Charge transfer interaction and nonlinear optical properties of barium chloride and thiourea complexes: a vibrational spectroscopic study

The nonlinear optical (NLO) semiorganic crystals barium thiourea chloride (BTC), bis(thiourea)barium chloride (BTBC) and barium(tetrakisthiourea) chloride (BTTC) were grown by the slow evaporation technique. FT-Raman and IR spectra of the crystallized NLO materials were recorded and analyzed. The equilibrium geometry, bonding features and harmonic vibrational wavenumbers were investigated with the help of B3LYP density functional theory (DFT) method. From the optimized geometry, the decrease in C-N bond length indicates the charge delocalization over the region of the molecules. Lengthening of C=S bond and the deviation of C=S center dot center dot center dot Cl angles clearly show the coplanarity of the amide planes of the complexes. The lowering of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy gap appears to be the cause for its enhanced charge transfer interactions. Copyright (C) 2011 John Wiley & Sons, Ltd.