Spectroscopic and theoretical investigations of vibrational frequencies in binary unsaturated transition-metal carbonyl cations, neutrals, and anions

Matrix Isolation Infrared Spectroscopic and Theoretical Study of Noble Gas Coordinated Rhodium−Dioxygen Complexes

Reactions of rhodium atoms with dioxygen molecules in solid argon have been investigated using matrix isolation infrared absorption spectroscopy. The rhodium-dioxygen complexes, Rh(eta2-O2), Rh(eta2-O2)2, and Rh(eta2-O2)2(eta1-OO), are produced spontaneously on annealing. The Rh(eta2-O2) complex rearranges to the inserted RhO2 molecule under visible light irradiation. Experiments doped with xenon in argon show that the rhodium-dioxygen complexes are coordinated by one or two noble gas atoms in solid noble gas matrixes. Hence, the Rh(eta2-O2), Rh(eta2-O2)2, and Rh(eta2-O2)2(eta1-OO) molecules trapped in solid noble gas matrixes should be regarded as the Rh(eta2-O2)(Ng)2, Rh(eta2-O2)2(Ng)2, and Rh(eta2-O2)2(eta1-OO)(Ng) (Ng = Ar or Xe) complexes. The product absorptions are identified on the basis of isotopic substitution and density functional theory calculations.

Infrared Spectra and Density Functional Calculations of CH2MHX and CH⋮MH2X Complexes Prepared in Reactions of Methyl Halides with Mo and W Atoms

The simple methylidene and methylidyne complexes (CH2=MHX and CH[triple bond]MH2X; X = F, Cl, Br, and I) are prepared in reactions of laser-ablated Mo and W atoms with the methyl halides and investigated by matrix infrared spectroscopy and density functional theory calculations. These complex structures are photoreversible: visible irradiation converts the methylidene complex to the methylidyne complex, and UV irradiation reverses this effect via alpha-hydrogen migration. While the higher oxidation state complexes are readily formed regardless of halogen size, the Mo methylidyne complex is relatively less favored with increasing halogen size, and the W complex shows the opposite tendency. The group 6 metal methylidenes are predicted to have the most agostically distorted structures among the early transition-metal methylidenes. The computed carbon-metal bond shortens with increasing halogen size for both the methylidene and methylidyne complexes. Harmonic and anharmonic frequencies computed by DFT converge on the experimental values and thus provide support for the identification of these new Mo and W complexes.

Group 4 Transition-Metal Atom Reactions with CS2 and OCS: Infrared Spectra and Density Functional Calculations of SMCS, SM-(η2-CS), SMCO, and OMCS in Solid Argon

Laser-ablated titanium, zirconium, and hafnium atoms were reacted with CS2 and OCS molecules during condensation in excess argon. With CS2, the SMCS and S-M(eta2-CS) products were formed on sample deposition. Photolysis increased both complexes, while annealing favored the lower energy S-M(eta2-CS) side-bound isomer. The OCS reactions produced SMCO, OMCS, and the simple M(eta2-CO)S adduct. Product absorptions are identified by comparison with density functional theory frequency calculations and isotopic substitutions. Investigations with OCS emphasized differences in the CS and CO bond insertion products.

Theoretical studies on vibrational spectra of some mixed carbonyl-halide complexes of Osmium(II)

The vibrational spectra of Os(CO)(6)(2+) and some of its mixed carbonyl-halide complexes, cis-Os(CO)(2)X(4)(2-), fac-Os(CO)(3)X(3)(-) and Os(CO)(5)X(+) (X=F, Cl, Br and I), have been systematically investigated by ab initio RHF and density functional B3LYP methods with LanL2DZ and SDD basis sets. The calculated vibrational frequencies of complexes Os(CO)(6)(2+), cis-Os(CO)(2)X(4)(2-) and fac-Os(CO)(3)X(3)(-) are evaluated via comparison with the experimental values. In infrared frequency region, the C-O stretching vibrational frequencies calculated at B3LYP level with two basis sets are in good agreement with the observed values with deviations less than 5%. In the far-infrared region, the B3LYP/SDD method achieved the best results with deviations less than 9% for Os-X stretching and less than 8% for Os-C stretching vibrational frequencies. The vibrational frequencies for Os(CO)(5)X(+) that have not been experimentally reported were predicted.

