δMM*-πL Odd Electron Delocalization onto Aromatic Bridging Ligands in a Paramagnetic Dirhodium Complex and Intermolecular π-Stack Interaction in Crystal

Abstract

Abstract The odd electron in the δRhRh* orbital of (3,1)-[Rh2(mhq)4py]+ (1+; Hmhq = 4-methyl-2-quinolinol) was estimated to be delocalized onto each π system of the four mhq bridges to the extent of ca. 9% based on its 1H NMR paramagnetic shifts. The experimental spin distribution in the mhq ligands is consistent with a model of mixing of the π HOMOs of the mhq ligands into the δRhRh* singly occupied molecular orbital (SOMO). In crystals of (3,1)-[Rh2(hq)4py] (2; Hhq = 2-quinolinol) and its cationic radical salts, 2 or 2+ molecules form intermolecular π-stack arrangements of hq ligands. Intermolecular interaction between 2+ molecules in crystal was studied by examining electronic spectra, magnetic susceptibility, ESR, and electrical conductance of its salts.