Infrared spectra of CH(3)-MoH, CH(2)=MoH(2), and CH(triple bond)MoH(3) formed by activation of CH(4) by molybdenum atoms

Reaction of laser-ablated Mo atoms with CH(4) in excess argon forms the CH(3)-MoH, CH(2)=MoH(2), and CH(triple bond)MoH(3) molecules, which are identified from infrared spectra by isotopic substitution and density functional theory frequency calculations. These simple methyl, methylidene, and methylidyne molybdenum hydride molecules are reversibly interconverted by alpha-H transfers upon visible and ultraviolet irradiations. The methylidene dihydride CH(2)=MoH(2) exhibits CH(2) and MoH(2) distortion and agostic interaction to a lesser degree than CH(2)=ZrH(2). Molybdenum methylidyne trihydride CH(triple bond)MoH(3) is a stable C(3v) symmetry molecule.     

Reactions of methane with titanium atoms: CH3TiH, CH2=TiH2, agostic bonding, and (CH3)2TiH2

Laser-ablated titanium atoms react with methane to form the insertion product CH3TiH, which undergoes a reversible photochemical alpha-H transfer to give the methylidene complex CH2=TiH2. On annealing a second methane activation occurs to produce (CH3)2TiH2. These molecules are identified from matrix infrared spectra by isotopic substitution (CH4, 13CH4, CD4, CH2D2) and comparison to DFT frequency calculations. The computed planar structure for singlet ground-state CH2=TiH2 shows CH2 distortion and evidence for agostic bonding (H-C-Ti, 91.4 degrees), which is supported by the spectra for CHD=TiHD.     

Mechanism of vinylic and allylic carbon-fluorine bond activation of non-perfluorinated olefins using Cp*(2)ZrH(2)

Cp(2)ZrH(2) (1) (Cp = pentamethylcyclopentadienyl) reacts with vinylic carbon-fluorine bonds of CF(2)=CH(2) and 1,1-difluoromethylenecyclohexane (CF(2)=C(6)H(10)) to afford Cp(2)ZrHF (2) and hydrodefluorinated products. Experimental evidence suggests that an insertion/beta-fluoride elimination mechanism is occurring. Complex 1 reacts with allylic C-F bonds of the olefins, CH(2)=CHCF(3), CH(2)=CHCF(2)CF(2)CF(2)CF(3), and CH(2)=C(CF(3))(2) to give preferentially 2 and CH(3)-CH=CF(2), CH(3)-CH=CF-CF(2)CF(2)CF(3), and CF(2)=C(CF(3))(CH(3)), respectively, by insertion/beta-fluoride elimination. In the reactions of 1 with CH(2)=CHCF(3) and CH(2)=CHCF(2)CF(2)CF(2)CF(3), both primary and secondary alkylzirconium olefin insertion intermediates were observed in the (1)H and (19)F NMR spectra at low temperature. A deuterium labeling study revealed that more than one olefin-dihydride complex is likely to exist prior to olefin insertion. In the presence of excess 1 and H(2), CH(2)=CHCF(3) and CH(2)=CHCF(2)CF(2)CF(2)CF(3) are reduced to propane and (E)-CH(3)CH(2)CF=CFCF(2)CF(3), respectively.     

Infrared spectrum and bonding in uranium methylidene dihydride, CH2=UH2

Uranium atoms activate methane upon ultraviolet excitation to form the methyl uranium hydride CH3-UH, which undergoes alpha-H transfer to produce uranium methylidene dihydride, CH2=UH2. This rearrangement most likely occurs on an excited-quintet potential-energy surface and is followed by relaxation in the argon matrix. These simple U+CH4 reaction products are identified through isotopic substitution (13CH4, CD4, CH2D2) and density functional theory frequency and structure calculations for the strong U-H stretching modes. Relativistic multiconfiguration (CASSCF/CASPT2) calculations substantiate the agostic distorted C1 ground-state structure for the triplet CH2=UH2 molecule. We find that uranium atoms are less reactive in methane activation than thorium atoms. Our calculations show that the CH2=UH2 complex is distorted more than CH2=ThH2. A favorable interaction between the low energy open-shell U(5f) sigma orbital and the agostic hydrogen contributes to the distortion in the uranium methylidene complexes.     

