Vibrational spectra,force fields and NMR-data for triorganyl-tetrelomethanes CH4−n(TtR3)n (Tt = Sn and Pb)

Based on vibrational spectra normal coordinate calculations have been carried out for trimethyltetrelomethanes CH_4−n(TtMe₃)_n (Tt = Sn and Pb, n = 2 and 4). The resulting comparable force constants of the two distinguishable types of carbon-metal bonds for Tt = Sn (range K(C-Sn) 220 - 180 Nm⁻¹) are 10 – 15% higher than for Tt = Pb (K(C-Pb) 190 - 170 Nm⁻¹). These force constants K(C-Tt) are similar to the K(C-Hg) values of corresponding methylmercuriomethanes CH_4−n(HgMe)_n. The force constants K (C-Tt), and also the coupling constants ¹J(Tt,C) from NMR spectra, indicate weakening of the carbon-metal bonds in the central CTt_n groups with growing n, whereas the peripheral TtMe bonds are almost unaffected by variations of n.     

Electronic structure calculations on RNO2 species,R = H,CH3, NH2, HO,and F

The relative singlet—triplet separations of five simple species of general formula RNO₂ has been estimated by GVB calculations with both double-zeta and polarized double-zeta basis sets. Electronegative substituents raise the calculated singlet—triplet separation. Qualitative aspects of these substituent effects are discussed.     

Synthese und spektroskopische charakterisierung von cyclopentadienyleisen-komplexen mit PN-liganden des typs (C6H5)3−nP(NR2)n (n = 0−3; R = CH3, C2H5

The complex cations [C₅H₅Fe(CO)₂L]BF₄ (L = (C₆H₅)_3−nP(NR₂)_n; n = 0−3 R = CH₃, C₂H₅) have been obtained from the reaction of [C₅H₅Fe(CO)₂THF]BF₄ (I) with L. The reaction of I with E(NR₂)₃ (E = As, Sb; R= CH₃) is also described. Spectroscopic investigations (IR, ¹H, ¹³C and ³¹P NMR) indicate an increase in electron density on the iron center through increase of the number of P-bound NR₂ groups.     

Comparative mass spectrometric investigation of transition metal polymethylcyclopentadienylcarbonyl complexes: I. Mass spectra of RnC5H5−nRe(CO)3 (R = CH3, n = 0-5; R = t-C(CH3)3, n = 1)

Mass spectra of π-(CH₃)_nC₅H_5−nRe(CO)₃ Me_nCpReT) (n = 0–5) and t-BuCpReT were recorded, from which it was found that molecular ion (M⁺) fragmentation for Me_nCpReT (_n = 0, 1) differs from that for Me_nCpReT (_n = 2–5). The (M – 2CO)⁺ ions have maximum intensity in n = 0, 1 complexes, and the (M – 2CO – H₂)⁺ ions, in _n = 2–5 complexes. H₂ elimination from (M – 2CO)⁺ is typical of rhenium π-cyclopentadienyl complex fragmentation, where the number of methyl groups in the Cp ring is > 1, and seems to occur with participation of the Re atom.     

Theoretical studies of the reactions of Cl atoms with CF3CH2OCH n F(3−n) (n = 1, 2, 3)

This paper presents the theoretical studies of the reactions of Cl atoms with CF₃CH₂OCH₃, CF₃CH₂OCH₂F and CF₃CH₂OCHF₂ using an ab initio direct dynamics theory. The geometries and vibrational frequencies of the reactants, complexes, transition states and products are calculated at the MP2/6-31+(d,p) level. The minimum energy path is also calculated at same level. The MC-QCISD method is carried out for further refining the energetic information. The rate constants are evaluated with the canonical variational transition state theory (CVT) and CVT with small curvature tunneling contributions in the temperature range 200–1,500 K. The results are in good agreement with experimental values.     

Spatial structure and electronic spectrum of TiSi n − clusters (n = 6–18)

Results from optimizing the spatial structure and calculated electronic spectra of anion clusters TiSi _n ^? (n = 6–18) are presented. Calculations are performed within the density functional theory. Spatial structures of clusters detected experimentally are established by comparing the calculated and experimental data. It is shown that prismatic and fullerene-like structures are the ones most energetically favorable for clusters TiSi _n ^? . It is concluded that these structures are basic when building clusters with close numbers of silicon atoms.     

