(3)-O atoms, resulting in a similar, near-planar [Mn(7)(mu(3)-OR)(6)(mu-OR)(6)](5+) core for all three complexes. The Mn(7) anions of 1 and 2 are connected via Na(+) cations to yield one-dimensional zigzag chains and three-dimensional windmill-like "hexagons-of-hexagons", respectively. In contrast, the Mn(7) anion of 3 forms a strong hydrogen-bond between the NHEt(3)(+) cation and a terminal Cl(-) ion giving a discrete ion-pair. Variable-temperature, solid-state direct current (dc) and alternating current (ac) magnetization studies were carried out in the 5.0-300 K range. Fits of dc magnetization versus field (H) and temperature (T) data by matrix diagonalization gave S = 11, g = 1.95, D = -0.15 cm(-1) for 1, S = 16, g = 1.95, D = -0.02 cm(-1) for 2, and S = 11, g = 1.92, D = -0.13 cm(-1) for 3 (D is the axial zero-field splitting parameter). Complexes 4 and 5 were also found to possess S = 11 and S = 16 ground states, respectively. The different ground states of 1 and 2 were rationalized on the basis of the sign and magnitude of the various Mn(2) exchange parameters obtained from density functional theory (DFT) calculations. This analysis confirmed the presence of spin frustration effects, with the ground states being determined by the relative magnitude of the two weakest interactions. The combined results demonstrate the usefulness of N-based dipodal and tripodal alkoxide-based chelates as a route to structurally and magnetically interesting Mn clusters.
The reaction of [Mn(3)O(O(2)CMe)(6)(py)(3)](ClO(4)) (1; 3Mn(III)) with [Mn(10)O(4)(OH)(2)(O(2)CMe... more The reaction of [Mn(3)O(O(2)CMe)(6)(py)(3)](ClO(4)) (1; 3Mn(III)) with [Mn(10)O(4)(OH)(2)(O(2)CMe)(8)(hmp)(8)](ClO(4))(4) (2; 10Mn(III)) in MeCN affords the new mixed-valent complex [Mn(21)O(14)(OH)(2)(O(2)CMe)(16)(hmp)(8)(pic)(2)(py)(H(2)O)](ClO(4))(4) (3; 3Mn(II)-18Mn(III); hmp(-) is the anion of 2-(hydroxymethyl)pyridine), with an average Mn oxidation state of +2.85. Complex 3.7MeCN crystallizes in the triclinic space group P. The structure consists of a low symmetry [Mn(21)(micro(4)-O)(4)(micro(3)-O)(12)(micro-O)(16)] core, with peripheral ligation provided by 16 MeCO(2)(-), 8 hmp(-), and 2 pic(-) groups and one molecule each of water and pyridine. The magnetic properties of 3 were investigated by both dc and ac magnetic susceptibility measurements. Fitting of dc magnetization data collected in the 0.1-0.8 T and 1.8-4.0 K ranges gave S = (17)/(2), D approximately -0.086 cm(-)(1), and g approximately 1.8, where S is the molecular spin of the Mn(21) complex and D is the axial zero-field splitting parameter. ac susceptibility studies in the 10-997 Hz frequency range reveal the presence of a frequency-dependent out-of-phase ac magnetic susceptibility (chi(M)' ') signal consistent with slow magnetization relaxation rates. Fitting of dc magnetization decay versus time data to the Arrhenius equation gave a value of the effective barrier to relaxation (U(eff)) of 13.2 K. Magnetization versus applied dc field sweeps exhibited hysteresis. Thus, complex 3 is a new member of the small but growing family of single-molecule magnets.