Probing the Interaction of Poly(vinylpyrrolidone) with Platinum Nanocrystals by UV−Raman and FTIR

The vibrational spectra of platinum nanoparticles (2.4-9 nm) capped with poly(N-vinylpyrrolidone) (PVP) were investigated by deep UV-Raman and FTIR spectroscopy and compared with those of pure PVP. Raman spectra of PVP/Pt show selective enhancement of C=O, C-N, and CH2 vibrational modes attributed to the pyrrolidone ring. Selective enhancement of ring vibrations is attributed both to the resonance Raman effect and SERS chemical enhancement. A red shift of the PVP carbonyl frequency on the order of 60 cm-1 indicates the formation of strong >C=O-Pt bonds. It is concluded that PVP adheres to the nanoparticles through a charge-transfer interaction between the pyrrolidone rings and surface Pt atoms. Heating the Pt nanoparticles under reducing conditions initiates the decomposition of the capping agent, PVP, at a temperature 100 degrees C below that of pure PVP. Under oxidizing conditions, both PVP/Pt and PVP degrade to form amorphous carbon.

Reactions of Gadolinium Atoms and Dimers with CO: Formation of Gadolinium Carbonyls and Photoconversion to CO Activated Molecules

Reactions of gadolinium atoms and dimers with carbon monoxide molecules in solid argon have been studied using matrix isolation infrared absorption spectroscopy. Mononuclear Gd(CO)x (x = 1-3) and dinuclear Gd2(CO)x (x = 1, 2) gadolinium carbonyls formed spontaneously on annealing. The Gd(CO)x complexes are CO terminal-bonded carbonyls, whereas the Gd2CO and Gd2(CO)2 carbonyl complexes were characterized to have asymmetrically bridging and side-on-bonded CO, which are drastically activated with remarkably low C-O stretching frequencies. The cyclic Gd2(mu-C)(mu-O) and Gd3(mu-C)(mu-O) molecules in which the C-O triple bond is completely cleaved were also formed on annealing. The Gd2(CO)2 complex rearranged to the more stable c-Gd2(mu-O)(mu-CCO) isomer, which also has a four-membered ring structure with one CO being completely activated.

Effect of Model Potential of Adsorptive Bond on the Thermodynamic Properties of Adsorbed CO Molecules on Ni(111) Surface

The effect of anharmonicity on the adsorption of CO molecules on the Ni(111) surface has been investigated. The DFT calculations are used to obtain the effective adsorption potential of the CO molecule on the Ni(111) surface. First, using an appropriate slab model, the geometry of adsorption system corresponding to hcp, fcc, bridge, and on-top sites with p(2 x 2) arrangement and coverage of 0.25 ML is optimized by the DFT calculations using a plane wave basis set and ultrasoft pseudopotentials; this gives the hcp site as the most stable site with De = 185 kJ/mol, for which the equilibrium distance of CO from the surface and C-O bond length on the surface are found to be 1.31 and 1.192 A, respectively. Then, the potential function of adsorption versus adsorptive bond distance was plotted, which is significantly different from that of a harmonic oscillator, i.e., the anharmonicity for the adsorptive bond is significant. Also the harmonic and anharmonic shifts of vibrational frequencies of adsorptive and C-O bonds are calculated to be -22.6 and 7.8 cm(-1), respectively. Hence, two potential models are selected for which their Schrödinger equations are solved analytically, namely the hard repulsion-soft attraction (HS) and Morse potential (MP) models. The adsorption isotherms, internal energy, isochoric heat capacity, and entropy of adsorbed CO molecules have been calculated for the mentioned model potentials and compared with those of the harmonic oscillator (H). As a result, the adsorption isotherms are not considerably sensitive to the model potential. The anharmonicity of CO-Ni bond, which is included in HS and MP models, gives an average deviation in pressure as much as 1.4% for HS and 5.8% for MP, compared to 6.1% for the H model. However, isochoric heat capacity and entropy depend on the model potential significantly, and the differences may be as high as 69% and 55% for isochoric heat capacity and entropy, respectively.

Matrix Isolation Infrared Spectroscopic and Theoretical Study of NgMO (Ng = Ar, Kr, Xe; M = Cr, Mn, Fe, Co, Ni) Complexes

The matrix isolation infrared spectroscopic and quantum chemical calculation results indicate that late transition metal monoxides CrO through NiO coordinate one noble gas atom in forming the NgMO complexes (Ng = Ar, Kr, Xe; M = Cr, Mn, Fe, Co, Ni) in solid noble gas matrixes. Hence, the late transition metal monoxides previously characterized in solid noble gas matrixes should be regarded as the NgMO complexes, which were predicted to be linear. The M-Ng bond distances decrease, while the M-Ng binding energies increase from NgCrO to NgNiO. In contrast, the early transition metal monoxides, ScO, TiO, and VO, are not able to form similar noble gas atom complexes.

