Aromatic N-oxides in construction of different carboxylate coordination polymers of zinc(II), cadmium(II) and mercury(II)

Abstract

The coordination polymers [Zn(C 6H 5COO) 2(PNO)] n ( 1), [Zn 2(C 6H 5COO) 4(4,4′-BPNO)] n ( 2), [Zn 4(C 6H 4C 2O 4) 4(4,4′-BPNO) 2(H 2O) 5] n · nH 2O ( 3), [Cd(C 6H 5COO) 2(PNO)] n ( 4), [Cd 3(C 6H 5COO) 6(4,4′-BPNO) 2] n·2 nH 2O ( 5), [Cd(C 6H 4C 2O 4)(4,4′-BPNO)(H 2O)] n ( 6) and [Hg(C 6H 5COO) 2(4,4′-BPNO) 2] n ( 7), (where PNO = pyridine N-oxide, 4,4′-BPNO = 4,4′-bipyridyl- N,N′-dioxide) are synthesized and structurally characterized. The structures of these coordination polymers exhibit mononuclear to trinuclear nodes built by ligation of carboxylate to metal ions connected by N-oxide ligands. Pyridine N-oxide interconnects metal nodes by acting as μ 2-bridging ligand in complexes 1, and 4. In the linear coordination polymer 2, the paddle wheel structure of zinc(II) benzoate units are interconnected by 4,4′-bipyridyl- N,N′-dioxide which acts as a bidentate spacer ligand adopting a trans μ 2–η 1 : η 1 coordination mode. The polymeric structure of 3 formed by terephthalate and 4,4′-bipyridyl- N,N′-dioxide with zinc(II) contains self-assembled dinuclear Zn 2O 2 type of carboxylate cores, with 4,4′-bipyridyl- N,N′-dioxide coordinating through cis μ 2–η 1 : η 1 coordination mode. The cadmium coordination polymer 5, comprising of 4,4′-bipyridyl- N,N′-dioxide and benzoate, has trinuclear cadmium benzoate cores wherein the terminal cadmium ions are interconnected by monodentate 4,4′-bipyridyl- N,N′-dioxide bridges. The coordination polymer 6 comprises of mononuclear cadmium nodes independently bridged by terephthalate and 4,4′-bipyridyl- N,N′-dioxide thereby leading to a 3-fold interpenetrated three dimensional network. Double helical polymeric structure is observed in the coordination polymer 7 derived from mononuclear mercury(II) benzoate nodes bridged by 4,4′-bipyridyl- N,N′-dioxide with cis μ 2–η 1 : η 1 coordination mode.