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Electroreduction of 1,3- and 1,4-benzene-bridged bis(diselenadiazolium) salts [1,4-Se][SbF6]2 and [1,4-Se][SbF6]2 in acetonitrile, at a Pt wire and in the presence of iodine affords the 1:1 charge-transfer salts [1,4-Se][I] and [1,3-Se][I]. Crystals of [1,4-Se][I] belong to the monoclinic space group C2/m, with FW = 598.9, a = 10.586(2), b = 16.713(2), c = 3.5006(14) A, β = 104.26(2)°, V = 600.2(3) A3, Z = 2. Crystals of [1,3-Se][I] belong to the orthorhombic space group Ima2, with FW = 598.9, a = 28.489(7), b = 3.543(2), c = 12.283(2) A, V = 1239.8(8) A3, Z = 4. In the presence of an excess of iodine, electrocrystallization of [1,4-Se]2+ affords the mixed iodide/triiodide salt [1,4-Se][I][I3], space group C2/c, FW = 979.59, a = 12.862(3), b = 15.063(2), c = 9.028(3) A, β = 100.62(2)°, V = 1719.1(7) A3, Z = 4. The structures of the two 1:1 compounds consist of perfectly superimposed stacks of molecular units interspersed by columns of disordered iodines. Interstack contacts in both structures are limited,...

Alkali ammonia complex fullendes form a rich variety of compounds with unique structural and electronic properties. Intercalation of NH3 into K3C60 produces orthorhombic NH3C60, which undergoes a metal-insulator transition instead of superconductivity that is expected to occur at around 30 K from the empirical relation betweenTc and the lattice parameter. Synthesis in liquid ammonia yields new superconducting fullerides(NH3)xNaA2C60 (0.5

We present studies of the electronic structure of polymerized orthorhombic and dimerised using electron energy-loss spectroscopy in transmission. From the C1s excitation spectra a reduced density of π ? states is ob- served for polymerized . This is in contrast to and can be explained by the different type of 'doping' and by the different bonding between the fullerene molecules in the two systems. Additional information about the optical prop- erties was obtained from the low energy loss function. Using a Kramers-Kronig analysis, the dielectric function, (e), and the optical conductivity, (σ), have been derived. e and the onset of the spectral weight have been compared between the polymer, the dimer and . This onset of spectral weight is found to be at : and : for o- and for , respectively.

Optical and magneto-optical properties of YVO3 single crystals have been studied in IR, visible, and UV regions. Below 74 K we have observed a large Kerr rotation, comparable to those in ferromagnets. This observation introduces a new class of materials: insulating antiferromagnets with strong magneto-optical Kerr effect, which can have advantages for practical applications. We look into the details of electronic and crystal structure changes. YVO3 was found to undergo two structural phase transitions. Initially, the orthorhombic Pbnm symmetry is lowered below a second-order phase transition at 200 K and recovers below 74 K at a first-order phase transition. Two Mott–Hubbard (MH) bands dominate the electronic spectrum in the visible range, followed by charge-transfer gap in UV. Below the 200 K a transfer of the spectral weight to higher frequencies occurs and a third MH band appears at 3 eV . We discuss the results on the basis of spin and orbital ordering theory, proposed for YVO3.