Structure and reactivity of di-<i>n</i>-butyltin(IV) derivative of chlordiazepoxide based on electronic structure calculations

Abstract

Density functional theory calculations in electronic structure studies of <i>n</i>-Bu₂SnL₂ (where L is the monoanion of chlordiazepoxide (LH), a benzodiazepine derivative with hypnotic action) have been reported using the Gaussian09 software. The molecular geometries of LH and tetrahedral <i>n</i>-Bu₂SnL₂ have been optimized at B3LYP/6-31G(d,p) and B3LYP/6-31G(d,p)/Def2-SVP(Sn) level of theory, respectively. Harmonic vibrational frequencies are computed at the same level of theory to find the true potential energy surface minima. The effect of functional, basis set and computational cost is analyzed. The various geometrical and thermochemical parameters have been obtained in gas phase and in the solvent. The atomic charges at all the atoms are calculated using Mulliken population analysis, Hirshfeld population analysis and natural population analysis. The charge distribution within the studied complex is explained on the basis of molecular electrostatic potential maps, and conceptual-DFT based global reactivity descriptors using the finite difference approximation method. The calculated parameters suggest a distorted tetrahedral geometry around the central Sn atom. The calculated Sn-O bond lengths reveals different degree of interaction of two chlordiazepoxide units with the di-<i>n</i>-butyltin(IV) moiety. Among the atoms coordinated to the central Sn atom, oxygen from one LH unit is nucleophilic, whereas the second oxygen atom from the other LH unit is electrophilic in nature. The results provide an insight into the efficacy of computational methods in understanding the structure and reactivity of organotin(IV) derivatives of hetero donor atoms.