The Relationship Between Aromaticity and Charge‐Transfer Transitions: A Combined Study of Square‐Planar Metal Complexes Based on DFT, NMR and Nucleus‐Independent Chemical Shifts

Abstract

AbstractThe aromaticity of square‐planar metal complexes, in this case mixed diiminodithiolate complexes of group VIII metals, has been investigated by 1H and 1H‐15N NMR spectroscopy, both experimentally and theoretically, as well as NICS indices. The electron‐donating/‐attracting ability of the substituent group and the metal ion interact with each other and control the aromaticity of the chelated rings and, as a consequence, the extent of the delocalization in the molecular plane. Evolution of the nucleus‐independent chemical shift (NICS) of the ligands upon complexation is consistent with the change in their electron distribution. At the same time, and in analogy with the EMF in closed circuits, a positive difference of the NICS value (ΔNICS) between two points (where HOMO and LUMO are located) can be envisioned as the driving force for charge‐transfer transitions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)