Methane activation by laser-ablated V, Nb, and Ta atoms: Formation of CH3-MH, CH2=MH2, CHMH3-, and (CH3)2MH2

Methane activation by group 5 transition-metal atoms in excess argon and the matrix infrared spectra of reaction products have been investigated. Vanadium forms only the monohydrido methyl complex (CH3-VH) in reaction with CH4 and upon irradiation. On the other hand, the heavier metals form methyl hydride and methylidene dihydride complexes (CH3-MH and CH2=MH2) along with the methylidyne trihydride anion complexes (CHMH3-). The neutral products, particularly the methylidene complex, increase markedly on irradiation whereas the anionic product depletes upon UV irradiation or addition of a trace of CCl4 or CBr4 to trap electrons. Other absorptions that emerge on irradiation and annealing increase markedly at higher precursor concentration and are attributed to a higher-order product ((CH3)2MH2)). Spectroscopic evidence suggests that the agostic Nb and Ta methylidene dihydride complexes have two identical metal-hydrogen bonds.     

Infrared spectra of CH3-CrH, CH3-WH, CH2=WH2, and CH[triple bond]WH3 formed by activation of CH4 with Cr and W atoms

Laser-ablated W atoms react with CH4 in excess argon to form the CH3-WH, CH2=WH2, and CH[triple bond]WH3 molecules with increasing yield in this order of product stability. These molecules are identified from matrix infrared spectra by isotopic substitution. Tungsten methylidene and methylidyne hydride molecules are reversibly interconverted by alpha-H transfers upon visible and ultraviolet irradiations. Matrix infrared spectra and DFT/B3LYP calculations show that CH[triple bond]WH3 is a stable molecule with C3v symmetry, but other levels of theory were required to describe agostic distortion for CH2=WH2. Analogous reactions with Cr gave only CH3-CrH, which is calculated to be by far the most stable product.     

Millimeter wave spectrum of bromomethyl radical, CH2Br

The rotational spectra of the two isotopic species of the bromomethyl radical, CH2 79Br and CH2 81Br, have been observed in their ground electronic state 2B1 in the 180-470 GHz frequency region, corresponding to a-type transitions from N=8-7 to N=21-20. The radical was produced by hydrogen abstraction of methylbromide (CH3Br) either by chlorine or by fluorine atoms in a free space cell. Hyperfine structure due to the bromine nucleus has been resolved in the observed spectra, and the rotational constants as well as the fine and hyperfine interaction constants were accurately determined for both isotopomers. The inertial defect was determined to be 0.028 96(20) and 0.028 95(20) amu A(2), for CH2 79Br and CH2 81Br, respectively, suggesting a planar structure. By fixing the [angle]HCH bond angle at 124.5 degrees , an effective molecular structure can be derived as r0(CBr)=1.848 A and r0(CH)=1.084 A. A comparison of the molecular structure of various halogen-substituted methyl radicals with respect to the planarity of these radicals is discussed.     

Formation and characterization of thorium methylidene CH2=ThHX complexes

Laser-ablated thorium atoms react with methyl fluoride to give the CH2=ThHF molecule as the major product observed and trapped in solid argon. Infrared spectroscopy, isotopic substitution, and density functional theoretical frequency calculations confirm the identification of this methylidene complex. The four strongest computed absorptions (Th-H stretch, Th=C stretch, CH2 wag, and Th-F stretch) are the four vibrational modes observed. The CH2=ThHCl and CH2=ThHBr species formed from methyl chloride and methyl bromide exhibit the first three of these modes in the infrared spectra. The computed structures (B3LYP and CCSD) show considerable agostic interaction, similar to that observed for the Group 4 CH2=MHX (M = Ti, Zr, Hf) methylidene complexes, and the agostic angle and C=Th bond length decrease slightly in the CH2=ThHX series (X = F, Cl, Br).     

