Enantiomer associations in the crystal structures of racemic and (2S,3S)-(+)-3-hydroxy-2-(4-methoxyphenyl)2,3-dihydro-1,5-benzothiazepin-4(5H)-one

The crystal structures of racemic and optically active cis-3-hydroxy-2-(4-methoxyphenyl)-2,3-dihydro-1,5-benzothiazepin-4(5H)-one (C16H15NO3S) were determined to investigate the enantiomer associations formed in the solid state. X-ray diffraction data were collected with Cu K alpha (lambda = 1.54184 Angstrom) radiation at 122.0(5) K. Optically active: monoclinic, space group P2(1), with a = 7.8605(8), b = 16.148(2), c = 11.3477(11) Angstrom, beta = 97.607(8)degrees, V = 1427.7(3) Angstrom(3), Z = 4, D-x = 1.402 g cm(-3), mu = 20.53 cm(-1), refined to R = 0.0282 for 2922 observed reflections. Racemic: monoclinic, space group P2(1)/n, with a = 10.3322(14), b = 7.7110(11), c = 18.901(3) Angstrom, beta = 99.781(13)degrees, V = 1484.0(4) Angstrom(3), Z = 4, D-x = 1.349 g cm(-3), mu = 19.75 cm(-1), refined to R = 0.0277 for 2909 observed reflections. In both structures the strongest intermolecular interactions are N-H ... O and O-H ... O hydrogen bonds formed between molecules of identical chirality. The racemate and enantiomer crystal structures differ in that there are two different conformers in the crystal structure of the optically pure compound, in the symmetry relation between molecules connected by strong hydrogen bonds, and in the formation of weak C-H ... O hydrogen bonds. The structure determinations do not support the formation of the hydrogen-bonded dimers that had been proposed to cause the difference in NMR chemical shifts of the methoxy protons.