Femtosecond coherent anti-Stokes Raman-scattering polarization beat spectroscopy of I2-Xe complex in solid krypton

Time-resolved coherent anti-Stokes Raman-scattering (CARS) measurements are carried out to study the interaction between xenon atom and iodine molecule in a solid krypton matrix. Interference between the CARS polarizations of the "free" and complexed iodine molecules is observed, while the quantum beats of the complex are not detected due to low concentration. Vibrational analysis based on the polarization beats yields accurate molecular constants for the I2-Xe complex. The harmonic frequency of the I2-Xe complex is found to be redshifted by 0.90 cm-1 when compared to the free I2, whereas the anharmonicity is approximately the same. The dephasing rate of the complex is found to be somewhat higher than that of the free iodine molecule in solid Kr, showing that the complexation affects dephasing, although not dramatically. Molecular dynamics simulations are carried out to find the conformation of the complex, and wave packet simulations are used to reproduce the CARS signal to confirm the assignments of the observed beatings as quantum and polarization beats. The results show that the polarization beats are a useful tool for investigating weak interactions in condensed phase.     

Electronic structures of organo-transition-metal complexes I. Silver(I)-Olefin complexes

By using the closed-shell SCF-MO method with the CNDO type approximation for all valence electron systems, the electronic structures of some Ag⁺-olefin complexes are investigated. The calculated values of -H increase with the increasing number of methyl groups on the double bond and this trend agrees with the experimental result. Also calculation reproduces many experimental results, such as the infrared, Raman, and¹³C NMR spectra. These experimental results are discussed on the basis of the calculated electronic structures of Ag⁺-olefin complexes.     

Electronic spectroscopy of C2 in solid rare gas matrixes

Electronic spectroscopy of the C(2) molecule is investigated in Ar, Kr, and Xe matrixes in the 150-500 nm range. In the Ar matrix, the D ((1)Sigma(u)(+)) <-- ((1)Sigma(g)(+)) Mulliken band near 240 nm is the sole absorption in the UV range, whereas in the Kr matrix additional bands in the 188-209 nm range are assigned to the Kr(n)()(+)C(2)(-) <-- Kr(n)()C(2) charge-transfer absorptions. Because of the formation of a bound C(2)Xe species, the spectral observations in the Xe matrix differ dramatically from the lighter rare gases: the Mulliken band is absent and new bands appear near 300 and 423 nm. The latter is assigned to the forbidden B'((1)Sigma(g)(+)) <-- X ((1)Sigma(g)(+)) transition, but the origin of the former remains unclear. The spectral assignments are aided by electronic structure calculations at the MCSCF, CCSD(T), and BCCD(T) levels of theory and correlation consistent basis sets. A significant presence of multireference character of the C(2)Xe system was noted and a linear ground-state structure is predicted. The computational results contradict previous density functional studies on the same system.     

Electronic emission and absorption spectroscopy of the rhenium complexes Re(CO)3Cl(phosphine)2

Summary The compounds Re(CO)₃Cl(L)₂,L=triphenylphosphine, tri-p-tolyphosphine, and Re(CO)₃-Cl(L),L=1,2-bis(diethylphosphinoethane) are luminescent in solution and in crystalline form when excited between 351 nm and 514 nm at temperatures ranging from 10 K to room temperature. The absorption spectra contain a weak (E 10M ^–1 cm^–1) band in the visible region of the spectrum between 400 and 500 nm. The lowest energy transition giving rise to these spectroscopic features is assigned to a d-d transition.

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Elektronenemissions- und Absorptionsspektroskopie der Rheniumkomplexe Re(CO)₃Cl(Phoshin)₂

Zusammenfassung Die Verbindungen Re(CO)₃Cl(L)₂ mitL=Triphenylphosphin, Tri-p-tolylphosphin und Re(CO)₃Cl(L)₂ mitL=1,2-Bis(diethylphosphinoethan) sind in Lösung und im kristallinen Zustand bei Anregung zwischen 351 und 514 nm im Temperaturbereich von 10 K bis Raumtemperatur lumineszent. Die Absorptionsspektren enthalten im sichtbaren Bereich zwischen 400 und 500 nm eine schwache Bande von 10M ^–1 cm^–1. Der energetisch tiefstliegende Übergang, der für dieses Verhalten verantwortlich ist, wird einem d-d-Übergang zugeordnet.

