Properties of Cationic Pnicogen-Bonded Complexes F_4–nH_nP⁺:N-Base with F–P···N Linear and n = 0–3

Abstract

Ab initio MP2/aug′-cc-pVTZ calculations were performed to investigate the pnicogen-bonded complexes F 4−n H n P + :N-base, for n = 0−3, each with a linear or nearly linear F−P•••N alignment. The nitrogen bases include the sp 3 bases NH 3 , NClH 2 , NFH 2 , NCl 2 H, NCl 3 , NFCl 2 , NF 2 H, NF 2 Cl, and NF 3 and the sp bases NCNH 2 , NCCH 3 , NP, NCOH, NCCl, NCH, NCF, NCCN, and N 2 . The binding energies vary between −20 and −180 kJ•mol −1 , while the P−N distances vary from 1.89 to 3.01 Å. In each series of complexes, binding energies decrease exponentially as the P−N distance increases, provided that complexes with sp 3 and sp hybridized bases are treated separately. Different patterns are observed for the change in the binding energies of complexes with a particular base as the number of F atoms in the acid changes. Thus, the particular acid−base pair is a factor in determining the binding energies of these complexes. Three different charge-transfer interactions stabilize these complexes. These arise from the nitrogen lone pair to the σ*P−F ax , σ*P−F eq , and σ*P−H eq orbitals. The dominant single charge-transfer energy in all complexes is N lp → σ*P−F ax . However, since there are three N lp → σ*P−F eq charge-transfer interactions in complexes with F 4 P + and two in complexes with F 3 HP + , the sum of the N lp → σ*P−F eq charge-transfer energies is greater than the N lp → σ*P− F ax charge-transfer energies in the former complexes, and similar to the N lp → σ*P−F ax energies in the latter. The total chargetransfer energies of all complexes decrease exponentially as the P−N distance increases. Coupling constants 1p J(P−N) across the pnicogen bond vary with the P−N distance, but different patterns are observed for complexes with F 4 P + and complexes of the sp 3 bases with F 3 HP + . These initially increase as the P−N distance decreases, reach a maximum, and then decrease with decreasing P−N distance as the P•••N bond acquires increased covalent character. For the remaining complexes, 1p J(P−N) increases with decreasing P−N distance. Complexation increases the P−F ax distance and 1 J(P−F ax ) relative to the corresponding isolated ion. 1 J(P−F ax ) correlates quadratically with the P−N distance.

Properties of cationic pnicogen-bonded complexes F4-nHnP+:N-base with H–P···N linear andn= 1–4

“…The bases are divided into sp 3 and sp groups, and are listed in order of decreasing binding energy in complexes with F 3 HP + . This ordering is the same as that in [30] for complexes F 4 P + :N-base with F-P···N linear. There is a wide range of binding energies for these complexes.…”

“…The remaining trendlines have reduced correlation coefficients R 2 of 0.885, 0.857, and 0.748 for complexes with the acids F 2 H 2 P + , FH 3 P + , and H 4 P + , respectively. There is considerably more scatter in these data than found for complexes with F-P···N linear, which have trendline correlation coefficients of 0.946, 0.978, 0.966, and 0.987 in complexes with the acids F 4 P + , F 3 HP + , F 2 H 2 P + , and FH 3 P + , respectively [30]. We attribute the greater scatter in the data for complexes with H-P···N linear to the weaker pnicogen bonds in these complexes.…”

“…The results of this study led us to ask what would be the effect on the properties of related pnicogen-bonded complexes if the number of equatorial F atoms was allowed to vary. To answer this question, we undertook a second investigation of a series of complexes with the general formula F 4-n H n P + :N-base, for n = 0-3, with F-P···N linear or nearly linear, with the same nitrogen bases [30]. To obtain further insight into the P···N pnicogen bond, we have now extended this investigation to the properties of a closely related series of complexes also with the general formula F 4-n H n P + :Nbase with the same set of nitrogen bases, but with H-P···N linear and n = 1-4.…”

Dissection of the Factors Affecting Formation of a CH∙∙∙O H-Bond. A Case Study

“…Examples from the recent literature include halogen [9][10][11][12][13][14][15][16][17], chalcogen [18][19][20][21][22], and OPEN ACCESS pnicogen [23][24][25][26][27][28][29][30] bonds where an atom from one of these families is attracted to an electronegative atom, such as O, S, or even P. This attraction is facilitated by a highly anisotropic charge distribution. That is, a halogen atom X, for example, is characterized by an overall partial negative charge.…”

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

“…Another possible mechanism for the formation of pnicogen bonds is the charge transfer from the lone pair of the base to the * X P  orbital of the acid. The extensive studies performed by Scheiner [11][12][13][14][15][16][17] and Alkorta's group [18][19][20][21][22][23][24][25][26][27][28] in the last few years highlight the significant role of orbital interaction as a potential source of the stability of pnicogen-bonded complexes. For a given base, the favorable mechanism depends on the nature of the pnicogen atom itself as well as the pnicogen-containing molecule.…”