Hydrogen bonding-tuned hydroxo-bridged tetra-copper Cu4(bipy)4-cluster supramolecular network to layered coordination polymer†
Abstract
Three tetranuclear Cu(II) coordination compounds have been synthesized by the self-assembly of copper(II) nitrate with N/O donating bi-ligands through ammonia aqueous/ethanol mixture solution reaction. Single crystal structural analyses have shown that the three compounds feature chair-like hydroxo-bridged tetra-copper(II) cluster: symmetric [Cu4(bipy)4(OH)4(H2O)2]4+ in 1, asymmetric [Cu4(bipy)4(OH)4(H2O)(1,3-DBC)]2+ in 2, and symmetric [Cu4(bipy)4(OH)2(1,2-BDC)2]2+ in 3 (bipy = 2,2′-bipyridineand H2BDC = benzene dicarboxylic acid). Three bitopic benzene dicarboxylic ligands (1,4-DBC2−, 1,3-DBC2−, and 1,2-DBC2−) act as a hydrogen bond acceptor, a mono-dentate terminal ligand, as well as a bi-dentate bridging ligand, respectively. Thus, hydrogen bonding plays a key role in influencing the transformation of the Cu4-cluster⋯ligand hydrogen net to the 2-D layered metal–carboxylate coordination polymer. Meanwhile, the magnetic properties of 1 and 2 have been investigated.