S. Yu. Ketkov

Electron density distribution in vanadocene (η5-C5H5)2V and mixed metallocenes (η5-C5H5)M(η5-C7H7) (M = Ti, V, or Cr) and (η5-C5H5)Ti(η8-C8H8). Effect of the nature of the cyclic ligand on the character of the M--(π-ligand) bond

The electron density distribution and atomic displacements were analyzed based on the results of precision low-temperature X-ray diffraction studies of a series of isostructural (Pnma, Z = 4) mixed metallocenes (η5-C5H5)M(η5-C7H7) (M = Ti, V, or Cr) and (η5-C5H5)Ti(η8-C8H8). The barriers to rotation of the cyclic ligands were evaluated based on rms libration amplitudes. Analysis of the deformation electron density demonstrated that the character of the M--(π-ligand) chemical bond depends substantially both on the nature of the metal atom and the size of the ligand. Lowering of the local symmetry of the (η5-C5H5)M(η5-C7H7) complexes to CS leads to distortion of the cylindrical symmetry of the electron density distribution observed in vanadocene (η5-C5H5)2V and titanocene (η5-C5H5)Ti(η8-C8H8).

Electronic excited states of bis(η6-arene) tungsten: an investigation by ultraviolet photoabsorption spectroscopy in the vapour and solution phases

Abstract The electronic absorption spectra of (Bz) 2 W and (Tol) 2 W (Bz = η 6 -C 6 H 6 , Tol = η 6 -C 6 H 5 Me) in the gas phase show comparatively narrow bands which are absent from the spectra in heptane solution. These bands form two Rydberg series converging on the first ionization potential. Series 1 is characterized by the quantum defect δ = 3.40 in both compounds. Series 2 shows δ = 3.15 in (Bz) 2 W and δ = 3.21 in (Tol) 2 W. Series 1 arises from the a 1g → R n p(e 1u ) transitions. Its first and second members are split into two components on going from (Bz) 2 W to (Tol) 2 W. Series 2 corresponds to the a 1g → R n p(a 2u ) excitations. In addition to these two series, the (Tol) 2 W vapour-phase spectrum contains the a 1g → R6s and a 1g → R6d transitions which were interpreted on the basis of their term values. The first member of the R n p(a 2u ) series is broadened beyond detection by admixture of valence-shell transitions. The interaction between electronic excited states results in deviation of the position of the second R n p(e 1u ) series member from that predicted by the Rydberg formula. The frequency of the lowest R n p(e 1u ) transition deviates also from the theoretical value but this is mainly due to stronger penetrating properties of the corresponding terminating orbital in comparison with the higher Rydberg orbitals. The vapour-phase spectra of (Bz) 2 W and (Tol) 2 W show no Rydberg features which might be considered a consequence of spin-orbit coupling caused by the presence of the heavy metal atom.

Structures of Rydberg transitions in the absorption spectra of methyl-substituted derivatives of bis(η6-benzene)chromium

The effect of methylation of ligands in bis(η6-benzene)chromium (1) on the structure of Rydberg transitions in absorption spectra has been studied. A detailed analysis and interpretation of all Rydberg elements of the vapor-phase spectra of bis(η6-benzene)chromium (2), bis(η6-o-xylene)chromium (3), bis(η6-m-xylene)chromium (4), and bis(η6-mesitylene)chromium (5) was carried out. The vapor-phase electronic absorption spectrum of bis(η6-p-xylene)chromium (6) was measured, and the assignment of the Rydberg bands was made for the first time. The first ionization potentials of complexes 2–5 were refined. The energy of detachment of the 3dz2 electron and the parameters of the Rydberg excitations for molecule 6 were determined. The vibronic components of the 3dz2→R4px,y transition in the spectra of complexes 2 and 6 were assigned. The differences in the Rydberg structure of the spectra of compounds 2–6 were analyzed in terms of the selection rules for optical transitions in the corresponding symmetry groups. The vapor-phase spectra correspond to conformers with the symmetry groupsC2v andC2 for complexes 2–4, with the symmetry groupsD3h andD3 for compound 5, and with the symmetry groupD2d for complex 6.

