H2XP:OH2 Complexes: Hydrogen vs. Pnicogen Bonds

Abstract

A search of the Cambridge Structural Database (CSD) was carried out for phosphine-water and arsine-water complexes in which water is either the proton donor in hydrogen-bonded complexes, or the electron-pair donor in pnicogen-bonded complexes. The range of experimental P-O distances in the phosphine complexes is consistent with the results of ab initio MP2/aug'-cc-pVTZ calculations carried out on complexes H 2 XP:OH 2 , for X = NC, F, Cl, CN, OH, CCH, H, and CH 3 . Only hydrogen-bonded complexes are found on the H 2 (CH 3 )P:HOH and H 3 P:HOH potential surfaces, while only pnicogen-bonded complexes exist on H 2 (NC)P:OH 2 , H 2 FP:OH 2 , H 2 (CN)P:OH 2 , and H 2 (OH)P:OH 2 surfaces. Both hydrogen-bonded and pnicogen-bonded complexes are found on the H 2 ClP:OH 2 and H 2 (CCH)P:OH 2 surfaces, with the pnicogen-bonded complexes more stable than the corresponding hydrogen-bonded complexes. The more electronegative substituents prefer to form pnicogen-bonded complexes, while the more electropositive substituents form hydrogen-bonded complexes. The H 2 XP:OH 2 complexes are characterized in terms of their structures, binding energies, charge-transfer energies, and spin-spin coupling constants 2h J(O-P), 1h J(H-P), and 1 J(O-H) across hydrogen bonds, and 1p J(P-O) across pnicogen bonds.

Comparison of Various Means of Evaluating Molecular Electrostatic Potentials for Noncovalent Interactions

“…The same can be said of the chalcogen, pnicogen, and tetrel bonds, in which the halogen is replaced by an atom of the eponymous family of the periodic table. [23][24][25][26][27][28][29][30][31][32][33][34][35][36] Gadre's group has been heavily involved in providing some basic concepts by which the MEP might be interpreted and utilized to best advantage. An early analysis of the theoretical underpinnings of MEPs [37] showed that while minima can occur, the presence of a true local maximum is not possible, although of course a maximum can occur if one is restricted to a particular isodensity surface.…”

“…Halogen and HBs have comparable strength, strive toward linearity, can be decomposed into components of similar magnitude, and manifest the same sort of n→σ* charge transfer phenomenon. The same can be said of the chalcogen, pnicogen, and tetrel bonds, in which the halogen is replaced by an atom of the eponymous family of the periodic table …”

Complexes H2CO:PXH2and HCO2H : PXH2for X=NC, F, Cl, CN, OH, CCH, CH3, and H: Pnicogen Bonds and Hydrogen Bonds

“…[18] Studies by other authors which should be mentioned are the paper by Sundararajan et al [19] and that by Roohi et al, [20] as well as those from Zhang and colleagues. [21,22] In a previous study, we investigated hydrogen bonds and pnicogen bonds in complexes of the saturated oxygencontaining molecule H 2 O with PXH 2 , for X = NC, F, Cl, CN, OH, CCH, CH 3 , and H. [23] We have now turned our attention to complexes of PXH 2 with the unsaturated oxygen-containing molecules H 2 CO and HCO 2 H. These molecule may serve as models for aldehydes and ketones, and carboxylic acids. In this work, we have employed the PFH 2 molecule and other monosubstituted phosphines in a further extension of our studies of noncovalent interactions.…”

Characterization of N⋯O non-covalent interactions involving σ-holes: “electrostatics” or “dispersion”

“…However, it has been established both experimentally and computationally that under a suitable electronic environment N can have a s-hole character and can participate in the formation of pnicogen bonds. 44,53,54 Also, while there are reports of P/As/SbÁ Á ÁO pnicogen bonds, 55,56 there is no study on NÁ Á ÁO pnicogen bonds involving s-holes. However, NÁ Á ÁO bonds involving p-bonds have been reported in the literature.…”