Investigations on nucleation thermodynamical parameters are very essential for the successful growth of good quality single crystals. The metastable zone-width studies have been carried out for organometallic crystals of Tetrathiourea mercury (II) tetrathiocyanato zincate (II) (TMTZ) for different temperature range. The induction period measurements were done and the critical nucleation parameters were evaluated based on the classical theory of homogenous nucleation and the results will be discussed. The interfacial energy values for TMTZ were determined for different super saturation ratio. The growth parameters of TMTZ were optimized for the growth of large size crystals.