Yu. A. Shevelev

The thermodynamic properties of bis(η6-ethoxybenzene)chromium fulleride from T → 0 to 340 K

The temperature dependence of the heat capacity of crystalline bis-(η6-ethoxybenzene)chromium fulleride [(η6-(EtOPh))2Cr]·+[C60]·− was studied for the first time by adiabatic vacuum calorimetry over the temperature range 6–340 K with errors of ±0.2%. The temperature dependence of the EPR signal parameters of bis-(η6-ethoxybenzene)chromium fulleride was studied for the first time from 120 to 340 K. A reversible endothermic transformation was observed between 160 and 250 K during heating; it was caused by the dissociation of the [(C60)2]2− dimer and the formation of the [(η6-(EtOPh))2Cr]·+[C60]·− fulleride; its standard thermodynamic characteristics were estimated and analyzed. The experimental data were used to calculate the standard thermodynamic functions, including the heat capacity, enthalpy, entropy, and Gibbs function of the fulleride dimer from T → 0 to 160 K and the [(η6-(EtOPh))2Cr]·+[C60]·− monomeric complex over the temperature range 250–340 K. The standard thermodynamic properties of the fulleride studied, fullerides studied earlier, and fullerite C60 were compared.

Synthesis, structure, and thermolysis of (fullerene)(toluene)dicarbonylchromium

Fullerene C 60 has 30 essentially localized double bonds and can form η 2 complexes with transition metals. Molybdenum and tungsten π complexes of dihaptocoordinated fullerene with different ligands, such as CO, phenanthroline, α , α -dipyridyl, triphenylphosphine, and maleic and fumaric acid esters, have been prepared and structurally characterized [1–4]. The η 2 -C 60 complex with the (diphosphine)tricarbonylchromium moiety has been characterized by spectral methods [5]. As is known, (arene)tricarbonylchromium complexes can exchange the CO group for alkenes when exposed to UV irradiation [6]. Therefore, we studied the interaction of C 60 with (toluene)tricarbonylchromium under UV irradiation.

The thermodynamic properties of bis(η6-o-xylene)chromium(I) fulleride over the temperature range from T → 0 to 340 K

The temperature dependence of the heat capacity of bis(η6-o-xylene)chromium(I) fulleride, [(η6-(o-xylene))2Cr]+•[C60]•−, over the temperature range 6–340 K was measured on an adiabatic vacuum calorimeter. The low-temperature (20 K ≤ T ≤ 50 K) heat capacity was subjected to multifractal processing; conclusions about the heterodynamic character of the structure were drawn. The experimental data were used to calculate the standard thermodynamic functions Cp∘(T), H∘(T)-H∘(0), S∘(T), and G∘(T)-H∘(0) over the temperature range from T → 0 to 340 K and estimate the standard entropy of fulleride formation from simple substances at 298.15 K. The standard thermodynamic characteristics of [(η6-(o-xylene))2Cr]+•[C60]•− were compared with those of the initial fullerene C60.

Thermodynamic Characteristics of Bis(η 6 ethylbenzene)chromium Fulleride

The temperature dependence of heat capacity of crystalline bis(η6-ethylbenzene)chromium fulleride [(η6-EtPh)2Cr]·+ [C60]·− was studied in adiabatic vacuum calorimeter in the range of 6.7 to 344 K with an error of ±0.3%. Dependence of the parameters of EPR signal of bis(η6-ethylbenzene)chromium fulleride on temperature was studied by electron paramagnetic resonance (EPR) in the range of 120 to 290 K. In the range of 204 to 246 K, upon heating, reversible endothermic transformation was recorded, which is caused by the dissociation of dimer (C60−)2 and formation of fulleride [(η6-EtPh)2Cr]·+ [C60]·−; its standard thermodynamic parameters were estimated and analyzed. Standard thermodynamic functions were calculated by the experimental data obtained: heat capacity, enthalpy, entropy, and Gibbs function of fulleride dimmer in the range of T → 0 to 204 K and monomer complex [(η6-EtPh)2Cr]·+ [C60]·− in the range of 246 to 344 K. Standard thermodynamic properties of fulleride under study, fullerides studied earlier, and fullerite C60 were compared.

Interaction of fullerenes with metallic lithium in the condensed state

The relative stability of exo-and endohedral lithium complexes with the C60 fullerene was estimated using quantum chemistry and molecular-dynamics methods. Endohedral compounds were shown to have a higher stability. The possible maximum filling of the C60 inner sphere by lithium was estimated theoretically. The interaction of metallic lithium with the C60 fullerene and a C60 + C70 mixture was studied using DTA and EPR and established to proceed in several stages.

Reaction of chromium atoms with acetophenone

1. Bis (acetophenone) chromium(0) was obtained by the cocondensation of chromium and acetophenone vapors at 77°K. 2. The reductive condensation of acetophenone to 2,3-diphenyl-2,3-butanediol, due to the oxidation of atomic chromium by acetophenone, goes in parallel with the direct synthesis of bis (acetophenone) chromium(0).

Low temperature synthesis of ferrocenyl-substituted bisarenechromium complexes

Conclusions1.The reaction of Cr vapors with phenylferrocene and p-tolylferrocene in a high vacuum at 77°K gave bis(ferrocenylbenzene)chromium and bis(p-ferrocenyltoluene)chromium.2.The mutual effect of the ferrocenyl and bisarenechromium fragments in the neutral Cr(0) and oxidized Cr(I) forms of these complexes was discussed.

Oxidation of bisbenzenechromium(0) by stable phenoxyl radical

1. (C6H6)2Cr(0) is oxidized by the stable 2,4,6-tri-tert-butylphenoxyl radical to the saltlike bisbenzenechromium 2,4,6-tri-tert-butylphenolate. 2. It was shown that the phenolate can undergo dissociative sublimation. 3. The phenolate undergoes thermal decomposition by the disproportionation mechanism, in which the initial step is dissociation of the phenolate to (C6H6)2Cr(O) and the phenoxyl radical.