Reactions of Cerium Atoms and Dicerium Molecules with CO: Formation of Cerium Carbonyls and Photoconversion to CO-Activated Insertion Molecules

Reactions of cerium with carbon monoxide molecules in solid argon have been studied using matrix isolation infrared absorption spectroscopy. The cerium carbonyls CeCO and Ce2CO are produced spontaneously on annealing and they are photochemically rearranged to the CCeO and c-Ce2(mu-C)(mu-O) isomers, where Ce and Ce2 are inserted into the CO triple bond. Theoretical calculations indicate that CeCO is an end-on-bonded carbonyl with a quintet ground state, whereas Ce2CO is a rare dinuclear lanthanide carbonyl complex with CO serving as an asymmetrically bridged, side-on ligand. The CCeO molecule was theoretically characterized to have a linear structure with a singlet ground state. Evidence is also presented for the CeCO- anion and other cerium carbonyls with higher coordination numbers.

Size and charge effects on the binding of CO to late transition metal clusters

We report on the size and charge dependence of the C-O stretching frequency, nu(CO), in complexes of CO with gas phase anionic, neutral, and cationic cobalt clusters (Co(n)CO(-0+)), anionic, neutral, and cationic rhodium clusters (Rh(n)CO(-0+)), and cationic nickel clusters (Ni(n)CO(+)) for n up to 37. We develop models, based on the established vibrational spectroscopy of organometallic carbonyl compounds, to understand how cluster size and charge relate to nu(CO) in these complexes. The dominating factor is the available electron density for backdonation from the metal to the CO pi* orbital. Electrostatic effects play a significant but minor role. For the charged clusters, the size trends are related to the dilution of the charge density at the binding site on the cluster as n increases. At large n, nu(CO) approaches asymptotes that are not the same as found for nu(CO) on the single crystal metal surfaces, reflecting differences between binding sites on medium sized clusters and the more highly coordinated metal surface sites.

Reactions of Laser-Ablated Zinc and Cadmium Atoms with CO: Infrared Spectra of the Zn(CO)x (x = 1−3), CdCO-, and Cd(CO)2 Molecules in Solid Neon

Reactions of laser-ablated zinc and cadmium atoms with carbon monoxide molecules in solid neon have been investigated using matrix-isolation infrared spectroscopy. Based on the isotopic substitution, absorptions at 1852.2, 1901.9, 1945.9, and 1995.2 cm(-1) are assigned to the C-O stretching vibrations of the ZnCO, Zn(CO)(2), and Zn(CO)(3) molecules. Absorptions at 1735.8, 1961.3, and 2035.7 cm(-1) are assigned to the C-O stretching vibrations of the CdCO(-) and Cd(CO)(2) molecules. In contrast with the previous argon experiments, more species and more valuable information about the reaction of zinc and cadmium atoms with CO have been obtained in solid neon. Density functional theory calculations have been performed on these zinc and cadmium carbonyls. The agreement between the experimental and calculated vibrational frequencies, relative absorption intensities, and isotopic shifts substantiates the identification of these carbonyls from the matrix infrared spectrum. The present experiments also reveal that zinc is more reactive with CO than cadmium.

Density Functional Study of the Interaction of Carbon Monoxide with Small Neutral and Charged Silver Clusters

CO adsorption on small neutral, anionic, and cationic silver clusters Ag(n) (n = 1-7) has been studied with use of the PW91PW91 density functional theory (DFT) method. The adsorption of CO on-top site, among various possible sites, is energetically preferred irrespective of the charge state of the silver cluster. The cationic silver clusters generally have a greater tendency to adsorb CO than the anionic and neutral silver ones, except for n = 3 and 4, and the binding energies reach a local minimum at n = 5. The binding energies on the neutral clusters, instead, reach a local maximum at n = 3, which is about 0.87 eV, probably large enough to be captured in the experiments. Binding of CO to the silver clusters is generally weaker than that to the copper and gold counterparts at the same size and charge state. This is due to the weaker orbital interaction between silver and CO, which is caused by the larger atomic radius of the silver atom. In contrast, Au atoms with a larger nuclear charge but a similar atomic radius to silver owing to the lanthanide contraction are able to have a stronger interaction with CO.

