Synthesis, crystal structure and computational studies of 4-nitrobenzylphosphonic acid

Abstract

4-Nitrobenzylphosphonic acid (1a) has been synthesized and structurally characterized by vibrational spectroscopy (IR and Raman) and single-crystal X-ray diffraction. Additionally, Hirshfeld surface analysis and computational methods have been used to compare the intermolecular interactions in the crystal structures of 1a and its carboxylic analogue, 4-nitrobenzylcarboxylic acid (4-NBCA). The crystal structure analysis of 1a has revealed that the acid molecules are extended into helical chains along the b axis using one of the hydrogen bonds established between phosphonic groups. The second (P)OH⋯O(P) hydrogen bond cross-links the inversion-related chains to form a thick monolayer with phosphonic groups arranged inwards and aromatic rings outwards. The nitro groups serve to link the neighbouring monolayers by weak CH⋯O(N) hydrogen bonds. Computations have confirmed the great contribution of electrostatic interactions for the crystal lattice stability. The cohesive energy, computed for the crystal structure of 1a exceeds 200kJmol−1 in magnitude and is nearly twice as large as that of 4-NBCA. The calculated cohesive energy values have been further related to the results of thermal analyses.