Syntheses, structural diversities and characterization of a series of coordination polymers with two isomeric oxadiazol-pyridine ligands

In this work two positional-isomeric oxadiazol-pyridine ligands 3-(5-methyl-1,3,4-oxadiazol-2-yl)pyridine (L-1) and 4-(5-methyl-1,3,4-oxadiazol-2-yl) pyridine (L-2) have been designed and synthesized. A series of novel coordination polymers, namely [Cd-2(mu(2)-L-1)(2)(mu(2)-NCS)(4)](n) (1), {[Cd(L-1)(mu(2)-dca)(2)(H2O)]center dot H2O}(n) (2), {[Cu(mu(2)-L-1)(2)(NCS)(2)]center dot 0.5H(2)O}(n) (3), {[Ag-2(mu(2)-L-1)(m(3)-L-1)(2)]center dot 2PF6}(n) (4), {[Ag-3(mu(2)-L-1)(4)(mu(2)-CF3SO3)(CF3SO3)]center dot CF3SO3} (5), {[Cd(L-2)(2)(mu(2)-NCS)(2)]}(n) (6), [Ag(mu(2)-L-2)(mu(2)-CF3SO3)](n) (7) and {[Ag(mu(2)-L-2)]center dot BF4}(n) (8) have been isolated. Both 1 and 2 are 2D Cd-II coordination polymers containing infinite {Cd-NCS-Cd} chains (for 1) or infinite {Cd-dca-Cd} layers (for 2), respectively. 3 is a 2D Cu-II coordination polymer, in which central metal ions are bridged via a bidentate bridging L-1 ligand. While when different Ag-I salts were introduced into the reaction system, 1D Ag-I coordination polymers 4 and 5 with diverse coordination modes can be isolated. Furthermore, when the isomeric oxadiazol-pyridine L-2 is used to replace L-1 in the reaction system, 6-8 can be isolated. 6 is a 2D Cd-II coordination polymer containing {Cd-NCS-Cd} layers. 7 is a 2D neutral Ag-I coordination polymer while 8 is a 2D cationic AgI coordination polymer. Variable temperature magnetic susceptibility measurements (2-300 K) reveal anti-ferromagnetic interactions between central copper(II) ions for 3. Solid-state luminescent properties of 1, 2 and 4-8 have been investigated indicating strong fluorescent emissions. Additionally, luminescent measurements illustrate that complex 8 exhibits highly sensitive luminescence sensing for Cr2O72- ions in aqueous solutions with high quenching efficiency K-sv = 2.08 x 10(4) L mol(-1) and low detection limit (0.19 mu M (S/N = 3)). 8 also represents the first report of a coordination polymer based on oxadiazol-pyridine derivatives with a luminescence response to Cr2O72- anion pollutants in aqueous solutions.