Infrared-Spectroscopic and Density-Functional-Theory Investigations of the LaCO, La2[η2(μ2-C,O)], andc-La2(μ-C)(μ-O) Molecules in Solid Argon

Reactions of laser-ablated lanthanum atoms with CO molecules in solid argon have been studied. The neutral lanthanum monocarbonyl (LaCO), produced upon sample deposition at 7 K, exhibits a C-O stretching frequency of 1772.7 cm(-1); to the best of our knowledge this is the lowest yet observed for a terminal CO in a neutral metal-carbonyl molecule (MCO, M = metal atom), implying anomalously enhanced metal-to-CO back-bonding. The infrared (IR) absorption band at 1145.9 cm(-1) is assigned to the C-O stretching mode of the side-on-bonding CO in the La2[eta2(mu2-C,O)] molecule. This CO-activated molecule undergoes an UV/Vis-photoinduced rearrangement to the CO-dissociated molecule, c-La2(mu-C)(mu-O). Density functional theory (DFT) calculations have been performed on these molecules, the results of which lend strong support to the experimental assignments of the IR spectra. LaCO is predicted to have a quartet ground state, corresponding to a linear geometry. Its formation involves La 6s-->4f promotion, which increases the strength of La-CO bonding by decreasing the sigma repulsion and, remarkably, by increasing the La 5d and 4f-->CO 2pi back-bonding. The observations schematically depict the whole process, starting with the interaction of CO with metal and ending with CO dissociation by the lanthanum dimer.

Infrared Spectroscopic and Density Functional Theory Studies on the CO Dissociation by Scandium and Yttrium Dimers

Reactions of laser-ablated scandium and yttrium atoms with dilute carbon monoxide molecules in solid argon have been investigated using matrix-isolation infrared spectroscopy. On the basis of the results of the isotopic substitution, the change of laser power and CO concentration and the comparison with density functional theory (DFT) calculations, the absorption at 1193.4 cm(-1) is assigned to the C-O stretching vibration of the Sc(2)[eta(2)(mu(2)-C,O)] molecule, which has a single bridging CO that is tilted to the side. This CO-activated molecule undergoes ultraviolet-visible photoinduced rearrangement to the CO-dissociated molecule, c-Sc(2)(mu-C)(mu-O). The cyclic c-Sc(2)(mu-C)(mu-O) molecule has a bridging carbon on one side of the Sc(2) unit and a bridging oxygen on the other. The analogous Y(2)[eta(2)(mu(2)-C,O)] molecule has not been observed, but the CO-dissociated c-Y(2)(mu-C)(muO) molecule has been observed in the Y + CO experiments. DFT calculations of the geometry structures, vibrational frequencies, and IR intensities strongly support the assignments. The CO activation mechanism has also been discussed. Our experimental and theoretical results schematically depict an activation process to CO dissociation.

Infrared diode laser spectroscopy of jet-cooled NiCO, Ni(CO)3(C13O), and Ni(CO)3(CO18)

Gas phase infrared spectroscopic investigations of the CO vibration of jet-cooled NiCO, Ni(CO)3(13CO), and Ni(CO)3(C18O) are reported. The spectra were obtained using a recently assembled pulsed-discharge slit-jet IR diode laser spectrometer. The rotationally resolved spectrum of NiCO was collected as it was formed in the discharge, while the spectra of Ni(CO)3(13CO) and Ni(CO)3(C18O) were recorded as they were destroyed. For NiCO, band origins of 2010.692 89(34) and 2010.645 28(23) cm(-1) were measured, along with values of B0=0.151 094(7) and 0.149 597(6) cm(-1) and B(1)=0.150 244(7) and 0.148 742(6) cm(-1) for 58NiCO and 60NiCO, respectively. The B0 values for these isotopologs were used to determine the two bond lengths in NiCO, giving r0 (Ni-C)=1.641(40) A and r0 (C-O)=1.193(53) A, in agreement with recent microwave measurements. The constants determined for Ni(CO)3(13CO) were upsilon0=2022.075 753(95) cm(-1), B"=0.034 736(2) cm(-1), and B'=0.034 688(2) cm(-1). For Ni(CO)3(C18O), upsilon0=2021.936 83(18) cm(-1), B"=0.033 764(4) cm(-1), and B'=0.033 710(4) cm(-1) were obtained. From these rotational constants, bond lengths of r0 (Ni-C)=1.839+/-0.007 A and r0 (C-O)=1.121+/-0.010 A were obtained. These values are discussed in relation to the bond lengths measured by electron and x-ray diffraction methods.

