Novel Pb and Zn Coordination Polymers: Synthesis, Molecular Structures, and Third-Order Nonlinear Optical Properties

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Abstract
Three novel coordination polymers [Pb(bbbm)2(NO3)2]n (bbbm = 1,1‘-(1,4-butanediyl)bis-1H-benzimidazole) 1, [Zn(bbbt)(NCS)2]n (bbbt = 1,1‘-(1,4-butanediyl)bis-1H-benzotriazole) 2, and [Zn(pbbt)(NCS)2]n (pbbt = 1,1‘-(1,3-propylene)bis-1H-benzotriazole) 3 were synthesized and structurally characterized. Polymer 1 exhibits a two-dimensional rhombohedral grid network structure, the dimensions of the grid are 14.274 × 14.274 Å, and the diagonal-to-diagonal distances are 24.809 × 14.125 Å. Polymer 2 possesses a concavo-convex chain structure different from those of the known one-dimensional polymers, which are linear chain, zigzag chain, helical chain, double-stranded chain, and ladder chain. Polymer 3 exhibits a one-dimensional zigzag chain structure, and these chains were packed as an ...ABAB... layered structure. The third-order nonlinear optical (NLO) properties of polymers 1, 2, and 3 were determined with a 7-ns pulsed laser at 532 nm. 1 shows strong third-order NLO absorptive and refractive properties, and its α2 and n2 values were calculated to be 5.8 × 10-9 m W-1 and 4.67 × 10-18 m2 W-1 in a 3.4 × 10-4 mol dm-3 DMF solution, respectively. Both 2 and 3 exhibit weaker NLO absorption and strong refractive properties, and their n2 values are 4.53 × 10-18 m2 W-1 for 2 in a 5.2 × 10-4 mol dm-3 DMF solution and 3.02 × 10-18 m2 W-1 for 3 in a 4.35 × 10-4 mol dm-3 DMF solution. The χ(3) values of 1, 2, and 3 were calculated to be 1.67 × 10-11, 1.62 × 10-11, and 1.08 × 10-11 esu, respectively, and the values are larger than those of the reported coordination polymers. We deduce that the valence shell structures of metal ions may have some influence on the strength of NLO properties, and discuss the relationships between the crystal structures of coordination polymers and the observed NLO properties.