An improved synthesis, crystal structures, and metallochromism of salts of [Ru(tolyl-terpy)(CN)3]−

The previously reported complex [Ru(ttpy)(CN)3]− [ttpy = 4′(p-tolyl)-2,2′:6′,2″-terpyridine] is conveniently synthesised by reaction of ttpy with Ru(dmso)4Cl2 to give [Ru(ttpy)(dmso)Cl2], which reacts in turn with KCN in aqueous ethanol to afford [Ru(ttpy)(CN)3]− which was isolated and crystallographically characterised as both its (PPN)+ and K+ salts. The K+ salt contains clusters containing three complex anions and three K+ cations connected by end-on and side-on cyanide ligation to the K+ ions. The solution speciation behaviour of [Ru(ttpy)(CN)3]− was investigated with both Zn2+ and K+ salts in MeCN, a solvent sufficiently non-competitive to allow the added metal cations to associate with the complex anion via the externally-directed cyanide lone pairs. UV–Vis spectroscopic titration of (PPN)[Ru(ttpy)(CN)3] with Zn(ClO4)2 showed a blue shift of 2900 cm−1 in the 1MLCT absorption manifold due to the ‘metallochromism’ effect; a series of distinct binding events could be discerned corresponding to formation of 4:1, 1:1 and then 1:3 anion:cation adducts, all with high formation constants, as the titration proceeded. In contrast titration of (PPN)[Ru(ttpy)(CN)3] with the more weakly Lewis-acidic KPF6 resulted in a much smaller blue-shift of the 1MLCT absorptions, and the titration data corresponded to formation of 1:1 and then 2:1 cation:anion adducts with weaker stepwise association constants of the order of 104 and then 103 M−1. Although association of [Ru(ttpy)(CN)3]− resulted in a blue-shift of the 1MLCT absorptions, the luminescence was steadily quenched, as raising the 3MLCT level makes radiationless decay via a low-lying 3MC state possible.

The complex anion [Ru(ttpy)(CN)3]−, for which crystal structures of its K+ and (PPN)+ salts are presented, aggregates with Zn2+ and K+ ions in MeCN via the externally-directed lone pairs on the cyanide groups to form adducts with a range of stiochiometries; this association results in a blue-shift of the 1MLCT absorption maxima but also causes quenching of the luminescence.Figure optionsDownload as PowerPoint slide