Exploring the Coordination Modes of a Keggin-Type [ZnW₁₂O₄₀]^6– Anionic Cluster: Bonding Patterns, Crystal Structure, and Semiconducting Properties

Abstract

Polyoxometalate-based organic-inorganic hybrid compounds (POIHCs) have been greatly developed due to their wide application prospects, but the pursuit of their directed synthesis via molecular design still remains a challenge. Herein, we demonstrate that the coordination modes of the Keggin-type [ZnW₁₂O₄₀]^6- anion can be tuned, which leads to different semiconductor characteristics. Using the same building block, ligand, and metal ion (ZnW₁₂, phen, Cu²⁺), we synthesized three new POIHCs with different bonding patterns by means of different coordination modes of ZnW₁₂. The three POIHCs (H₂phen){ZnW₁₂O₄₀[Cu(phen)₂]₂}·3H₂O (<b>1</b>), {ZnW₁₂O₄₀[Cu(phen)(H₂O)₂]₂[Cu(phen)(H₂O)]}_<i>n</i>·3H₂O (<b>2</b>), and (Me₄N)₂{ZnW₁₂O₄₀[Cu(phen)(H₂O)]₂}_<i>n</i>·5H₂O (<b>3</b>) (phen = 1,10-phenanthroline) have been structurally characterized by single-crystal X-ray diffraction. Compound <b>1</b> appears as a zero-dimensional coordination complex cluster, while compounds <b>2</b> and <b>3</b> are both 1D chain structures with different Cu²⁺ bridge linkages. Although these three POIHCs possess the same chemical components, their semiconductor properties are different, which is demonstrated by measurements of transient photocurrent and band gap (<i>E</i>_g) values. Furthermore, we carried out comparative experiments on the photoconductivity performance of compounds <b>1</b>-<b>3</b> and their photocatalytic reduction from O₂ to H₂O₂, indicating the significant influence of the energy level matching on the photocatalytic activity.