Solvation dynamics in Ni+ (H2O)n clusters probed with infrared spectroscopy

Infrared photodissociation spectroscopy is reported for mass-selected Ni+ (H2O)n complexes in the O-H stretching region up to cluster sizes of n = 25. These clusters fragment by the loss of one or more intact water molecules, and their excitation spectra show distinct bands in the region of the symmetric and asymmetric stretches of water. The first evidence for hydrogen bonding, indicated by a broad band strongly red-shifted from the free OH region, appears at the cluster size of n = 4. At larger cluster sizes, additional red-shifted structure evolves over a broader wavelength range in the hydrogen-bonding region. In the free OH region, the symmetric stretch gradually diminishes in intensity, while the asymmetric stretch develops into a closely spaced doublet near 3700 cm(-1). The data indicate that essentially all of the water molecules are in a hydrogen-bonded network by the size of n = 10. However, there is no evidence for the formation of clathrate structures seen recently via IR spectroscopy of protonated water clusters.

Oxidation of Carbon Monoxide on Group 11 Metal Atoms: Matrix-Isolation Infrared Spectroscopic and Density Functional Theory Study

Laser-ablated Cu, Ag, and Au atoms react with CO and O2 mixture in solid argon to produce carbonyl metal oxides, (O2)Cu(CO)(n) (n = 1, 2), (eta(1)-OO)MCO (M = Ag, Au), OCAuO2CO, and OAuCO, as well as group 11 metal carbonyls and oxides. These carbonyl metal oxides are characterized using infrared spectroscopy on the basis of the results of the isotopic substitution and the CO concentration change. Density functional theory (DFT) calculations have been performed on these molecules. The identifications of these carbonyl metal oxides are confirmed by the good agreement between the experimental and calculated vibrational frequencies, relative absorption intensities, and isotopic shifts. Carbon dioxide is eliminated from these carbonyl metal oxides upon UV irradiation, providing the evidence for the oxidation of carbon monoxide on group 11 metal atoms. The present experiments also reveal that the reactivity of copper toward CO is prior to O2, and the reactivity of silver toward O2 is prior to CO, whereas the reactivity of gold toward CO is comparable to O2.

Coordination of ScO+ and YO+ by Multiple Ar, Kr, and Xe Atoms in Noble Gas Matrixes: A Matrix Isolation Infrared Spectroscopic and Theoretical Study

The combination of matrix isolation infrared spectroscopic and quantum chemical calculation results provide strong evidence that scandium and yttrium monoxide cations, ScO+ and YO+, coordinate multiple noble gas atoms in forming noble gas complexes. The results showed that ScO+ coordinates five Ar, Kr, or Xe atoms, and YO+ coordinates six Ar or Kr and five Xe atoms in solid noble gas matrixes. Hence, the ScO+ and YO+ cations trapped in solid noble gas matrixes should be regarded as the [ScO(Ng)5]+ (Ng = Ar, Kr, or Xe), [YO(Ng)6]+ (Ng = Ar or Kr) or [YO(Xe)5]+ complexes. Experiments with dilute krypton or xenon in argon or krypton in xenon produced new IR bands, which are due to the stepwise formation of the [ScO(Ar)(5-n)(Kr)n]+, [ScO(Kr)(5-n)(Xe)n]+ (n = 1-5), [YO(Ar)(6-n)(Kr)n]+ (n = 1-6), and [YO(Ar)(6-n)(Xe)n]+ (n = 1-4) complexes.

