Paleomagnetic evidence for Neoarchean plate mobilism.

Plate tectonics is a unique feature of Earth, but its proposed time of initiation is still controversial, with published estimates ranging from ca. 4.2 to 0.

Comparisons of the Paleo-Mesoproterozoic large igneous provinces and black shales in the North China and North Australian cratons.

Comparisons of large igneous provinces (LIPs) and black shales from different cratons can provide important constraints on Precambrian paleogeographic reconstructions and a better understanding of the environmental effects of large-scale volcanic events. A comparison of intraplate mafic events mostly interpreted as LIPs or portions of LIPs (LIP fragments/remnants due to continental breakup or erosion) from the North China Craton (NCC) and North Australian Craton (NAC) shows good correlation in the age range from 1800 Ma to 1300 Ma, and four robust age matches at ca. 1790-1770 Ma, ca.

A chemist remains a chemist.

Science, music, art, life: Nobel Laureate Richard Ernst discusses the influence of music and art on his life and how advanced Raman spectroscopy comes to his aid as a "hobby chemist" and art restorer.

Charge density analysis of the (C-C)-->Ti agostic interactions in a titanacyclobutane complex.

The experimental electron density study of Ti(C(5)H(4)Me)(2)[(CH(2))(2)CMe(2)] provides direct evidence for the presence of (C-C)-->Ti agostic interactions. In accord with the model of Scherer and McGrady, the C(alpha)-C(beta) bond densities no longer show cylindrical symmetry in the vicinity of the Ti atom and differ markedly from those of the other C-C bonds. At the points along the C(alpha)-C(beta) bond where the deviation is maximal the electron density is elongated toward the metal center.

Solid-state 13C NMR and quantum chemical investigation of metal diene complexes.

This paper presents novel measurements and calculations of the olefinic (13)C chemical shift tensor principal values in several metal diene complexes. The experimental values and the calculations show shifts as large as 70 ppm with respect to the values in the parent olefinic compounds. These shifts are highly anisotropic, with the largest ones observed in the less shielded principal components and the smallest ones in the most shielded principal components of the tensor.

Indirect costs and cost-effectiveness analysis.

This article examines the methodological implications of the societal perspective in cost-effectiveness analyses in which the costs of health-care interventions are defined as the sums of direct and indirect costs. In the model of cost-effectiveness analysis in which the planner distributes patients among many treatments for many illnesses, the definition requires that total indirect costs be constrained, and the article proposes an iterative computational procedure for choosing a constraint under the assumption that the planner maintains a target trade-off rate between losses of health benefits and reductions in indirect costs. In the more common model in which the planner decides which of two treatments for one illness to provide to patients, the adoption of a societal perspective introduces ambiguities into the welfare properties of the decision rule, and in general the conclusion that a treatment is cost-effective is valid only if switching or assigning patients to the cost-effective treatment does not increase the planner's total direct costs.

Structural and spectroscopic demonstration of agostic C-C interactions in electron-deficient metallacyclobutanes and related cage complexes: possible implications for olefin polymerizations and metatheses.

The reaction of the half-open titanocene, Ti(C5H5)(c-C8H11)(PMe3) (c-C8H11 = cyclooctadienyl), with two equivalents of PhC2SiMe3 leads to their incorporation and coupling to the dienyl fragment. One alkyne inserts into a C-H bond of the central CH2 group of the c-C8H11 ligand's edge-bridge, while the second undergoes a 5+2 coupling with the dienyl fragment, yielding coordinated sigma-allyl and olefin fragments, as demonstrated by X-ray diffraction. Together with the C5H5 and PMe3 coordinations, this leads to a 14-electron count.

Reactions of SF6 with organotitanium and organozirconium complexes: the "inert" SF6 as a reactive fluorinating agent.

The normally remarkably inert SF6 has been found to be quite reactive toward low valent organometallic compounds, under conditions in which usually powerful fluorinating agents may be less reactive. Reaction of SF6 with Ti[1,3-C5H3(t-Bu)2](6,6-dmch)(PMe3), for example, leads to {Ti[1,3-C5H3(t-Bu)2]F2}4 (dmch = dimethylcyclohexadienyl), whose structure is based on a cube of fluoride ions with the ligated titanium centers situated above four coplanar face centers.

The Günther Laukien Prize.

The Günther Laukien Prize, established in 1999, intends to recognize recent cutting-edge experimental NMR research with a high probability of enabling beneficial new applications. It is awarded yearly at the Experimental NMR Conference (ENC).

Enhancement in the reducibility of cobalt oxides on a mesoporous silica supported cobalt catalyst.

The silylation of SBA-15 enhances the reducibility of cobalt oxides on a SBA-15 supported cobalt catalyst, and consequently increases the catalytic activity for Fischer-Tropsch synthesis of hydrocarbons from syngas and selectivity for longer chain products.

Pentadienyls vs cyclopentadienyls and reversal of metal-ligand bonding affinity with metal oxidation state: synthesis, molecular structures, and electronic structures of high-valent zirconium pentadienyl complexes.

Molecules of the form Cp(6,6-dmch)ZrX(2) (Cp = eta(5)-cyclopentadienyl, X = Cl, Br, I; 6,6-dmch = eta(5)-6,6-dimethylcyclohexadienyl) have been synthesized, and the molecular and electronic structures have been investigated. These molecules allow direct comparison of the bonding and properties of pentadienyl and cyclopentadienyl ligands in the same high-oxidation-state metal complexes. Unlike the well-known Cp(2)ZrX(2) analogues, these Cp(6,6-dmch)ZrX(2) molecules are intensely colored, indicating significantly different relative energies of the frontier orbitals.

Syntheses and structural systematics of trialkylphosphine complexes of open titanocenes, zirconocenes and hafnocenes.

The synthesis and characterization of the open hafnocene, Hf(2,4-C7H11)2(PMe3)(C7H11 = dimethylpentadienyl), is reported. Additionally, a much improved synthetic procedure has been developed for Hf(2,4-C7H11)2(PEt3). Structural data have been obtained for these complexes, and for Ti(2,4-C7H11)2(PEt3) and Zr(2,4-C7H11)2(PMe3), thereby allowing for detailed comparisons between all M(2,4-C7H11)2(PX3) species (M = Ti, Zr, Hf; X = Me, Et).

Investigation of Zr-C, Zr-N, and potential agostic interactions in an organozirconium complex by experimental electron density analysis.

The crystal structure and electron density (ED) distribution of an imine coupling product with an open zirconocene, Zr(2,4-C(7)H(11))[(i-Pr)NCHPhCH(2)CMe=CHCMe=CH(2)] (C(7)H(11) = dimethylpentadienyl), have been derived from accurate synchrotron X-ray diffraction measurements. The molecular structure reveals asymmetric coordination of Zr by the pentadienyl (2,4-C(7)H(11)) ligand ( = 2.56(6) A), the butadiene fragment ( = 2.