Noncovalent and Covalent O–H···O Interactions in PPh3O Cocrystals: A Correlation Study Involving QTAIM, SAPT, NBO, and IBSI Methods

PPh₃O.hemihydrate polymorphs and 11 assorted PPh₃O cocrystals collectively constitute a reliable stock to pursue a systematic analysis aiming to investigate the impacts of some vital issues on the TPPO.H-bond donor aggregates. The issues highlighted herein are (i) effect of varying acidity of H-bond donors on the degeneracy of lone pairs of the H-bond acceptor (PPh₃O), (ii) effectiveness of the |V(r)|/G(r) and H(r)/ρ(r) parameters as a covalency metric, (iii) 3c-4e bonding in the covalent PPh₃O.nitric acid cocrystal, (iv) salient features of H-bond interaction energy and an interplay of its components, (v) an intrinsic bond strength scale for the PPh₃O cocrystals, and (vi) reliable empirical relations between several bond descriptors for a quick estimation of interaction energy. To be specific about point (vi), we have propounded two promising avenues for a fast semiquantitative calculation of interaction energy from an endearing nonenergetic parameter, viz., bond length: d_O-H···O → ρ_BCP (MAPE = 2.36%) → E_SAPT0 (MAPE = 9.26%), and d_O-H···O → IBSI (MAPE = 1.87%) → E_SAPT0 (MAPE = 9.66%). All the aforesaid issues have been explored in detail through the QTAIM, NBO, and IBSI analyses (M06-2X-D3/def2-TZVP level), as well as by the SAPT study at the SAPT0/aug-cc-pVDZ platform. The statistically valid correlation studies can be particularly conducive for practical purposes as a transformative extension of the established facts into postulates for the unknown cocrystals.