Polyoxometalate charge directed coordination assemblies: Macrocycles and polymer chains

Abstract

To investigate the charge influence of polyoxometalates (POMs) on the compound structures, six POM-containing transition metal complexes (TMCs), [Cu^I₂L₂][Mo₆O₁₉] (1), [Cu^I₃L₃]₂[PMo₁₂O₄₀]₂ (2), [Cu^I₄L₄][SiMo₁₂O₄₀] (3), [Cu^I₄L₄][SiW₁₂O₄₀] (4), [Cu^I₄L₄][GeMo₁₂O₄₀] (5), [Cu^I₅L₅][BW₁₂O₄₀]·H₂O (6), [L = 1,4-bis(pyrazol-1-ylmethyl)benzene], were hydrothermally synthesized by using polyoxoanions with different charges as the building blocks and characterized by elemental analysis, IR spectra, PXRD, XPS, electrochemistry, surface photovoltaic spectra (SPS) and X-ray crystallography. Compound 1 consists of Lindqvist type [Mo₆O₁₉]²⁻ anions with two negative charges linking zigzag-type {[Cu^I₂L₂]²⁺}_n cationic chains to construct a 2D neutral 6³ wall-like network. In compound 2 the [PMo₁₂O₄₀]³⁻ anions with three negative charges act as the template directing L ligands to link with Cu^I ions forming an interesting triangular [Cu^I₃L₃]³⁺ macrocyclic type TMC. Compounds 3–5 are crystallographically isomorphous, and they contain Keggin type POMs anions of [SiMo₁₂O₄₀]⁴⁻, [SiW₁₂O₄₀]⁴⁻, and [GeMo₁₂O₄₀]⁴⁻ with four negative charges as the template that induce the square [Cu^I₄L₄]⁴⁺ cationic macrocyclic structures of the TMC moieties. Compound 6 is composed of [BW₁₂O₄₀]⁵⁻ anions with five negative charges linking 1D zigzag-type {[Cu^I₅L₅]⁵⁺}_n cationic chains to build up a novel 2D neutral network. The structural differences of compounds 1–6 indicate that POM anions serve as the structure-directing components performing a crucial influence on the assembly progress of TMCs in 1–6. In addition, the electrochemical properties of 1–6, and the SPS responses of 1, 5, 6 were studied, suggesting that these compounds could be used as potential electrocatalytic or photocatalytic materials.