First use of the maleamate(−1) ligand in coordination chemistry: Dinuclear copper(II) complexes with N-donors and their interesting ‘organic’ chemistry

A systematic investigation of the reactions of 3d-metal ions with the maleamate(−1) ligand (HL−) in the presence of mono- , bi- or tridentate chelating N-donors has been initiated and the first results are described. Reaction schemes involving Cu(ClO4)2 · 6H2O, HL− and 1,10-phenanthroline or 2,6-bis(pyrazol-1-yl)pyridine (bppy) in MeCN gave complexes [Cu2(HL)3(phen)2](ClO4) (1) and [Cu2(HL)2(bppy)2](ClO4)2 (3), respectively. The same reaction systems in MeOH afforded the new complexes [Cu2L′2(ClO4)(phen)2(MeOH)](ClO4) (2b) and [Cu2L′2(bppy)2](ClO4)2 (4) in which the maleamate(−1) ion has been transformed to the monomethyl maleate(−1) ligand L′− via a novel, metal ion-assisted process. The reaction that leads to 2b takes place through the formation of the 1D coordination polymer [Cu(ClO4)(phen)(MeOH)2]n(ClO4)n (2a), whose structure was assigned on the basis of its spectral similarity with the structurally characterized complex [Cu(ClO4)(phen)(MeCN)2]n(ClO4)n (2c). Only the carboxylate oxygen atoms of HL− and L′− are coordinated to copper(II) in 1, 2b, 3 and 4.