A STUDY OF 2 POLYMORPHIC MODIFICATIONS OF (S)-1-PHENYLETHYLAMMONIUM (S)-MANDELATE AND THE STRUCTURAL FEATURES OF DIASTEREOMERIC MANDELATE SALTS

A low-temperature modification of (S)-1-phenylethylammonium (S)-mandel ate has been investigated: C8H12N+.C8H7O3-, M(r) = 273.33, monoclinic, P2(1), a = 8.322(4), b = 6.801(2), c = 12.885(3) angstrom, beta = 91. 74 (3)-degrees, V = 728.9 (8) angstrom, Z = 2, D(x) = 1.245 g CM-3 , l ambda(Cu Kalpha) = 1.5418 angstrom, mu = 6.60 cm-1, F(000) = 292, T = 122.0 (5) K, R = 0.044 for 1571 observed reflections. In this polymorp h both the stereochemistry of the ions and their hydrogen bonding are identical to the orthorhombic modification obtained at 298 K. An analy sis of 23 different mandelate stuctures showed the existence of a pref erred conformation of the mandelate ion with an almost planar arrangem ent of the carboxy and the hydroxy groups. The hydrogen bonding in the mandelates is described by graph theory. This shows that, although a single common motif is not observed in all the mandelate structures, c hains of hydrogen bonds are found in all the mandelates of primary and secondary amines.