MOLECULAR COCRYSTALS OF CARBOXYLIC-ACIDS .6. THE CRYSTAL-STRUCTURES OF THE ADDUCTS OF TRIPHENYL-PHOSPHINE OXIDE WITH BENZENE-1,3,5-TRICARBOXYLIC ACID AND (2,4,5-TRICHLOROPHENOXY)ACETIC ACID

The crystal structures of the triphenylphosphine oxide adducts with benzene-1,3,5-tricarboxylic acid (2:1) (1) and (2,4,5-trichlorophenoxy)acetic acid (1:1) (2) have been determined and refined to residuals R 0.085 and 0.032 for 2531 and 3348 observed reflections, respectively. Both are triclinic with two heteromeric units in cells of dimensions a 8.66(1), b 13.58(2), c 18.17(3) angstrom, alpha-99.12(8), beta-101.45(8), gamma-107.54(7)-degrees for (1), and a 9.062(6), b 9.726(7), c 15.19(1) angstrom, alpha-103.80(4), beta-104.94(4), gamma-96.42(5)-degrees for (2). In each structure, strong single directed hydrogen bonds are found between the protons of the carboxylic acid donor groups and the triphenylphosphine oxide acceptors. With (1), only two of the carboxylic acid groups are heteromerically associated [O ... 0, 2.50(1), 2.54(1) angstrom] while the third forms a single intermolecular association [2.61(1) angstrom]. In the case of (2), a single acid-oxide association is found [O ... 0, 2.540(3) angstrom]. The (2,4,5-trichlorophenoxy)acetic acid molecule has an antiplanar conformation which contrasts with the synplanar conformation of the parent acid.