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

Abstract

In this work two positional-isomeric oxadiazol-pyridine ligands 3-(5-methyl-1,3,4-oxadiazol-2-yl)pyridine (L1) and 4-(5-methyl-1,3,4-oxadiazol-2-yl)pyridine (L2) have been designed and synthesized. A series of novel coordination polymers, namely [Cd2(μ2-L1)2(μ2-NCS)4]n (1), {[Cd(L1)(μ2-dca)2(H2O)]·H2O}n (2), {[Cu(μ2-L1)2(NCS)2]·0.5H2O}n (3), {[Ag2(μ2-L1)(μ3-L1)2]·2PF6}n (4), {[Ag3(μ2-L1)4(μ2-CF3SO3)(CF3SO3)]·CF3SO3} (5), {[Cd(L2)2(μ2-NCS)2]}n (6), [Ag(μ2-L2)(μ2-CF3SO3)]n (7) and {[Ag(μ2-L2)]·BF4}n (8) have been isolated. Both 1 and 2 are 2D CdII coordination polymers containing infinite {Cd-NCS-Cd} chains (for 1) or infinite {Cd-dca-Cd} layers (for 2), respectively. 3 is a 2D CuII coordination polymer, in which central metal ions are bridged via a bidentate bridging L1 ligand. While when different AgI salts were introduced into the reaction system, 1D AgI coordination polymers 4 and 5 with diverse coordination modes can be isolated. Furthermore, when the isomeric oxadiazol-pyridine L2 is used to replace L1 in the reaction system, 6-8 can be isolated. 6 is a 2D CdII coordination polymer containing {Cd-NCS-Cd} layers. 7 is a 2D neutral AgI 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 Ksv = 2.08 × 104 L mol−1 and low detection limit (0.19 μM (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.