Theoretical studies on the electronic structure of Ti8C12 isomers

Density functional calculation are performed to study Ti(8)C(12) isomers (T(d), C(3v), and D(2d)) in the neutral, cationic, and anionic charge states. C(3v) symmetry is found to be the most stable geometry for the neutral and anion, and the C(3v) and D(2d) isomers to be quasi-iso-energetic lowest for the cation. The electronic structure analysis show that d electron tends to be localized in the ground state. The theoretical assignment for the features in the experimental photoelectron spectra is given. All results obtained are in good agreement with the available experimental data and indicate that the C(3v) and D(2d) isomers may coexist in the photoelectron spectroscopy experiment.     

A synthetic breakthrough into an unanticipated stability regime: a series of isolable complexes in which C6, C8, C10, C12, C16, C20, C24, and C28 polyynediyl chains span two platinum atoms

The reaction of trans-[PtCl(p-tol){P(p-tol)3}2] (PtCl) and H(C[triple chemical bond]C)2H (cat. CuI, HNEt2) gives PtC4H (82 %), which can be cross-coupled with excess HC[triple chemical bond]CSiEt3 (acetone, O2, CuCl/TMEDA; Hay conditions) to yield PtC6Si (77 %). The addition of nBu4N+F- in wet acetone gives PtC6H (84 %), and further addition of ClSiMe3 (F- scavenger) and excess HC[triple chemical bond]CSiEt3 (Hay conditions) yields PtC(8)Si (23 %). Similar cross-coupling reactions of PtCxH (generated in situ for x>6) and excess H(C[triple chemical bond]C)2SiEt3 give a) x=4, PtC8Si (29 %), PtC12Si (30 %), and PtC16Si (1 %); b) x=6, PtC10Si (59 %) and PtC14Si (7 %); c) x=8, PtC12Si (42 %); and d) x=10, PtC14Si (20 %). Hay homocoupling reactions of PtC4H, PtC6H, PtC8H, and PtC10H give PtC8Pt, PtC12Pt, PtC16Pt, and PtC20Pt (88-70 %), but PtC12H decomposes too rapidly. However, when PtC12Si and PtC14Si are subjected to Hay conditions, protodesilylation occurs in the presence of the oxidizing agent and PtC24Pt (36 %) and PtC28Pt (51 %) are isolated. Reactions of PtC6H and PtC10H with PtCl (CuI, HNEt2) give PtC6Pt (56 %) and PtC10Pt (84 %). The effect of the chain lengths in PtCxPt upon thermal stabilities (>200 degrees C for x< or =20), IR nu(C[triple chemical bond]C) patterns (progressively more bands), colors (yellow to orange to deep red), UV/Vis spectra (progressively red-shifted and more intense bands with epsilon>400,000 M(-1) cm(-1)), redox properties (progressively more difficult oxidations), and NMR spectra (many monotonic trends) are analyzed, including implications for the sp carbon allotrope carbyne. Whereas all other dodecaynes and tetradecaynes rapidly decompose at room temperature, PtC24Pt and PtC28Pt remain stable at >140 degrees C. Crystal structures of PtCxSi (x=6, 8, 10) and PtCxPt (x=6, 8, 10, 12) have been determined.     

Synthesis, characterization and studies on the third-order optical non-linearities of novel charge-transfer heteropoly complexes (C8H12N2)5H7PMo12O40 and (C8H12N2)3H3PMo12O40·5H2O

