IR and NMR properties of N-base:PH₂F:BeX₂ ternary and corresponding binary complexes stabilised by pnicogen and beryllium bonds

Abstract

Ab initio MP2/aug'-cc-pVTZ calculations have been performed to determine selected stretching frequencies and chemical shieldings for ternary complexes N-base:PH 2 F:BeX 2 and the corresponding binary complexes, with NH 3 , H 2 C = NH, and HCN as the nitrogen bases and H, F, and Cl as the substituents X. Be-F and P-F stretching frequencies depend on the Be-F and P-F distances, respectively, while P and F chemical shieldings depend on the N-P and P-F distances, respectively. The graph of the P chemical shieldings versus the P-F distance bears a remarkable resemblance to the graph of the P-F stretching frequencies versus that same distance. EOM-CCSD spin-spin coupling constants have also been evaluated for binary and ternary complexes. 1p J(N-P) is negative at the longer N-P distances found in ternary complexes with HCN in which the N ... P bond is a traditional pnicogen bond with some phosphorous-shared character, gains phosphorus-shared character as the N-P distance continues to decrease, and then becomes a phosphorous-transferred bond with ion-pair character at the shorter distances in the complexes with NH 3 and H 2 C = NH. 1 J(P-F) values are large and negative in complexes with HCN, but increase and become positive in complexes with H 2 C = NH and NH 3 as the P-F distance increases.

Dissection of the Origin of π-Holes and the Noncovalent Bonds in Which They Engage

“…The intensive scrutiny of σ-hole bonds has led to a solid understanding of the fundamental phenomena from which they draw their strength. The chain of processes, beginning with the distortion of the σ­(R–X) covalent bond arising from the R–X electronegativity difference, and the resulting σ-hole in the density, which in turn leads to the positive potential, have been characterized. ,,,− Also studied extensively has been the relationship between the magnitude of the σ-hole potential and the strength of the ensuing interaction with a nucleophile and how other factors enter into the equation such as charge transfer and dispersion. ,− Research has also built a body of understanding of the effects of the σ-hole bond on the intermolecular distance and perturbations within the individual monomers, both geometric and spectroscopic. − …”

Characterization of Type I and II Interactions between Halogen Atoms

“…Unlike most of the other properties, this coupling constant is considerably larger for T1 than for T2. It should be pointed out finally that these various spectral changes are not unique to the FX dimers examined here but are general features of halogen bonds in general and even occur in complexes containing closely related interactions such as chalcogen and pnicogen and even hydrogen bonds. ,− …”

Influence of Substituents in the Benzene Ring on the Halogen Bond of Iodobenzene with Ammonia

“…For example, the signal of the bridging proton moves downfield by several ppm upon formation of a H-bond, and the degree of this shift is closely related to the strength of the bond. There have been several studies in recent years [43][44][45][65][66][67][68][69][70][71] that suggest that these ideas can be extended to halogen and other related noncovalent bonds.…”