Rupam Sarmaa and Jubaraj B. Baruah
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Abstract
The coordination polymers [Zn(C6H5COO)2(PNO)]n (1), [Zn2(C6H5COO)4(4,4′-BPNO)]n (2), [Zn4(C6H4C2O4)4(4,4′-BPNO)2(H2O)5]n·nH2O (3), [Cd(C6H5COO)2(PNO)]n (4), [Cd3(C6H5COO)6(4,4′-BPNO)2]n·2nH2O (5), [Cd(C6H4C2O4)(4,4′-BPNO)(H2O)]n (6) and [Hg(C6H5COO)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 μ2-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 μ2–η1 : η1 coordination mode. The polymeric structure of 3 formed by terephthalate and 4,4′-bipyridyl-N,N′-dioxide with zinc(II) contains self-assembled dinuclear Zn2O2 type of carboxylate cores, with 4,4′-bipyridyl-N,N′-dioxide coordinating through cis μ2–η1 : η1 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 μ2–η1 : η1 coordination mode.
