Influence of Hydrogen Bonds on the P···P Pnicogen Bond

Abstract

Ab initio MP2/aug'-cc-pVTZ calculations have been carried out to investigate the influence of F-H···F hydrogen bonds on the P···P pnicogen bond in complexes nFH:(PH2F)2 for n = 1-3. The formation of F-H···F hydrogen bonds leads to a shortening of the P-P distance, a lengthening of the P-F distance involved in the hydrogen bond, a strengthening of the P···P interaction, and changes in atomic populations, NMR (31)P chemical shieldings, and (1p)J(P-P) coupling constants. The magnitude of these changes depends on the number of FH molecules and their positions in the complex and are relatively modest except for complexes 2FH:(PH2F)2 and 3FH:(PH2F)2 that have all FH molecules hydrogen bonded to the same F-atom. For these two complexes, (1p)J(P-P) decreases as the P-P distance decreases and approaches the value of (1)J(P-P) for P2H4. The dramatic changes in these two complexes reflect the changing nature of the hydrogen bonds and the pnicogen bond. Thus, the complex 3FH:(PH2F)2 acquires ion-pair character represented as [3(FH)F(-):(H2P-PH2F)(+)], and the P···P pnicogen bond acquires significant covalent character. These changes are observed to a lesser extent in 2FH:(PH2F)2.

Pnicogen–pnicogen interactions in O2XP:PH2Y complexes (X=H, F, CN; Y=H, OH, OCH3, CH3, NH2)

“…Table 5 lists the components and total spin−spin coupling constants ( 1p J(P-P)) across intermolecular P···P bonds of the complexes O 2 XP:PH 2 Y. These data show that the Fermicontact (FC) term is an excellent approximation to total 1p J(P-P), an observation reported previously for other pnicogen-pnicogen bonded complexes [38][39][40][41][42][43]. The largest difference between the FC term and total coupling constant is less than 4 Hz in O 2 (CN)P:PH 2 CH 3 , and no more than 3 Hz in the remaining complexes.…”

“…the strength and properties of the resulting pnicogenbonded complexes can be varied as desired [34]. Therefore, pnicogen bonds can be used as a new possible molecular linker in supramolecule chemistry and self-assembly in solid state [35].…”

“…Using quantum mechanical calculations, Alkorta and co-workers [38][39][40][41][42] have extensively investigated the structural, bonding aspects and spin−spin coupling constants of P···P bonded complexes. They showed that the weak interactions between pnicogen centers are strong enough to compete with F-H···F hydrogen bond in nFH:(PH 2 F) 2 (n=1−3) complexes [43].…”

Non-additivity between substitution and cooperative effects in enhancing hydrogen bonds

“…Clearly, HB and ZB become stronger in the triads with respect to the respective dyads, and this result confirms the conclusion that there is positive cooperativity between ZB and HB. 13,50,51 The increase of the HB interaction energy is close to that of the ZB interaction energy in most triads, but the increased percentage of interaction energy is greater for HB. That is, the stronger ZB has a greater effect on the weaker HB, and the stronger ZB is, the greater is the HB enhancement, and vice versa.…”

“…50 The similar cooperative effect was found in H 2 FY:C 2 H 4 :XH (Y = P and As; X = HO, NC, and F) 13 and FH:(PH 2 F) 2 . 51 ZB also shows cooperative effects with other kinds of interactions such as dihydrogen bond, 52 halogen bond, 53 and cation-π interaction. 54 In all the above study on the cooperativity of ZB, the σ-hole is taken as a Lewis acid in ZBs, but cooperativity concerning ZBs with a π-hole is few.…”