delta(*)(MM)-pi(L) odd electron delocalization onto aromatic bridging ligands in a paramagnetic dirhodium complex and intermolecular pi-stack interaction in crystal

The odd electron in the delta(RhRh)* orbital of (3,1)-[Rh-2(mhq)(4)py](+) ( 1(+); Hmhq = 4-methyl-2-quinolinol) was estimated to be delocalized onto ea ch pi system of the four mhq bridges to the extent of ca. 9% based on its H -1 NMR paramagnetic shifts. The experimental spin distribution in the mhq l igands is consistent with a model of mixing of the pi HOMOs of the mhq liga nds into the delta(RhRh)* singly occupied molecular orbital (SOMO). In crys tals of (3,1)-[Rh-2(hq)(4)py] (2; Hhq = 2-quinolinol) and its cationic radi cal salts, 2 or 2(+) molecules form intermolecular pi-stack arrangements of hq ligands. Intermolecular interaction between 2(+) molecules in crystal w as studied by examining electronic spectra, magnetic susceptibility, ESR, a nd electrical conductance of its salts.