Theoretical modeling of the square-planar to tetrahedral isomerization of bis-chelate nickel(II) complexes

The B3LYP/6-311++G(d,p) calculations of square-planar to tetrahedral conformational isomerization of bis-(propane-1,3-dionato)Ni(II) I and bis-(N-methyl-oxyvinylaldiminato)Ni(II) II complexes have been performed and the energy profiles for the low-energy barrier spin crossover rearrangements have been evaluated. The transitions between two forms of the complexes occur via the minimal energy crossing points (MECP) located at the intersection of the lowest singlet and triplet PESs. The calculated relative energies of the MECPs (7.0 and 7.1 kcal mol−1) correspond to the estimated energy barriers to the conformational isomerizations of I and II.