     

Electronic spectroscopy of UO2 isolated in a solid Ar matrix

Dispersed fluorescence spectra have been recorded for UO(2) isolated in a solid Ar matrix. Near UV excitation produced groups of emission bands in the 370-420 and 465-645 nm spectral regions. These bands originated from two energetically close upper levels and terminated on a range of low-lying electronic states. Comparisons with electronic structure calculations indicate that the ground and low-lying electronic states of UO(2) are derived from the U(5f7s) configuration. The level of agreement between the observed and predicted electronic energies provides an impressive validation of the calculations. In previous studies of matrix isolated UO(2), it had been suggested that the ground state in solid Ar is U(5f(2)) (3)H. The present results do not appear to be consistent with this hypothesis.     

Electronic and molecular structures of trans-dioxotechnetium(V) polypyridyl complexes in the solid state

The structures of novel Tc(V) complexes trans-[TcO(2)(py)(4)]Cl·2H(2)O (1a), trans-[TcO(2)(pic)(4)]Cl·2H(2)O (2a), and trans-[TcO(2)(pic)(4)]BPh(4) (2b) were determined by X-ray crystallography, and their spectroscopic characteristics were investigated by emission spectroscopy and atomic scale calculations. The cations adopt a tetragonally distorted octahedral geometry, with a trans orientation of the apical oxo groups. trans-[TcO(2)(pic)(4)]BPh(4) has an inversion center located on technetium; however, for trans-[TcO(2)(py)(4)]Cl·2H(2)O and trans-[TcO(2)(pic)(4)]Cl·2H(2)O, a strong H bond formed by only one of the oxo substituents introduces an asymmetry in the structure, resulting in inequivalent trans Tc-N and Tc═O distances. Upon 415 nm excitation at room temperature, the complexes exhibited broad, structureless luminescences with emission maxima at approximately 710 nm (1a) and 750 nm (2a, 2b). Like the Re(V) analogs, the Tc(V) complexes luminesce from a (3)E(g) excited state. Upon cooling the samples from 278 to 8 K, distinct vibronic features appear in the spectra of the complexes along with increases in emission intensities. The low temperature emission spectra display the characteristic progressions of the symmetric O═Tc═O and the Tc-L stretching modes. Lowest-energy, triplet excited-state distortions calculated using a time-dependent theoretical approach are in good agreement with the experimental spectra. The discovery of luminescence from the trans-dioxotechnetium(V) complexes provides the first opportunity to directly compare fundamental luminescence properties of second- and third-row d(2) metal-oxo congeners.     

Rhenium(I) complexes of (2-cyanoethyl)diphenylphosphine

Rhenium pentacarbonyl halides react with (2-cyanoethyl) diphenylphosphine (L) to yield complexes of the stoichiometry [Re(CO)₃LX]_n. The infrared spectra of the complexes are consistent with structures containing terminal halogens and bridging L groups. Molecular weight studies indicate that n is two for solutions of 10⁻³M. The nitrile portion of the ligand is readily displaced by σ donor ligands to yield complexes in which L functions as a monodentate phosphine.     

Gold(I) eta2-arene complexes

The reaction of 9-{[N-n-propyl-N-(diphenylphosphino)amino]methyl}anthracene (1) with Au(SMe2)Cl yields complex 2 with an arm-opening configuration. The latter is treated with AgClO4 to form complex 4 and then respectively reacted with acetonitrile, pyridine, and triphenylphosphine sulfide to afford novel gold(I) eta2-arene complexes 3a-c, which have arm-closing configurations and feeble or weak fluorescence emissions. The observation can be attributed to charge transfer from the anthracene unit to the Au+ ion. When the solution of 3a or 4 in CH2Cl2 was added with 1 equiv of Ph3P, complex 5 with the arm-opening configuration was formed and strong emission was restored.     

