Structures and redox-switchable second-order nonlinear optics properties of N-legged piano stool shaped 12-vertex rhenacarborane half-sandwich complexes

Three sets of n-legged piano stool shaped (–Re(CO)3 or –Re(CO)3I) 12-vertex rhenacarborane half-sandwich complexes (n = 3 or 4) have been investigated by density functional theory (DFT). Natural bond orbital (NBO) analysis shows that introducing iodine (I) atom changes the bond formations between rhenium (Re) ion and carborane cage or 3/4-legged piano stools. The redox-switchable second-order nonlinear optics (NLO) properties of sets 1 and 3 are different, notably, the total first hyperpolarizability (βtot) of complex 231e is about 20 times larger than that of its parent complex 3. Furthermore, time-dependent density functional theory (TDDFT) calculations were employed to account for the redox-switchable NLO properties, the plots of frontier molecular orbitals (FMOs) and electron density difference maps (EDDM) visually indicate that the intramolecular interactions among I atom, Re ion and carborane cage contribute to the redox property of set 3.