I. G. Zaitseva

Structure and Energetics of β-Diketonates. XII. Structure of Lanthanide tris-Dipivaloylmethanates for Er(thd)3 Used as an Example

A simultaneous electron diffraction and mass spectroscopic study of saturated vapors of erbium tris-dipivalylmethanate has revealed that at 136(5)°C, the vapor consists solely of Er(thd)3 molecules. Electron diffraction data may be described by two alternative models (of C_3 and D_3 symmetry), for which ra, rg, and rα structural parameters have been determined. D3 symmetry is recognized to be preferable for free Er(thd)3 molecules. The main structural parameters of the model are rα (Er − O) 2.218(5), rα (O − C) 1.279(5), rα (C − Cr) 1.404(6), rα (C − Ct) 1.512(3), rα(Ct − Cm) 1.542(5), rα (rm Cm− H) 1.804(4) Å, The ErO 75.0(0.4)°. The ErO6 coordination polyhedron has a structure close to an antiprism. A rotational angle of the O–O–O trigonal face relative to the position in a regular prism is 20.7(0.8)°. Possible reasons for the differences in the structure of Er(thd)3 molecules in the gas phase and crystal are discussed.

Structure and Energy Studies of β-Diketonates. X. Molecular Structure of Sc(aa)3 According to Gas-Phase Electron Diffraction Data

Synchronous electron diffraction and mass spectrometric investigation of the saturated vapor of scandium tris-acetylacetonate was carried out. It was stated that at 155(5)°C the vapor contains only monomeric Sc(aa)3 molecules, whose structural parameters ra, rg, and rα were determined. The internuclear distances in the chelate ring were found to be rα(Sc–O) = 2.076(4) Å, rα(O–C) = 1.271(3) Å, rα(C–Cr) = 1.386(4) Å. The coordination polyhedron ScO6 has a nearly antiprism structure of D3 symmetry. The angle of rotation of the O–O–O trigonal faces relative to their position in a regular prism is 26.8(1.1)°.

A mass spectrometric study of the vaporization of erbium hexafluoroacetylacetonate

The sublimation of erbium tris-hexafluoroacetylacetonate Er(C5O2HF6)3 was studied by the Knudsen effusion method with the mass spectrometric determination of vapor composition. Groups of ions containing one, two, and three metal atoms were recorded. The enthalpies of sublimation of the monomeric, dimeric, and trimeric forms ΔSH°(362 K) were found to be 133 ± 4, 135 ± 7, and 139 ± 38 kJ/mol, respectively. The melting point of Er(C5O2HF6)3 was 390 ± 2 K. No oligomeric forms were observed in vapor superheated above 430 K.

Ytterbium tris(hexafluoroacetylacetonate) Yb(C5O2HF6)3: The composition of overheated vapor and sublimation thermodynamics

A mass spectrometric study of the saturated vapor over ytterbium tris(hexafluoroacetylacetonate) Yb(hfa)3 (hfa = CF3-C(O)-CH-C(O)-CF3) and of the vapor overheated up to the thermal decomposition temperature of the complex is presented. The vapor composition changes markedly with increasing temperature. At T ≈ 370 K, the mass spectrum of the vapor over Yb(hfa)3 indicates the presence of ions containing one to three metal atoms. As the temperature is raised, the ion currents due to oligomer ions decrease. The oligomers are not detected at T > 440 K. The total decomposition temperature of Yb(hfa)3 is 663(9) K. The second-law enthalpy of sublimation (ΔHso (380 K)) is 134 ± 7 kJ/mol for the monomer and 138 ± 10 kJ/mol for the dimer. The enthalpy of dissociation of the dimer into monomer molecules is nearly equal to the enthalpy of sublimation of the monomer and dimer: ΔHdis(380 K) = 130 ± 15 kJ/mol.

Mass spectrometric study of superheated vapors of lanthanide tris(hexafluoroacetylacetonates)

Superheated vapors of La(hfa)3, Nd(hfa)3, Sm(hfa)3, Gd(hfa)3, Dy(hfa)3, Ho(hfa)3, Yb(hfa)3, and Lu(hfa)3 have been studied by mass spectrometry using a double two-temperature effusion cell in order to identify the molecular species present in the vapor at different degrees of superheating and the temperature of complete decomposition of the complexes. For equal temperatures of the upper and low compartments of the cell and for moderate superheating, the vapors of the listed complexes are highly oligomerized (mono-, di-, and trimers were detected). Vapor superheating shows low thermal stability of oligomers, whose stability decreases along the series La-Lu. The metal nature is shown to have an effect on the volatility and the fragmentation pattern of the chelates. The conditions of existence of monomeric complexes are identified.

A study of the structure and energy of β-diketonates. XVIII. Molecular structure of chromium and cobalt tris-acetylacetonates according to quantum chemical calculations and gas electron diffraction

The molecular structure of chromium and cobalt tris-acetylacetonates is studied by the synchronous electron diffraction and mass spectrometric experiment and quantum chemically. It is found that molecules have the D3 symmetry with internuclear distances rh1(Cr-O) = 1.960(4) Å rh1(Co-O) = 1.893(4) Å. Quantum chemical calculations by the DFT methods with different basis sets yield a structure well consistent with that found in the experiment. Changes in the structural parameters of chromium and cobalt β-diketonate complexes whose ligands differ in −CH3, −C(CH3)3, −CF3 substituents are considered.