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

Abstract

Reactions of CuCl 2 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 I 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 CuC 4 pseudo-tetrahedral geometry, while the Cu2 ion presents a CuN 5 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 μ 3 coordination mode and bridges two Cu I and one Cu II ion, while the two other CN groups act as μ 2 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 Cu I centres, and Cu2 presumably Cu II centres). The Cu2 ion presents centrosymmetric CuN 4 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 ( θ = 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.