Theoretical Investigation of the Electronic Properties of Three Vanadium Phthalocyaninato (Pc) Based Complexes: PcV, PcVO, and PcVI

The electronic properties of three vanadium phthalocyaninato (Pc) based complexes (PcV, PcVO, and PcVI; I–III, respectively) were theoretically investigated and corresponding VL2,3-edge XAS spectra modeled. Ground state (GS) DFT outcomes indicated that IIis more stable than IIIby 141 kcal/mol; moreover, the Ziegler transition state method allowed us to estimate the PcV–X bond dissociation energy and to quantify σ/π contributions to the V–X interaction. As such, the Nalewajski–Mrozek V–X and V–N bond multiplicity indexes (V–O/V–I = 2.48/1.22; V–N = 0.64, 0.51, and 0.58 in I–III, respectively) state that the V–X bond strength and nature affect the V–N interaction. The coordination of X to V in the I→ II/I→ IIIreactions implies the transfer of two/one electrons from Ito X. In both cases, the oxidation involves only the V ion; moreover, V 3d based orbitals from which electrons are transferred were identified. Literature I/IIL2,3-edge XAS data were modeled by exploiting the DFT/ROCIS method. The same protocol was adopted to predict IIIL2,3-edge XAS spectra. Theoretical results indicated that, along the whole series, spectral features lying at the lowest excitation energies (EEs) are mostly generated by states having the same GS spin multiplicity and involve 2pV→ SOMO (single occupied molecular orbital) single electronic excitations. XAS features at higher EEs include only states with the same GS spin multiplicity in I, while states with both ΔS= 0 and ΔS= +1 (S= total spin quantum number) are present in IIand IIIwith significant, in some cases prevailing, contributions from metal to ligand charge transfer (MLCT) excitations. Beyond the role played by MLCT transitions in determining XAS patterns, it is noteworthy that they involve only Pc-based empty orbitals with no participation of the X-based virtual levels.