Summary Two novel charge-transfer (CT) heteropoly complexes, (C₈H₁₂N₂)₅H₇PMo₁₂O₄₀ (1) and (C₈H₁₂N₂)₃H₃-PMo₁₂O₄₀·5H₂O (2), prepared by reacting p-Me₂NC₆H₄NH₂ with the four-electron heteropoly blue H₇PMo₁₂O₄₀·12H₂O and heteropoly acid H₃PMo₁₂O₄₀· xH₂O, respectively, were characterized by elemental analysis, and u.v., i.r., XPS and e.s.r. spectroscopies. A sizable electron-transfer interaction occurs within the product molecules and the heteropoly anions retain their Keggin structure. Their third-order optical non-linearity coefficients were measured using the Z-scan technique at a concentration of 4.68 × 10⁻⁶ mol dm⁻³ for (1) and 2.79 × 10⁻⁶ mol dm⁻³ for (2), with I ₀ = 2.38 × 10¹³ w m⁻² and λ = 532nm. The |χ⁽³⁾| for (1) is 2.61 × 10⁻¹⁰ esu and |χ⁽³⁾| for (2) is 1.05 × 10⁻¹⁰ esu.     

Activation of CH bonds by ruthenium hydride complexes. Deuteration of triisopropyl and tricyclohexylphosphine using C6D6 or C7D8 as the deuterium source

Complexes of the type RuH₄P₃ (P=P(Prⁱ)₃, P(C₆H₁₁)₃ or P(N(C₂H₅)₂)₃) in solution in deuterated aromatic solvents undergo H-D exchange between the solvent and the coordinated phosphines. The reaction works better with RuH₄P(Prⁱ₃)₃, in which about 70% of the phosphine protons can be so exchanged. A mechanism involving dissociation of a phosphine followed by activation of the solvent CD bond and the phosphine CH bond is proposed.     

Condensed two- and three-dimensional aromatic systems: a theoretical study on the relative stabilities of isomers of CB19H16+, B20H15Cl, and B20H14Cl2 and comparison to B12H10Cl22-, C6H4Cl2, C10H7Cl, and C10H6Cl2

DFT studies (B3LYP/6-31G) on mono- and dichloro derivatives of benzene, naphthalene, B12H12(2-), four-atom-sharing condensed systems B20H16, and monocarborane isomers of B20H16 are used to compare the variation of relative stability and aromaticity between condensed aromatics. The trends in the variation of the relative energies and aromaticity in these two- and three-dimensional systems are similar. Aromaticity, estimated by NICS values, does not change considerably with condensation or substitution. The minor variation in the relative energies of the isomers of chloro derivatives is explained by the topological charge stabilization rule of Gimarc. The compatibility of the cap and ring orbitals decides the relative stability of CB19H16+.     

Infrared spectroscopy of [XFeC24H12]+ (X = C5H5, C5(CH3)5) complexes in the gas phase: experimental and computational studies of astrophysical interest

We report the first experimental mid-infrared (700-1600 cm (-1)) multiple-photon dissociation (IRMPD) spectra of [XFeC 24H 12] (+) (X = C 5H 5 or Cp, C 5(CH 3) 5 or Cp*) complexes in the gas phase obtained using the free electron laser for infrared experiments. The experimental results are complemented with theoretical infrared (IR) absorption spectra calculated with methods based on density functional theory. The isomers in which the XFe unit is coordinated to an outer ring of C 24H 12 (+) (Out isomers) were calculated to be the most stable ones. From the comparison between the experimental and calculated spectra, we could derive that, (i) for [CpFeC 24H 12] (+) complexes, the (1)A Out isomer appears to be the best candidate to be formed in the experiment but the presence of the (1)A In higher energy isomer in minor abundance is also plausible; and (ii) for [Cp*FeC 24H 12] (+) complexes, the three calculated Out isomers of similar energy are likely to be present simultaneously, in qualitative agreement with the observed dissociation patterns. This study also emphasizes the threshold effect in the IRMPD spectrum below which IR bands cannot be observed and evidence strong mode coupling effects in the [XFeC 24H 12] (+) species. The effect of the coordination of Fe in weakening the bands of C 24H 12 (+) in the 1000-1600 cm (-1) region is confirmed, which is of interest to search for such complexes in interstellar environments.     