Infrared Spectroscopic and Density Functional Theory Studies on the Reactions of Cadmium Atoms with Carbon Monoxide in Solid Argon

Reactions of laser-ablated cadmium atoms with carbon monoxide molecules in solid argon have been investigated using matrix isolation infrared spectroscopy. On the basis of isotopic substitution, the absorption at 1858.2 cm(-1) is assigned to the C-O stretching of the CdCO molecule, which is formed during the sample deposition. Cadmium di- and tricarbonyls, Cd(CO)n (n = 2, 3), have not been observed under the same experimental conditions. Density functional theory calculations have been performed on the cadmium carbonyls Cd(CO)n (n = 1-3), which lend strong support to the experimental assignments of the infrared spectra. It is predicted that the CdCO molecule is a linear triplet molecule and its formation involves Cd 5s --> 5p promotion. This promotion increases the Cd-CO bonding by decreasing the sigma repulsion and increasing the Cd 5p orbital --> CO pi back-donation. The absence of cadmium di- and tricarbonyls, Cd(CO)n (n = 2, 3), has also been discussed in some detail.

Electronic and geometric structure of the 3d-transition metal monocarbonyls MCO, M=Sc, Ti, V, and Cr

The electronic and geometric structure of the 3d-transition metal monocarbonyls MCO, M=Sc, Ti, V, and Cr was investigated through coupled cluster (CC) and multireference variational methods (MRCI) combined with large basis sets. For the ground and a few low-lying excited states complete potential energy profiles were constructed at the CC-level of theory. The M-CO dissociation energies of the ground states X 4Sigma-,X 5Delta,X 6Sigma+, and X 7A' are calculated to be 36, 27, 18, and 2 kcal/mol for ScCO, TiCO, VCO, and CrCO, with respect to Sc(4F),Ti(5F),V(6D),Cr(7S)+CO(X 1Sigma+). The bonding is rather complicated and could be attributed mainly to pi-conjugation effects between the M and CO pi-electrons, along with weak sigma-charge transfer from CO to M atoms. Almost in all cases the metal atoms appear to be slightly positively charged, at least according to the direction of the dipole moment vectors and the MRCI population densities.

Noble Gas−Transition Metal Complexes: Coordination of ScO+ by Multiple Ar, Kr, and Xe Atoms in Noble Gas Matrixes

The combination of matrix isolation infrared spectroscopic and density functional calculation results provides strong evidence that the transition metal monoxide cation, ScO+, coordinates five noble gas atoms in forming the [ScO(Ng)5]+ (Ng = Ar, Kr, or Xe) complexes in noble gas matrixes.

Experimental and Theoretical Evidence for the Formation of Zinc Tricarbonyl in Solid Argon

Zinc carbonyls are extremely rare. Here we report experimental and theoretical evidence of unprecedented zinc tricarbonyl, Zn(CO)3, the next member of the series of 18-electron metal carbonyls Cr(CO)6 --> Fe(CO)5 --> Ni(CO)4, whereas there is no evidence for the formation of the zinc mono- and dicarbonyls Zn(CO)n (n = 1, 2). DFT calculations predict that the Zn(CO)3 molecule has a singlet ground state with D3h symmetry. The formation of Zn(CO)3 involves 4s --> 4p promotion of the Zn atom, which increases the Zn-CO bonding by decreasing the sigma repulsion and significantly increasing the Zn 4sp hybrid orbitals --> CO pi* back-donation.

IR Spectroscopy and Density Functional Theory of Small V+(N2)n Complexes

V+(N2)n clusters are generated in a pulsed nozzle laser vaporization source. Clusters in the size range of n = 3-7 are mass selected and investigated via infrared photodissociation spectroscopy in the N-N stretch region. The IR forbidden N-N stretch of free nitrogen becomes strongly IR active when the molecule is bound to the metal ion. Photodissociation proceeds through the elimination of intact N2 molecules for all cluster sizes, and the fragmentation patterns reveal the coordination number of V+ to be six. The dissociation process is enhanced on vibrational resonances and the IR spectrum is obtained by monitoring the fragmentation yield as a function of wavelength. Vibrational bands are red-shifted with respect to the free nitrogen N-N stretch, in the same way seen for the C-O stretch in transition metal carbonyls. Comparisons between the measured IR spectra and the predictions of density functional theory provide new insight into the structure and bonding of these metal ion complexes.

