Crystalline Effects on the Properties of the Dative Bond:  A Computational Study of HCN−BF₃

Abstract

The changes in molecular structure associated with the crystallization of the donor-acceptor complex HCN-BF 3 are studied using density functional theory. Short-range dipole-dipole interactions have been attributed to be one of the main causes of the 0.84 Å shortening of the B-N bond in the crystal phase compared to the gas phase. Natural bond orbital analysis is used to obtain information regarding the electron distribution and possible delocalization effects. The lone pair on the fluorine atoms shows significant delocalization toward the boron-nitrogen antibonding orbital, leading to substantial structural changes occurring that can be manipulated by increasing or decreasing the degree of overlap. Because the overlap is dependent on the position of the fluorine atom, the steric and electronic influences created by the surroundings of a molecular unit in the crystal are of considerable importance when the experimentally observed changes are explained.

Abnormal synergistic effects between Lewis acid–base interaction and halogen bond in F3B···NCX···NCM

“…BF 3 is often taken as a Lewis acid in partially bound Lewis acid-base adducts [22,23], due to its electron-deficient nature. Very recently, Grabowski performed a detailed analysis for the complexes of triel trifluorides with hydrogen cyanide and named these interactions as triel bonds [24,25].…”

The BF3Affinity Scale

“…A comparison of the solid-and gas-phase structures of the same complex shows that the dative bond is usually shorter in the solid phase. This shortening has been studied theoretically [8,[31][32][33]. This shortening has been studied theoretically [8,[31][32][33].…”

A computational study of the effect of an external electric field on the geometry of selected donor–acceptor complexes

“…In our previous paper [23], the importance of fluorine lone pair delocalization in determining the structure of this molecule was discussed. It was pointed out that an intricate relationship exists between the length of r(B-N) and the value of the N-B-F angle, and that bond changes of the observed order would not be possible if the N-B-F angle did not change correspondingly.…”

“…Calculations were performed enforcing both C i symmetry, as in the model used earlier [23,24], and C 2h symmetry. We report the results where the (HCN-BF 3 ) 2 system was constructed to conform to the higher C 2h symmetry, this being a minimum on the PES.…”

“…In a previous paper [23], we studied the effect of the crystalline state on the length of the dative bond in HCN-BF 3 using explicit molecular models to simulate the solid phase. It was found that the lone pairs of the fluorine atoms show significant delocalization into the antibonding BN orbital and hence, play a crucial role in the process of shortening or lengthening this bond.…”