Unimolecular rectification of monolayers of CH3C(O)S-C14H28Q(+)-3CNQ(-) and CH3C(O)S-C16H32Q(+)-3CNQ(-) organized by self-assembly, Langmuir-Blodgett, and Langmuir-Schaefer techniques

The advantage of "self-assembly" (strong covalent binding to substrates) was combined with the advantage of Langmuir-Blodgett (LB) or Langmuir-Schaefer (LS) transfer to a solid substrate (quantitative transfer of monolayers to the substrate). The electrical rectification (asymmetric conduction) by a monolayer of thioacetylalkylquinolinium tricyanoquinodimethanide was critically compared when these molecules had been transferred, by such competing techniques, onto gold electrodes, and then covered by a "cold gold" pad electrode. Unimolecular rectification was observed in the expected directions in the LB and LS monolayers. The Self-Assembled Monolayers (SAMs) were disordered; macroscopic measurements of rectification were unsuccessful for the SAMs, but successful for the down-stroke LB and LS monolayers, whose orientation and potential bonding to the Au surface should be identical to that of an ideal SAM.     

Solution and solid state studies on the binding of isomeric carboranes C2B10H12 by p-Bu(t)-calix[5]arene

p-Bu(t)-calix[5]arene forms crystalline inclusion complexes with o- and m-carboranes in toluene or dichloromethane-hexane, but not with the p-isomer, the extended structures being based on 1 : 1 host-guest supermolecules, with the p-Bu(t)-substituents creating a snug fit for o- and m-carborane; p-carborane forms a highly hexane soluble complex, induced by grinding, which crystallizes as fibres. Solution phase studies showed the presence of a 1 : 1 host-guest stoichiometry with all three isomeric carboranes as determined from Job plots. The association constants for the o- and m-carborane complexes are 6.4 +/- 0.3 M(-1) and 3.8 +/- 0.1 M(-1) respectively, whereas the p-isomer is only weakly associated. Competition experiments involving all three isomers show rapid exchange on the NMR time scale, and no selectivity in solution is evident. Selective association involving the o- and m-isomers in the solid state is therefore remarkable, and it is a manifestation of crystal packing forces which embodies the differences in dipole moments of the carboranes.     

Controlling the dimensionality of oxalate-based bimetallic complexes: The ferromagnetic chain {[K(18-crown-6)][Mn(bpy)Cr(ox)3]}∞(18-crown-6 = C12H24O6, ox=C2O42-, bpy = C10H8N2)

The bimetallic ferromagnetic chain {[K(18-crown-6)][Mn(bpy)Cr(ox)₃]}_∞ (1) has been synthesized and characterized. It crystallizes in the orthorhombic chiral space group P2₁2₁2₁ [a = 9.0510(2) Å, b = 14.4710(3) Å, c = 26.8660(8) Å, V = 3510.97(1) Å³, Z = 2]. Compound 1 is made up by anionic [Mn(bpy)Cr(ox)₃]⁻ 1D chains and cationic [K(18-crown-6)]⁺ complexes. The magnetic exchange within the chain is ferromagnetic [J = +7.8(7) cm⁻¹]. In the solid state, the ferromagnetic chains are well isolated magnetically and no long range magnetic ordering has been observed above 2 K.     

Vibrational spectroscopic studies on the en-Td-type benzene clathrates: M(ethylenediamine)M′(CN)4·2C6H6 (M=Mn or Cd,M′=Cd or Hg)

IR spectra of Mn(en)M(CN)₄·2C₆H₆ (M=Cd or Hg), and IR and Raman spectra of Cd(en)M(CN)₄·2C₆H₆ (M=Cd or Hg) clathrates are reported. The spectral features suggest that the first two compounds are similar in structure to the later two Td-type clathrates.     

