Assemblies Possessing Rich Hydrogen Bonds Derived from trans-Oxamidato-Bridged Dicopper(II) Complexes and Carboxyl Auxiliary Ligands

Three complexes [{Cu2(trans-oxap)(nic)(H2O)2}n](ClO4)n·0.5nH2O 1, [Cu2(trans-oxen)(nic)2(H2O)2]·2H2O 2, [Cu2(trans-oxen)(hyba)2(H2O)2] 3 have been obtained from reactions of the trans-oxamidato-bridged dicopper(II) unit [Cu2(trans-L)]^2+ (L = oxen or oxap, H2oxen = N,Nʹ-bis(2-aminoethyl)oxamide, H2oxap = N,Nʹ-bis(2-aminopropyl)oxamide) with the auxiliary ligands hydroxybenzoic acid (Hhyba) and nicotinic acid (Hnic). Their structures were determined by X-ray crystallography. Results showed that polymeric chains are formed in 1, since the auxiliary ligand nic behaves as the spacer connecting the dicopper units. However, 2 and 3 contain only discrete dinuclear units, since nic in 2 and hyba in 3 are terminal ligands. Chains in 1 and dinuclear units in 2 and 3 further fabricate extended structures through hydrogen bonds. The structural diversity of these complexes results from the different affinity of the coordination donors to the copper(II). The magnetic property is exemplified by 3; thermal behaviors of all complexes have been investigated.