Geometric distortions and Jahn-Teller effects in Bis(terpyridine)metal complexes
Jeanet Conradie, Chijioke Olisah, Kovo G. Akpomie, Alhadji Malloum, Samson O. Akpotu, Kayode Adesina Adegoke, Emmanuel Sunday Okeke, Elizabeth Oyinkansola Omotola, Chinemerem Ruth Ohoro, James F. Amaku
Abstract
• Bis(terpyridine)metal complexes display a distorted octahedral geometry. • Elongation Jahn-Teller distortion occurs along opposite terminal metal-nitrogen bonds. • Compression Jahn-Teller distortion occurs along the central metal-nitrogen bonds. • Guidelines to identify the kind of Jahn-Teller distortion in bis(terpyridine)metal. All bis(terpyridine)metal complexes exhibit a distorted octahedral geometry due to the steric strain imposed by the terpyridine ligand. In these complexes, the central metal-nitrogen bonds are consistently shorter than the terminal metal-nitrogen bonds, indicating that every bis(terpyridine)metal complex is inherently compressed along the direction of the central metal-nitrogen bonds. However, due to the Jahn-Teller effect, additional geometric distortion and symmetry breaking occur in Jahn-Teller active bis(terpyridine)metal complexes to stabilize the system. Examples include high-spin d 4 bis(terpyridine)manganese(III) and d 4 bis(terpyridine)chromium(II), high-spin d 6 bis(terpyridine)iron(II), low-spin d 7 bis(terpyridine)cobalt(II) and bis(terpyridine)nickel(III), and d 9 bis(terpyridine)copper(II). Elongation Jahn-Teller distortion in bis(terpyridine)metal complexes occurs along the opposite terminal metal-nitrogen bonds of one of the terpyridine ligands, with the highest symmetry achieved in such elongation Jahn-Teller distorted bis(terpyridine)metal compounds being C 2v . Compression Jahn-Teller distortion occurs along the central metal-nitrogen bonds, with the highest symmetry in these compressed bis(terpyridine)metal compounds being D 2d , although C 2v symmetry is also observed, with the z-axis defined along the central metal-nitrogen bonds. Distinguishing between the two possible Jahn-Teller distorted geometries for bis(terpyridine)metal complexes under C 2v (or lower) symmetry is not straightforward. This contribution discusses, with examples, experimental and theoretical results reported on Jahn-Teller distortion observed in bis(terpyridine)metal complexes, providing guidelines on how to identify the kind of Jahn-Teller distortion observed. In bis(terpyridine)metal complexes, the elongation Jahn-Teller distortion occurs along opposite terminal metal-nitrogen bonds of one of the terpyridine ligands, whereas compression Jahn-Teller distortion occurs along the central metal-nitrogen bonds of both terpyridine ligands.