Infrared spectroscopy of phenylalanine Ag(I) and Zn(II) complexes in the gas phase

Infrared multiple-photon dissociation (IR-MPD) spectroscopy has been applied to singly-charged complexes involving the transition metals Ag(+) and Zn(2+) with the aromatic amino acid phenylalanine. These studies are complemented by DFT calculations. For [Phe+Ag](+) the calculations favor a tridentate charge solvation N/O/ring structure. The experimental spectrum strongly supports this as the predominant binding geometry and, in particular, rules out a significant presence of the salt-bridge conformation. Zn(2+) forms a deprotonated dimer complex with Phe, [Zn+Phe(2)-H](+), in which the +2 oxidation state serves as a useful biomimetic model for zinc protein sites. A number of low-energy conformations were located, of which the lowest-energy conformer predicted by the calculations involves a Phe ligand deprotonated on the carboxylic acid, while the other Phe ligand is in the tridentate charge solvation conformation. The calculated IR spectrum of this conformer gives a close fit to the experimental spectrum, strongly supporting this as the predominant binding geometry. This most stable calculated complex is characterized by N/ O/ring metal chelation with a tetrahedral-type coordination core of Zn(2+) to N and O of both ligands. Another similar tightly chelated structure shows a square-planar-type coordination core, but this structure is computed to be less stable and gives a less satisfactory match to the experimental spectrum. This preference for the tetrahedral geometry of the Lewis-basic atomic ligands parallels the common Zn(II) coordination geometry in proteins. The number of clearly identifiable peaks resolved in the IR-MPD spectra as well as the much-improved matches between the observed spectra and the DFT-calculated spectra of the most stable geometries compared to previous studies are noteworthy for systems of this size and complexity. These results demonstrate that IR spectroscopy of transition metal-amino acid complexes in combination with DFT calculations is a very powerful structural tool, readily applicable to biomimetic systems that model, for example, the reaction centers of proteins in the solvent-free environment. In addition, we present a novel ion-capturing method for Fourier transform ion cyclotron resonance mass spectrometry which removes the necessity of a buffer gas pulse, while allowing ion trapping at moderate voltages with apparently reduced collisional excitation of the ions.     

Electronic structure of ferrocence derivatives studied by He(I) photoelectron spectroscopy and CNDO /2 method

The effect of substituents in the Cp ligands on the electronic structure has been studied for the 1,1′-disubstituted ferrocenes Fe(CpX)₂, with X = C₂H₅, OCH₃, CN, COCH₃, COOCH₃, OOCCH₃, CH₂C₆H₅, or C₆H₅, by UV photoelectron spectroscopy and by CNDO /2 calculations. The energy gap between the ²E_2g and ²AT_1g ion states, 0.36 eV in the parent ferrocene, is affected only by the COCH₃ and COOCH₃ substituents, which lower it to 0.22 and 0.28 eV, respectively. Splitting of e_1u(π) level due to the lowering of the symmetry is the only effect observed in the photoelectron spectra. There is a strong conjugation between the phenyl and cyclopentadienyl β-orbitals in 1,1′-diphenylferrocene. The changes in the a_1g(d) ionization energy calculated by the ΔSCF method using CNDO /2 total energies are in a good agreement with the experimental data.     

Photoelectron spectroscopy of actinide organometallic compounds I. Bis(cyclooctatetraene)actinide(IV) complexes

The He(I) photoelectron spectra of the antinocene species Th(cot)₂ and U(cot)₂ (cot = cyclooctatetraene) have been determined. The 5f metal ionization has been detected at the onset of the uranocene spectrum. The low ionization energy region of both spectra is discussed in terms of simple qualitative molecular orbital scheme.     

