Abstract Electron spin resonance (ESR) spectroscopy was used to characterize the ligand environment of VO 2+ absorbed on boehmite and noncrystalline aluminosilicates. Boehmite possessed a relatively low capacity to chemisorb VO 2+ at discrete sites at low pH, a fact attributed to the chemical inactivity of the dominant (020) surfaces of the mineral. The chemisorbed cation is rigidly bound by one or two surface oxyanions. Chemisorption on allophane produced slightly different ESR parameters for VO 2+, a possible consequence of the participation of silanol groups in the metal-surface bond. Evidence for ternary surface complexes was seen upon the addition of phosphate to the VO 2+-surface complexes, with changes occurring in the ESR spectrum of bound VO 2+. Oxalate also appeared to perturb the ligand environment of sorbed VO 2+, but other anionic species had little or no effect. The experimental results point to the coadsorption of a vanadyl-phosphate complex, in which both the VO 2+ and the PO 4 3− are chemisorbed to surface Al atoms. The ESR spectra of VO 2+ in model phosphate compounds are used to establish the effect of PO 4 3− coordination with VO 2+ on the spectral parameters.