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For optical modeling and other purposes, we have created a library of 57 liquids for which we have measured the complex optical constants n and k. These liquids vary in their nature, ranging in properties that include chemical structure, optical band strength, volatility, and viscosity. By obtaining the optical constants, one can model most optical phenomena in media and at interfaces including reflection, refraction, and dispersion. Based on the works of others, we have developed improved protocols using multiple path lengths to determine the optical constants n/k for dozens of liquids, including inorganic, organic, and organophosphorus compounds. Detailed descriptions of the measurement and data reduction protocols are discussed; agreement of the derived optical constant n and k values with literature values are presented. We also present results using the n/k values as applied to an optical modeling scenario whereby the derived data are presented and tested for models of 1 µm and 100 µm layers for dimethyl methylphosphonate (DMMP) on both metal (aluminum) and dielectric (soda lime glass) substrates to show substantial differences between the reflected signal from highly reflective substrates and less-reflective substrates.

Absolute rate constants were determined for the abstraction of hydrogen atoms from (OC)(3)Fe(mu-SH)(2)Fe(CO)(3) (Fe(2)S(2)H(2)) and (OC)(3)Fe(mu-SCH(3))(mu-SH)Fe(CO)(3) (Fe(2)S(2)MeH) by benzyl radicals in benzene. From the temperature-dependent rate data for Fe(2)S(2)H(2), DeltaH(++) and DeltaS(++) were determined to be 2.03 +/- 0.56 kcal/mol and -19.3 +/- 1.7 cal/(mol K), respectively, giving k(abs) = (1.2 +/- 0.49) x 10(7) M(-1) s(-1) at 25 degrees C. For Fe(2)S(2)MeH, DeltaH(++) and DeltaS(++) were determined to be 1.97 +/- 0.46 kcal/mol and -18.1 +/- 1.5 cal/(mol K), respectively, giving k(abs) = (2.3 +/- 0.23) x 10(7) M(-1) s(-1) at 25 degrees C. Temperature-dependent rate data are also reported for hydrogen atom abstraction by benzyl radical from thiophenol (DeltaH(++) = 3.62 +/- 0.43 kcal/mol, DeltaS(++) = -21.7 +/- 1.3 cal/(mol K)) and H(2)S (DeltaH(++) = 5.13 +/- 0.99 kcal/mol, DeltaS(++) = -24.8 +/- 3.2 cal/(mol K)), giving k(abs) at 25 degrees C of (2.5 +/- 0.33) x 10(5) and (4.2 +/- 0.51) x 10(3) M(-1) s(-1), respectively, both having hydrogen atom abstraction rate constants orders of magnitude slower than those of Fe(2)S(2)H(2) and Fe(2)S(2)MeH. Thus, Fe(2)S(2)MeH is 100-fold faster than thiophenol, known as a fast donor. All rate constants are reported per abstractable hydrogen atom (k(abs)/M(-1) s(-1)/H). DFT calculations predict S-H bond strengths of 73.1 and 73.2 kcal/mol for Fe(2)S(2)H(2) and Fe(2)S(2)MeH, respectively. Free energy and NMR chemical shift calculations confirm the NMR assignments and populations of Fe(2)S(2)H(2) and Fe(2)S(2)MeH isomers. Derived radicals Fe(2)S(2)H(*) and Fe(2)S(2)Me(*) exhibit singly occupied HOMOs with unpaired spin density distributed between the two Fe atoms, a bridging sulfur, and d(sigma)-bonding between Fe centers. The S-H solution bond dissociation free energy (SBDFE) of Fe(2)S(2)MeH was found to be 69.4 +/- 1.7 kcal/mol by determination of its pK(a) (16.0 +/- 0.4) and the potential for the oxidation of the anion, Fe(2)S(2)Me(-), of -0.26 +/- 0.05 V vs ferrocene in acetonitrile (corrected for dimerization of Fe(2)S(2)Me(*)). This SBDFE for Fe(2)S(2)MeH corresponds to a gas-phase bond dissociation enthalpy (BDE) of 74.2 kcal/mol, in satisfactory agreement with the DFT value of 73.2 kcal/mol. Replacement of the Fe-Fe bond in Fe(2)S(2)MeH with bridging mu-S (Fe(2)S(3)MeH) or mu-CO (Fe(2)S(2)(CO)MeH) groups leads to (DFT) BDEs of 72.8 and 66.2 kcal/mol, the latter indicating dramatic effects of the choice of bridge structure on S-H bond strengths. These results provide a model for the reactivity of hydrosulfido sites of low-valent heterogeneous FeS catalysts.

