Polyoxometalate charge directed coordination assemblies: Macrocycles and polymer chains

To investigate the charge influence of polyoxometalates (POMs) on the compound structures, six POM-containing transition metal complexes (TMCs), [(Cu2L2)-L-I][Mo6O19] (1), [(Cu3L3)-L-I](2)[PMo12O40](2) (2), [(Cu4L4)-L-I][SiMo12O40] (3), [(Cu4L4)-L-I][SiW12O40] (4), [(Cu4L4)-L-I][GeMo12O40] (5), [(Cu5L5)-L-I][BW12O40]center dot 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 {[(Cu2L2)-L-I](2+)}(n) cationic chains to construct a 2D neutral 6(3) 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 [(Cu3L3)-L-I](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 [(Cu4L4)-L-I](4+) cationic macrocyclic structures of the TMC moieties. Compound 6 is composed of [BW12O40](5-) anions with five negative charges linking 1D zigzag-type {[(Cu5L5)-L-I](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.