Ruthenium diimine ion pairs exhibit diverse intra- and intermolecular dynamics

The chemistry of cationic complexes depends on attendant anions, yet we know little about ion pairing. Here, we use mass spectrometry to study intra-cation and cation-anion interactions between ruthenium diimines [Ru(bipy) 3 ] 2+ (bipy = 2,2′-bipyridine), [Ru(phen) 3 ] 2+ (phen = 1,10-phenanthroline), and [Ru(bipy) 2 (phen)] 2+ and X − = F − , Cl − , Br − , I − , PF 6 − , HCO 2 − , AcO − , BPh 4 − , and BAr F 4 − (Ar F = 3,5-bis(trifluoromethyl)phenyl). Ion pairs {[Ru(bipy) 3 ]X} + undergo ionic bond cleavage to give [Ru(bipy) 3 ] 2+ or experience bipy loss or fracture. X − can effect hydride or electron transfer or deprotonation to afford [Ru(bipy) 2 (bipyH)] + , [Ru(bipy) 2 (bipy⋅)] + , and [Ru(bipy) 2 (bipy−H)] + , respectively. Electron transfer and deprotonation correlate with anion redox potentials and proton affinities, respectively. Ion mobility spectrometry and density functional theory suggest that halides bind between diimines, while large anions protrude. Ion pair sizes follow radii of gyration predicted by molecular dynamics, which show ion pairs of non-basic anions to be especially fluxional. Our methods offer detailed information on inner- and outer-coordination spheres.