In situ infrared spectroscopic studies on the mechanism of the selective catalytic reduction of NO by C3H8 over Ga2O3/Al2O3: high efficiency of the reducing agent

The partial oxidation of propane and the mechanism of selective catalytic reduction (SCR) of NO by propane over Ga2O3/Al2O3 in excess of O2 have been investigated using in situ Fourier transform infrared spectroscopy. An optimized Ga2O3/Al2O3 catalyst shows high activity and efficiency of the reducing agent propane (100% conversion of NO at 623 K, GHSV: 10,000 h(-1)). One molecule of propane converts more than 4 NO molecules to N2. The reaction starts with the partial oxidation of C3H8 by O2 and carboxylates (acetate, formate) are formed on the catalyst surface above 573 K. This oxidation represents the rate-determining step of the SCR reaction. These surface carboxylates represent a dominating intermediate and (easily) react with (adsorbed) NO forming nitrogen-containing organic species. The latter are proposed to react with NO to form N2. Total oxidation of propane was enhanced at temperatures above 773 K leading to decreased reductant efficiency. Surface nitrite and nitrate species can also be observed, but they were found to be spectators only. This could be concluded from the electron balance (conversion of propane relative to NO) and from the relative rates of the single reaction steps. On the basis of these investigations and stoichiometric calculations, a conclusive reaction mechanism is proposed.     

(C4N3H15)[(BO2)2(GeO2)4]: the first organically templated 3D borogermanate showing 1D 12-rings, large channels, and a novel zeolite-type framework topology constructed from Ge8O24 and B2O7 cluster units

The first organically templated 3D borogermanate with a novel zeolite-type topology, (C4N3H15)[(BO2)2(GeO2)4] FJ-17, has been solvothermally synthesized and characterized by IR spectroscopy, powder X-ray diffraction (PXRD), TGA, and single-crystal X-ray diffraction. The compound crystallized in the monoclinic space group P2(1)/c with a = 6.967(1) A, b = 10.500(1) A, c = 20.501(1) A, beta = 90.500(3) degrees , V = 1499.68(8) A3, and Z = 4. The framework topology of this compound is the previously unknown topology with the vertex symbols 3.4.3.9.3.8(2) (vertex 1), 3.8.3.4.6(2).9(2) (vertex 2), 3.8(2).4.6(2).6(2).8 (vertex 3), 4.8.4.8.8(3).12 (vertex 4), 4.8.4.8.8(2).12 (vertex 5), and 3.8.4.6(2).6.8(2) (vertex 6). The structure is constructed from Ge8O24 and B2O7 clusters. The Ge8O24 cluster contains eight GeO4 tetrahedra that share vertices; the B2O7 unit is composed of two BO4 tetrahedra sharing a vertex. The cyclic Ge8O24 clusters connect to each other through vertices to form a 2D layer with 8,12-nets. The adjacent layers are further linked by the dimeric B2O7 cluster units, resulting in a 3D framework with 12- and 8-ring channels along the a and b axes, respectively. In addition, there is a unique B2GeO9 3-ring in the structure.     

Thermodynamics of Coordination Bonds in Metal closo-Heteroclusters of the Endofullerene Type M@N k B r C s n – (m = k + r + s = 12, 24, or 28; n = 0–4), Where M = Li,Mg, Al,Ti, Zr,Hf, V,Nb, Mo,Ru, Rh,Ir, Ta,Pt, Pd,and Au

The energy of coordination-induced stabilization and the enthalpy of formation of gaseous metal closo-heteroclusters of the M@N _k B _r C _s ^{n –} type (m = k + r + s = 12, 24, or 28; n = 0–4), where M = Li, Mg, Al, Ti, Zr, Hf, V, Nb, Mo, Ru, Rh, Ir, Ta, Pt, Pd, and Au, were estimated in terms of a structural-thermodynamic model. The stabilizing role of metals in clusters was demonstrated. The energies D ₀ of M–N, M–B, and M–C bonds were found to be underestimated by the MO LCAO method at the HF/6-31G* level.     

ChemInform Abstract: Computational Study of Analogues of the Uranyl Ion Containing the —N=U=N— Unit: Density Functional Theory Calculations on UO22+, UON+, UN2, UO(NPH3)3+, U(NPH3)24+, [UCl4{NPR3}2] (R: H,Me), and [UOCl4{NP(C6H5)3}]‐

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