Synthesis, Structure and Photoluminescence of(CH3-4, 4'-H2bipy)-(HgCl4)with CH3-4, 4'-H2bipy Generated in Situ

A novel viologen(4,4'bipyridinium)-based complex(CH3-4,4'-H2bipy)(HgCl4)(1),in which the CH3-4,4'-H2bipy(MQ2+)was generated in situ,has been synthesized via hydrothermal reaction and structurally characterized.Complex 1 crystallizes in the space group P21/c of monoclinic system with four formula units in a cell:a = 8.1848(6),b = 21.809(2),c = 9.0285(6)(A),β =.107.377(1)°,V= 1538.0(2)(A)3,C11H11Cl4HgN2,Mr = 513.61,Dc = 2.218 g/cm3,S = 1.009,μ(MoKα)= 10.685 mm-1,F(000)= 956,R = 0.0360 and wR = 0.0812.The crystal structure analysis reveals that the title complex features an isolated structure based on a CH3-4,4'-H2bipy moiety and a mercury atom terminally bound by four chlorine atoms.Photoluminescence investigation reveals a strong emission in blue region,which may originate from π→π* charge-transfer interaction of the CH3-4,4'-H2bipy moiety.     

镧系四元混合阴离子配合物［Pr(CH3CH2COO)2(NO3)(phen)2］合成和晶体结构

在含水溶剂、酸性环境中合成了镧系四元混合阴离子配合物［Pr(CH₃CH₂COO)₂(NO₃)(phen)］₂并解析了其晶体结构,三斜,空间群P1,a=0.9650(2) nm, b=1.2949(4) nm,c=0.8994(2)nm, α=95.37(3)°,β=111.05(2)°,γ=102.87(2)°,V=1.0037(5) nm^{3, Dc=1.758 g·cm-3, Z=1, F(000)=528, μ(MoKα)=24.64 cm-1, R=0.024, R_W=0.034。四个丙酸根呈二种配位方式,Pr3+为九配位。}     

Defluorination of perfluoropropene using Cp*2ZrH2 and Cp2ZrHF: a mechanism investigation from a joint experimental-theoretical perspective

Cp*(2)ZrH(2) (1) (Cp* = pentamethylcyclopentadienyl) reacts with perfluoropropene (2) to give Cp*(2)ZrHF (3) and hydrodefluorinated products under very mild conditions. Initial C-F bond activation occurs selectively at the vinylic terminal position of the olefin to exchange fluorine for hydrogen. Subsequent hydrodefluorination leads to the formation of the n-propylhydride complex Cp*(2)ZrH(CH(2)CH(2)CH(3)), which can be cleaved with dihydrogen to give propane and 1. A theoretical study of the reaction of Cp*(2)ZrH(2) (Cp* = cyclopentadienyl) and CF(2)[double bond]CF(CF(3)) has been undertaken. Several mechanisms have been examined in detail using DFT(B3PW91) calculations and are discussed for this H/F exchange: (a) internal olefin insertion/beta-fluoride elimination, (b) external olefin insertion/beta-fluoride elimination, and (c) F/H metathesis from either an inside or outside approach. Of these, the first case is found to be energetically preferred. Selective defluorination at the terminal carbon has been shown to be favored over defluorination at the substituted and allylic carbons.     

Infrared spectra of the CH3-MX and CH2-MHX complexes formed by reactions of laser-ablated group 3 metal atoms with methyl halides

Reactions of laser-ablated group 3 metal atoms with methyl halides have been carried out in excess of Ar during condensation and the matrix infrared spectra studied. The metals are as effective as other early transition metals in providing insertion products (CH3-MX) and higher oxidation state methylidene complexes (CH2-MHX) (X = F, Cl, Br) following alpha-hydrogen migration. Unlike the cases of the group 4-6 metals, the calculated methylidene complex structures show little evidence for agostic distortion, consistent with the previously studied group 3 metal methylidene hydrides, and the C-M bond lengths of the insertion and methylidene complexes are comparable to each other. However, the C-Sc bond lengths are 0.013, 0.025, and 0.029 A shorter for the CH2-ScHX complexes, respectively, and the spin densities are consistent with weak C(2p)-Sc(3d) pi bonding. The present results reconfirm that the number of valence electrons on the metal is important for agostic interaction in simple methylidene complexes.     

