A novel intercluster compound, {[}(n-C4H9)4P]3{[}H3V10O28] (IL01-V10), constructed from the tetrabutylphosphonium cation and decavanadate, has been synthesized and unequivocally characterized by elemental analysis, FTIR spectroscopy, mass spectrometry, X-ray crystallography, and solution 1H, 13C, 31P\{1H\}, and 51V NMR spectroscopy. Compound IL01-V10 was formed by ionic interaction between the phosphonium cation and the decavanadate anion. Cryospray high-resolution mass spectrometry revealed the {[}H3V10O28]3 cluster remains intact in solution. Three further phosphonium polyoxovanadates were synthesized and characterized by the same techniques as used for IL01-V10.