Syntheses, crystal structures, and magnetic properties of Mn-Nb and Co-Nb cyanido-bridged bimetallic assemblies

We report three-dimensional (3D) cyanido-bridged Mn-Nb and Co-Nb bimetal assemblies, Mn-2(II)[Nb-IV(CN)(8)]center dot(L)(2)center dot nH(2)O (1: L = 5-aminopyrimidine, n = 5; 2: L = 5-methylpyrimidine, n = 4), and Co-2(II)[Nb-IV(CN)(8)] (4-pyridinealdoxime)(8)center dot 2H(2)O (3). The single-crystal X-ray structural analyses show that 1 and 2 consist of isomorphic 3D cyanido-bridged network (monoclinic, P2(1)/n) composed of square antiprism Nb sites and distorted octahedral Mn sites. Both 1 and 2 show ferrimagnetism with Curie temperatures (T-C) of 32 and 34 K, respectively, which is caused by the antiferromagnetic superexchange interaction between Mn-II (S = 5/2) and Nb-IV (S = 1/2) through the CN groups. 3 has a 3D cyanido-bridged network (tetragonal, I4(1)/a) composed of a dodecahedral Nb site and axially distorted pseudo-octahedral Co site. This compound shows ferromagnetic ordering with a T-C of 18 K. Magnetization versus rotation angle of single crystal reveals that 3 has a large coercive field of 15000 Oe as crystal is oriented to a-axis, which is due to the strong magnetic anisotropy on distorted Co-II. (C) 2014 Elsevier B.V. All rights reserved.