Coulombic Basis for Relative Hydrogen-Bonding Basicities and Conformational Energies of Tertiary Amine Oxides and Phosphine Oxides

The structures, energies, and natural atomic charges of 2-dimethylaminophenol oxide, 2-Me₂N-(O)C₆H₄OH, and 2-dimethylphosphinylphenol, 2-Me₂P(O)C₆H₄OH, in three different conformations were computed at the ab initio MP2/6-31G* level. Computed natural charges indicate distributions of electron density in amine oxides and phosphine oxides that are quite different from what is normally assumed on the basis of the formal charges in the usual representations of these compounds. The charges on nitrogen and phosphorus in these compounds are typically computed to be approximately zero on nitrogen and +2 on phosphorus, and the oxygen is considerably more negative in the phosphine oxide than in the amino oxide. Electronegativity differences thus play a larger role and formal charges a smaller one in determining atomic charges in these compounds than is generally believed. Despite the more negative oxygen in phosphine oxides, amine oxides are computed to be considerably more basic when participating in hydrogen bonding. Calculations treating the computed natural charges on these six conformations as point charges for classical approximations of the coulombic energies support the idea that the quantum mechanically computed relative energies are largely determined by coulombic interactions.     

Theoretical study of endohedral metallofullerenes: Sc3−nLanN@C80 (n=0–3)

To provide theoretical insight into the structures and properties of Sc₃N@C₈₀, which has been isolated in high yield and purity as a new stable endohedral metallofullerene, density functional calculations are carried out for the Sc_3?nLa_nN@C₈₀ (n=0–3) series. Because of electron transfer from Sc₃N to C₈₀, the electronic structure of Sc₃N@C₈₀ is formally described as (Sc₃N)⁶⁺C$_{80}^{6-}$. The encapsulated Sc₃N cluster takes a planar structure with long Sc–Sc distances and is highly stabilized inside the I_h cage of C₈₀, which rotates rapidly. As the number of La atoms increases, the Sc_3?nLa_nN cluster is forced to maintain a pyramidal structure in Sc_3?nLa_nN@C₈₀. In addition, the C₈₀ cage takes an open‐shell electronic structure due to an increase in the number of electrons transferring from Sc_3?nLa_nN. These make the endohedral structure less stable and more reactive. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1353–1358, 2001     

Phenylmercury(II) derivatives of tetraorganodichalcogenoimidodiphosphorus acids. Crystal and molecular structure of [PhHg{(OPR2)(SPPh2)N}]2 (R=Me, Ph)

The reactions between PhHgCl or PhHgAc and M[(XPR₂)(YPR′₂)N] (M=Na, K; X, Y=O, S; R, R′=Me, Ph, OEt), in 1:1 molar ratio, have been investigated. PhHg[(XPR₂)(YPR′₂)N] derivatives were isolated as microcrystalline powders and were characterised using IR and NMR (¹H, ¹³C and ³¹P) spectroscopy and mass spectrometry. The molecular structure of PhHg[(OPR₂)(SPPh₂)N] [R=Me (1), Ph (2)] was investigated by X-ray diffraction. In the monomeric unit, PhHg[(OPR₂)(SPPh₂)N], the mercury atom forms the primary bonds with the carbon of the phenyl group and the sulfur atom of the phosphorus ligand [Hg(1)-S(1) 2.405(1) Å for 1, 2.398(2) Å for 2]. These primary bonds are significantly deviated from the expected linear arrangement [C(1)-Hg(1)-S(1) 166.4(2)° for 1, 165.0(2)° for 2]. Both compounds exhibit dimeric associations in the crystal through S,O-bridging organophosphorus ligands [Hg(1)-O(1) 2.556(4) Å for 1, 2.588(4) Å for 2], thus resulting in a distorted T-shaped arrangement of the CHgSO coordination core.. The formation of a 12-membered Hg₂O₂S₂P₄N₂ ring with different conformation in 1 and 2, respectively, results in different additional chalcogen atoms being in the proximity of the metal atom. Weak transannular Hg?O [2.753(4) Å] are also established in 1, leading to a tricyclic ladder structure with a planar central Hg₂O₂ ring.     

Tractability frontiers in probabilistic team semantics and existential second-order logic over the reals

Probabilistic team semantics is a framework for logical analysis of probabilistic dependencies. Our focus is on the axiomatizability, complexity, and expressivity of probabilistic inclusion logic and its extensions. We identify a natural fragment of existential second-order logic with additive real arithmetic that captures exactly the expressivity of probabilistic inclusion logic. We furthermore relate these formalisms to linear programming, and doing so obtain PTIME data complexity for the logics. Moreover, on finite structures, we show that the full existential second-order logic with additive real arithmetic can only express NP properties. Lastly, we present a sound and complete axiomatization for probabilistic inclusion logic at the atomic level.     

