Growth and characterization of Hexakis(thiourea)nickel(II) nitrate crystals

Single crystals of hexakis(thiourea)nickel(II) nitrate [Ni(SC(NH2)2)6](NO3)2 are grown by slow evaporation of methanolic solution at room temperature. Structural analysis by single crystal X-ray diffraction analysis reveals that the crystal belongs to monoclinic system with space group C2/c and the cell parameters are a=22.046(2) Å, b=9.3325(4) Å, c=16.221(2) Å, Z=8. The metal is coordinated by six thiourea groups with Ni–S–C bond angles ranging from 114.81° to 116.85° and Ni–S bond lengths lying in the range 2.35 to 2.61 Å in a distorted octahedral geometry. The interesting feature observed in this study is that although it crystallizes in centrosymmetric structure, contrary to expectations, it exhibits a positive second harmonic generation (SHG) result, quite likely due to the change in stereochemical arrangement. An Nd:YAG laser with a modulated radiation of 1064 nm directed on the powdered sample leads to local noncentrosymmetry and this could be due to the loss of thiourea ligands resulting in tetrakis(thiourea)nickel(II) complex causing green light emission. The powder X-ray diffraction study reveals the crystallinity of the grown material. The vibrational patterns in FT-IR clearly evidence the complex formation. Thermogravimetric analysis (TG) reveals the purity of the sample and no decomposition is observed up to the melting point. The crystal is further characterized by diffused reflectance spectroscopy, dielectric studies and microhardness analysis.

► A centrosymmetric crystal exhibiting a small but significant SHG efficiency.
► Controversial behavior is rationalized.
► A good material for microelectronic industries.