Pressure-Dependent Pseudo-Polymorphism of Polymeric {[Cu2(TBA)]·2H2O}n and Dinuclear [Cu2(TBA)(H2O)2]·2H2O Complexes Based on in Situ Tetramerization of DMBA

Two new pressure-dependent pseudo-polymorphism complexes, a 2D polymeric {[Cu2(TBA)]·2H2O}n (1) and a dinuclear [Cu2(TBA)(H2O)2]·2H2O (2), were successfully obtained and demonstrated to possess weak antiferromagnetic properties. The synthesis has been achieved through a novel one-pot reaction where four DMBA (DMBA = 1,3-dimethyl-barbitiric acid) molecules tetramerized in situ with EtOH to give (TBA)4– (H4TBA = 1,1′,2,2′-tetra-barbiturate-ethene) ligand. This unprecedented tetramerization involves one-pot formation of one new C═C bond and four new C–C bonds. It was shown that the formation of 1 strictly relied on the use of Cu(II) ion and EtOH and that reactions of oxidation, Knoevenagel condensation, and Michael addition probably induce the tetramerization.