1H, 13C and 31P NMR studies of some (C6H5)3−nPRn and (C6H5)3−nPRn Cr(CO)5 (n = 0–3; R  H,CH3, C2H5, i-C3H7, t-C4H9) derivatives

The ³¹P chemical shift of the (C₆H₅)_3−nPR_n and (C₆H₅)_3−nPR_nCr(CO)₅ (n = 0–3; R  H, CH₃, C₂H₅, i-C₃H₇, t-C₄H₉) derivatives is dominated by the steric effect. A small inductive effect is also operative but there are no indications of notable (d_Cr→d_P)π back-bonding. The ¹³C chemical shift of the phenyl carbon atoms indicates that (p_ring-d_P)π electron delocalization is unimportant.The ¹³C chemical shift of the carbonyl carbon atoms, which is mainly governed by the mean excitation energy, confirms the conclusion that there are no notable changes in (d_Cr→d_P)π back-bonding in this series of compounds.     

Relative permittivity increments for {xCH3OH + (1 − x)CH3OCH2(CH2OCH2)3CH2OCH3} fromT = 283.15 K toT = 323.15 K

Relative permittivities of { CH₃OH  +  CH₃OCH₂(CH₂OCH₂)₃CH₂OCH₃(2,5,8,11,14-pentaoxapentadecane, tegdme)} at temperatures from 283.15 K to 323.15 K and atmospheric pressure, were measured over the whole composition range. Experimental relative permittivities were fitted by a polynomial function in mole fraction. Values of relative permittivity were measured using a HP4284A precision LCR Meter together with the measuring cell HP16452A at 1 MHz. Relative permittivity increments were determined from experimental data and fitted to a variable-degree polynomial function. Different theoretical models were used to predict the permittivity of this mixture. The predictions are better when the volume change on mixing is considered.     

Vibrational spectra,force constants and mean amplitudes of trimethylsilylacetylene (CH3)3SiCCH and (CD3)3SiCCD

The infrared and Raman spectra of (CD₃)₃SiCCD have been obtained. Normal coordinate analysis of trimethylsilylacetylene and its complete     

Synthesis,crystal structure,and properties of hybrid-3D copper tetraphosphonate: [Cu3((HO3PCH2)2N–CH2C6H4CH2–N(CH2PO3H)2)(H2O)4] n

The new copper(II) tetraphosphonate, [Cu₃(HO₃PCH₂)₂N–CH₂C₆H₄CH₂–N(CH₂PO₃H)₂)(H₂O)₄] _n (1) was hydrothermally synthesized from the reaction of Cu(NO₃)₂ and (H₂O₃PCH₂)₂N–CH₂C₆H₄CH₂–N(CH₂PO₃H₂)₂, (H₈L). Compound 1 was structurally characterized by means of X-ray single crystal diffraction. The structure of 1 showed a 3D structure constructed from two types of Cu(II) and chelating and bridging modes of (HO₃PCH₂)₂N–CH₂C₆H₄CH₂–N(CH₂PO₃H)₂, and features a (4⁴.6¹⁰.8) topological network. The 3D compound is further stabilized by hydrogen bonds. UV–Vis diffuse reflectance and infrared spectroscopy as well as elemental analysis of compound 1 are also presented.     

Synthesis,characterization, and crystal structure of a 2-D metal diphosphonate: Cu3(H2O)2[HO3PCH2N(CH3)CH2PO3]2 · 2H2O

Hydrothermal reaction of N-methyl-iminobis(methylenephosphonic acid), CH₃N(CH₂PO₃H₂)₂, (H₄L) with copper(II) acetate afforded a new layered Cu(II) amino diphosphonate, Cu₃(H₂O)₂(HL)₂?·?2H₂O (1). Compound 1 was studied by IR spectroscopy, TGA/DTA data, and X-ray diffraction (XRD) techniques. The XRD patterns are the same for the hydrated and the dehydrated complexes. A single-crystal X-ray crystallographic determination reveals copper in two different coordination environments. Cu1 has a distorted elongated tetragonal octahedral geometry, whereas Cu2 has a square-pyramidal distorted geometry. The HL trianion is a pentadentate ligand with a deprotonated nitrogen atom and two oxygen atoms of each phosphonate binding to copper. Hydrogen bonds between lattice water molecules in interlayer spaces and the non-coordinated phosphonate oxygen atoms as well as water ligands leads to a 3-D supramolecular network structure.     

