1988 Volume 21 Issue 6 Pages 589-595
Polymorphous clathrate crystals of β- and γ-type were observed to precipitate by crystallization in methylcellosolve (MCS) solutions containing tetra(4-methylpyridine)nickel(II)dithiocyanate (Ni-complex) and 1-methylnaphthalene (1-MN). The relative precipitation behavior of these polymorphs was divided into three Parts (I, II, III) with respect to 1-MN concentration.
By solubility measurements of Ni-complex forming the host lattice of each polymorph, it was found that there is a cross-point of the solubility curves which can be regarded as the transition point between the polymorphs concerning 1-MN concentration.
A nucleation model was proposed, assuming a competitive nucleation process for the liquid clathrates of each polymorph. By using this model it was clarified that the relative nucleation behavior of the polymorphs depends on the ratio of their supersaturation ratios.
Transformation was observed when the metastable crystals were added to the solutions in Parts I or III, and it was suggested that the main transformation mechanism was "solution-mediated".
