New coordination polymer based on a triply bridged dicarboxylate ligand: Synthesis, structure, and magnetic properties of the adipato complex [Cu4(bpy)4(adip)3](tcnoet)2·2H2O {bpy=C10H8N2; adip2−=[O2C(CH2)4CO2]2−; tcnoet−=[(NC)2CC(OEt)C(CN)2]−}

Abstract : One-pot reaction of copper(II) chloride dihydrate CuCl2 · 2H2O with 2,2′-bipyridyl (bpy = C10H8N2) in the presence of sodium adipate Na2adip (adip2− = [O2C(CH2)4CO2]2−) and potassium 1,1,3,3-tetracyano-2-ethoxypropenide (tcnoet− = [(NC)2CC(OEt)C(CN)2]−) gives the new compound [Cu4(bpy)4(adip)3](tcnoet)2 · 2H2O (1), which was characterized by single crystal X-ray diffraction analysis. The Cu(II) metal ion presents an elongated square pyramidal CuN2O3 environment, with an oxygen atom in apical position and a base plane involving almost equivalent bond lengths. The structure can be described as a pseudo dinuclear species in which two Cu(bpy) units are triply bridged by two unsymmetrical bridging oxygen atoms of two carboxylate groups and by an almost symmetrical OCO unit with a bidentate syn–syn bridging mode. Each Cu2 dinuclear unit is triply bonded by aliphatic chains of the three adipate ligands to generate a ladder-like infinite chain. Magnetic measurements exhibit a maximum in the χm versus T plot (at ∼5.0 K) which is characteristic of weak antiferromagnetic exchange interactions between the Cu(II) ions bridged by the carboxylate groups. Fit of the magnetic data with appropriate model led to J value of −3.26(1) cm−1 (the Hamiltonian is written as H = −2JSaSb).