Properties of Complexes H₂C═(X)P:PXH₂, for X = F, Cl, OH, CN, NC, CCH, H, CH₃, and BH₂: P···P Pnicogen Bonding at σ-Holes and π-Holes

Abstract

Ab initio MP2/aug′-cc-pVTZ calculations have been carried out on complexes H2C(X)P:PXH2, for X = F, Cl, OH, CN, NC, CCH, H, CH3, and BH2. Three sets of complexes have been found on the potential surfaces. Conformation A complexes have A–P···P–A approaching linearity, with A the atom of X directly bonded to P. Conformation B complexes have A–P···P linear, but the P···PC orientation of H2CPX may differ significantly from linearity. Conformation C complexes are unique, since the pnicogen bond involves π-electron donation and acceptance by H2CPX. The order of binding energies of the three conformations of H2C(X)P:PXH2 is C > A > B, with two exceptions. Although the binding energies of conformation C complexes tend to be greater than the corresponding conformation A complexes, intermolecular distances in conformation C tend to be longer than those in conformation A. Charge transfer stabilizes H2C(X)P:PXH2 complexes. The preferred direction of charge transfer is from H2CPX to PXH2. In conformations A and B, charge transfer occurs from a P lone pair on one molecule to an antibonding σ* orbital on the other. However, in conformation C, charge transfer occurs from the π orbital of H2CPX to the σ*P–A orbital of PXH2, and from the lone pair on P of PXH2 through the π-hole to the π*PC orbital of H2CPX. Changes in charges on P upon complexation do not correlate with changes in 31P chemical shieldings. Computed EOM-CCSD spin–spin coupling constants correlate with P–P distances. At each distance, the ordering of 1pJ(P–P) is A > B > C. Binding energies and spin–spin coupling constants of conformation A complexes of (PH2X)2, H2C(X)P:PXH2, and (H2CPX)2 with A–P···P–A approaching linearity have been compared. For complexes with the more electronegative substituents, binding energies are ordered (PH2X)2 > H2C(X)P:PXH2 > (H2CPX)2, while the order is reversed for complexes formed from the more electropositive substituents. A plot of ΔE(PH2X)2/ΔE(H2CPX)2 versus ΔE[H2C(X)P:PXH2]/ΔE(H2CPX)2 indicates that there is a systematic relationship among the stabilities of these complexes. Complexes (PH2X)2 tend to have larger spin–spin coupling constants and shorter P–P distances than H2C(X)P:PXH2, which in turn have larger coupling constants and shorter P–P distances than (H2CPX)2, although there is some overlap. Complexes having similar P–P distances have similar values of 1pJ(P–P).

Homonuclear chalcogen–chalcogen bond interactions in complexes pairing YO3 and YHX molecules (Y = S, Se; X = H, Cl, Br, CCH, NC, OH, OCH3): Influence of substitution and cooperativity

“…Table results also reveal that the contribution of deformation energy ( E def ) in the interaction energy of O 3 Y⋅⋅⋅YHX complexes is quite small and is in the range of 0.22–2.64 kcal/mol. As Figure indicates, a good polynomial correlation is obtained between the binding distances and interaction energies of O 3 Y⋅⋅⋅YHX complexes, which is consistent with those reported by Alkorta and coworkers on P⋅⋅⋅P interactions.…”

“…In Figure , we have represented the ρ BCP values against the corresponding Y⋅⋅⋅Y distances. They show an exponential relationship, which is similar to the previously observed correlations in other chalcogen–chalcogen or pnicogen–pnicogen interactions . On the other hand, the values of the Laplacian at the BCPs are all positive, which correspond to a local depletion of the electron density from the bonding region.…”

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

“…Subsequent papers reported structures, binding energies, and spin-spin coupling constants of heterodimers in a variety of pnicogen-bonded binary complexes. [4,5,6,7,8,9,10,11] During the same year in which Hey-Hawkins and Kirchner published their seminal paper, Scheiner et al also published a study of the complexes between PFH 2 and a series of Lewis bases. [12,13,14] Another author who has contributed significantly to this field is Esrafili.…”

On the ability of pnicogen atoms to engage in both σ and π-hole complexes. Heterodimers of ZF2C6H5 (Z = P, As, Sb, Bi) and NH3

“…The pnicogen bond is a case in point. It has been reasonably widely examined [34,[61][62][63][64][65][66][67][68][69][70][71][72][73][74], but little has been determined in terms of competing configurations of a given pair of molecules. For example, the complexes PH 2 R•••BrCl (R = H, F, OH, OCH 3 , CH 3 ) were studied at the MP2 level [74], focusing on two possible σ-hole arrangements: halogen-bonded vs pnicogen-bonded.…”