Homoleptic and heteroleptic complexes of chromium(III) containing 4'-diphenylamino-2,2':6',2''-terpyridine ligands

Two heteroleptic bis(2,2′:6′,2″-terpyridine)chromium(III) complexes [Cr(1)(4′-(4-tolyl)tpy)][CF3SO3]3 and [Cr(2)(4′-(4-tolyl)tpy)][CF3SO3]3 (1 = 4-([2,2′:6′,2″-terpyridin]-4′-yl)-N,N-diphenylaniline, 2 = 4-([2,2′:6′,2″-terpyridin]-4′-yl)-N,N-bis(4-methoxyphenyl)aniline, 4′-(4-tolyl)tpy = 4′-(4-tolyl)-2,2′:6′,2″-terpyridine) have been prepared and their spectroscopic and electrochemical properties compared with those of [Cr(4′-(4-tolyl)tpy)2][CF3SO3]3 and [Cr(1)2][CF3SO3]3. The single crystal structure of [Cr(4′-(4-tolyl)tpy)2][CF3SO3]3·2MeCN is presented, and the effects of accommodating three triflate anions and two MeCN molecules per cation are discussed in terms of related structures. The coordination of 1 or 2 to chromium(III) red-shifts the intra-ligand charge transfer (ILCT) band and this band exhibits a negative solvatochromic effect in some solvents. However, in H2O, MeOH, DMSO and DMF, the tpy ligands are labile; changes in the absorption spectra of solutions of [Cr(2)(4′-(4-tolyl)tpy)][CF3SO3]3 are consistent with the formation of [Cr(4′-Xtpy)(Solv)3]3+ (Solv = solvent) rather than complete ligand displacement or a ligand redistribution.