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 NCP–H unit in the C(O)NHP(O) segment (compared to the NP–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 NCP–H···O=P intermolecular hydrogen bond.