Lithiated hydrocarbons, their conjugate bases, and corresponding radicals: a computational study of RLi (R = CH3, CH3CH2, CH2=CH, and HC triple bond C)

Organolithium compounds RLi (R = CH(3), CH(3)CH(2), CH(2)=CH, and HC(triple bond)C) and their corresponding hydrocarbons were fully optimized at the MP2/6-311+G(2df,2pd) level. Single-point energy calculations also were carried out at the CCSD(T) and B3LYP levels with the same triple split-valence basis set. Acidities, electron affinities, and bond dissociation energies are reported, and the following general results were found: (1) Alpha-lithio anions are ground-state triplet molecules. (2) Lithium is an acid-enhancing substituent. (3) Conjugate bases of organolithiums are stable with respect to electron loss and therefore are attractive targets for mass spectrometry investigations. (4) Lithium weakens alpha- and beta-C-H bonds, the latter by approximately 25 kcal mol(-1). Consequently, radical chemistry of lithiated compounds at remote sites is a promising area for exploration.     

Preparation of CH3TiF and (CH3)2TiF2 from the reaction of CH(3)F with laser-ablated Ti atoms

Laser-ablated Ti atoms react with CH(3)F upon condensation with excess argon to form primarily CH(3)TiF and (CH(3))(2)TiF(2). Irradiation in the UV region promotes alpha-hydrogen rearrangement of CH(3)TiF to CH(2)=TiHF and increases the yield of (CH(3))(2)TiF(2). Annealing to allow diffusion and reaction of more CH(3)F markedly increases the yield of (CH(3))(2)TiF(2). This shows that the CH(3)TiF + CH(3)F reaction is spontaneous and that triplet state CH(3)TiF is an extremely reactive molecule. B3LYP calculations are extremely effective in predicting vibrational frequencies and isotopic shifts for CH(3)TiF and (CH(3))(2)TiF(2) and thus in confirming their identification from matrix infrared spectroscopy.     

Combined vacuum ultraviolet laser and synchrotron pulsed field ionization study of CH2BrCl

The pulsed field ionization-photoelectron (PFI-PE) spectrum of bromochloromethane (CH2BrCl) in the region of 85,320-88,200 cm-1 has been measured using vacuum ultraviolet laser. The vibrational structure resolved in the PFI-PE spectrum was assigned based on ab initio quantum chemical calculations and Franck-Condon factor predictions. At energies 0-1400 cm-1 above the adiabatic ionization energy (IE) of CH2BrCl, the Br-C-Cl bending vibration progression (nu1+=0-8) of CH2BrCl+ is well resolved and constitutes the major structure in the PFI-PE spectrum, whereas the spectrum at energies 1400-2600 cm-1 above the IE(CH2BrCl) is found to exhibit complex vibrational features, suggesting perturbation by the low lying excited CH2BrCl+(A 2A") state. The assignment of the PFI-PE vibrational bands gives the IE(CH2BrCl)=85,612.4+/-2.0 cm-1 (10.6146+/-0.0003 eV) and the bending frequencies nu1+(a1')=209.7+/-2.0 cm-1 for CH2BrCl+(X2A'). We have also examined the dissociative photoionization process, CH2BrCl+hnu-->CH2Cl++Br+e-, in the energy range of 11.36-11.57 eV using the synchrotron based PFI-PE-photoion coincidence method, yielding the 0 K threshold or appearance energy AE(CH2Cl+)=11.509+/-0.002 eV. Combining the 0 K AE(CH2Cl+) and IE(CH2BrCl) values obtained in this study, together with the known IE(CH2Cl), we have determined the 0 K bond dissociation energies (D0) for CH2Cl+-Br (0.894+/-0.002 eV) and CH2Cl-Br (2.76+/-0.01 eV). We have also performed CCSD(T, full)/complete basis set (CBS) calculations with high-level corrections for the predictions of the IE(CH2BrCl), AE(CH2Cl+), IE(CH2Cl), D0(CH2Cl+-Br), and D0(CH2Cl-Br). The comparison between the theoretical predictions and experimental determinations indicates that the CCSD(T, full)/CBS calculations with high-level corrections are highly reliable with estimated error limits of <17 meV.     

