Bonding and electronic structure of XeF3-.

The xenon-fluoride bond dissociation energy in XeF3- has been measured by using energy-resolved collision-induced dissociation studies of the ion. The measured value, 0.84 +/- 0.

Effect of substituents on the strength of A-Cl- (A = Si, Ge, and Sn) bonds in hypervalent systems: ACl5-, ACl4F-, and A(CH3)3Cl2-.

The gas-phase strengths of the A-Cl(-) bonds in ACl(5)(-), ACl(4)F(-), and A(CH(3))(3)Cl(2)(-) (A = Si, Ge, and Sn) have been determined by measuring thresholds for collision-induced dissociation in a flowing afterglow-tandem mass spectrometer. Bond dissociation energies increase in the order Si < Ge < Sn. Replacement of the three equatorial chlorides with methyl groups weakens the bonds, while replacing one axial chloride with a fluoride strengthens the bonds.

Progressive systematic underestimation of reaction energies by the B3LYP model as the number of C-C bonds increases: why organic chemists should use multiple DFT models for calculations involving polycarbon hydrocarbons.

[reaction: see text] Computational studies of three different reaction types involving hydrocarbons (homolytic C-C bond breaking of alkanes, progressive insertions of triplet methylene into C-H bonds of ethane, and [2+2] cyclizations of methyl-substituted alkenes to form polymethylcyclobutanes) show that the B3LYP model consistently underestimates the reaction energy, even when extremely large basis sets are employed. The error is systematic and cumulative, such that the reaction energies of reactions involving hydrocarbons with more than 4-6 C-C bonds are predicted quite poorly. Energies are underestimated for slightly and highly methyl-substituted cyclic and acyclic hydrocarbons, so the errors do not arise from structural issues such as steric repulsion or ring strain energy.

The thermochemistry of group 15 tetrachloride anions.

Bond strengths for a series of Group 15 tetrachloride anions ACl4 (A = P, As, Sb, and Bi) have been determined by measuring thresholds for collision-induced dissociation of the anions in a flowing afterglow-tandem mass spectrometer. The central atoms in these systems have ten electrons, which violates the octet rule: the bond dissociation energies for ACl4- help to clarify the effect of the central atom on hypervalent bond strengths. The 0 K bond energies in kJ mol(-1) are D(Cl3A-CL-) = 90 +/- 7,115 +/- 7,161 +/- 8, and 154 +/- 15, respectively.

Synthesis and Structural Analysis of BaCrS(2).

A new ternary chromium sulfide, BaCrS(2), was synthesized. This solid state compound crystallizes in the orthorhombic, centrosymmetric space group Pmmn (No. 59) with a = 4.