Three-dimensional supramolecular networks constructed from Keggin anions and metal–organic complex with unpredicted oxidation of an N-heterocycle ligand

Abstract

Two novel Keggin polyoxometalate compounds, [Cu 2(PCA) 4(H 2O) 2][SiW 12O 40]·8H 2O ( 1) and [Cu(PCA) 2(H 2O) 4][Cu(PCA) 3(H 2O)][SiW 12O 40]·H 2O ( 2) (PCA = pyridine-4-carboxylic acid), were synthesized by in situ generation of pyridine-4-carboxylic acid ligand from 1,3-bis(4-pyridyl)propane precursor under hydrothermal conditions. Compounds 1 and 2 were structurally characterized by elemental analysis, IR and UV spectrography, TGA and single-crystal X-ray diffraction analysis. The variable-temperature magnetic susceptibility was measured at 2–300 K for 1. The compound 1 consists of polyoxoanions [α-SiW 12O 40] 4−, dimer cations [Cu 2(PCA) 4(H 2O) 2] 4+ and lattice water molecules. The water molecules link [α-SiW 12O 40] 4− and [Cu 2(PCA) 4(H 2O) 2] 4+ into three-dimensional (3D) architecture via hydrogen bonds. Polyoxoanions of 2 are linked into 1D chains through hydrogen bonds. Moreover, 1D chains are further extended into 3D supramolecular networks by hydrogen bonds and π···π stacking interactions of pyridine-4-carboxylic acid molecules. The variable-temperature magnetic measurement of 1 shows an antiferromagnetic interaction in the 2–300 K temperature range.