Insertion of V Ions into the Polyoxotungstate Archetype {AsW}.

A new polyoxometalate compound consisting of the 39-tungsto-4-arsenate(III) unit with four incorporated V ions, isolated as (NH)[(VO)(VO(HO))(AsWO)(AsWV(OH)O)(WO)]·48HO (-), was synthesized and fully characterized. SQUID magnetometry shows three weakly coupled V centers with an antiferromagnetic exchange interaction and one isolated V ion as a spin-/ Curie paramagnet. UV-vis spectroscopy indicates that the structure remains intact in aqueous solution for at least 24 h. To enable the deposition of from solution on gold surfaces, its trihexyltetradecylphosphonium salt, , was prepared. The IR spectra of both congeners reveal the structural identity of independent of the countercations. The X-ray absorption near-edge structure data confirm the presence of V centers in a distorted square-pyramidal coordination geometry in - and . X-ray photoelectron spectroscopy of the latter, deposited on Au(111), shows that the 4 V and 35 W centers preserve their IV+ and VI+ oxidation states, while the remaining 4 W ions are reduced to IV+.