Reactions of Gold Atoms and Small Clusters with CO: Infrared Spectroscopic and Theoretical Characterization of AunCO (n = 1−5) and Aun(CO)2 (n = 1, 2) in Solid Argon

Laser-ablated Au atoms have been co-deposited with CO molecules in solid argon to produce gold carbonyls. In addition to the previously reported Au(CO)n (n = 1, 2) and Au2(CO)2 molecules, small gold cluster monocarbonyls Au(n)CO (n = 2-5) are formed on sample annealing and characterized using infrared spectroscopy on the basis of the results of the isotopic substitution and CO concentration change and comparison with theoretical predictions. Of particular interest is that the mononuclear gold carbonyls, Au(CO)n (n = 1, 2), are favored under the experimental conditions of higher CO concentration and lower laser energy, whereas the yields of the gold cluster carbonyls, Au(n)CO (n = 2-5) and Au2(CO)2, remarkably increase with lower CO concentration and higher laser power. Density functional theory (DFT) calculations have been performed on these molecules and the corresponding small naked gold clusters. The identities of these gold carbonyls Au(n)CO (n = 1-5) and Au(n)(CO)2 (n = 1, 2) are confirmed by the good agreement between the experimental and calculated vibrational frequencies, relative absorption intensities, and isotopic shifts.

Observation of the lead carbonyls, PbnCO (n=1–4): Reactions of lead atoms and small clusters with carbon monoxide in solid argon

Reactions of laser-ablated Pb atoms with CO molecules in solid argon lead to the formation of the lead carbonyls, PbnCO (n=1-4), using matrix-isolation infrared spectroscopy. Absorption at 2027.7 cm(-1) is assigned to C-O stretching mode of the PbCO product, which appears and increases on annealing, disappears on broadband irradiation, and recovers on further annealing. Small lead cluster mono-carbonyls PbnCO (n=2-4) are also observed in the present infrared spectra. Based on the results of stepwise annealing and the comparison with theoretical predictions, the absorptions at 1915.5, 1923.8, and 2042.8 cm(-1) are assigned to Pb2CO, Pb3CO, and Pb4CO, respectively. Bridging CO is found in Pb2CO or Pb3CO, whereas terminal CO in Pb4CO. The density functional theory calculations have been performed on these molecules and small naked lead clusters. The good agreement between experimental and calculated vibrational frequencies, relative absorption intensities, and isotopic shifts provides strong support for the identifications of these lead mono-carbonyls PbnCO (n=1-4). Furthermore, energetic analysis for the possible reactions of lead atoms with CO molecules is also given.

V, Nb, and Ta Complexes with Benzene in Solid Argon: An Infrared Spectroscopic and Density Functional Study

Vanadium, niobium, and tantalum metal atoms, produced by laser ablation, are reacted with benzene vapor diluted in argon and codeposited onto a 7 K CsI window. The resulting reaction products are trapped, and the M(C6H6) and M(C6H6)2 complexes are identified by benzene isotopic substitution (C6H6, 13C6H6, C6D6). Density functional theory (DFT) frequency calculations are used to support molecular complex assignments. On the basis of the computed energies and a comparison of calculated and observed vibrational isotopic shifts, the ground electronic states and geometries are predicted. The bonding and electronic interactions in these molecules are discussed on the basis of the observed aromatic C-C breathing modes activated in the complexes.

Comparative Density Functional Theory Study of the Binding of Ligands to Cu+ and Cu2+: Influence of the Coordination and Oxidation State

BP86, B3LYP and MP2 methods, generally used to study large systems containing transition metals, were compared for their ability to accuratly evaluate bond dissociation energies of copper complexes. Various [Cu-L]+ and [Cu-L]2+ complexes in which L are small ligands and the higher coordinated complexes, [Cu(NH3)(4)]+ and [Cu(NH3)4]2+ were studied. For monoligated complexes, the BDEs calculated by the three methods differed by 2 to 60 kcal/mol, the larger differences being obtained for [Cu-L]2+ complexes. The BDEs calculated using the B3LYP functional were in general close to the experimental values whereas the BDEs calculated using the BP86 functional were too high and the BDEs calculated using the MP2 were too low. If we rank the whole ligands according to their increased bond strength, the resulting orders obtained with the three methods are different for the [Cu-L]+ complexes, the B3LYP giving the same order as the experimental one. This result indicates that the BDEs of [Cu-L]+ complexes are better modeled using the B3LYP than using the BP86 and MP2 methods. For [Cu-L]2+, B3LYP also gave the most reliable results whereas BP86 gave too large BDEs and MP2 gave too small BDEs. However, symmetries of ground states can be different using DFT and post-Hartree-Fock methods. For [Cu-N2O]2+ the use of the B1LYP provides a better symmetry of the complex than the B3LYP, as has been recently shown in the literature for [Cu-H2O]2+. MP2 led to an incorrect bent structure for [Cu-N2]2+ in contrast to a linear structure obtained with the other methods, including CCSD(T). However, due to the lack of experimental data for [Cu-L]2+ complexes and to contrasted results for the methods, it is not possible to conclude definitely. For the high coordinated complexes [Cu(NH3)4]+ and [Cu(NH3)4]2+, the PBE calculation method was used in addition to the BP86, B3LYP and MP2. The BDE values were very close to each other when there is no change of the oxidation state during the reaction. On the basis of these calculations, the choice of the method was less crucial for high coordinated complexes [Cu(NH3)4]+ and [Cu(NH3)4]2+ so long as the oxidation state remained the same during the reaction. In contrast, when [Cu(NH3)4]2+ is reduced in [Cu(NH3)3]+ and NH3, the BDE calculated using the four methods were markedly different.

