Electronic Structures of Cr(III) and V(II) Polypyridyl Systems: Undertones in an Isoelectronic Analogy.

A recently reported description of the photophysical properties of V polypyridyl systems has highlighted several distinctions between isoelectronic, d, Cr, and V tris-homoleptic polypyridyl complexes of 2,2'-bipyridine (bpy) and 1,10-phenanthroline (phen). Here, we combine theory and experimental data to elucidate the differences in electronic structures. We provide the first crystallographic structures of the V complexes [V(bpy)](BPh) () and [V(phen)](OTf) () and observe pronounced trigonal distortion relative to analogous Cr complexes. We use electronic absorption spectroscopy in tandem with TD-DFT computations to assign metal-ligand charge transfer (MLCT) properties of and that are unique from the intraligand transitions, (IL), solely observed in Cr analogues. Our newly developed natural transition spin density (NTρ) plots characterize both the Cr and V absorbance properties. A multideterminant approach to DFT assigns the energy of the E state of as stabilized through electron delocalization. We find that the profound differences in excited state lifetimes for Cr and V polypyridyls arise from differences in the characters of their lowest doublet states and pathways for intersystem crossing, both of which stem from trigonal structural distortion and metal-ligand π-covalency.