Interestingly, recent studies indicate that the Lewis-base adducts of these crystals possess superior NLO property than the parent metal SCN crystals. The metal SCNs and their Lewis-base adducts are some of the interesting themes of structural chemistry [3]. This encouraging switch-over is mainly attributed to the improvement of NLO property, by the addition of DMSO ligand. The introduction of DMSO aids in better electronic oscillations in SCN ligand, leading to an enhancement in NLO efficiency. The present study deals with manganese mercury thiocyanate bis-dimethyl sulfoxide (MMTD), a Lewis-base adduct of MMTC [2]. In the structure of MMTD, the hard Mn2+ ion is coordinated with the harder N-(SCN) and O-(DMSO) ligands, while the soft Hg2+ is coordinated with the softer S-(SCN) ligands. The Hg2+ ion is coordinated with four SCN S-atoms and is in a tetrahedral geometry [4]. The Mn2+ ion has six coordinates and is in an octahedral geometry; both the O-atoms of the DMSO molecules are coordinated axially, while the four SCN N-atoms are coordinated equatorially. A comparative study shows that MMTD is the second best material in terms of second harmonic efficiency among the other organo-metallic crystals reported so far. Its SHG efficiency is 23 times that of urea and thus next to ZCTC (51 times urea) only [5] and [6].
The present investigation stems from our continuing research on organo-metallic crystals [7] and [8] and it deals with the growth aspects of bulk-size single crystals of MMTD, grown from a mixed solvent of water–DMSO. The crystal structure, spectroscopic properties and thermal decomposition of MMTD have been reported earlier [5] and [9]. In the present work, the optical properties of grown crystals have been studied by recording its FTIR, FT-Raman and UV–Vis–NIR spectra. The dielectric constant and dielectric loss measurements as well as the thermal diffusivity, thermal effusivity, thermal conductivity and microhardness studies of MMTD have been carried out and are reported for the first time.