Structure–Property Relationships in a Series of Hybrid Halopyridinium Ruthenium(IV) Halides

The synthesis and characterization of a family of hybrid ruthenium halides are reported, consisting of haloruthenium octahedra (X = Cl, Br) charge-balanced with halopyridinium (XPy; X = H, Cl, Br, I) organic cations that assemble via noncovalent interactions (NCIs) between ion pairs. Diffuse reflectance spectroscopy showed that compounds containing RuBr62– octahedra displayed a lower band gap (1.05 eV < x < 1.08 eV) compared to compounds with RuCl62– octahedra (1.22 eV < x < 1.43 eV). Additionally, computational density functional theory-based natural bonding orbital analysis and density of state methods were used to characterize second-sphere NCI strengths and explicate molecular orbital perturbations to elucidate their influence on Ru–X orbital constructs and in turn rationalize band-gap trends. Analyses showed that ligand-to-metal charge transfer is responsible for the small band-gap energies and are unperturbed by second-sphere interactions. This report serves as a platform for probing the relationship between the structural and photophysical properties within the haloruthenium family of low-dimensional transition metal halide perovskite derivatives.