Synthesis,properties, and reactions of enantiomerically pure,chiral fluorous phosphines of the formula (menthyl)P(CH2CH2(CF2)n−1CF3)2 (n=6, 8)

Reactions of (menthyl)PH₂ and H₂CCHR_f6 (menthyl=1R,3R,4S; R_fn=(CF₂)_n−1CF₃) or H₂CCHR_f8 (AIBN, refluxing THF) give (menthyl)PH(CH₂CH₂R_fn) and then (menthyl)P(CH₂CH₂R_fn)₂ (n=6, 7; n=8, 8), but with purification or other difficulties at each stage. Reactions of (menthyl)PCl₂ with IMgCH₂CH₂R_fn give, under careful conditions, analytically pure 7 or 8 in 28–32% yields after distillation. Some R_fn(CH₂)₄R_fn also form. These represent the first chiral (and non-racemic) fluorous phosphines. Reactions of 7 or 8 with [Ir(COD)Cl]₂ and CO give trans-[(menthyl)P(CH₂CH₂R_fn)₂]₂Ir(Cl)(CO) (n=6, 71%; 8, 51%) as analytically pure yellow oils. Their IR ν_CO values show the donor/acceptor properties of 7 and 8 to be intermediate between those of P((CH₂)₃R_f8)₃ and P((CH₂)₄R_f8)₃. The CF₃C₆F₁₁:toluene partition coefficients of 7 and 8 (27°C, 78.4:21.6 and 93.7:6.3) are distinctly lower than those of P((CH₂)₂R_fn)₃ (n=6, 98.8:1.2; n=8, >99.7:<0.3), reflecting the replacement of a linear C₈–C₁₀ group that is ca. 75–80% fluorinated by a cyclic C₁₀ terpenyl group. Reactions of 7 or 8 with [Rh(COD)Cl]₂ give [(menthyl)P(CH₂CH₂R_fn)₂]Rh(Cl)(COD) (n=6, 69%; 8, 70%) as orange crystallizable oils.     

Crystal,molecular, and electronic structure of carboxylate [Fe3O(CH3COO)6(H2O)3]NO3·4H2O

Results of X-ray structural analysis, IR spectroscopy, and quantum chemical study of the [Fe₃O(CH₃COO)₆(H₂O)₃]NO₃·4H₂O complex are reported. The crystal belongs to the monoclinic system with a=15.688(3), b=11.767(2), c=15.318(4) Å, γ=92.54(3)^o, space group P2₁/a, R=0.078. The molecule has a trinuclear structure: three iron atoms occupy the vertices of an equilateral, triangle with an Fe−Fe distance of 3.29 Å and are bonded by the μ₃-oxo and μ-CH₃COO⁻ (O,O′) ligands. To each iron atom, one water molecule is coordinated. Using the obtained values of populations on 3d AO of Fe (d _xy ^1.34 ; d _xz ^1.39 ; d _yz ^1.46 ; ; ) and charges on oxygen atoms (O _c ^−0.5 ; O _ac ^−0.31 ; O _w ^−0.31 ), we estimated the values of isomeric shift and quadrupole splitting (0.75 and 0.70 mm/sec, respectively; these are close to the experimental values of 0.75 and 0.58 mm/sec, (300 K)). Institute of Chemistry, Moldovian Academy of Sciences. Moldovian State University. Institute of Applied Physics, Moldovian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii., Vol. 35, No. 2, pp. 112–120, March–April, 1994. Translated by T. Yudanova     

The synthesis and spectral properties of the novel monodentate(s) coordinated thiosemicarbazide and thiosemicarbazone complexes [Fe(CO)2L(η5-C5H5)][PF6] (L = H2NNHCSNH2, cy-C5H10CNNHCSNH2 or R′R″CNNHCSNH2, R′ = R″ = Me; R′= H,R″ = Ph; R′= H,R″ = p-NO2Ph,R′= Me,R″ = p-MePh)

The acetone complex [Fe(CO)₂(Me₂CO)(η⁵-C₅H₅)][PF₆] reacts with L (L = H₂NNHCSNH₂, cy-C₅H₁₀CNNHCSNH₂, or R′R″CNNHCSNH₂ where R′ = R″ = Me; R′ = H, R″ = Ph; R′ = H, R″ = p-NO₂Ph; R′ = p-MePh) in refluxing trichloromethane to give the new complexes [Fe(CO)₂L(η⁵-C₅H₅)][PF₆]. The complexes are clearly coordinated through the sulphur atom since the thiosemicarbazide complex reacts with benzaldehyde to afford the corresponding thiosemicarbazone compound.     

