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Epitaxial Retrieval of a Disappearing Polymorph

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posted on 17.12.2015 by Jeremiah P. Tidey, Alice E. O’Connor, Alexander Markevich, Elena Bichoutskaia, Joseph J. P. Cavan, Geoffrey A. Lawrance, Henry L. S. Wong, Jonathan McMaster, Martin Schröder, Alexander J. Blake
Recrystallization of [PdCl2([9]­aneS2O)] ([9]­aneS2O = 1-oxa-4,7-dithiacyclononane), 1, and [PtCl2([9]­aneS2O)], 2, by diffusion of Et2O vapor into solutions of the complexes in MeNO2 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.