N. V. Tverdova

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.

IR Spectra of N,N′-Ethylene-Bis(salicylaldiminates) and N,N′-ethylene-Bis(acetylacetoniminates) of Ni(II), Cu(II), and Zn(II)

Vibrational spectra of N,N′-ethylene-Bis(salicylaldiminaates) and N,N′-ethylene-Bis(acetylacetoniminates) of nickel (II), copper (II), and zinc (II) are studied experimentally (IR spectroscopy, 400–4000 cm−1) and theoretically (B3LYP), band assignment is given, and the distribution of potential energy of normal vibrations in internal coordinates is studied. Differences between vibrational spectra of the complexes are discussed. Thermodynamic functions of gas-phase complexes corresponding to temperatures of 298 and 800 K are calculated.

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)°.

Structure and Energetics of β–Diketonates. XI. Molecular Structure of Sc(thd)3 from Gas–Phase Electron Diffraction Data

Electron–diffraction and mass–spectrometric studies of saturated vapor of scandium tris–dipivaloyl–methanate showed that at 135(5)°, the vapor contains only monomeric Sc(thd)3, whose structural parameters ra, rg, and rα were determined. The internuclear distances in the chelate ring were found to be rαSc=O) = 2.066(5)Å, rα(O=C) = 1.272(3)Å, and rα(C=Cr) = 1.385(3)Å. The ScO6 coordination polyhedron has a D3 symmetry configuration close to a regular antiprism. The angle of rotation of the O=O=O trigonal faces relative to their position in a regular prism is 25.7(1.5)°.

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 the overheated vapor over Ni(II), Cu(II), and Zn(II) N,N′-ethylenebis(acetylacetoniminato) complexes

A mass spectrometric study of the overheated vapor over the complexes Ni(acacen), Cu(acacen), and Zn(acacen) (H2acacen = N,N′-ethylenebis(acetylacetonimine)) has been carried out in the temperature range of 180–760°C. Irrespective of the degree of overheating, the vapor phases over all of these compounds contain no ions heavier than the molecular ion [MO2N2C12H18]+. The existence of molecular ions in the overheated vapor in the double-chamber two-temperature effusion cell is evidence of the high thermal stability of the complexes. The onset temperature of the thermal decomposition of Ni(acacen), Cu(acacen), and Zn(acacen) is 690, 610, and 560°C, respectively. The way of fragmentation of the chelates under electron impact ionization depends on the nature of the metal.

Mass spectrometric study of the overheated vapor over nickel(II), Copper(II), and Zinc(II) N,N′-Ethylenebis(salicylaldiminato) complexes

A mass spectrometric study of the overheated vapor over the nickel(II), copper(II), and zinc(II) N,N′-ethylenebis(salicylaldiminato) complexes between 300 and 865°C has been carried out. Throughout this temperature range, the overheated vapor over all of the complexes contains no ions heavier than the molecular ion [MO2N2C16H14]+. At ∼600°C, Cu(salen) and Zn(salen) interact with the structural material of the double-chamber two-temperature effusion cell (Kh18N10T steel). The complexes are thermally very stable. The fragmentation pattern of the chelates under electron-impact ionization is metal-dependent.

DFT Study of molecular and electronic structure of magnesium (II) tetra(1,2,5-chalcogenadiazolo)porphyrazines, [TXDPzMg] (X = O, S, Se, Te)

The influence of the chalcogen atom (X) on the molecular and electronic structures for the series of MgII tetra(1,2,5-chalcogenadiazolo)porphyrazines [TXDPzMg] (X = O, S, Se, Te) and their monoaqua complexes [TXDPzMg(OH2)] was studied using DFT methods (B3LYP and PBE0 functionals) with cc-pVTZ basis sets. The chalcogen atom X changes strongly the geometry of the fused 1,2,5-chalcogenadiazole rings, but has only a weak influence on the dimensions of the coordination cavity of the porphyrazine macrocycle in [TXDPzMg] leading to its slight expansion in the sequence S < Se < Te < O. The electron density distribution was considered in terms of the natural bond order (NBO) and the natural population analysis (NPA). The frontier molecular orbitals are destabilzed along with the decrease of electronegativity of the chalcogen atoms. The a1u and eg∗ orbitals (HOMO and LUMO) are mainly localized on atoms constituting the internal 16-membered macrocycle, while the chalcogen atoms have the strongest effect on the composition of the filled π-MOs having the a2u symmetry – 2a2u and lower lying 1a2u orbitals. The Gouterman type a2u orbital with predominant localization on the nitrogen atoms of the internal 16-membered macrocycle is 2a2u for the O- and S-containing complexes and for the Se- and Te-analogs it becomes 1a2u, while the higher lying 2a2u orbital resides mainly on the fused heterocycles (Se/Te and Cβ atoms). The lowest excited states have been calculated for [TXDPzMg] and used for the explanation of the peculiarities and tendencies observed in the experimental electronic absorption spectra available for the S, Se- and Te-containing MgII complexes.

The Structure of Mn(acac)3 - A Rare Experimental Evidence of a Static Jahn-Teller Effect in the Gas-Phase

The structure of free manganese(III) tris(acetylacetonate) [Mn(acac)3 ] was determined by mass-spectrometrically controlled gas-phase electron diffraction. The vapor of Mn(acac)3 at 125(5) °C is composed of a single conformer of Mn(acac)3 in C2 symmetry with the central structural motif of a tetragonal elongated MnO6 octahedron and 47(2) mol % of acetylacetone (Hacac) formed by partial thermal decomposition of Mn(acac)3 . Three types of Mn-O separations have been refined (rh1 =2.157(16), 1.946(5), and 1.932(5) Å. We have found no indication for a significant deviation of the -C-C-C-O-Mn-O- six-membered rings from planarity, which is observed in the solid state.

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.