Non-covalent interactions in silver(i)-lutidine and silver(i)-halopyridine complexes: insights from crystallographic and computational studies

Abstract

Discrete silver(I) coordination complexes with pyridyl derivatives were investigated to determine the prominent non-covalent interactions (NCIs) that stabilize the complexes. Four dimethylpyridines (or lutidines) were used to prepare [Ag(2,3-Lut)₂(NO₃)] (I), [Ag(2,6-Lut)₂(NO₃)] (II), [Ag(3,4-Lut)₂(NO₃)(H₂O)] (III), and [Ag(3,5-Lut)₃(NO₃)] (IV). Another series of complexes were prepared from 3-chloropyridine and 3-bromopyridine: [Ag(3-Clpy)₃NO₃] (V), [Ag(3-Brpy)₃(NO₃)] (VI) and [Ag(3-Brpy)₂(NO₃)] (VII). Spectroscopic and structural studies revealed a range of NCIs in each structure, including hydrogen bonding, halogen bonding, Ag⋯H agostic interactions, and Ag⋯π and π⋯π interactions. The AgL₂ complexes adopted an almost linear coordination geometry, except for VII, which exhibited a bent geometry. The AgL₃ complexes adopted a propeller conformation and were packed in a tail-and-groove arrangement. Computational studies were used to confirm the metal–ligand charge transfer (MLCT) characteristics of the electronic transitions observed in the UV spectra. A potential energy surface scan of compound I revealed two distinct conformations with a low rotational energy barrier.