Experimental and computational bonding study: I. Solid state materials. II. Gas-phse thermochemistry of main-group halides

A new ternary silver-rich sulfide, BaAg₈S₅, was synthesized. This solid state compound crystallizes in the monoclinic, centrosymmetric space group P2₁/m with a = 7.6720(2) Å, b = 17.6660(4) Å, c = 8.9370(2) Å, β = 107.890(1)°, Z = 4, and V = 1152.70(5) Å3. The refinement results are R1 = 0.0490 and wR2 = 0.1136 for I > 2σ(I) using 2552 reflections and 137 parameters. As in the binary α-Ag₂S and β-Ag₂S solids, the coordination geometry of both Ag and S is complex. However, if only the bonding of Ag to S is concerned, the arrangement is simple. Ag of the first type is connected to two S atoms in both linear and bent fashions. Ag of the second type is coordinated to three S atoms in a pyramidal shape. The structure can be viewed as a three-dimensional network formed by Ag and S atoms with Ba atoms occupying channels parallel to the c-axis. Theoretical analysis using the extended Hückel method indicates that the solid should be a semiconductor.; Diffuse and polarization functions have been optimized for the LANL2DZ basis set for elements in Groups 14–17. The optimized exponents are in most cases similar to those optimized with different effective core potentials, valence basis sets, or computational models. The average of the LANL2DZ results for different models is taken to be the best generalized set of exponents. The extended basis set gives good results (average deviation from experiment 0.11 eV) for atomic electron affinities with the B3LYP model, but is consistently low with the MP2 model. The extended basis set gives similar performance to the all-electron 6-31+G(d) basis set in calculations of vibrational frequencies and bond energies in selected main-group compounds, and is intermediate in speed between the 6-31+G(d) basis set and the unmodified LANL2DZ basis set.; Bond strengths for a series of Group 15 tetrachloride anions ACl ₄− (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. Computational results using the B3LYP/LANL2DZpd level of theory are higher than the experimental bond energies. Calculations give a geometry for BiCl₄− that is essentially tetrahedral rather than the see-saw observed for the other tetrachlorides. NBO calculations predict that the phosphorus and arsenic systems have 3C–4E bonds, while the antimony and bismuth systems are more ionic.