New high-spin iron complexes based on bis(imino)acenaphthenes (BIAN): synthesis, structure, and magnetic properties

The reactions of iron diiodide with one and two equivalents of the monopotassium salt of 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene (dpp-BIAN) in diethyl ether gave the complexes [(dpp-BIAN)FeI]2 (1) and (dpp-BIAN)2Fe (2), respectively. The bis-ligand complex (tms-BIAN)2Fe (3) was synthesized by the exchange reaction of the monosodium salt of 1,2-bis(trimethylsilylimino)acenaphthene (tms-BIAN) with iron diiodide. The reaction of FeI2 with tms-BIAN affords the chelate complex (tms-BIAN)FeI2 (4), whereas the reaction of FeBr2·2H2O with tms-BIAN is accompanied by elimination of trimethylsilyl groups to form the tris-ligand acenaphthene-1,2-diimine complex [(H2BIAN)3Fe][FeBr3·THF]2 (5) containing two types of iron ions. Compounds 1–5 were characterized by IR spectroscopy and elemental analysis. The molecular structures of 1–5 were determined by single-crystal X-ray diffraction. For high-spin complexes 1–3, the temperature-dependent magnetic susceptibilities were measured in the range of 4–300 K.

Stoichiometric synthesis of fullerene compounds with lithium and sodium and analysis of their IR and EPR spectra

A modified method is proposed for preparing fullerene compounds with alkali metals in a solution. The compounds synthesized have the general formula MenC60(THF)x, where Me = Li or Na; n=1–4, 6, 8, or 12; and THF = tetrahydrofuran. The use of preliminarily synthesized additives MeC10H8 makes it possible to prepare fullerene compounds with an exact stoichiometric ratio between C60n− and Me+. The IR and EPR spectra of the compounds prepared are analyzed and compared with the spectra of their analogs available in the literature. The intramolecular modes Tu(1)-Tu(4) for the C60n− anion are assigned. The splitting of the Tu(1) mode into a doublet at room temperature for MenC60(THF)x (n=1, 2, 4) compounds indicates that the fullerene anion has a distorted structure. An increase in the intensity of the Tu(2) mode, a noticeable shift of the Tu(4) mode toward the long-wavelength range, and an anomalous increase in the intensity of the latter mode for the Li3C60(THF)x complex suggest that, in the fullerene anion, the coupling of vibrational modes occurs through the charge-phonon mechanism. The measured EPR spectra of lithium-and sodium-containing fullerene compounds are characteristic of C60− anions. The g factors for these compounds are almost identical and do not depend on temperature. The g factor for the C60n− anion depends on the nature of the metal and differs from the g factor for the C60− anion.

New hybrid material based on multiwalled carbon nanotubes decorated with rhenium nanoparticles

The deposition of rhenium nanoparticles on the surface of multiwalled carbon nanotubes (MWCNTs) is conducted by metal organic chemical vapor deposition (MOCVD) technology. The synthesized hybrid materials are analyzed using scanning electron microscopy, high-resolution transmission electron microscopy and powder X-ray diffraction. The dependence of the sizes and shapes of the deposited rhenium nanoparticles on the initial synthesis parameters is established. It is found that the size distribution of rhenium nanoparticles is bimodal on the surface of MWCNTs.

Interaction of sodium fullerene derivatives with trimethylchlorosilane

AbstractSoluble dimer compounds of the general formula [C60(Me3Si)n]2 (where n = 3, 5, 7, or 9 and Me = CH3) and a soluble monomer compound, C60(Me3Si)12, are synthesized by the reaction of the compound C60Nan(THF)x (where n = 4, 6, 8, 10, or 12 and THF = tetrahydrofuran) with trimethylchlorosilane Me3SiCl. The compounds synthesized are identified using IR and NMR spectroscopy and mass spectrometry. An irreversible endothermic effect exhibited by the [C60(Me3Si)7]2 compound in the temperature range 448–570 K is revealed by dynamic adiabatic calorimetry. From analyzing the experimental results, it becomes possible for the first time to demonstrate the structural flexibility of the fullerene in the following sequence of reactions:

Compounds of chromium, titanium, and zirconium with different reduced forms of acenaphthene-1,2-diimine

\begin{array}{*{20}c} {C_{60} \xrightarrow[{ - 12C_{10} H_8 }]{{ + 12NaC_{10} H_8 }}C_{60} Na_{12} \xrightarrow[{ - 12NaCl}]{{ + excess Me_3 SiCl}}C_{60} (Me_3 Si)_{12} \xrightarrow[{ - 12Me_3 SiCl}]{{ + HCl(gas)}}[C_{60} H_n ]\xrightarrow[{ - 1/2nH_2 }]{{hv}}C_{60} } \\ {C_{60} \xrightarrow[{ - 8C_{10} H_8 }]{{ + 8NaC_{10} H_8 }}C_{60} Na_8 \xrightarrow[{ - 8NaCl}]{{ + excess Me_3 SiCl}}[C_{60} (Me_3 Si)_7 ]_2 \xrightarrow{{573K}}\begin{array}{*{20}c} {products of the} \\ {transformation of + } \\ {Me_3 Si groups} \\ \end{array} C_{60^ - } } \\ \end{array}