Two isolated Zn-ε-Keggin decorated by pyridine-imidazole with excellent electrocatalytic and third-order NLO properties

Abstract

Based on {ε-PMoV8MoVI4O40Zn4} POM units, two novel organic–inorganic hybrids, [TBA]2[H3PMoV8MoVI4O40Zn4]2[4-pyim]6·7H2O (1) (4-pyim = 4-(imidazol-2-yl)pyridine) and [H3PMoV8MoVI4O40Zn4][2-pyim]4·3H2O (2) (2-pyim = 2-(imidazol-2-yl)pyridine), have been triumphantly gained under the hydrothermal conditions via self-assembly method. Compound 1 is made up of two Zn-ε-Keggin units jointed by two ZnO bonds, which modified by three 4-pyim ligands, respectively, to form a dimer, while compound 2 consists of a Zn-ε-Keggin unit coordinated with four 2-pyim ligands. The coordination mode of the different ligands causes a change in the number of ligands coordinated on each Zn-ε-Keggin unit, resulting in the formation of dimers and monomers. What’s more, the third-order non-linear optical (NLO) properties of the two compounds were detected in detail due to the existence of a large number of conjugated organic ligands. Compound 1 has a superiority over compound 2 in NLO performance and the two-photon absorption (TPA) cross section (σ) are 7320 GM for 1 and 1573 GM for 2, which is attributed to the fact that 1 own more conjugated organic ligands. The NLO testing results of compound 1 and 2 show that Zn-ε-Keggin unit can provide a good NLO response through combining with conjugated organic ligands, indicating that it is a wally choice for NLO materials. Furthermore, the electrochemistry properties of two compounds were also amply explored.