[Mn<sup>III</sup>(Schiff Base)]<sub>3</sub>[Re<sup>IV</sup>(CN)<sub>7</sub>], Highly Anisotropic 3D Coordination Framework:
Synthesis, Crystal Structure, Magnetic Investigations, and Theoretical
Analysis
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Abstract
A new highly anisotropic
coordination heterobimetallic polymer [Mn<sup>III</sup>(Schiff-base)]<sub>3</sub>[Re<sup>IV</sup>(CN)<sub>7</sub>] 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 Mn<sup>III</sup> 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)<sub>7</sub>]<sup>3–</sup> and [Mn<sup>III</sup>(acacen)]<sup>+</sup>, where acacen = <i>N</i>,<i>N</i>′-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 Mn<sup>II</sup>–[Mo(CN)<sub>7</sub>]<sup>4–</sup> systems.
Unusual magnetic properties of [Mn<sup>III</sup>(acacen)]<sub>3</sub>[Re<sup>IV</sup>(CN)<sub>7</sub>] (<b>1</b>) originate
from an interplay of Re–Mn anisotropic spin coupling and ZFS
effect of Mn<sup>III</sup> 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 [Re<sup>IV</sup>(CN)<sub>7</sub>]<sup>3–</sup> complexes and Mn<sup>III</sup> ions is developed, and specific microscopic mechanisms
of highly anisotropic spin coupling in Re<sup>IV</sup>–CN–Mn<sup>III</sup> linkages in complex <b>1</b> are analyzed in detail
