DFT Study on Electronic Charge Distribution and Quantum−Chemical Descriptors for the Kinetic Stability of Vanadium Aquo Complex Ions [V(H2O)6]2+ and [V(H2O)6]3+

Abstract

Despite the predominant existence of [V(H₂O)₆]²⁺ and [V(H₂O)₆]³⁺ complex ions in medicinal and biological fluid matrices, their critical roles in electrochemical, environmental, and industrial aspects of chemistry, and their typical chemical properties including high chemical instability, and fast disproportionation type chemical reactions, an in−depth study concentrated on electronic charge distributions in them and their relative chemical reactivity through quantum mechanical molecular orbitals approach is rarely available. In this insight, the hybrid density functional B3LYP with 6−31G (d, p) basis set has been employed computationally, and calculated Mulliken atomic charges distribution, HOMO−LUMO interactions and their band gaps (DE_gap), and global quantum−chemical descriptors (QCDs) for these two aquo complex ions separately. The general results depict that the [V(H₂O)₆]²⁺ ion has a: (1) higher oxidation tendency (IP = 11.332 eV), (2) stronger electron donating propensity (EA = 8.377 eV), (3) lower polarizability, (η = 1.477 eV, s  = 0.677 eV), and (4) weaker electrophilic character (ω = 32.871 eV) than the [V(H₂O)₆]³⁺ ion (IP = 18.445 eV, EA = 15.772 eV,  η = 1.336 eV, s  = 0.748 eV, and ω = 109.537 eV). Moreover, the theoretically predicted wavelengths l₁ = 420.17 nm (violet), and l₂ = 494.81 nm (green) of the visible light to be absorbed respectively by [V(H₂O)₆]²⁺ and [V(H₂O)₆]³⁺ complex ions in their aqueous solutions have confirmed their real practical colors. The major significance and novelty of this study lies in elucidating relative kinetic stability of the V (II) and V (III) aquo complex ions through ab initio type quantum mechanical method.