Synthesis and characterization of cobalt(II) complexes of croconate and dicyanomethylene-substituted derivatives†

Abstract

The crystal structures of cobalt(II) complexes of croconate [CoL¹(H₂O)₃] 1 (L¹ = C₅O₅^2–) and croconate violet K₂[CoL²₂(H₂O)₂]·2H₂O 2 [L² = 3,5-bis(dicyanomethylene)cyclopentane-1,2,4-trionate] have been determined. Complex 1 consists of infinite zig-zag chains constituted by one metal atom, one croconate acting as a bridge and three water molecules. Moreover these chains, parallel to the c axis, are stacked with metal–metal distances of 7.9891(3) Å inside a chain and 5.0035(6) Å between chains. Complex 2 consists of dianionic and mononuclear entities in which the ligand is O-co-ordinated. The magnetic properties of 1 and 2 have been investigated in the 4–300 K temperature range (µ_eff = 3.65 to 5.02 µ_B for 1 and µ_eff = 4.00 to 4.90 µ_B for 2). Their redox properties are discussed and compared to those of the free ligands.