It has been demonstrated in several instances that the 0.001 a.u. (electrons per bohr3) isodensity mapped electrostatic surface potentials on the fluorines along the outermost extensions of the CF covalent bonds in tetrafluoromethane (CF4) are entirely negative, they are thereby unable to engage in σhole bonding interactions with the negative sites on another molecules. In this study, we have attempted at resolving this controversy by performing various high‐level electronic structure calculations with Quadratic Configuration Integrals of Singles and Doubles QCISD(full), second‐order Møller–Plesset MP2(full), and 12 other Density Functional Theory (DFT) based functionals with and without dispersion corrections, all in conjunction with the 6–311++G(2d,2p) basis set. The results achieved with all the levels of theory utilized suggest that the fluorine's σholes in CF4 are positive regardless of the 0.001‐, 0.0015‐, and 0.002‐a.u. isodensity mapped electrostatic surfaces examined. Because of this specific quality, the fluorines in CF4 have displayed their capacities to form not only 1:1 clusters with the Lewis bases such as water (H2O), ammonia (NH3), formaldehyde (H2CO), hydrogen fluoride (HF), and hydrogen cyanide (HCN), but also 1:2, 1:3, and 1:4 clusters with the latter three randomly chosen Lewis bases. Various topological and nontopological features obtained from applications of atoms in molecules, noncovalent interaction reduced‐density‐gradient and natural bond orbital analytical tools reveal that the N···F, O···F, and F···F long‐ranged interactions developed between the interacting monomers in H3N···FCF3, H2O···FCF3, and (YD)n=1–4···F4C (YD = H2CO, HCN, and HF) are reminiscent of halogen bonding. The nonadditive cooperative and anticooperative energetic effects emerged on cluster formations are discussed in detail. © 2015 Wiley Periodicals, Inc.

With the goal of understanding the reason for the specific binding affinity of the chlorine in Cl-CH3 in the H2C=O···Cl-CH3 complex, we performed molecular electrostatic surface potential (MESP) analysis for isolated H3C-Cl with B3PW91, M06-2X, and MP2(full), all in conjunction with twenty-three Dunning- and Pople-type basis sets of double- and triple-ς valence qualities. The results obtained were benchmarked against the best level of theory employed, CCSD/6-311++G(3d,2p). It was found that the local maximum of the electrostatic potential, Vs,max, on the surface of the chlorine along the outermost extension of the C-Cl bond in Cl-CH3 would vary dramatically from slightly negative to slightly positive values with respect to the basis set sizes and correlation methods employed. Its value, mapped on the 0.001 electrons per bohr(3) isodensity surface, is approximately +1.0 kcal mol(-1) at the best level. This specific nature of the chlorine's Vs,max is ipso facto more plausible, and is clarified considering the 0.0015 and 0.002 electrons per bohr(3) isodensity envelopes, in which cases, Vs,max is apparently small and positive despite the varied basis sets and methods utilized. The thirteen binary complexes investigated using MP2(full)/6-311++G(3d,2p) are thus formed upon the interaction of chlorine's positive σ-hole in Cl-CH3 with the local most negative areas of electrostatic potential, Vs,min, confined on the surface of the nitrogen in the RN series of thirteen monomers, where RN = FCN, ClCN, BrCN, CH3CN, HOCN, HSCN, PCCN, PN, CCl3CN, SiH3CN, NCCN, CNCN, and NaCN. In all instances, the NCl intermolecular distances of separation evaluated are less than the sum of the chlorine and nitrogen van der Waals radii, 3.48 Å. The NCl contacts are all stable and have quasi-linear geometries (∠N···Cl-C ≅ 175-180°), unraveling the directional nature of the chlorine's positive σ-hole. The effect of substituents -R on the binding energies ΔE of the RNCl-CH3 complexes was found to be marginal, with values ranging from -0.39 to -1.29 kcal mol(-1) with MP2(full) and values from -0.02 to -0.84 kcal mol(-1) with CCSD(T). Applications of atoms in molecules and noncovalent interaction reduced-density-gradient methods revealed the N···Cl interactions to be of electrostatic origin. The red- and blue-shifts in the vibrational stretching frequencies of the C-Cl bonds estimated with MP2(full) were found to be accompanied with an increase and decrease in the corresponding bonds upon formation of the RN···Cl-CH3 complexes, respectively. Natural bond orbital analysis showed that there are several weak interorbital charge transfer interactions persisting between the electron-acceptor and -donor orbitals of the monomers interacting in the RN···Cl-CH3 complexes.

The F(δ-)···F(δ-) intermolecular synthon was recently observed to be useful for generating a two-dimensional layered supramolecular architecture on the Ag(111) surface (Kawai, et al., ACS Nano, 2015). This was formed when the entirely negative covalently bonded fluorine atoms in phenyleneethynylene(bis(2,3,5,6-tetrafluoro-4-(2,3,4,5,6-pentafluorophenylethynyl)phenyl)-ethyne (BPEPE-F18)) were in close proximity to the same atoms in another BPEPE-F18 molecule. With a view to provide rigorous insights into the physical chemistry of such an intermolecular synthon, we have selected perfluorobenzene (C6F6) as a model compound, and have performed extensive DFT-M06-2X/6-311++G(d,p) investigations on a number of its homomolecular dimers, trimers, and tetramers. Of the twelve (C6F6)2 dimers investigated, a displaced-parallel arrangement with an uncorrected binding energy (ΔE) of -7.4 kcal mol(-1) was found to be the most stable, and an incorporation of the basis set superposition error (BSSE) has significantly reduced its ΔE to -4.7 kcal mol(-1). Besides, the ΔE for a minimum-energy least stable conformation of the same dimer, which involves a single σhole(-)···σhole(-) type F(δ-)···F(δ-) intermolecular bonding interaction, amounts to -0.62 and -0.24 kcal mol(-1) without and with BSSE, respectively. The geometry of another conformation of the dimer, which accompanies a set of three F(δ-)···F(δ-) intermolecular interactions somehow similarly to those observed in the layered supramolecular structure formed by the BPEPE-F18 molecules, lies at a relative energy of 6.5 kcal mol(-1) above the most stable conformation. Passing from the latter dimer to an analogous (C6F6)3 trimer, as well as from the trimer to an analogous (C6F6)4 tetramer, the latter two clusters comprising windmill-type F(δ-)···F(δ-) intermolecular topologies, we have marked a preferential increase in the value of ΔE from -0.94 (dimer) to -2.76 (trimer) to -4.49 kcal mol(-1) (tetramer), thereby suggesting the presence of cooperative binding. An energy decomposition analysis has revealed that dispersion and polarization are the principal driving forces that bring the C6F6 molecules together in complex configurations. While a reasonable agreement was found between the charge density based topological results of the intermolecular bonding interactions that emerged from the application of Quantum Theory of Atoms in Molecules (QTAIM) and Reduced Density Gradient approaches to all the polymeric compounds, the results of the latter method were found to be too vague especially near the (3, +1) ring critical point regions. QTAIM's source function analysis has suggested that the fully negatively charged fluorine atoms in C6F6 serve as sinks for the F(δ-)···F(δ-) bond formation.

The study presents the possibility for the formation of attractive intermolecular interactions between various entirely negative Lewis bases, leading to the formation of the thirteen isolated binary complexes examined.