Synthesis, crystal growth, structural, spectral and optical properties of tri-allylthiourea mercury bromide (ATMB) single crystals

Metal-organic tri-allylthiourea mercury bromide (ATMB) is a new kind of double ligand complex single crystal. Incorporation of metals into NLO systems give a new dimension of study and introduce many new variables. Transfer of unlocalized electrons from the double ligand allylthiourea to the central metal ion (Hg2+) through the sulphur atom display a large molecular hyperpolarizability. Experimental results show that the solubility of ATMB in aqueous solution is very low and also it is difficult to grow a large size crystal. Attempts were made to grow single crystals of ATMB by solution growth methods. Structural, spectral, optical and surface features of ATMB were studied with different characterization techniques. Trigonal crystal structure of the as-grown single crystals was identified from the powder X-ray diffraction. X-ray rocking curve contains a single sharp peak and indicates that the specimen is free from structural grain boundaries. Vibrational spectral analyses reveal that the metal-ligand coordination occur, only through sulphur and not with nitrogen by shifting the vibration frequencies of υ (N-C-N) to the higher and υ(C=S) to the lower values. ATMB has UV cut-off wavelength at 340 nm and there is no absorption up to 1500 nm which is more desirable for non-linear applications.