Synthesis and crystal structures of new phosphoric triamides: study of intermolecular interactions by semi-empirical calculations and Hirshfeld surface analysis

Abstract

In the present paper, crystal structures and Hirshfeld surface analyses of two new phosphoric triamides [2,3,6-F₃–C₆H₂C(O)NH]P(O)(X)₂ (X=N(CH₃)C₆H₁₁ and N(C₂H₅)₂) and an improved model of [OH₈C₄N]₃P(O) are investigated. Moreover, the semi-classical density sums (PIXEL) method, which enables the calculation of interaction energies for molecule–molecule pairs, and AIM calculations were used to evaluate intermolecular forces in the studied compounds. The previously reported structure [2,6-F₂-C₆H₃C(O)NH]P(O)[NHC(CH₃)₃]₂ with a [C(O)NH]P(O)[NH(C)]₂ segment, which is different than the [C(O)NH]P(O)[N(C)(C)]₂ segment in structures [2,3,6-F₃–C₆H₂C(O)NH]P(O)(X)₂, is compared to those of the newly determined structures. The Hirshfeld surface method shows that the crystal cohesions of structures [2,3,6-F₃–C₆H₂C(O)NH]P(O)(X)₂ are established via H···H, O···H/H···O, C···H/H···C, and F···H/H···F contacts, while for [OH₈C₄N]₃P(O), H···H and O···H/H···O are the dominant contacts. From PIXEL and AIM calculations and the decomposition of the interaction energies for different molecular pairs, it is shown that the donor and acceptor capability of the atoms involved in an interaction introduces the nature and strength of that interaction. The more acidic N_CP–H unit in the C(O)NHP(O) segment (compared to the N_P–H unit in the P(O)[NH(C)]₂ segment) and the higher H-atom acceptor group P=O (compared to C=O) in the studied structures form the strongest N_CP–H···O=P intermolecular hydrogen bond.

Graphical abstract