Infinite lexicographic products

We generalize the lexicographic product of first-order structures by presenting a framework for constructions which, in a sense, mimic iterating the lexicographic product infinitely and not necessarily countably many times. We then define dense substructures in infinite products and show that any countable product of countable transitive homogeneous structures has a unique countable dense substructure, up to isomorphism. Furthermore, this dense substructure is transitive, homogeneous and elementarily embeds into the product. This result is then utilized to construct a rigid elementarily indivisible structure.     

Left invariant special Kähler structures

We construct left invariant special Kähler structures on the cotangent bundle of a flat pseudo-Riemannian Lie group. We introduce the twisted cartesian product of two special Kähler Lie algebras according to two linear representations by infinitesimal Kähler transformations. We also exhibit a double extension process of a special Kähler Lie algebra which allows us to get all simply connected special Kähler Lie groups with bi-invariant symplectic connections. All Lie groups constructed by performing this double extension process can be identified with a subgroup of symplectic (or Kähler) affine transformations of its Lie algebra containing a nontrivial 1-parameter subgroup formed by central translations. We show a characterization of left invariant flat special Kähler structures using étale Kähler affine representations, exhibit some immediate consequences of the constructions mentioned above, and give several non-trivial examples.     

Carbocyclic and nitrogen-containing fused CH-acids with an annelated indenyl fragment. Thermogravimetric and X-ray structural analysis of 6H-indeno[1,2-b]quinoline

Based on thermogravimetric characteristics first obtained for the model 6H-indeno [1,2-b]quinoline, the scheme of thermal conversions of this compound in the temperature range 20–700 °C has been proposed, and the limit of its thermal stability (300 °C) has been determined. This temperature is recommended as the optimum for synthesizing fused benzoaza(diaza)fluorenes. Based on the results of X-ray structural analysis, the molecules of the studied indenoquinoline form centrosymmetric pairs, which are arranged in (110) layers. The molecules are orientationally disordered. The observed self-association of these molecules is similar to the - association of fused heterocyclic systems with-excessive and ****- deficient fragments. It has been suggested that interferon-inducing and antitumor compounds with an annelated indenyl fragment have a common mechanism of action according to the intercalation model of stacking structures.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 703–709, April, 1995.     

Copolymers of methyl methacrylate with some benzanthrone dyes, photo-stabilisers and their combined structures

Copolymerisation of methyl methacrylate with nine novel monomer compounds, triazinyl benzanthrone dyes, triazinyl benzotriazole stabilisers and their combined structures, was investigated. Chemical bonding of the compounds in the polymers obtained was confirmed spectrophotometrically. The quantity of the chemically bonded monomer compounds was determined to be over 50%, providing a colour and a fluorescence stable to solvents. Their influence on the rate of the copolymerisation was studied. It was found that the compounds under study did not significantly affect the rate of copolymerisation. A stabilizing effect towards photo-degradation of PMMA was achieved at 0.1 wt.% initial concentration of the compounds, which made them suitable for “one-step” colouration and stabilisation of PMMA.     

Synthesis and structural characterization of novel bridged platinum(II) biscarbene complexes

Novel bridged platinum(II) biscarbene complexes are reported: 1,1′-dimethyl-3,3′-methylene-4-diimidazolin-2,2′-diylidene platinum(II) (3) and 1,1′-dimethyl-3,3′-ethylene-4-diimidazolin-2,2′-diylidene platinum(II) complexes 4 are directly accessible in high yields starting from platinum halides. The one-pot synthesis obviates the need for multi-step reactions via metal precursors or free carbenes. An X-ray crystal structure of 1,1′-dimethyl-3,3′-methylene-4-diimidazolin-2,2′-diylidene platinum(II) dibromide (3b) confirmed the structural similarity to the known corresponding palladium complexes. Since free 1,1′-di-R-3,3′-methylene-4-diimidazolin-2,2′-diylidenes are only available in low yields this synthetic route provides an easy access to the corresponding carbene complexes.     

Paradigms and Paradoxes: Thoughts on the Enthalpy of Formation of Guanidine and Its Monosubstituted Derivatives

Despite their seeming simplicity, substituted guanidines have not particularly caught the attention of the thermochemical community. The current paper compares the enthalpy of formation of solid substituted guanidines with correspondingly substituted benzenes, also as solids.