High-dimensional mixed-valence copper cyanide complexes: Syntheses, structural characterizations and magnetism

Reactions of CuCl2 with different CN complexes in presence of a neutral ancillary ligand lead to two novel mixed-valence Cu complexes [Cu-II(bpy)Cu-I(CN)(3)](n), 1 (bpy = 2,2'-bipyridine) and {[Cu-II(tn)(2)][Cu-4(CN)(6)]}(n). 2 (tn = 1,3-diaminopropane). For compound 1, the asymmetric unit involves two Cu ions Cu1 and Cu2 (Cu-I and Cu-II centres, respectively) which strongly differ in their environments. The Cu1 ion presents a CuC4 pseudo-tetrahedral geometry, while the Cu2 ion presents a CuN5 slightly distorted square-pyramidal geometry. The extended structure of 1 is generated by three cyano ligands which differ in their coordination modes. One CN group has a mu(3) coordination mode and bridges two Cu-I and one Cu-II ion, while the two other CN groups act as 12 bridges leading to a sophisticated 3-D structure. As for 1, the asymmetric unit of 2 involves three crystallographically different Cu ions (Cu1A and Cu1B, presumably Cu1 centres, and Cu2 presumably Cu-II centres). The Cu2 ion presents centrosymmetric CuN4 coordination environments involving four nitrogen atoms from two bidentate tn ligands; while the Cu1A and Cu1B ions are three coordinated to cyano groups. The structure can be described as formed by 18-membered "[Cu-I(CN)](6)" planar metallocycles that are connected to their six neighbors to generate 2-D sheets; these sheets stack forming infinite hexagonal channels in which the [Cu(tn)(2)](2+) units are located. Magnetic measurements show an unexpected weak ferromagnetic coupling (theta = 0.239(1) K) of the Cu-II ions through the long and "a priori diamagnetic" NC-Cu-I-CN- bridges in compound 1 and an essentially paramagnetic behavior in compound 2. (C) 2009 Elsevier Ltd. All rights reserved.