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The polarizable valence state potential energy curve (pVS-PEC) is derived through the systematic improvement of the valence state potential energy curve (VS-PEC) and is given as U(R) = -[(K1/R) + (K2/R (super 4)) + (K3/R (super 7)) + T/R exp (-Lambda R). The potential is tested on a broad variety of homonuclear diatoms and heteronuclear halides and hydrides.

The relationship between the newly introduced (atomic and molecular) compressibility and polarizability is rationalized. Evidence of linear variation of a plot of the molecular compressibility against polarizability is found and analysis is made on assumptions that atomic polarizability is proportional to the atomic volume(super 11) and the molecular polarizability is roughly proportional to the sum of the atomic polarizabilities.

Monovalent boron, free borylene species of the form B-R are notoriously unstable. Consequently, there are substantial gaps in the literature concerning the potential utility of those species in organic and inorganic synthesis either as ligands or as critical intermediates in reactions. We show that the relative stability of borylene complexes varies widely, depending on the electron donating ability of the R group. We find that borylenes can form, in the gas phase, weak sigma hole type interactions to saturated carbon centers and stronger dative bonds to tetravalent silicon and germanium. An insertion reaction of the form FH3M + BR → FH2MBHR competes against dative bonding, however, and the reaction is barrierless in several cases when M = Si and in a few cases when M = Ge. For M = C, the barriers are high enough to stabilize monovalent boron complexes. In each case, the barrier heights to M-H bond activation and BR insertion are very sensitive to the nucleophilicity of BR. We confirm, at the MP2(full) and CCSD(T) levels, a substantial preference in borylenes for the singlet over the triplet state. An account is provided at the B3LYP-D3 and MP2(full) levels for the facile insertion reaction on the singlet surface when M = Si and for the stability of FH3M·BR type complexes and the higher barriers to insertion when M = C and Ge. [ABSTRACT FROM AUTHOR]

Nobroadly applicable and well-defined measure for the inductiveeffects of substituents (outside of the context of substituted benzenes)exists. We assess the viability of two different forms of weak interactionsas tools for this purpose. The responses of interatomic (I···Nand Ge···N) separations in the halogen-bonded and dativecovalent complexes F3CI···Y and FH3Ge···Y, where Y = NH2R, afford a directordering of a diverse set of substituents, R, according to their influenceon the availability of the N lone pair in the base (NH2R) for bonding. Despite their structural and electronic differences,the two bonding modes that we consider show good qualitative agreementon the electron-withdrawing inductive tendencies of substituents becauseof their sensitivity to the electronic environment at the donor site(the N center, in this case) on the base. The choice of the monosubstituted(NH2R) base minimizes steric interactions, resonance, andother electronic effects that could interfere with the bonding betweenN and the I or Ge centers in the complexes. We find, moreover, thatthe inductive tendencies for substituents in these complexes are,in general, not additive. Depending on the identity of R, the trisubstitutedbase (NR3) may actually reverse rather than enhance changesin the acid–base interactions that are achieved going fromNH3to NH2R. These outcomes are observed atthe MP2(full) and the M06-2X levels of theory, for both halogen anddative bonding interactions. A conservative ordering of substituentsaccording to the observed inductive tendencies is presented. [ABSTRACT FROM AUTHOR]

Wefind for distinct classes of halogen bonded complexes (MF3X···Y) that the ab initio BSSE-correctedbinding energies (ΔE) andenthalpies (ΔH) are predictedby functions of the form y = A/rn+ C. Here X is a halogen atom, Y is a base, ris the X···Y separation, and A, n, and Care constants. The actualvalue of n(5.5 < n< 7.0for ΔE) for each class isdetermined evidently by the availability of the lone pairs on thebase and is insensitive to M such that all of the complexes of a givenbase fall on the same curve for yversus r. Remarkably, several bases show the same behavior in somecases such that just three curves account for 55 MF3I···Ycomplexes of 11 bases, where M = C, Si, Ge, Sn, and Pb. Two additionalbases, THF and NF3, which form especially strong and weakcomplexes, respectively, are in classes by themselves. Anomalous modesof halogen bonding are identified; in particular, furan forms sigma-holecomplexes via carbons 2 and 3 (through the π system) in thering in preference to the oxygen site. These results are in line withexperimental observations for furan–dihalogen complexes, andseveral other small MF3I···Y pairs are proposedin this work for experimental interrogation. Instead of halogen bonding,CF4tends to form weak sigma-hole bonds to bases via thepolarized central carbon atom, and new examples of such pro-dativeinteractions to carbon in CF4are identified in this work.We find that GeF3I and SnF3I form I···Yhalogen bonds of comparable energies to those formed by the smallerand better studied CF3I. PbF3I forms the strongesthalogen bond regardless of the identity of the base; SiF3I consistently forms the weakest link. [ABSTRACT FROM AUTHOR]

