The vanadium(V) cation structures in mixed acid based electrolyte solution were analyzed by density functional theory (DFT) based computational modeling and V-51 and Cl-35 nuclear magnetic resonance (NMR) spectroscopy. The vanadium(V) cation exists as di-nuclear [V2O3Cl2 center dot 6H(2)O](2+) compound at higher vanadium concentrations (>= 1.75 M). In particular, at high temperatures (>295 K) this di-nuclear compound undergoes ligand exchange process with nearby solvent chlorine molecule and forms chlorine bonded [V2O3Cl center dot 6H(2)O](2+) compound. This chlorine bonded [V2O3Cl2 center dot 6H(2)O]2+ compound might be resistant to the de-protonation reaction which is the initial step in the precipitation reaction in vanadium based electrolyte solutions. The combined theoretical and experimental approach reveals that formation of chlorine bonded [V2O3Cl2 center dot 6H(2)O](2+) compound might be central to the observed higher thermal stability of mixed acid based vanadium(V) electrolyte solutions. (C) 2013 Elsevier B.V. All rights reserved.