The reactivity of the S-H bond in Cp*Mo(mu-S) 2(mu-SMe)(mu-SH)MoCp* ( S 4 MeH) has been explored by determination of kinetics of hydrogen atom abstraction to form the radical Cp*Mo(mu-S) 3(mu-SMe)MoCp* ( S 4 Me*), as well as reaction of hydrogen with the radical-dimer equilibrium to reform the S-H complex. From the temperature dependent rate data for the abstraction of hydrogen atom by benzyl radical, Delta H (double dagger) and Delta S (double dagger) were determined to be 1.54 +/- 0.25 kcal/mol and -25.5 +/- 0.8 cal/mol K, respectively, giving k abs = 1.3 x 10 (6) M (-1) s (-1) at 25 degrees C. In steady state abstraction kinetic experiments, the exclusive radical termination product of the Mo 2S 4 core was found to be the benzyl cross-termination product, Cp*Mo(mu-S) 2(mu-SMe)(mu-SBz)MoCp* ( S 4 MeBz), consistent with the Fischer-Ingold persistent radical effect. S 4 Me* was found to reversibly dimerize by formation of a weak bridging disulfide bond to form the tetranuclear complex (Cp*Mo(mu-S) 2(mu-SMe)MoCp*) 2(mu-S 2) ( ( S 4 Me) 2 ). The radical-dimer equilibrium constant has been determined to be 5.7 x 10 (4) +/- 2.1 x 10 (4) M (-1) from EPR data. The rate constant for dissociation of the dimer was found to be 1.1 x 10 (3) s (-1) at 25 degrees C, based on variable temperature (1)H NMR data. The rate constant for dimerization of the radical has been estimated to be 6.5 x 10 (7) M (-1) s (-1) in toluene at room temperature, based on the dimer dissociation rate constant and the equilibrium constant for dimerization. Structures are presented for ( S 4 Me) 2 , S 4 MeBz, and the cationic Cp*Mo(mu-S 2)(mu-S)(mu-SMe)MoCp*(OTf) ( S 4 Me ( + )), a precursor of the radical and the alkylated derivatives. Evidence for a radical addition/elimination pathway at an Mo 2S 4 core is presented.

Surfactant templated synthesis of mesoporous ceramics provides a versatile foundation upon which to create high efficiency environmental sorbents. These nanoporous ceramic oxides condense a huge amount of surface area into a very small volume. The ceramic oxide interface is receptive to surface functionalization through molecular self-assembly. The marriage of mesoporous ceramics with self-assembled monolayer chemistry creates a powerful new class of environmental sorbent materials called self-assembled monolayers on mesoporous supports (SAMMS). These SAMMS materials are highly efficient sorbents whose interfacial chemistry can be fine-tuned to selectively sequester a specific target species, such as heavy metals, tetrahedral oxometalate anions, and radionuclides. Details addressing the design, synthesis, and characterization of SAMMS materials specifically designed to sequester actinides, of central importance to the environmental cleanup necessary after 40 years of weapons-grade plutonium production, as well as evaluation of their binding affinities and kinetics are presented.

