Structural and Spectroscopic Characterization of Rhenium Complexes Containing Neutral, Monoanionic, and Dianionic Ligands of 2,2'-Bipyridines and 2,2':6,2″-Terpyridines: An Experimental and Density Functional Theory (DFT)-Computational Study.

Abstract

The molecular and electronic structures of the members of the following electron transfer series have been determined by single crystal X-ray crystallography, temperature dependent magnetic susceptibility measurements, and UV-vis-NIR and electron paramagnetic resonance spectroscopy and verified by density functional theory calculations (DFT B3LYP): [Re((Me)bpy)3](n), [Re(tpy)2](n), [Re(Tp)(bpy)Cl](n) (n = 2+, 1+, 0, 1-), and [Re(bpy)(CO)3](1+,0,1-) ((Me)bpy = 4, 4'-dimethyl-2,2'-bipyridine; Tp(-) = tris-pyrazolylborate, tpy = 2, 2':6, 2″-terpyridine). For each series we show that the average Cpy-Cpy bond length and the average C-Nchel bond distance vary in a linear fashion with the charge n of the N,N'-coordinated (bpy)(n) and N,N',N″-coordinated (tpy)(n) ligand. Consequently, the difference Δ between these two bond lengths varies also linearly with n. Δ is shown to be a useful single marker for the oxidation level of these two heterocyclic ligands (neutral, π-radical anion, and dianion). In addition, we have synthesized and structurally as well as spectroscopically characterized the following complexes: [((cy)DAB(•))Re(IV)Cl3(PPh3)](0) 1, [Re(III)(tpy(•))Cl(PPh3)2]Cl 2, [Re(III)(tpy(0))2Cl](OTf)2·2Et2O 8. There are no structurally significant (experimentally detectable) π-back-bond effects of the neutral bpy(0) or tpy(0) ligands irrespective of the d(N) configuration (N = 0-7) of the central Re atom.