Novel Zn (II) and Pb (II) coordination networks with large circuits: Synthesis, crystal structures and self-focusing effects

Two coordination polymers {[Zn(btx)₂(NO₃) ₂]}_n (1) and {[Pb(btx)_1.5(NCS)]NO ₃}_n (2) (btx = 1,4-bis(triazol-1-ylmethyl)benzene) have been synthesized and characterized by X-ray diffraction. Polymer 1 exhibits a 2-D network with square grid units and polymer 2 possesses an unusual 2-D layered structure with 78-membered rings. By studying the third-order nonlinear optical properties of ligand btx, polymers 1 and 2, we find that they all show strong self-focusing effects. A reasonably good fit between the experimental data and the theoretical curves suggests that the experimentally obtained NLO effects are effectively third-order in nature. The refractive index n ₂ values are 4.50 × 10^-18 m² W ^-1 for btx, 3.09 × 10^-18 m² W ^-1 for 1, and 6.01 × 10^-18 m² W ^-1 for 2. All these data can match those of the best-known third-order NLO materials such as inorganic oxides, semiconductors, and cluster compounds. In addition, we discuss the influence of the ligand and central metals on the third-order NLO properties of coordination polymers.