Self-assembly of silver(I) and gold(I) N-heterocyclic carbene complexes in solid state, mesophase, and solution

The assembly of silver(I) and gold(I) complexes of functionalized N-heterocyclic carbenes (NHCs) of the type [M(C(n),amide-imy)(2)][anion] were studied, in which C(n),amide-imy stands for an NHC of imidazol-2-ylidene having one N-alkyl substituent (C(n)H(2n+1)) and one N-acetamido substituent, while the anions are Br(-), NO(3)(-), BF(4)(-) or PF(6)(-). A single crystal X-ray diffraction study reveals that self-assembly of [Ag(C(10),amide-imy)(2)][PF(6)] through Coulombic, hydrogen bonding, and hydrophobic interactions gives a lamellar structure with tubular architecture around the metal ion head core. Self-assembly of these functionalized NHC complexes also leads to the formation of the first example of thermotropic liquid crystals of silver(I)-NHCs and gels of gold(I)-NHC. Results from an infrared spectroscopy study show that the degree of chain motion in the gel state is smaller than that in the mesophase, yet comparable to that in the solid state. In addition, the technique of nuclear magnetic resonance diffusion ordered spectroscopy was found for the first time to be a good tool to study the phase transition of gels. Xerogels of gold(I)-NHCs display fibers, oriental lantern-shaped bundles of belts and helical fibers when observed under scanning electron and transmission electron microscopes.     

Ethynylgold(I) complexes

Reactions between R₃PAuCl, NaOEt, and HCCR′ under mild conditions produce R₃PAuCCR′ in excellent yield. When R′ = H, a second step leading to the formation of R₃PAuCCAuPR₃ can take place. Exchange reactions of ethynyl for chloride between the ethynylgold complexes and HgCl₂, cis-[PtCl₂L₂cis-[PtCl₂(CO)L], and R₂″PAuCl have been monitored, revealing R₃PAuCCR′ to be useful alkynylating agents. In the reaction with cis-[PtCl₂(CO)L], the first substitution step is non-specific.     

Polyfluorophenylgold(I) complexes

Neutral polyfluorophenyl complexes of the type RAuL and RAuL-LAuR and anionic complexes of the type [AuR₂]^? (R = 2,3,5,6-C₆F₄H, 2,4,6-C,F₃H₂, 3,6-C₆F₂H₃, 4-C₆ FH₄ or 3-CF₃C,H₄) are obtained by the reaction of ClAuL (L = PPh₃, P(cyclohexyl)₃, AsPh₃ or tetrahydrothiophen; L-L = Ph₂PCH₂PPh₂ or Ph₂PCH₂CH₂PPPh₂) with an organolithium derivative and/or the replacement of the initial ligands L by other mono- or bi-dentate ligands.The outcome of the reaction of [AuR₂]^? with [Au(PCy₃)₂]⁺ (Cy = cyclohexyl), depends on the nature of the ligand R; thus with R = 3,6-C₆,F₂H₃ the product is [Au(PCy₃)₂][AuR₂], while with R = 2,4,6-C₆F₃H₂, the product is [Au(PCy₃)(2,4,6-C₆F₃H₂)].     

Halonickel(I) complexes

Summary The reduction of nickel(II) halides with NaBH₄ in the presence of different ligands, L=PPh₃, AsPh₃, SbPh₃, has been studied. With a molar ratio L/Ni=3, new complexes NiX(SbPh₃)₃, X=Cl, Br, I, were obtained. With a molar ratio L/Ni=2, dimeric species [NiXL₂]₂, X=Cl, Br, I; L=PPh₃, AsPh₃, SbPh₃, were isolated. They are unstable and decompose easily in the solid and rapidly in solution, so that pure samples were only identified for X=Cl, L=PPh₃, AsPh₃, SbPh₃; X=Br, L=PPh₃ and X=I, L=PPh₃. With a molar ratio L/Ni=1, complexes [NiXL]_n (probably polymeric) were obtained. They are very unstable and pure samples could only be isolated when X=Cl, L=PPh₃. Impure substances containing variable amounts of decomposition products were obtained in all the remaining cases. The chemical and structural behaviour of these complexes is discussed.     

