Synthesis, Structure and Magnetic properties of Chiral and Nonchiral Transition‐Metal Malates

Abstract

Carboxylate-bridged complexes of transition metals, M(II)=Mn(II), Fe(II), Co(II), Ni(II), Zn(II), were synthesised by reaction of M(II) salts with dl-malate and L-malate under hydrothermal conditions. These complexes form four series of compounds, which have been fully characterised structurally, thermally and magnetically. The crystal structures of the new chiral compounds, [Mn(L-mal)(H(2)O)] (1), [Fe(L-mal)(H(2)O)] (2), [Co(L-mal)(H(2)O)] (3) and [Zn(L-mal)(H(2)O)] (4) as well as those of the bimetallic analogues [Mn(0.63)Co(0.37)(L-mal)(H(2)O)] (5) and [Mn(0.79)Ni(0.21)(L-mal)(H(2)O)] (6) have been solved by single-crystal X-ray diffraction. The six L-malate monohydrates crystallise in the chiral space group P2(1)2(1)2(1) and consist in a three-dimensional network of metal(II) centres in octahedral sites formed by oxygen atoms. These structures were compared to those of the chiral trihydrate compounds [Co(L-mal)(H(2)O)]2 H(2)O (7), [Ni(L-mal)(H(2)O)]2 H(2)O (8) and [Co(0.52)Ni(0.48)(L-mal)(H(2)O)]2 H(2)O (9), which exhibit helical chains of M(II) centres, and those of dl-malate dihydrates [Co(dl-mal)(H(2)O)]H(2)O (10) and [Ni(dl-mal)(H(2)O)H(2)O (11) and trihydrate [Mn(L-mal)(H(2)O)]2 H(2)O (12) highlighting the great flexibility of the coordination by the malate ligand. UV/Vis spectroscopic results are consistent with octahedral coordination geometry of high-spin transition-metal centres. Extensive magnetic characterisation of each homologous series indicates rather weak coupling interaction between paramagnetic centres linked through carboxylate bridges. Curie-like paramagnetic, antiferromagnetic, ferromagnetic or weak ferromagnetic behaviour is observed and discussed on the basis of the structural features. The bimetallic compounds 5 and 6 represent new examples of chiral magnets.

1D CoII and NiII Chiral Polymers That Exhibit Ferromagnetic Interactions

“…In the case of cobalt-based chiral polymers, a significant dichroism signature is observed in the 450-629 nm region, which corresponds to the 4 T 1g (F) Ǟ 4 T 1g (P) (ν 3 ) transition of Co 2+ ions located in an octahedral environment. [31,[41][42][43] The deviation from a symmetric shape of opposite signals in CD spectra between I L (Co) and I D (Co) is likely to be related to uncertainties in the background correction because the latter is very sensitive to small differences in the thickness and transparency of KBr pellets. Unfortunately, the presence of perchlorate ions in these compounds does not allow one to apply the strong pressure that is indispensable to fabricating KBr pellets of good quality.…”

“…Model 1 [43] Model 2 [50] Model 3 [52] Model 4 [56] I L (Ni) Table 4. Single-crystal X-ray data collection details and refinement results.…”

“…[31,43,55,63,64] The E 2 parameter reflects the very small ferromagnetic interaction (0.02 cm -1 ) within the Ising chain approximation.…”

“…Similar small ferromagnetic interactions between octahedral Co II centers through a bridged carboxylic group have been recently reported in the literature. [31,43,55] To get an estimated value for exchange interactions, a simple model that involves the spin-orbit coupling and the exponential low-temperature divergence of the susceptibility [χTϰexp(+J/2kT)] of an Ising chain of anisotropic magnetic centers can be used. [31,55,60,61] Two contributions are included in the equation: in which A 1 + A 2 is equal to the Curie constant, and the limiting Curie-Weiss equation χ = A 1 + A 2 T -θ was applied to constrain the fitting procedure.…”

Effect of Mixing of Metal Cations on the Topology of Metal Oxide Networks

“…[17,18] In the case of cobalt, we demonstrated that condensation of the inorganic species increased with increasing temperature and pH, and this led to seven cobalt succinate topologies. [18] Comparison of these compounds to known nickel succinates indicates that the phases that occur at lower temperatures tend to be isostructural (consistent with other Co II and Ni II coordination polymers) [19,20] while the hydrothermal phases differ significantly. In particular conditions used for synthesizing the cobalt structure MIL-9, [21][22][23] which exhibits a 2D array of metal octahedra, gave a remarkable 3D inorganic framework when applied to nickel.…”