Mesoporous TiO2 thin films were synthesized by sol-gel processing using an aqueous-based, inexpensive, and environmentally friendly precursor and cationic surfactants as templates under mild reaction conditions. The films were prepared by spin-coating on glass substrates followed by calcination to remove the surfactant. N2 sorption, X-ray diffraction, and transmission electron microscopy were used to characterize the porosity, pore size, and pore structure before and after calcination. Films were found to have wormlike pore structures after calcination and surface areas on the order of 200 m2/g. These results show that the mesostructure and porosity of the thin films can be controlled by the surfactant template chemistry such as surfactant/Ti ratio, pH, and rate of solvent evaporation., (Copyright 2004 American Chemical Society)

This paper provides evidence from kinetic experiments and electronic structure calculations of a significantly reduced S-H bond strength in the Mo(micro-SH)Mo function in the homogeneous catalyst model, CpMo(micro-S)(2)(micro-SH)(2)MoCp (1, Cp = eta(5)-cyclopentadienyl). The reactivity of 1 was explored by determination of a rate expression for hydrogen atom abstraction by benzyl radical from 1 (log(k(abs)/M(-)(1) s(-)(1)) = (9.07 +/- 0.38) - (3.62 +/- 0.58)/theta) for comparison with expressions for CH(3)(CH(2))(7)SH, log(k(abs)/M(-)(1) s(-)(1)) = (7.88 +/- 0.35) - (4.64 +/- 0.54)/theta, and for 2-mercaptonaphthalene, log(k(abs)/M(-)(1) s(-)(1)) = (8.21 +/- 0.17) - (4.24 +/- 0.26)/theta (theta = 2.303RT kcal/mol, 2sigma error). The rate constant for hydrogen atom abstraction at 298 K by benzyl radical from 1 is 2 orders of magnitude greater than that from 1-octanethiol, resulting from the predicted (DFT) S-H bond strength of 1 of 73 kcal/mol. The radical CpMo(micro-S)(3)(micro-SH)MoCp, 2, is revealed, from the properties of slow self-reaction, and exclusive cross-combination with reactive benzyl radical, to be a persistent free radical.

The beneficial effects humidity treatments have on molecularly templated mesoporous silica films with respect to elastic modulus, with minimal detrimental effects on porosity and dielectric constant, were identified.

The beneficial effects that alkali metal and alkylammonium salt additions to molecularly templated silica sols have on the resulting mesoporous silica films formed from evaporative-coating methods with respect to porosity, elastic modulus, dielectric constant, and film surface uniformity were investigated and identified.

The effects of storage temperature and time on deposition characteristics of molecularly templated silica sols, used in synthesis of mesoporous silica films, were investigated by preparing acid catalysed water-ethanol-TEOS sols with surfactant and analysing by silicon-29 NMR spectroscopy over a period of multiple days, and by producing films after specific storage times corresponding to collection of NMR spectral data, and analysed for thickness and porosity.

The synthesis of carbamoylphosphonate silanes (CMPO analogs) designed for sequestering actinide cations in self-assembled monolayers on mesoporous supports (SAMMS) is described.

The oxidation of cyclohexane by the H2O2-trifluoroacetic acid system is revisited. Consistent with a previous report (Deno, N.; Messer, L. A. Chem. Comm. 1976, 1051), cyclohexanol forms initially but then esterifies to cyclohexyl trifluoroacetate. Small amounts of trans-1,2-cyclohexadiyl bis-(trifluoroacetate) also form. Although these products form irrespective of the presence or absence of O2, dual mechanisms are shown to operate. In the absence of O2, the dominant mechanism is a radical chain reaction that is propagated by CF3. abstracting H from C6H12 and SH2 displacement of C6H11. on CF3CO2OH. The intermediacy of C6H11. and CF3. is inferred from production of CHF3 and CO2 along with cyclohexyl trifluoroacetate, or CDF3 when cyclohexane-d12 is used. In the presence of O2, fluoroform and CO2 are suppressed, the reaction rate slows, and the rate law approaches second order (first order in peracid and in C6H12). Trapping of cyclohexyl radicals by quinoxaline is inefficient except at elevated (approximately 75 degrees C) temperatures. Fluoroform and CO2, telltale evidence for the chain pathway, were not produced when quinoxaline was present in room temperature reactions. These observations suggest that a parallel, nonfree radical, oxenoid insertion mechanism dominates when O2 is present. A pathway is discussed in which a biradicaloid-zwiterionic transition state is attained by hydrogen transfer from alkane to peroxide oxygen with synchronous O-O bond scission.