Tricarbonylrhenium(I) and manganese(I) complexes of 2-(pyrazolyl)-4-toluidine

A series of tricarbonyl rhenium(I) and manganese(I) complexes of the electroactive 2-(pyrazolyl)-4-toluidine ligand, H(pzAn^Me), has been prepared and characterized including by single crystal X-ray diffraction studies. The reactions between H(pzAn^Me) and M(CO)₅Br afford fac-MBr(CO)₃[H(pzAn^Me)] (M = Mn, 1a; Re, 1b) complexes. The ionic species {fac-M(CH₃CN)(CO)₃[H(pzAn^Me)]}(PF₆) (M = Mn, 2a; Re, 2b) were prepared by metathesis of 1a or 1b with TlPF₆ in acetonitrile. Complexes 1a and 1b partly ionize to {M(CH₃CN)(CO)₃[H(pzAn^Me)]⁺}(Br⁻) in CH₃CN but retain their integrity in less donating solvents such as acetone or CH₂Cl₂. Each of the four metal complexes reacts with (NEt₄)(OH) in CH₃CN to give poorly-soluble crystalline [fac-M(CO)₃(μ-pzAn^Me)]₂ (M = Mn, 3a; Re, 3b). The solid state structures of 3a and 3b are of centrosymmetric dimeric species with bridging amido nitrogens and with pyrazolyls disposed trans- to the central planar M₂N₂ metallacycle. In stark contrast to the diphenylboryl derivatives, Ph₂B(pzAn^Me), none of the tricarbonyl group 7 metal complexes are luminescent.     

Electronic structure of Ni complexes by X-ray resonance Raman spectroscopy (resonant inelastic X-ray scattering)

The potential of 1s2p resonant inelastic (Raman) X-ray scattering (RIXS) is demonstrated for a series of Ni coordination complexes. In this technique, incident and scattered photon energies lie in the hard X-ray range (>5 keV). The 1s2p RIXS contour plots provide information that is complementary to K-edge and L-edge spectroscopy. RIXS spectroscopy promises to be a valuable probe of electronic structure     

Tricarbonylrhenium(I) and -technetium(I) complexes with bis(2-pyridyl)phenylphosphine and tris(2-pyridyl)phosphine

(NEt₄)₂[Re(CO)₃Br₃] or (NEt₄)₂[Tc(CO)₃Cl₃] react with bis(2-pyridyl)phenylphosphine (PPhpy₂) or tris(2-pyridyl)phosphine (Ppy₃) under formation of neutral tricarbonyl complexes of the composition [M(CO)₃X(L)] (M = Re, X = Br; M = Tc, X = Cl; L = PPhpy₂ or Ppy₃). In all isolated products, the ligands coordinate solely via two of their nitrogen atoms. All attempts to force a tripodal coordination of the phosphinopyridines failed. Removal of the bromo ligands from (NEt₄)₂[Re(CO)₃Br₃] by the addition of AgNO₃ in THF/water, and subsequent reaction of the resulting [Re(CO)₃(THF)₃](NO₃)with Ppy₃ yielded the complex [Re(CO)₃(NO₃)(Ppy₃-N,N′)] with a monodentate coordinated nitrato ligand. The products have been characterized spectroscopically and by X-ray structure analyses.     

Infrared absorptions of NH3(H2) complexes trapped in solid neon

When a very small concentration of H2 is added to a Ne:NH3=800:1 sample and the resulting mixture is deposited at 4.3 K, a new absorption appears at 4151.1 cm(-1) which can be assigned to the H2 stretching fundamental of H2 (j=1) complexed with NH3. Other new absorptions which appear near the vibrational fundamentals of NH3 are assigned to the NH3 moiety in this complex and in the complex of NH3 with H2 (j=0). The results of experiments in which HD or D2 is added to the Ne:NH3 mixture support these assignments. Ab initio and density functional calculations predict the observed infrared activation of the H2-stretching vibration for a structure in which the axis of the H2 molecule is collinear with the threefold axis of the NH3. The dependence of the observed absorption patterns on the concentration of H2 in the sample indicates that complexes of NH3 with two or more H2 molecules also form readily.     

Copper(I) complexes withN-methylbenzothiazole-2-thione and -2-selone

Summary N-methylbenzothiazole-2-thione (bttme) and -2-selone (btseme) form complexes with CuX₂ (X=Cl, Br, NO₃, 1/2SO₄ or BF₄). The reaction, carried out in MeOH, produces complexes of copper(I), whose stoichiometry mainly depends on the ligand. Infrared evidence shows that the coordination occurs through the exo-sulphur and selenium atoms.