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

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(Mebpy)3]n, [Re­(tpy)2]n, [Re­(Tp)­(bpy)­Cl]n (n = 2+, 1+, 0, 1−), and [Re­(bpy)­(CO)3]1+,0,1– (Mebpy = 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: [(cyDAB•)­ReIVCl3(PPh3)]0 1, [ReIII(tpy•)­Cl­(PPh3)2]Cl 2, [ReIII(tpy0)2Cl]­(OTf)2·2Et2O 8. There are no structurally significant (experimentally detectable) π-back-bond effects of the neutral bpy0 or tpy0 ligands irrespective of the dN configuration (N = 0–7) of the central Re atom.