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

摘要

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-2nH_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'-bipyridyI-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 η~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 η~2-η~1 : η~1 coordination mode.