Magnetostructural characterisation of the first bimetallic assemblies derived from the anionic building block [Cr(NCS)6]3− [M(en)3]n[{M(en)2-μ-SCN-Cr(NCS)4-μ-NCS}2n] with M = Ni(ii), Zn(ii)

Abstract

Two bimetallic complexes [M(en)₃]_n[{M(en)₂Cr(NCS)₆}_2n] (M = Ni 1, Zn 2; en = ethylenediamine) have been prepared and structurally and magnetically characterised. They present a unique structure consisting of two distinct units: the catena-μ-NCS-M(en)₂-μ-SCN-Cr(NCS)₄ 1-D polymeric anion and the monomeric cations [M(en)₃]²⁺. Complex 1 crystallized in the monoclinic system, space group C2/c, with a = 28.330(3), b = 14.256(1), c = 16.013(1) Å, β = 117.26(1)°, V = 5748.9(8) ų and Z = 4. The crystal structure of 1 has been refined to R1 = 0.0808. The bridging NCS ligands occupy the rare cis positions in the Ni²⁺ coordination sphere and are coordinated to nickel via their sulfur atoms. The coordination sphere of Cr³⁺ is formed by six nitrogen atoms of the NCS ligands. The Ni–N distances vary from 2.052(5) to 2.131(5) Å, the Ni–S distances are 2.584(2) and 2.632(2) Å, whereas the Cr–N distances vary from 1.971(6) to 2.003(6) Å. A variable temperature magnetic susceptibility study of 1 has been performed over the temperature range of 4–300 K. The compound shows antiferromagnetic coupling (J ≈ −20 cm⁻¹). This moderate antiferromagnetic interaction could be explained by the structural features related to μ-_N,S-NCS bridged units being in cis positions at both metallic centres. The isostructural complex 2 exhibits magnetic behaviour that agrees well with that expected for isolated [Cr(NCS)₆]³⁻ units with small inter- and/or intra-chain antiferromagnetic interactions.