Cocrystal design gone awry? A new dimorphic hydrate of oxalic acid.
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.
Wenger
Mazal
M
Department of Chemistry, Ben-Gurion University of the Negev, PO Box 653, Be'er Sheva 84105, Israel.
Bernstein
Joel
J
D001216:Asparagine / Q000737:chemistry; D003460:Crystallization; D018360:Crystallography, X-Ray; D005973:Glutamine / Q000737:chemistry; D006860:Hydrogen Bonding; D008958:Models, Molecular; D015394:Molecular Structure; D019815:Oxalic Acid / Q000737:chemistry*; D033362:Powder Diffraction
D005973:Glutamine; D001216:Asparagine; D019815:Oxalic Acid