HAL (Le Centre pour la Communication Scientifique Directe), 2011
International audienceThe use of both azide and triethanolamine, with or without the presence of ... more International audienceThe use of both azide and triethanolamine, with or without the presence of carboxylate groups, has provided new Mn-17, Mn-18 and {Mn-62}(n) complexes with aesthetically-pleasing cage, layered, and linked-chain-type structures; two are also new single-molecule magnets
Three complexes are reported from the initial use of dimethylarsinic acid (Me2AsO2H) in Mn(III/IV... more Three complexes are reported from the initial use of dimethylarsinic acid (Me2AsO2H) in Mn(III/IV) cluster chemistry, [Mn4O4(O2AsMe2)6] (3; 2Mn(III), 2Mn(IV)), and [Mn16X4O8(O2CPh)16(Me2AsO2)24] (X = Ca(2+) (4) or Sr(2+) (5); 16Mn(III)). They were obtained from reactions with [Mn12O12(O2CR)16(H2O)4] (R = Me, Ph) either without (3) or with (4 and 5) the addition of X(2+) salts. Complex 3 contains a [Mn4O4](6+) cubane, whereas isostructural 4 and 5 contain a planar loop structure comprising four Mn4 asymmetric "butterfly" units linked by alternating anti,anti μ-O2AsMe2 and {X2(O2AsMe2)(O2CPh)2} units. Variable-temperature magnetic susceptibility (χM) data were collected on dried microcrystalline samples of 3-5 in the 5.0-300 K range in a 0.1 T (1000 G) direct-current (dc) magnetic field. Data for 3 were fit to the appropriate Van Vleck equation (using the [Formula: see text] = -2JŜi·Ŝj convention) for a cubane of virtual C2v symmetry, giving J33 = 0.0(1) cm(-1), J34 = -3.4(4) cm(-1), J44 = -9.8(2) cm(-1), and g = 1.99(1), where the Jij subscripts refer to the oxidation states of the interacting Mn atoms. The ground state thus consists of two coupled Mn(IV) and two essentially noninteracting Mn(III). For 4 and 5, low-lying excited states from the high nuclearity and weak couplings prevent fits of dc magnetization data, but in-phase alternating current susceptibility χ'MT data down to 1.8 K indicate them to possess S = 4 ground states, if considered single Mn16 units. If instead they are treated as tetramers of weakly coupled Mn4 units, then each of the latter has an S = 2 ground state. Complexes 4 and 5 also exhibit very weak out-of-phase χ″M signals characteristic of slow relaxation, and magnetization versus dc field scans on a single crystal of 4·15MeCN at T ≥ 0.04 K showed hysteresis loops but with unusual features suggesting the magnetization relaxation barrier consists of more than one contribution.
The use has been explored in Mn cluster chemistry of N(3)(-) or Cl(-) in combination with N-methy... more The use has been explored in Mn cluster chemistry of N(3)(-) or Cl(-) in combination with N-methyldiethanolamine (mdaH(2)) or triethanolamine (teaH(3)). The reactions of Mn(ClO(4))(2).6H(2)O, NEt(3), NaN(3), and either mdaH(2) or teaH(3) (1:2:1:2) in DMF/MeOH afford {[Na(MeOH)(3)][Mn(7)(N(3))(6)(mda)(6)]}(n) (1) and {Na[Mn(7)(N(3))(6)(teaH)(6)]}(n) (2), respectively, whereas the 2:1:1 reaction of MnCl(2).4H(2)O, mdaH(2), and NEt(3) in MeCN gives (NHEt(3))[Mn(7)Cl(6)(mda)(6)] (3). Similar reactions using NBu(n)(4)N(3) in place of NaN(3) gave (NHEt(3))[Mn(7)(N(3))(6)(mda)(6)] (4) and (NHEt(3))[Mn(7)(N(3))(6)(teaH)(6)] (5). The Mn(7) anions consist of a Mn(6) hexagon of alternating Mn(II) and Mn(III) ions surrounding a central Mn(II) ion. The remaining ligation is by six bridging and chelating mda(2-) or teaH(2-) groups, and either six terminal N(3)(-) (1, 2, 4, 5) or Cl(-) (3) ions. Each bridging mda(2-) or teaH(2-) ligand contains both mu- and mu(3)-O atoms, resulting