Conformational analysis of trans-[ReO2(pn)2]+ in aqueous solution by NMR and DFT calculations

In this work we report a conformational study of [ReVO2(pn)]2+ (pn = 1,2-propylenediamine) in aqueous solution using experimental and theoretical approaches. The studies in aqueous solution were carried out by 1H and 13C NMR spectroscopy and applying the Altona's equation. Theoretically, the studies were performed by means of the Density Functional Theory (DFT) and the Gauge-Including Atomic Orbitals (GIAO) method. All 12 spatial dispositions arising from the relative orientation of the CH3 substituents were studied. The results are consistent with the predominance of complexes with λλ ligand conformation. The computation analysis shows that only the λλ conformers exhibit a 1H-signal pattern in agreement with the experimental evidence. We proposed that only two main species can predominate in an aqueous solution of {ReVO2[(R)-pn]2}+. They should have a λλ conformation of the (R)-pn ligands and the energy difference (PCM (Polarizable Continuum Model) methodology) between them is only 1.5 kJ mol−1.