Nonlinear optical (NLO) material of diaqua (thiocyanato) manganese mercury-N,N-dimethylacetamide (MMTWD) was synthesized in an aqueous solution, and bulk single crystals were grown by slow-cooling and slow-evaporation methods using dimethyl acetamide (DMA) and water (1:1) as a mixed solvent. Elemental analysis of the synthesized MMTWD was studied by CHN analysis. The crystal structure and morphology of MMTWD single crystal were studied by X-ray diffraction analysis. The presence of functional groups, coordination of dimethyl acetamide (DMA) and the water molecules were confirmed by Fourier transform infrared (FTIR) spectrum, which was further confirmed by the laser Raman studies. The thermal stability and thermal decomposition of MMTWD crystals were investigated by means of thermo-gravimetric analysis and differential thermal analysis. Optical transparency of the grown crystal was studied by UV-vis spectroscopy. The linear refractive index of the MMTWD single crystal was measured using Abbey's refractometer. The second-harmonic generation (SHC) study was carried out by Kurtz powder method. The dielectric loss and dielectric constant measurement as a function of frequency and temperature were measured on MMTWD single crystal. The formation of rectangular etch pits pattern shows the two-dimensional nucleation mechanism. (C) 2008 Elsevier B.V. All rights reserved.