The mercury dihalides show a remarkable diversity in the structural preferences in their minimum energy structure types, spanning molecular to strongly bound ionic solids. A challenge in the development of density functional methods for extended systems is to arrive at strategies that serve equally well such a broad range of bonding modes or structural preferences. The chemical bonding and the stabilities of mercury dihalides and the general utility and reliability of the van der Waals density functional with C09 exchange (vdW-DF-C09) in predicting or describing the energetics and structural preferences in these metal dihalides is examined. We show that, in contrast with the uncorrected generalized gradient approximation of the Perdew-Burke-Erzenhoff (PBE) exchange-correlation functional, qualitative and quantitative patterns in the bonding of the mercury dihalide solids are well reproduced with vdW-DF-C09 for the full series of Hg X 2 systems for X = F, Cl, Br, and I. The possible existence of a low-temperature cotunnite polymorph for HgF 2 and PbF 2 is posited.

Bonding interactions between an electron-deficient region (a sigma-hole) on M and electron donors in MF4-Base complexes, where M = C, Si, Ge, Sn, and Pb, are examined and rationalized. These interactions are seen to transition from weak primarily noncovalent interactions for all bases when M = C to stronger primarily covalent bonds in adducts as the valence shell expands for the heavier M atoms. For M = Ge, Sn, and Pb, the complexes are particularly stable. The consistent axial preference in these systems is anticipated by previous studies and is readily explained from the vantage point of sigma-hole interactions. A series of bound complexes of common bases such as pyridine, tetrahydrofuran, and water are identified, some of which are even more stable than the SiF4·NH3 and SiF4·N(CH3)3 complexes that have already been identified experimentally. Sigma-hole bonding to di- and poly-substituted central atoms, perhaps on par with halogen bonding, is expected to become increasingly important as an ordering interaction in materials science and engineering. Group 14 compounds have distinct advantages in this respect.

A computational analysis of the charge distribution in halomethanes and their heavy analogues (MH(4-n)X(n): M = C, Si, Ge, Sn, Pb; X = F, Cl, Br, I) as a function of n uncovers a previously unidentified saturation limit for fluorides when M ≠ C. We examine the electron densities obtained at the CCSD, MP2(full), B3PW91, and HF levels of theory for 80 molecules for four different basis sets. A previously observed substituent independent charge at F in fluoromethanes is shown to be a move toward saturation that is restricted by the low polarizability of C. This limitation fades into irrelevance for the more polarizable M central atoms such that a genuine F saturation is realized in those cases. A conceptual model leads to a function of the form [q(M(n')) - q(M(n))] = a[χ(A') - χ(A)] + b that links the electronegativities (χ) of incoming and leaving atoms (e.g., A' = X and A = H for the halogenation of MH(4-n)X(n)) and the associated charge shift at M. We show that the phenomenon in which the charge at the central atom, q(M), is itself independent of n (e.g., at carbon in CH(4-n)Br(n)) is best described as an "M-neutral substitution"--not saturation. Implications of the observed X saturation and M-neutral substitutions for larger organic and inorganic halogenated molecules and polymeric materials are identified.

Halogen bonding between halide sites (in substituted organic molecules or inorganic halides) and Lewis bases is a rapidly progressing area of exploration. Investigations of this phenomenon have improved our understanding of weak intermolecular interactions and suggested new possibilities in supramolecular chemistry and crystal engineering. The capacity for halogen bonding is investigated at the MP2(full) level of theory for 100 compounds, including all 80 MH(4-n)X(n) systems (M = C, Si, Ge, Sn, and Pb; X = F, Cl, Br, and I). The charge redistribution in these molecules and the (in)stability of the sigma-hole at X as a function of M and n are catalogued and examined. For the mixed MH(3-m)F(m)I compounds, we identify a complicated dependence of the relative halogen bond strengths on M and m. For m = 0, for example, the H(3)C-I----NH(3) halogen bond is 6.6 times stronger than the H(3)Pb-I----NH(3) bond. When m = 3, however, the F(3)Pb-I----NH(3) bond is shorter and approximately 1.6 times stronger than the F(3)C-I----NH(3) bond. This substituent-induced reversal in the relative strengths of halogen bond energies is explained.