Non-Topotactic Phase Transformations in Single Crystals of β-Glycine

Abstract

The metastable β polymorph of glycine exhibits a single-crystal-to-single-crystal transformation (SCSCT) to either the α or γ phase with retention of the crystal habit of the parent β phase. X-ray diffraction and optical microscopy reveal that of 51 single crystals of the β parent phase, 24 form single domain crystals of α or γ with a single orientation matrix, confirming an SCSCT. The remaining 27 β parent crystals transform to crystals with a few domains of either α and/or γ, each domain arising from a single nucleation event. In three cases the β → α and β → γ transformations occurred within the same glycine single crystal. In all cases, regardless of the number of domains, the transformation occurred with retention of the original habit of the parent phase. Both β → α and β → γ transformations proceed in a non-topotactic manner, as evident from the random orientations of the daughter phases in the crystallographic reference frame of the parent β phase. The transformation rates, as measured by advancement of the growth front with polarized optical microscopy, vary from crystal to crystal as well as for different regions within the same crystal. Moreover, the transformation rate increases substantially with relative humidity, and at a relative humidity of 90% α-glycine was observed as the only product.

Does the choice of the crystal structure influence the results of the periodic DFT calculations? A case of glycine alpha polymorph GIPAW NMR parameters computations

“…[42] DOLBIR10 was obtained from a single-crystal-tosingle-crystal transformation (SCSCT) studies of the metastable b polymorph of glycine which is also an unusual type of experiment. [43] The analysis of the RMSD values of the initial structures (Table S1) confirmed the significant molecular differences between the GLYCIN99 and the other structures. In addition, a group of very similar structures (GLYCIN03, 05, 19,20,21,22,23) emerged and a group of five structures different from the others (GLYICN29, 30, 63, 64 and 80), referred from now on as a "G5" could also be observed.…”

“…GLYCIN99 was received from an nonconventional and innovative experiment in which the authors desired to obtain the structures of single crystallites while analyzing the mixture of powders of three compounds rather than obtain the very good quality crystal structure of the single compound . DOLBIR10 was obtained from a single‐crystal‐to‐single‐crystal transformation (SCSCT) studies of the metastable β polymorph of glycine which is also an unusual type of experiment …”

On Layered Silicates and Zeolitic Nanosheets

“…MNSRC rule out dissolution governing the LS‐to‐MFI‐nanosheet transition, but also state that “the nanolayered silicates transform into zeolite MFI nanosheets non‐topotactically” . Non‐topotactic transformation that does not involve dissolution‐recyrstallisation is very rare, and, to our knowledge, has been shown to occur in crystals made‐up by single‐molecule units, where only geometric rearrangement of the building blocks is required for the transformation . Such chemical inheritance—in which no bonds have to be broken in the transition between the parent and the resulting solid—involves a known criterion for a transformation to occur within the condensed state (the interested reader is referred to a short additional note in the Supporting Information file).…”

An Appreciation of Organic Solid‐State Chemistry and Challenges in the Field of “Molecules, Materials, Medicines”

“…300 nm) have resulted in the production of polymorphs not generated using growth methods aimed at larger crystals—frequently such large crystals require post‐crystallisation milling to much smaller particles—a “top‐down” approach. Whether such a milling process (e.g., ball milling or jet‐milling) will inadvertently result in polymorph conversion is likely to depend on the need for a solid−solid transformation pathway, rather than perhaps a preferred nucleation process involved with the growth of small crystals . The top‐down approach also produces high surface energy particles and possibly highly defective particles and stress‐induced phase transformations .…”