In an attempt to improve on our earlier W3 theory [A. D. Boese et al., J. Chem. Phys. 120, 4129 (2004)] we consider such refinements as more accurate estimates for the contribution of connected quadruple excitations (T4), inclusion of connected quintuple excitations (T5), diagonal Born-Oppenheimer corrections (DBOC), and improved basis set extrapolation procedures. Revised experimental data for validation purposes were obtained from the latest version of the Active Thermochemical Tables thermochemical network. The recent CCSDT(Q) method offers a cost-effective way of estimating T4, but is insufficient by itself if the molecule exhibits some nondynamical correlation. The latter considerably slows down basis set convergence for T4, and anomalous basis set convergence in highly polar systems makes two-point extrapolation procedures unusable. However, we found that the CCSDTQ-CCSDT(Q) difference converges quite rapidly with the basis set, and that the formula 1.10[CCSDT(Q)cc-pVTZ+CCSDTQcc-pVDZ-CCSDT(Q)cc-pVDZ] offers a very reliable as well as fairly cost-effective estimate of the basis set limit T4 contribution. The T5 contribution converges very rapidly with the basis set, and even a simple double-zeta basis set appears to be adequate. The largest T5 contribution found in the present work is on the order of 0.5 kcal/mol (for ozone). DBOCs are significant at the 0.1 kcal/mol level in hydride systems. Post-CCSD(T) contributions to the core-valence correlation energy are only significant at that level in systems with severe nondynamical correlation effects. Based on the accumulated experience, a new computational thermochemistry protocol for first- and second-row main-group systems, to be known as W4 theory, is proposed. Its computational cost is not insurmountably higher than that of the earlier W3 theory, while performance is markedly superior. Our W4 atomization energies for a number of key species are in excellent agreement (better than 0.1 kcal/mol on average, 95% confidence intervals narrower than 1 kJ/mol) with the latest experimental data obtained from Active Thermochemical Tables. Lower-cost variants are proposed: the sequence W1-->W2.2-->W3.2-->W4lite-->W4 is proposed as a converging hierarchy of computational thermochemistry methods. A simple a priori estimate for the importance of post-CCSD(T) correlation contributions (and hence a pessimistic estimate for the error in a W2-type calculation) is proposed.

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Corrole complexes with gold(I) and gold(III) were synthesized and their structural, photophysical, and electrochemical properties investigated. This work includes the X-ray crystallography characterization of gold(I) and gold(III) complexes, both chelated by a corrole with fully brominated β-pyrrole carbon atoms. The mononuclear and chiral gold(I) corrole appears to be the first of its kind within the porphyrinoid family, while the most unique property of the gold(III) corrole is that it displays phosphorescence at ambient temperatures.

SILAR (successive ionic layer adsorption and reaction) is a solution process used to deposit semiconductors that has become very common in the past few years as a method to deposit light absorbers in nanoporous solar cells. Films of CdS (possibly the most commonly deposited semiconductor using this method) often show an anomalously low apparent bandgap (lowered by as much as 10%) for sufficiently thick films, although this effect has been ignored in most cases. Here, we study this bandgap lowering and show that it is due not so much to a lower bandgap but rather to a particularly long absorption tail that extends far into the red, and that is amplified by a large optical thickness in the high surface area nanoporous films. The tail is presumably due to as yet unidentified, but probably bulk defects in the CdS. Additionally, the absorption coefficient of the SILAR CdS was nearly twice as high as normal values.

The infrared spectra of silica gels made from alkoxides are different from those made from fumed silica, and from the infrared spectra of other amorphous silicas in which the SiO2 network is relatively complete. One important feature of these spectra is the occurrence of an absorption band at 960 cm−1 due to the vibration of dangling -Si-OH bonds in the alkoxide gels, which is not present in many other silicas. There also are less well-defined absorption bands due to structural defects for the alkoxide gels, but their interpretation is speculative. Dried gels made with more concentrated reactants contain more defects, and heat treatment reduces the concentration of dangling bonds, especially above 900°C. For gels containing fluorine, two absorption bands appear at 932 and 980 cm−1, and these are interpreted as arising from terminal -SiF and -SiF2 groups, respectively.