Arene-mercury complexes stabilized aluminum and gallium chloride: synthesis and structural characterization.

Reaction of HgCl(2) with 2 equiv of MCl(3) in an aromatic solvent yields Hg(arene)(2)(MCl(4))(2) where, arene = C(6)H(5)Me, M = Al (1), Ga (2); arene = C(6)H(5)Et, M = Al (3) and Ga (4); o-C(6)H(4)Me(2), M = Al (5), Ga (6); C(6)H(3)-1,2,3-Me(3), M = Al (7) and Ga (8). The solid-state structures of compounds 1-5 and 7 have been determined by X-ray crystallography. In the solid state, compounds 1-4 and 7 exist as neutral complexes in which two arenes are bound to the mercury, and the MCl(3) groups are bound through bridging chlorides to the mercury; compound 5 exists as a cation-anion pair [Hg(o-C(6)H(4)Me(2))(2)(AlCl(4))][AlCl(4)]. However, in solution compounds 1-8 all exist as neutral complexes. The structures of Hg(arene)(2)(AlCl(4))(2) and [Hg(arene)(2)(AlCl(4))](+) have been determined by DFT calculations [B3LYP level] to facilitate the assignment of the (13)C CPMAS NMR spectra and are in good agreement with the X-ray diffraction structures of compounds 1 and 5. Reaction of HgCl(2) with MCl(3) in benzene, m-xylene, and p-xylene results in the formation of liquid clathrates whose spectroscopic characterization is consistent with ionic structures, [Hg(arene)(2)(MCl(4))][MCl(4)]. The calculated energy difference between Hg(C(6)H(5)Me)(2)(AlCl(4))(2) and [Hg(C(6)H(5)Me)(2)(AlCl(4))][AlCl(4)] is discussed with respect to the structure of compound 5 in the solid state versus solution state and the proposed speciation in the liquid clathrates.

Very fast MAS and MQMAS NMR studies of the spectroscopically challenging minerals kyanite and andalusite on 400, 500, and 800 MHz spectrometers.

The well-characterized minerals kyanite and andalusite have long presented great challenges in using solid state 27Al NMR to determine the isotropic chemical shift deltaCS, quadrupole coupling constant e2qQ/h, and asymmetry parameter eta for each of the inequivalent aluminum sites in these minerals. Indeed, these minerals have frequently been used to test advances in instrumentation. Recent advances in magnet technology (up to 18.8 T = 800 MHz 1H) and in MAS probe technology (spinning up to 35 kHz and considerably stronger rf) and refinements of the two-dimensional, multiple quantum magic angle spinning (MQMAS) technique suggested that these developments could be profitably used to study kyanite and andalusite by solid state 27Al NMR. The benefit of being able to study kyanite both by MAS and MQMAS techniques on 400, 500, and 800 MHz spectrometers is demonstrated. The two octahedral aluminum sites with the largest (and nearly equal) e2qQ/h values give overlapping 1D MAS or 2D 3QMAS signals at all three field strengths. Nevertheless, quantitatively accurate 3Q signal intensities at 9.4 T for all four octahedral aluminum sites (with e2qQ/h values up to 10 MHz) allow more detailed analysis. Even if the 3Q signal intensities are not quantitative, their isotropic shifts provide an approach (if accurate e2qQ/h and eta values are available) other than deconvolution of the MAS spectrum for calculating deltaCS values. For andalusite, 34 kHz MAS on the 800 MHz spectrometer significantly narrows the extremely broad signal for the octahedral aluminum, and only slight difficulties are encountered in quantitating the relative amounts of AlO5 and AlO6 present. Even with e2qQ/h = 15.3 MHz, the octahedral aluminum in andalusite gives a signal in a MQMAS experiment, albeit of reduced intensity. As appropriate, we discuss some of the benefits and limitations of these advances in instrumentation and of different experimental approaches for studying non-integral spin quadrupolar nuclei in solids.

Gallium arsenide transistors: realization through a molecularly designed insulator.

A GaAs-based transistor, analogous to commercial silicon devices, has been fabricated with vapor-deposited cubic GaS as the insulator material. The n-channel, depletion mode, GaAs field-effect transistor shows, in addition to classical transistor characteristics, a channel mobility of 4665.6 square centimeters per volt per second, an interfacial trap density of 10(11) per electron volt per square centimeter, and a transconductance of 7 millisiemens for a 5-micrometer gate length at a gate voltage of 8 volts. Furthermore, the GaAs transistor shows an on-to-off resistance ratio comparable to that of commercial devices.

Synthesis of polycrystalline chalcopyrite semiconductors by microwave irradiation.

Polycrystalline samples of the chalcopyrites CulnS(2), CulnSe(2), and CulnSSe were Prepared from stoichiometric mixtures of the pure elements by microwave irradiation. The reactions were performed in sealed quartz tubes in as few as 3 minutes. The products were analyzed by x-ray diffraction, scanning electron microscopy, energy dispersive x-ray analysis, and x-ray photoelectron spectroscopy. The surface morphology and shape of the particles produced by this method suggest that the products are formed from liquid melts. This method could be applied to the production of bulk chalcopyrite as sources for thin film growth.