Ligand and Substituent Effect on Regium-π Bonding in Cu and Ag π-Conjugated Complexes: A Density Functional Study.

Density functional theory investigation of regium (Rg)-π bonding using the RgL-X model system, where Rg = Cu and Ag; L = CN, NO 2 , and OH; X = π-conjugated system (benzene, cyanobenzene, benzoic acid, pyridine, 2-methoxy aniline, 1,4-dimethoxy benzene, and cyclophane), has been performed. Conclusive evidence of the Rg-π bond has been provided by analysis of molecular electrostatic potential surfaces, Rg-π bond length, interaction energy (Δ E ), second-order perturbation energy ( E 2 ), charge transfer (Δ q ), quantum theory of atom in molecules, and noncovalent interaction plots for 42 structural arrangements with varying ligands and the substituted aromatic ring. The Rg-π bond length in the optimized model systems varies from 2.03 to 2.12 Å in Cu complexes ( 1 - 21 ) and from 2.26 to 2.38 Å in Ag complexes ( 22 - 42 ) at the PBE0-D3 functional. While the ligand (L) attached to the Rg metal has a bargaining effect on the strength of the Rg-π bond (in the order of -OH > -CN = -NO 2 ), the π-conjugated systems have a diminutive effect. Two X-ray crystal structures (CUCSOI and AHIDQU) having the Rg-π bond, accessed from Cambridge Crystallographic Data Centre (CCDC), are discussed here to signify the influence of Rg-π bonding on the crystal structure.