Analyzing carboxylic acid and amine-nitro hydrogen-bond geometry in the cocrystal of 4-aminobenzoic acid and 3,5-dinitrobenzoic acid by use of 298 K X-ray and 15 K neutron diffraction.

摘要

Structure of the cocrystal (1) of 4-aminobenzoic acid (2) and 3,5-dinitrobenzoic acid (3), C(sub 7)H(sub 7)NO(sub 2) (center dot) C(sub 7)H(sub 4)N(sub 2)O(sub 6), Mr = 349.26, was determined at 298 K by X-ray diffraction (XRD) and at 15 K by neutron diffraction (ND). XRD structure: Fdd2, a = 21.49 (3), b = 7.041 (7), c = 20.65 (2) (Angstrom), V = 3120 (1) (Angstrom)(sup 3), Z = 8, D(sub x) = 1.48 Mg(center dot)m(sup (minus)3), (lambda)(Mo K(alpha)) = 0.71073 (Angstrom), (mu) = 1.17 cm(sup (minus)1), F(000) = 1440, R(F(sub o)) 0.032, R(sub w)(F(sub o)) = 0.029. ND structure: a = 21.135 (3), b = 6.8567 (7), c 20.602 (2) (Angstrom), V= 2985.6 (6) (Angstrom)(sup 3), Z = 8, D(sub x) = 1.5541 Mg(center dot)m(sup (minus)3), time of flight neutronim diffraction, (lambda) = 0.7-4.2 (Angstrom), (mu) = 0.968-2.896 cm(sup (minus)1), R(F(sub o)) = 0.061, R(sub w)(F(sub o)(sup 2)) = 0.118. In 1, hydrogen-bond formation between the acid groups of 2 and 3 results in a cyclic heterodimer. ND data were collected to accurately locate the acid protons and to determine the geometry of the hydrogen bonds. The two acid hydrogen bonds are related by a two-fold crystallographic rotation axis and the protons are disordered over two sites. The heterodimers are organized into two-dimensional polar arrays as a consequence of hydrogen bonding between an amine group and nitro goups on neighboring heterodimers. Determining the structure of 1 at two different temperatures revealed significant changes in the amino-nitro hydrogen-bond geometry, but virtually no change in the acid-acid hydrogen-bond geometry.