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

Abstract

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 aremore » 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.« less