The phase diagram of an organic analogue of a metal-nonmetal system, involving succinonitrile-pentachloronitrobenzene, shows the formation of a eutectic and a monotectic. The two immiscible liquid phases are in equilibrium with a single liquid phase and the consolute temperature being 53.5 degrees C above the monotectic horizontal. The phase equilibrium study confirms the alloy composition of monotectic and eutectic at 0.150 and 0.985 mol fractions of succinonitrile, respectively. The solidification behaviour shows the validity of Hilling-Turnbull equation. The thermal properties such as heat of mixing, entropy of fusion, roughness parameter, interfacial energy, grain boundary energy and excess thermodynamic functions for parent components, monotectic and eutectic have been studied using their enthalpy of fusion values. The effects of solid-liquid interfacial energy on morphological change of monotectic have also been discussed. The microstructure of monotectic shows the lamellar growth along with droplets, however. eutectic infers the vertical growth of lamella. (C) 2010 Elsevier B.V. All rights reserved.