The reaction between HO and (H2O) n (n?=?1, 3) clusters: reaction mechanisms and tunneling effects

The reaction between the HO radical and (H₂O)n (n?=?1, 3) clusters has been investigated employing high-level quantum mechanical calculations using DFT-BH&HLYP, QCISD, and CCSD(T) theoretical approaches in connection with the 6-311?+?G(2df,2p), aug-cc-pVTZ, and aug-cc-pVQZ basis sets. The rate constants have also been calculated and the tunneling effects have been studied by means of time?Cdependent wavepacket calculations, performed using the Quantum?CReaction Path Hamiltonian method. According to the findings of previously reported theoretical works, the reaction between HO and H₂O begins with the formation of a pre-reactive complex that is formed before the transition state, the formation of a post-reactive complex, and the release of the products. The reaction between HO and (H₂O)₂ also begins with the formation of a pre-reactive complex, which dissociates into H₂O??HO?+?H₂O. The reaction between HO and (H₂O)₃ is much more complex. The hydroxyl radical adds to the water trimer, and then it occurs a geometrical rearrangement in the pre-reactive hydrogen-bonded complex region, before the transition state. The reaction between hydroxyl radical and water trimer is computed to be much faster than the reaction between hydroxyl radical and a single water molecule, and, in both cases, the tunneling effects are very important mainly at low temperatures. A prediction of the atmospheric concentration of the hydrogen-bonded complexes studied in this work is also reported.     

Tetramethyl(2-methoxyethyl)cyclopentadienyl complexes of zirconium(iv). Crystal structure of [η5:η1−C5(CH3)4(CH2CH2OCH3)]ZrCl3

Several novel zirconium(iv) complexes with the chelating oxygen-containing cyclopentadienyl ligand, tetramethyl(2-methoxyethyl)cyclopentadiene, have been synthesized. [⁵:¹-Tetra-methyl(2-methyl)cyclopentadienyl]trichlorozirconium (2), bis[⁵-tetramethyl(2-methoxyethyl)cyclopentadienyl]dichlorozirconium (3), [⁵-pentamethylcyclopentadienyl][⁵-tetra-methyl(2-methoxyethyl)cyclopentadienyl]dichlorozirconium (4), and [⁵-tetra-methyl(2-methylthioethyl)cyclopentadienyl][⁵-tetramethyl(2-methoxyethyl)-cyclopentadienyl]dichlorozirconium (5) have been prepared from the corresponding lithium cyclopentadienide (l). The crystal structure of cyclopentadienyl complex2 has been established by X-ray analysis. The coordination OZr bond in compound2 exists both in the crystalline state and in solutions. No coordination of this type was observed in complexes3–5. Synthesized complexes2–5 are discussed in comparison with their sulfur-containing analogs.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1828–1832, July, 1996.     

Synthesis and structures of the six-coordinate donor-acceptor complexes R3(C6H4O2)Sb…L (R=Ph, L=OSMe2 or ONC5H5; R=Me, L=ONC5H5 or NC5H5) and R3(C2H4O2)Sb…L (R=Ph, L=ONC5H5; R=Cl or C6F5, L=OPPh3)

One-pot oxidation of R₃Sb (R=Ph, Me, Cl, or C₆F₅) withtert-butyl hydroperoxide in the presence of 1,2-diols and monodentate donor compounds was studied. The structures of the resulting neutral organic donor-acceptor Sb^V complexes, Ph₃(C₆H₄O₂)Sb…OSMe₂, Ph₃(C₆H₄O₂)Sb…ONC₅H₅, Me₃(C₆H₄O₂)Sb…ONC₅H₅, Me₃(C₆H₄O₂)Sb…NC₅H₅, Ph₃(C₂H₄O₂)Sb…ONC₅H₅, and Cl(C₆F₅)₂(C₂H₄O₂)Sb…OPPh₃, were established by X-ray diffraction analysis. In these complexes, the coordination environment about the Sb atoms is a distorted octahedron. The Sb?O(N) distances and the Sb?O?E angles (E=S, N, or P) vary over wide ranges.