Three-dimensional bimetallic octacyanidometalates [MIV{(μ-CN)4MnII(H2O)2}2•4H2O]n (M = Nb, Mo, W): Synthesis, single-crystal X-ray diffraction and magnetism

We report the synthesis, the single-crystal X-ray crystallographic structures and the magnetic properties of three new isostructural cyanido-bridged networks: [M-IV{(mu-CN)(4)Mn-II(H2O)(2)}(2)center dot 4H(2)O](n) [M-IV = Nb-IV (1), Mo-IV (2), W-IV (3)]. For compound 1, the magnetic properties reveal a ferrimagnetic phase below 50 K. In contrast, compounds 2 and 3 show a paramagnetic behaviour with no magnetic ordering down to 2 K. The only electronic difference between the two kinds of compounds is the presence of two paired electrons on Mo-IV (2) and W-IV (3) (d(2) electronic configuration, S = 0) with no possible exchange interactions with Mn-II ions (d(5) electronic configuration, S = 5/2) and one unpaired electron on Nb-IV (1) (d(1), S = 1/2) which allows Nb-IV-Mn-II antiferromagnetic exchange interactions and the onset of a three-dimensional magnetic ordering under Curie temperature. These three compounds demonstrate how one unpaired electron, well located, can dramatically change the magnetic behaviour of isostructural octacyanido-based three-dimensional networks. To cite this article: Juan Manuel Herrera et al., C R. Chimie 11 (2008). (C) 2008 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.