Molecular recognition involving an interplay of O-H···O, C-H···O and ∏···∏ interactions. The anomalous crystal structure of the 1 : 1 complex 3,5-dinitrobenzoic acid-4-(n,n-dimethylamino)benzoic acid

Abstract

The crystal structure of the 1:1 donor-acceptor complex of 3,5-dinitrobenzoic acid and 4-(N,N-dimethylamino)benzoic acid contains the uncommon O-H ··· O hydrogen-bonded carboxy homodimers rather than the heterodimers found in nine other related complexes. The formation of these homodimers contradicts the general principle that in hydrogen-bonded networks, the strongest proton donor hydrogen bonds to the strongest proton acceptor. This unusual homodimer is obtained because of difficulties in C-H ··· O hydrogen bond formation, the consequent importance of ∏ ··· ∏ stacking interactions and the enhanced stability of homodimer stacks over heterodimer stacks. Additionally, it is concluded that: (i) O-H ···O hydrogen bonds can act as a conduit for charge transfer and may alter the polarization of atoms; (ii) C-H ··· O bonds can be used for molecular recognition and C-H ··· O patterns are sensitive to molecular stoichiometry and substituent positioning; (iii) stacking interactions influence the nature of hydrogen bonding and vice versa. This study shows that for precise supramolecular construction, strong and weak intermolecular interactions must be considered together.