Bonding Elucidation of the Three Common Acids H2SO4, HNO3, and HClO4

Breaking covalent bonds in the context of the many-body expansion (MBE). I. The purported "first row anomaly" in XHn (X = C, Si, Ge, Sn; n = 1-4)

We present a new, novel implementation of the Many-Body Expansion (MBE) to account for the breaking of covalent bonds, thus extending the range of applications from its previous popular usage in the breaking of hydrogen bonds in clusters to molecules. A central concept of the new implementation is the in situ atomic electronic state of an atom in a molecule that casts the one-body term as the energy required to promote it to that state from its ground state. The rest of the terms correspond to the individual diatomic, triatomic, etc., fragments. Its application to the atomization energies of the XHn series, X = C, Si, Ge, Sn and n = 1-4, suggests that the (negative, stabilizing) 2-B is by far the largest term in the MBE with the higher order terms oscillating between positive and negative values and decreasing dramatically in size with increasing rank of the expansion. The analysis offers an alternative explanation for the purported "first row anomaly" in the incremental Hn-1X-H bond energies seen when these energies are evaluated with respect to the lowest energy among the states of the XHn molecules. Due to the "flipping" of the ground/first excited state between CH2 (3B1 ground state, 1A1 first excited state) and XH2, X = Si, Ge, Sn (1A1 ground state, 3B1 first excited state), the overall picture does not exhibit a "first row anomaly" when the incremental bond energies are evaluated with respect to the molecular states having the same in situ atomic states.

Reappraising Schmidpeter's bis(iminophosphoranyl)phosphides: coordination to transition metals and bonding analysis

The synthesis and characterization of a range of bis(iminophosphoranyl)phosphide (BIPP) group 4 and coinage metals complexes is reported. BIPP ligands bind group 4 metals in a pseudo fac-fashion, and the central phosphorus atom enables the formation of d0-d10 heterobimetallic complexes. Various DFT computational tools (including AIM, ELF and NCI) show that the phosphorus-metal interaction is either electrostatic (Ti) or dative (Au, Cu). A bridged homobimetallic Cu-Cu complex was also prepared and its spectroscopic properties were investigated. The theoretical analysis of the P-P bond in BIPP complexes reveals that (i) BIPP are closely related to ambiphilic triphosphenium (TP) cations; (ii) the P-P bonds are normal covalent (i.e. not dative) in both BIPP and TP.

Hypervalent Bonding in the OF(a4Σ-), SF(a4Σ-), SF5/SF6, and OSF4 Species

Hypervalency has struggled the conventional wisdom of too many chemists for so many years. Numerous theories and bonding models have been introduced but the so-called "hypervalency" mystery remains. We offer a simple and appealing explanation for the bonding mechanism of OF(a⁴Σ^-), SF(a⁴Σ^-), SF₅/SF₆, and OSF₄ based solely on the fact that excited and/or ionic states of the constituent fragments may and actually do occur in the ground states of so many "every day" molecules. In particular, and through multireference methods, we have found that the bonding in all the studied species is ionic in nature, perhaps contrary to the present status of our chemical beliefs. Although the "atoms in molecules" hypothesis is certainly not the only way to explain the formation of the chemical bond, we strongly believe that it is the simplest and most economical conceptual principle that should guide our chemical thinking.

The role of O(1D) in the oxidation mechanism of ethylene by iodosobenzene and other hypervalent molecules

The role of the first excited state of oxygen (¹D) is proven essential for the description of terminal iodine-oxygen chemical bonds. The description of the I-O bond as a dative one from iodine to O(¹D) provides a simple and accurate picture which explains the oxidation properties of iodosobenzene and similar in nature molecules.

The classification and representation of main group element compounds that feature three-center four-electron interactions

This article provides a means to classify and represent compounds that feature 3-center 4-electron (3c-4e) interactions in terms of the number of electrons that each atom contributes to the interaction. Specifically, Class I 3c-4e interactions are classified as those in which two atoms provide one electron each and the third atom provides a pair of electrons (i.e. LX₂), while Class II 3c-4e interactions are classified as those in which two atoms each provide a pair of electrons and the third atom contributes none (i.e. L₂Z). These classes can be subcategorized according to the nature of the central atom. Thus, Class I interactions can be categorized according to whether the central atom provides one (i.e.μ-X) or two (i.e.μ-L) electrons, while Class II interactions can be categorized according to whether the central atom provides none (i.e.μ-Z) or two (i.e.μ-L) electrons. The use of appropriate structure-bonding representations for these various interactions provides a means to determine the covalent bond classification of the element of interest.

Recoupled-pair bonding and 4-electron 3-center bonding units

Consideration is given to recoupled-pair bonding and the origin of electronic hypervalence for formulations of the bonding for symmetric 4-electron 3-center ((4e,3c)) bonding units with one overlapping atomic orbital per atomic center. Molecular orbital and valence bond theory for symmetric (4e,3c) bonding units is redescribed and applied to aspects of the bonding for SF(6) and CLi(6). The results of minimal basis set calculations for CLi(6) provide support for a hypothesis that two Li-C-Li (3e,3c) bonding units rather than two (4e,3c) bonding units are preferred for this molecule. Brief comments are also made on the use of [Formula: see text] and [Formula: see text] as valence bond structures for the three electron bond.

Experimental and theoretical study of the reaction of POCl(3) (-) with O(2)

The oxidation of the trichlorooxyphosphorus anion (POCl(3) (-)), which takes place in combustion flames, has been examined experimentally at a variety of temperatures and theoretically via ab initio and density functional methods. The reaction was examined in a turbulent ion flow tube and kinetics was measured between 300 and 626 K, estimating an overall reaction barrier of 1.23 kcal/mol. Calculations at the density functional, Moller-Plesset second order perturbation, and coupled cluster levels of theory with basis sets up to augmented triple-zeta quality point to a multistep reaction mechanism involving an initial [OP(Cl)(3)(OO)](-) intermediate, an adduct between triplet O(2) with POCl(3) (-), subsequent formation of a four-membered nonplanar P-O-O-Cl ring transition state, with concomitant breaking of the P-Cl and O-O bonds to provide a transient intermediate [OP(Cl)(2)OO...Cl](-), which, in turn, converts to the product complex (POCl(2) (-))(ClO) upon formation of the Cl-O bond without barrier. The calculated energy of the four-membered transition state is considered to be in good agreement with the small overall barrier found by experiment. The final step is responsible for the large exothermicity of the reaction.