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.