Epitaxial Retrieval of a Disappearing Polymorph

Recrystallization of [PdCl 2 ([9]aneS 2 O)] ([9]aneS 2 O = 1-oxa-4,7-dithiacyclononane), 1 , and [PtCl 2 ([9]aneS 2 O)], 2 , by diffusion of Et 2 O vapor into solutions of the complexes in MeNO 2 yielded three phases of 1 and two phases of 2 . The known phase of 1 , herein designated α- 1 , was obtained under ambient conditions. A second phase, designated β- 1 , was initially also obtained by this method; however, following the advent of a third phase, γ- 1 , all subsequent efforts over a period of a year to crystallize β- 1 yielded either γ- 1 , obtained by carrying out the recrystallization at elevated temperature, or α- 1 , commonly found throughout the study. This persistent absence of a phase which could initially be crystallized with ease led us to the conclusion that β- 1 was an example of a "disappearing polymorph". The first phase obtained of 2 , designated α- 2 , was obtained by recrystallization under ambient conditions and is isomorphous and isostructural with α- 1 . The second phase β- 2 was obtained by slight elevation of the recrystallization temperature and was found to be isomorphous and isostructural with β- 1 . Subsequently, β- 2 was used to seed the growth of the disappearing polymorph β- 1 . No third phase of 2 (γ- 2 ) has been isolated thus far.