Cd[CH_3O(OH)C_6H_3CH=N(CH_2)_2OH]_2Br_2的合成、结构及微观二阶非线性光学系数

合成了标题配合物Cd[CH3O(OH)C6H3CH =N(CH2 ) 2 OH]2 Br2 ,对其进行了元素分析、红外和X射线结构分析。该配合物单晶的分子式为 :CdC2 0 H2 6N2 O6Br2 ,Mr=662 .66属于单斜晶系 ,P2 1 /n空间群 ,晶胞参数a =7.851 2 (2 ) ,b =1 7.391 (3) ,c=1 7.575(4) ,β =90 .86(3)°,V =2 392 (1 ) 3,Z =4,Dc=1 .834g·cm- 3,μ(MoKα) =4.2 4 1 9mm- 1 ,F(0 0 0 ) =1 30 4。用直接法解得结构 .R =0 .0 74,Rw=0 .0 84.在 2 99± 1K的温度下收集到 3744个独立衍射点 ,其中 2 4 70个为可观察的衍射点 [I≥ 3σ(I) ]。同时在 1 .0 64μm的Nd :YAG激光器上对配合物进行了粉末SHG实验 ,并用MOPAC软件包采用PM 3方法解得其分子的微观二阶极化率为 3.341× 1 0 - 30 esu。进一步讨论了微观二阶非线性极化率、宏观激光倍频效应和分子结构、晶体结构之间的关系。     

Structure and protonation of the bis-ethylene adduct [Pt(micro-PBut2)(eta2-CH2=CH2)]2. Pt-H-P agostic interaction and proton scrambling

The bis-ethylene derivative [Pt(micro-PBu(t)(2))(eta(2)-CH(2)=CH(2))](2) was prepared and characterized by X-ray diffraction; its protonation affords [Pt(2)(micro-PBu(t)(2))(micro-PBu(t)(2)H)(eta(2)-CH(2)=CH(2))(2)](CF(3)SO(3)), with a rarely observed P-H-M agostic proton in rapid exchange with those of the adjacent ethylene molecule.     

CH3--MoF], [CH2=MoHF], and [CH[triple bond]MoH2F] formed by reaction of laser-ablated molybdenum atoms with methyl fluoride: persistent photoreversible interconversion through alpha-hydrogen migration and agostic interaction

Simple molybdenum methyl, carbene, and carbyne complexes, [CH3--MoF], [CH2=MoHF], and [CH[triple chemical bond]MoH(2)F], were formed by the reaction of laser-ablated molybdenum atoms with methyl fluoride and isolated in an argon matrix. These molecules provide a persistent photoreversible system through alpha-hydrogen migration between the carbon and metal atoms: The methyl and carbene complexes are produced by applying UV irradiation (240-380 nm) while the carbyne complex is depleted, and the process reverses on irradiation with visible light (lambda>420 nm). An absorption at 589.3 cm(-1) is attributed to the Mo--F stretching mode of [CH3--MoF], which is in fact the most stable of the plausible products. Density functional theory calculations show that one of the alpha-hydrogen atoms of the carbene complex is considerably bent toward the metal atom (angle-spherical HCMo=84.5 degrees ), which provides evidence of a strong agostic interaction in the triplet ground state. The calculated C[triple chemical bond]Mo bond length in the carbyne is in the range of triple-bond values in methylidyne complexes.     

Infrared spectrum and structure of CH2=ThH2

The actinide methylidene CH2=ThH2 molecule is formed in the reaction of laser-ablated thorium atoms with CH4 and trapped in a solid argon matrix. The five strongest infrared absorptions computed by density functional theory (two ThH2 stretches, C=Th stretch, CH2 wag, and ThH2 bend) are observed in the infrared spectrum. The computed structure shows considerable agostic bonding distortion of the CH2 and ThH2 subunits in the simple actinide methylidene dihydride CH2=ThH2 molecule, which is similar to the transition metal analogue, CH2=HfH2.     

Synthesis and Crystal Structure of Cluster 〔C_6H_4-1,2-(CO_2CH_2C_2H-μ)_2〕〔Co_2(CO)_6〕_2

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