An original 1D Cu–Co heterometallic compound: synthesis, structure and magnetic properties

Abstract

A novel heterobimetallic system, ¹_∞[LCu^IICo^II(NCS)₂] (1), was obtained by reacting the neutral mononuclear complex [LCu] with cobalt(II) acetate in the presence of potassium thiocyanate (L is the dianion of the Schiff base resulting from the 2 ∶ 1 condensation of 3-methoxysalicylaldehyde with 1,3-propanediamine). The crystallographic investigation of 1 reveals a one-dimensional alternating zig-zag chain-like structure, made of dinuclear {LCuCo} units linked by thiocyanate bridges. The copper(II) ion is pentacoordinate to the N₂O₂ donor set of the Schiff base ligand in the basal plane, with the apical position occupied by the sulfur atom. The cobalt ion displays a strongly distorted (4 + 2) octahedral geometry. The distance between the phenoxo-bridged metal ions is 3.149(1) Å. The Cu⋯Co distance for the NCS⁻ bridged ions is equal to 6.125(1) Å. The magnetic properties of 1 were investigated in the temperature range 2–300 K and they are explained by a strong antiferromagnetic Cu(II)–Co(II) exchange interaction through the phenoxo bridges and a weak ferromagnetic Cu(II)–Co(II) interaction through the thiocyanato bridges. Several theoretical models are proposed to fit the magnetic data of 1, the most appropriate one being the full matrix diagonalization for a closed-chain of four dinuclear units [Cu^IICo^II], taking into account two different exchange parameters and a D term, which yielded the following results: J = −101.2 cm⁻¹, j = 2.8 cm⁻¹, D = −0.11 cm⁻¹, g = 2.38.