Investigation on the crystal growth and characterisation of an organometallic non linear optical crystal – Tetrathiourea mercury tetrathiocyanato manganate

An organometallic complex tetrathiourea mercury tetrathiocyanato manganate (TMTM) was synthesised by two step chemical route. The influence of pH on the solubility, stability of the growth solution and growth of TMTM single crystal was studied. The bulk crystal of dimension 2.7 cm × 0.5 cm × 0.4 cm was grown at an optimized pH value of 3.0 by solvent evaporation method using water as a solvent. The structure and the crystallinity of the grown crystal were confirmed from single crystal XRD and powder XRD studies. The presence of thiourea and thiocyanate ligand and their coordination with the metal ions are confirmed from the IR studies. The grown single crystal of TMTM shows 69% transparency over the entire range of visible region with a cut-off wavelength of 362 nm. The SHG efficiency of TMTM was found to be 0.08 time that of MMTC. The complex exhibits good thermal stability up to 205 °C and it is non-hygroscopic in nature. The surface analysis was carried out by etching studies which shows a layer growth pattern revealing the 2D nucleation growth mechanism. From the Vickers hardness studies, the work hardening coefficient and the elastic stiffness constant were calculated.