A cocrystal of gabapentin and oxalic acid has been prepared employing a strategy based on a hydrogen-bonded synthon described by the graph set notation R4
2(8). High throughput techniques and solvent drop grinding were used along with traditional crystallization methods, including crystallization in aqueous solutions at various pH. A number of new solid forms have been detected. The cocrystal of gabapentin and oxalic acid was fully characterized including single crystal structure analysis, which revealed the R4
2(8) synthon.
The crystal chemistry of oxalic acid has been studied since 1880, including 37 published structure determinations of the two anhydrous forms (alpha, beta) and the dihydrate, the latest in 2000. In attempts to cocrystallize asparagine or glutamine with oxalic acid, utilizing the particular hydrogen bond synthon R(4)(2)(8), we unexpectedly obtained two previously unreported sesquihydrates of oxalic acid. Form 1 is orthorhombic, Pnma, and the unit cell is a = 11.231(2) A, b = 12.330(2) A, c = 6.908(1) A. Form 2 crystallizes in the triclinic crystal system in space group P, and the unit cell is a = 6.337(2) A; b = 7.247(3) A, c = 10.571(4)A, alpha = 94.34(1) degrees, beta = 100.244(9) degrees, gamma = 97.67(1) degrees. Both of the new hydrate forms of oxalic acid utilized the R(4)(2)(8) hydrogen bonded synthon.
It takes two: The possibility of developing a strategy for the controlled preparation of cocrystals (see picture) with a predesigned structure is demonstrated. It relies on recognizing and utilizing a specific hydrogen‐bond pattern, defined in graph‐set notation (${{{\rm {\rm R}}{{2\hfill \atop 4\hfill}}}}$(8)), as a supramolecular synthon for the systematic generation of individual four‐molecule clusters.
Es gehören immer zwei dazu: Eine Strategie für die gezielte Herstellung von Cokristallen (siehe Bild) mit vorbestimmter Struktur beruht auf dem Erkennen und Nutzen spezifischer Wasserstoffbrückenmuster mit der Graphensatz‐Notation ${{{\rm {\rm R}}{{2\hfill \atop 4\hfill}}}}$(8). Dieses supramolekulare Synthon erzeugt systematisch individuelle Viermolekülcluster.
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