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5793same order in the ( E 2 -E , ) values, by which the dication state of l a is shown to be most stable among them.X-ray diffraction analysis of l b " indicates that the molecule belongs to the approximate DZd symmetry (excluding eight carbomethoxy groups with flexible conformations) and has the puckered structure of the central four-membered ring. Figure 1 shows a unique stacking structure of molecules of l b related by the crystallographic 2, symmetry along the c axis resulting in a one-dimensional column in the crystal lattice. Some van der Waals contacts are found between the sulfur atoms of interdonor molecules, the shortest one being 3.608 A (twice the van der Waals radius of sulfur is 3.70 A).These results suggest that the [4]radialenes, in particular l a , should be useful electron-donor candidates for organic metals. In fact, l a forms a 1:2 charge-transfer salt (black needle crystals, mp > 300 "C) with TCNQ, and the room temperature electrical conductivity on the compressed pellet is fairly high (0.032 R-I cm-I). Furthermore, the E, value (0.057 eV) is very small. The preparation and electrical characterization of la-TCNQ single crystals are currently under active investigation.Supplementary Material Aiailable: ORTEP drawing and full tables of fractional atomic coordinates and interatomic bond distances and angles in l b ( 5 pages). Ordering information is given on any current masthead page.(1 1) Crystal data of lb: C,,H 4016S8, FW = 921.1, orthorhombic, space group P2,2,2,, a = 17.9317 (1) 2, b = 25.757 (2) A, c = 8.539 (1) A, U = 3808.7 (4) A', D, = 1.606 g cm-,, Z = 4. X-Ray diffraction data were measured on a Rigaku four-circle diffractometer using nickel-filtered Cu Ka radiation. A total of 3217 reflections were collected up to 2% = 120° by the 8-28 scan technique. The structure was solved by the direct method (MUL-TAN-76) and refined by the full-matrix least squares (xRAY-76) by using the 3073 observed reflections [[POI 2 3u(Fo)] to the R index of 0.052 including non-hydrogen atoms with anisotropic thermal parameters

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Current density vs potential, open-circuit voltage vs temperature, and differential capacitance vs potential measurements have been used to show that n-GaAs and n-Al x Ga 1-x As electrodes exhibit partial Fermi level pinning in contact with CH 3 CN over a wide range of redox potentials. Despite a change of over 1.2 V in redox potential of the solution, the open-circuit voltage only changed by ∼300 mV. The slope of the opencircuit voltage vs redox potential of the solution was typically 0.33-0.44. Differential capacitance vs potential data also yielded a barrier height change of less than 300 mV for over 1.2 V change in the redox potential of the solution. The dependence of the current density vs potential behavior of n-GaAs/CH 3 CN-ferriceniumferrocene +/0 on variables such as the illumination intensity, dopant density of the semiconductor, concentration of redox acceptor in the solution, crystal face, electrolyte, and cell temperature was evaluated. The resultant kinetic data indicate that surface-state recombination is the dominant recombination mechanism at these interfaces, which are capable of producing an open-circuit voltage of 0.83 V at a short-circuit current density of 20 mA cm -2 , as well as energy conversion efficiencies of > 10%. X-ray photoelectron spectroscopy investigation of n-GaAs confirmed surface changes were induced by electrochemical operation of n-GaAs electrodes in CH 3 CN-cobaltocenium-cobaltocene +/0 electrolyte. The presence of Fermi level pinning and the existence of changes in n-GaAs and n-Al x Ga 1-x As electrode surfaces when these electrodes are in contact with CH 3 CN-cobaltocenium-cobaltocene +/0 electrolyte complicates the extraction of k et values from the steadystate current density vs potential behavior of n-GaAs or n-Al x Ga 1-x As/CH 3 CN contacts.

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