The Molecular and Crystal Structures of Three 4-(ω-Cyanoalkyloxy)Benzoic Acids and of A 1:1 Ordered Mixed Crystal Of 4-(ω-Cyanobutyloxy)Benzoic Acid and 4-(ω-Cyanopentyloxy)Benzoic Acid Formed by Hydrogen Bonding

Abstract

The crystal and molecular structures of 4-( y -cyanobutyloxy)benzoic acid (CN4BS), 4-( y -cyanopentyloxy)benzoic acid (CN5BS), 4-( y -cyanohexyloxy)benzoic acid (CN6BS), as well as 1:1 ordered mixed crystal of 4-( y -cyanobutyloxy)benzoic acid and 4-( y -cyanopentyloxy)benzoic acid formed by hydrogen bonding (CN4-5BS) have been determined by single crystal X-ray diffractometry at room temperature and solved by direct methods. The crystals of the three compounds CN4BS, CN5BS, and CN6BS belong to the same monoclinic centrosymmetric space groups No. 14 (the used settings are P2 1 /n, P2 1 /c, and P2 1 /n, respectively), with 4 molecules in the unit cell. The center of symmetry lies between the two carboxylic acid groups of adjacent molecules which are connected by hydrogen bonds. This center of symmetry is missing for the mixed 1:1 compound CN4-5BS, and its crystals belong to the noncentrosymmetric space group Pc with four molecules in the unit cell. The unitcell parameters are, for CN4BS: a=4.987(2), b=8.309(1), c=27.549(15) Å, g =94.65(3); for CN5BS: a=10.799(3),b=4.9733(6), c=23.038(7) Å, g =92.60(2); for CN6BS: a=15.217(4), b=4.8994(8), c=17.839(5) Å, g =92.52(1); for CN4-5BS: a=4.963(1), b=25.962(4), c=9.234(2) Å, g =99.586(6). The structures were refined by full-matrix least-squares calculations against F to R=0.044 for 2521 unique data (1839>3 ) for CN4BS; to R=0.063 for 2513 unique data (1602>3 ) for CN5BS, which exhibits a disordered conformation; to R=0.038 for 1414 unique data (883>3 ) for CN6BS; and to R=0.040 for 2190 unique data (1339>1 ) for CN4-5BS. The conformation of the y -cyanoalkoxy chain differs between the two compounds CN4BS and CN5BS, as compared to the mixed compound CN4-5BS, actually consists of these two molecules and leads to different packing arrangements.