Synthesis of new α-amino-1H indazolyl-phosphonate derivatives: Crystal structure, Hirshfeld surface analysis and DFT studies

A new α-amino-1H Indazolyl-phosphonates derivative 3a–e were synthesized and subjected to solid state characterization by single-crystal X-ray diffraction analysis, and to study their NMR and Hirshfeld surface analysis. The P atom exhibits tetrahedral geometry involving two O-ethyl groups, a C atom and a double-bonded O atom. The P–C bond has an approximately staggered conformation, with the aniline and substituted groups in gauche positions with respect to the P O double bond. The molecules are arranged as centrosymmetric or pseudocentrosymmetric dimers connected by two N–H⋯O P hydrogen bonds and also by C–H … π interaction in the case of structures 3a–e, which are responsible for the formation and stability of the molecular assemblies. Hirshfeld surface analysis (dnorm surface and two-dimensional (2D) fingerprint plots) revealed the nature of intermolecular contacts. The most important contributions for the crystal packing are from H⋯H, H⋯C/C⋯H, O⋯H/H⋯O, and H⋯N/N⋯H interactions. In addition, frontier molecular orbitals and Molecular Electrostatic Potential map of the compounds was produced by using the optimized structures.