[Mn^III(Schiff Base)]₃[Re^IV(CN)₇], Highly Anisotropic 3D Coordination Framework: Synthesis, Crystal Structure, Magnetic Investigations, and Theoretical Analysis

A new highly anisotropic coordination heterobimetallic polymer [MnIII(Schiff-base)]3­[ReIV(CN)7] was synthesized and characterized structurally and magnetically. The single crystal X-ray analysis has revealed that this is the first framework among the complexes composed of homoleptic cyanometallate and MnIII complex of the tetradentate Schiff base ligand. A formation of 3D assembly is possible due to both the pentagonal bipyrimidal geometry of the cyanometallate unit and suitable size of constituents: [Re­(CN)7]3– and [MnIII(acacen)]+, where acacen = N,N′-ethylenebis­(acetylacetoneiminato). The powder and crystal magnetic studies show that the compound undergoes an antiferromagnetic ordering of a complicated character below Neel temperature of 13 K, and exhibits a metamagnetic behavior and strong magnetic anisotropy similar to those observed in related 3D MnII–[Mo­(CN)7]4– systems. Unusual magnetic properties of [MnIII(acacen)]3­[ReIV(CN)7] (1) originate from an interplay of Re–Mn anisotropic spin coupling and ZFS effect of MnIII ions with a noncollinear orientation of the local magnetic axes in the cyano-bridged 3D network. A theoretical model of anisotropic spin coupling between orbitally degenerate [ReIV(CN)7]3– complexes and MnIII ions is developed, and specific microscopic mechanisms of highly anisotropic spin coupling in ReIV–CN–MnIII linkages in complex 1 are analyzed in detail.