Solvothermal synthesis of a novel mixed valence Cu(I)/Cu(II) complex containing sulphate, malate and 4,4′-bipyridine, [CuICuII2(mal)(SO4)(bpy)2 · H2O]n. Unique binding mode of the malate anion

The reaction of CuSO4 · 5H2O with 4,4′-bipyridine and malic acid at 140 °C under solvothermal conditions afforded a mixed valence three-dimensional coordination polymer [CuICuII2(mal)(SO4)(bpy)2 · H2O]n, (1). The building unit consists of a Cu2+-dimer in which copper centers are bridged by malate and sulphate anions. SO42− anion further connects dimeric unit with the Cu1+ center. Building units are linked by 4,4′-bipyridine ligands to form double chains, that are interconnected into 3D network through additional sulphate bridge.