Structures and third-order nonlinear optical properties of two three-dimensional Cd(ii) coordination polymers with trinodal (3, 4, 5) and dinodal (4, 5) connected network topologies

Abstract

Two Cd(II) coordination polymers, [Cd₃(1,2-bib)₄(STP)₂(H₂O)₂]·10H₂O (1) and [Cd₃(1,3-bib)₅(STP)₂]·3H₂O (2) (1,2-bib = 1,2-bis(imidazol-l-yl-methyl)benzene; 1,3-bib = 1,3-bis(imidazol-l-yl-methyl)benzene; NaH₂STP = sodium 3,5-dicarboxybenzenesulfonate), have been synthesized under hydrothermal conditions. Compound 1 presents a 3-nodal (3, 4, 5)-connected 3D framework with a point (Schläfli) symbol (4·6²)₂(4²·6⁴·8⁴)₂(4²·8⁴). Compound 2 exhibits a 3D framework with 2-nodal (4, 5)-connected (4²·5³·6⁵)₂(5²·6⁴) topology. The third-order nonlinear optical (NLO) properties of two compounds were determined in DMSO solution and thin films by a Z-scan technique. They show strong third-order nonlinear optical (NLO) absorption with absorptive coefficients β(MKS) 6.53 × 10⁻¹¹ m W⁻¹ for 1 and 7.15 × 10⁻¹¹ m W⁻¹ for 2 in DMSO solution. The third-order NLO susceptibility χ⁽³⁾ is calculated as 2.23 × 10⁻¹² for 1, 2.50 × 10⁻¹² esu for 2 in DMSO solution. While in thin films, both compounds show stronger NLO absorption with absorptive coefficients β(MKS) 31.1 × 10⁻⁶ m W⁻¹ for 1 and 3.80 × 10⁻⁶ m W⁻¹ for 2, and third-order NLO susceptibility χ⁽³⁾ is calculated as 1.09 × 10⁻⁶ for 1, 0.13 × 10⁻⁶ esu for 2. The electronic structures of the two compounds were investigated by density functional theory (DFT). The composition of the frontier orbitals and the origin of the NLO properties of the two compounds were discussed.