in a similar, near-planar [Mn(7)(mu(3)-OR)(6)(mu-OR)(6)](5+) core for all three complexes. The Mn(7) anions of 1 and 2 are connected via Na(+) cations to yield one-dimensional zigzag chains and three-dimensional windmill-like "hexagons-of-hexagons", respectively. In contrast, the Mn(7) anion of 3 forms a strong hydrogen-bond between the NHEt(3)(+) cation and a terminal Cl(-) ion giving a discrete ion-pair. Variable-temperature, solid-state direct current (dc) and alternating current (ac) magnetization studies were carried out in the 5.0-300 K range. Fits of dc magnetization versus field (H) and temperature (T) data by matrix diagonalization gave S = 11, g = 1.95, D = -0.15 cm(-1) for 1, S = 16, g = 1.95, D = -0.02 cm(-1) for 2, and S = 11, g = 1.92, D = -0.13 cm(-1) for 3 (D is the axial zero-field splitting parameter). Complexes 4 and 5 were also found to possess S = 11 and S = 16 ground states, respectively. The different ground states of 1 and 2 were rationalized on the basis of the sign and magnitude of the various Mn(2) exchange parameters obtained from density functional theory (DFT) calculations. This analysis confirmed the presence of spin frustration effects, with the ground states being determined by the relative magnitude of the two weakest interactions. The combined results demonstrate the usefulness of N-based dipodal and tripodal alkoxide-based chelates as a route to structurally and magnetically interesting Mn clusters.
The reaction of [Mn(3)O(O(2)CMe)(6)(py)(3)](ClO(4)) (1; 3Mn(III)) with [Mn(10)O(4)(OH)(2)(O(2)CMe... more The reaction of [Mn(3)O(O(2)CMe)(6)(py)(3)](ClO(4)) (1; 3Mn(III)) with [Mn(10)O(4)(OH)(2)(O(2)CMe)(8)(hmp)(8)](ClO(4))(4) (2; 10Mn(III)) in MeCN affords the new mixed-valent complex [Mn(21)O(14)(OH)(2)(O(2)CMe)(16)(hmp)(8)(pic)(2)(py)(H(2)O)](ClO(4))(4) (3; 3Mn(II)-18Mn(III); hmp(-) is the anion of 2-(hydroxymethyl)pyridine), with an average Mn oxidation state of +2.85. Complex 3.7MeCN crystallizes in the triclinic space group P. The structure consists of a low symmetry [Mn(21)(micro(4)-O)(4)(micro(3)-O)(12)(micro-O)(16)] core, with peripheral ligation provided by 16 MeCO(2)(-), 8 hmp(-), and 2 pic(-) groups and one molecule each of water and pyridine. The magnetic properties of 3 were investigated by both dc and ac magnetic susceptibility measurements. Fitting of dc magnetization data collected in the 0.1-0.8 T and 1.8-4.0 K ranges gave S = (17)/(2), D approximately -0.086 cm(-)(1), and g approximately 1.8, where S is the molecular spin of the Mn(21) complex and D is the axial zero-field splitting parameter. ac susceptibility studies in the 10-997 Hz frequency range reveal the presence of a frequency-dependent out-of-phase ac magnetic susceptibility (chi(M)' ') signal consistent with slow magnetization relaxation rates. Fitting of dc magnetization decay versus time data to the Arrhenius equation gave a value of the effective barrier to relaxation (U(eff)) of 13.2 K. Magnetization versus applied dc field sweeps exhibited hysteresis. Thus, complex 3 is a new member of the small but growing family of single-molecule magnets.
HAL (Le Centre pour la Communication Scientifique Directe), 2011
International audienceThe use of both azide and triethanolamine, with or without the presence of ... more International audienceThe use of both azide and triethanolamine, with or without the presence of carboxylate groups, has provided new Mn-17, Mn-18 and {Mn-62}(n) complexes with aesthetically-pleasing cage, layered, and linked-chain-type structures; two are also new single-molecule magnets
Uploads
Papers