Fullerene complexes with divalent metal dithiocarbamates: structures,magnetic properties,and photoconductivity

A series of complexes of fullerenes C₆₀ and C₇₀ with metal dithiocarbamates {M^II(R₂dtc)₂}·C_m (m = 60 or 70) and metal dithiocarbamates coordinated to nitrogen-containing ligands (L), {M^II(R₂dtc)₂)_x·L}·C₆₀ (x = 1 or 2), where M = Cu, Zn, Cd, Hg, Mn, or Fe, R = Me, Et, Prⁿ, Prⁱ, or Buⁿ, L is 1,4-diazabicyclo[2.2.2]octane (DABCO), N,N′-dimethylpiperazine, or hexamethylenetetramine, were synthesized. The shape of dithiocarbamate molecules is sterically compatible with the spherical shape of C₆₀, resulting in an efficient interaction between their π systems. The resulting compounds are characterized by a layered or three-dimensional packing of the fullerene molecules. In the C₆₀ complexes, iron(II) and manganese(II) dithiocarbamates exist in the high-spin states (S = 2 and 5/2). The magnetic susceptibility of {M^II(Et₂dtc)₂}₂·C_m (M = Fe or Mn, m = 60 or 70) in the temperature range of 200–300 K is described by the Curie-Weiss law with Θ = −250 and −96 K and with maxima at 110 and 46 K, respectively, which is indicative of a strong antiferromagnetic spin coupling between M^II. The Weiss constants for the [{M^II(Et₂dtc)₂}₂·DABCO]·C₆₀·(DABCO)₂ complexes (M = Fe or Mn) are 1.7 and 0.3 K, respectively. The magnetic moments of the complexes containing Fe and Mn dithiocarbamates slightly increase at temperatures below 50 and 35 K, respectively, which is evidence of the ferromagnetic spin coupling between M^II in {M^II(Et₂dtc)₂}₂·DABCO. Single crystals of the complexes exhibit low dark conductivity (10⁻¹⁰–10⁻¹¹ S cm⁻¹). The visible light irradiation of these crystals leads to an increase in the photocurrent by two–three orders of magnitude. The photogeneration of free charge carriers in the complexes occurs both due to the photoexcitation of metal dithiocarbamate (Cu^II(Et₂dtc)₂) and through the charge transfer from metal dithiocarbamate (M^II(Et₂dtc)₂, M = Zn or Cd) to C₆₀. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2072–2087, November, 2007.     

The experience in production of composite refraction lenses from beryllium

The choice of beryllium-based material for the use in X-ray optics has been substantiated based on electron microscopy and X-ray diffraction data. The first results of applying refraction lenses made of this material are reported.     

Magnetic Coupling and Optical Properties of the S6‐Dodecakis(trifluoromethyl)fullerene Radical Anions in the Layered Salt (PPN+)[C60(CF3)12.−]

Poly(trifluoromethyl)fullerene S₆‐C₆₀(CF₃)₁₂ was reduced by sodium fluorenone ketyl in the presence of (PPN)Cl (PPN=bis(triphenylphosphine)iminium) to afford the salt (PPN)[C₆₀(CF₃)₁₂] ( 1 ), which contains C₆₀(CF₃)₁₂^.? radical anions. In the crystal structure of 1 , C₆₀(CF₃)₁₂^.? layers alternate with the PPN⁺ cations. There are short F ??? F contacts between C₆₀(CF₃)₁₂^.? radical anions within the layers but no C ??? C contacts. DFT calculations revealed that the negative charge on C₆₀(CF₃)₁₂^.? is distributed mainly between sp² carbon and fluorine atoms, whereas spin density is localized mainly on the fullerene‐cage sp² carbon atoms. IR and UV/Vis/NIR spectra in the solid state and solution showed characteristic changes relative to those of neutral S₆‐C₆₀(CF₃)₁₂ due to the formation of radical anions. The solid‐state electronic spectrum of 1 exhibits a single broad band at 738 nm attributed to C₆₀(CF₃)₁₂^.?. Crystals of 1 show a narrow EPR signal with g=2.0025 (ΔH=0.45 mT) at 300 K. The temperature dependence of the integral intensity follows the Curie–Weiss law with a negative Weiss temperature of ?11.8 K (30–300 K) indicating antiferromagnetic interaction of spins. This dependence was approximated by the Heisenberg model for one‐dimensional chains of antiferromagnetically interacting spins with exchange interaction J/k_B=?9.1 K. It was assumed that magnetic interaction between the C₆₀(CF₃)₁₂^.? spins in the layers is mediated by short F ??? F contacts.     

Studies of intermediates formed under the conditions of preparative electroreduction of naphthalene 1-Nitro-3,6,8-Trisulfo acid

The effect is studied of the conditions of preparative reduction of naphthalene 1-nitro-3,6,8-trisulfo acid, particularly, the cathode material, temperature, and current density on the yield of intermediate naphthalene 1-hydroxylamino-3,6,8-trisulfo acid. It is shown that formation of naphthalene 1-hydroxy-lamino-3,6,8-trisulfo acid in reaction solutions results not only in a decrease in the yield of target naphthalene 1-amino-3,6,8-trisulfo acid, but also in a decrease in the quality of the latter, which is manifested in a decrease in the yield into its conversion to naphthalene 1-amino-8-oxy-3,6-disulfo acid. Conditions are found for preparative reduction of naphthalene 1-nitro-3,6,8-trisulfo acid providing the lowest yield of naphthalene 1-hydroxylamino-3,6,8-trisulfo acid in reaction solutions.