Condensed-Phase Effects on the Structural Properties of FCH₂CN–BF₃and ClCH₂CN–BF₃: A Matrix-Isolation and Computational Study

Abstract

We have measured several IR bands of FCH2CN-BF3 and ClCH2CN-BF3 in solid nitrogen, argon, and neon. These bands include the B-F asymmetric stretch (νBF(a)), the B-F symmetric stretch (νBF(s)), the BF3 symmetric deformation or "umbrella" mode (δBF(s)), and the CN stretch (νCN). For both complexes, the frequencies of these modes shift across the various media, particularly the B-F asymmetric stretching band, and thus they indicate that the inert gas matrix environments significantly alter the structural properties of FCH2CN-BF3 and ClCH2CN-BF3. Furthermore, the frequencies shift in a manner that parallels the dielectric constant of these media, which suggests a progressive contraction of the B-N distances in these systems and also that it parallels the ability of the medium to stabilize the increase in polarity that accompanies the bond contraction. We have also mapped the B-N distance potentials for FCH2CN-BF3 and ClCH2CN-BF3 using several density functional and post-Hartree-Fock methods, all of which reveal a flat, shelflike region that extends from the gas-phase minimum (near 2.4 Å) toward the inner wall (to about 1.7 Å). Furthermore, we were able to rationalize the medium effects on the structure by constructing hybrid bond potentials composed of the electrostatic component of the solvation free energy and the gas-phase electronic energy. These curves indicate that the solvation energies are greatest at short B-N distances (at which the complex is more polar), and ultimately, the potential minima shift inward as the dielectric constant of the medium increases.

Structural and energetic properties of haloacetonitrile – GeF4 complexes

“…Taken together, however, these results for complexes of weaker nitriles illustrate that condensed-phase sensitivity tends to increase when the gas-phase interaction is weaker, so long as the stabilizing effects of the medium are enough to overcome any energetic disincentives to bonding. Analogous effects have also been observed in bulk, condensed-phase environments, even inert, weakly interacting, noble gas matrices [16,17]. For CH 3 CN-BF 3 , key structurally-sensitive vibrational modes (e.g., the B-F asymmetric stretch) shift across a range of condensed-phase environments, and these shifts systematically parallel the charge stabilizing ability of these environments (e.g., polarizability, dielectric constant) [16,18].…”

“…Since the correlation between these shifts and a contraction of the B-N distance has been demonstrated [18,19], these data convey the extent to which the B-N bond contracts in the more polarizable (or polar) media. Furthermore, the dynamic range of the shifts is even greater for FCH 2 CN-BF 3 and ClCH 2 CN-BF 3 [17], once again illustrating the greater potential for condensed-phase structural change in systems that are weaker in the gas-phase, so long as they are apt to react with some degree of solvent stabilization.…”

Triel‐Bonded Complexes between TrR3 (Tr=B, Al, Ga; R=H, F, Cl, Br, CH3) and Pyrazine

“…The triel bond has been the subject of numerous quantum chemical and experimental studies,, in recent years. Most of this work agrees that these bonds can be quite strong, bordering on covalency.…”

Strong cooperative effects between π-hole and dihydrogen bonds interactions: a computational study

“…Politzer et al [28] recommended the term 'π-hole bonding' for the interaction in which an electron-rich area interacts with a π-hole. For instance, the boron atom in boron trihydrides or trihalides can form strong π-hole interactions with potential negative sites [32][33][34][35]. Bearing in mind that the boron atom in these molecules has six electrons in their outer shell, hence, the electrondeficient region is related to the outer vacant p orbital which is perpendicular to the plane of the molecule.…”