Issue 37, 2019

Revisiting π backbonding: the influence of d orbitals on metal–CO bonds and ligand red shifts

Abstract

The concept of π backbonding is widely used to explain the complex stabilities and CO stretch frequency red shifts of transition metal carbonyls. We theoretically investigate a non-transition metal 18-electron carbonyl complex (Mg(CO)8) and find a pronounced CO red shift without metal–carbon π bonds. Moreover, we use truncated basis sets on the “honorary” and true transition metals Ca and Ti in Ca(CO)8 and [Ti(CO)8]2+ complexes to probe the influence of d functions on carbonyl complex stability, C–O bond strength, metal-to-ligand charge transfer and bond order compared to hypothetical complexes without metal-d contributions. We find that the occurrence of metal–ligand π bonds through metal d functions greatly enhances the complex stabilities on one hand but only slightly affects the CO red shift on the other hand, compared to metal carbonyl systems with no d contributions. We also highlight the discrepancy between the formal oxidation state of 0 of Mg and Ca despite them carrying a significant positive charge.

Graphical abstract: Revisiting π backbonding: the influence of d orbitals on metal–CO bonds and ligand red shifts

Associated articles

Supplementary files

Article information

Article type
Paper
Submitted
21 Aug 2019
Accepted
04 Sep 2019
First published
05 Sep 2019

Phys. Chem. Chem. Phys., 2019,21, 20814-20821

Revisiting π backbonding: the influence of d orbitals on metal–CO bonds and ligand red shifts

D. Koch, Y. Chen, P. Golub and S. Manzhos, Phys. Chem. Chem. Phys., 2019, 21, 20814 DOI: 10.1039/C9CP04624K

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