Observation of Anomalous C−O Bond Weakening on Discandium and Activation Process to CO Dissociation

Sc2[eta2(mu2-C,O)], the first homoleptic dinuclear metal carbonyl with an unprecedented bridging and side-on-bonded CO, generated from the reaction of laser-ablated Sc atoms with CO in a solid argon matrix, exhibits an unusually low C-O stretching frequency at 1193.4 cm-1, characteristic of an anomalously weakened C-O bond. This CO-activated molecule undergoes ultraviolet-visible photoinduced rearrangement to the CO-dissociated molecule, c-Sc2(mu-C)(mu-O). The infrared absorptions of the new molecules are accurately predicted by quantum chemical calculations, and the activation energy for the isomerization of Sc2[eta2(mu2-C, O)] to c-Sc2(mu-C)(mu-O) is calculated to be 15.10 kcal/mol. Our experimental and theoretical results schematically depict an activation process to CO dissociation.

C?C Double- and Triple-Bond Formation from Reactions of B Atoms with CO: Experimental and Theoretical Characterization of OBBCCO and OBCCBO Molecules in Solid Argon

Reactions of boron atoms with CO molecules in solid argon form the following boron carbonyl species (which have been reported earlier): BCO, BBCO, OCBBCO, B(CO)2, and B4(CO)2. The OCBBCO molecule underwent a photochemical rearrangement where CO was activated to form the OBBCCO and OBCCBO molecules. The new molecules were identified on the basis of isotopic IR studies with 10B, 11B, 13C16O, 12C18O, and carbon dioxide mixtures in addition to comparison with quantum-chemical calculations of isotopic frequencies. Theoretical analyses showed that the OBBCCO and OBCCBO molecules are linear with C-C double and triple bonding, respectively, and lie at a much lower energy than the linear OCBBCO structure.

Gas-Phase IR Spectroscopy of Anionic Iron Carbonyl Clusters

The first gas-phase vibrational spectra are presented for several anionic iron carbonyl clusters, ranging in size from Fe(CO)4- to Fe5(CO)14- in the CO-stretching region (1600-2100 cm-1). The experimental spectra provide some immediate structural information about the clusters in the form of low-wavenumber (1750-1850 cm-1) bands marking the presence of bridging carbonyl ligands (mu2-COs). Supporting DFT calculations are presented for the smaller clusters (<3 Fe atoms) and give good agreement with the experimental data, allowing structural assignments for these cases. The Fe2(CO)7- spectrum suggests a structure lacking bridging carbonyl ligands, in agreement with the DFT results. For the case of Fe2(CO)8-, there are two possible structures based on the calculations, both with and without bridging carbonyls. The presence of a low-frequency band ( approximately 1770 cm-1) in the experimental spectrum conclusively demonstrates the existence of the bridged form. The ramifications of these data for metal-metal bonding in the clusters are also considered.

Fourier transform infrared-probed O(3P) microreactor: demonstration with ethylene reactions in argon matrix

To demonstrate the development of an oxygen atom microreactor in the form of liquid-helium-cooled solid argon matrix deposited on an infrared (IR) window, the oxidation of ethylene by mobile O atoms has been investigated. O atom diffusion through the argon matrix is confirmed and used to examine ethylene-oxygen atom reactions. In a bench-scale matrix isolation system probed with a Fourier transform infrared (FT-IR) spectrometer, matrices of solid Ar at 8-10 K doped with NO2 and ethylene have been prepared on a ZnSe window within an evacuated cryostat. The matrices have been photolyzed using 350-450 nm photons, and the reaction products resulting from the reaction of O(3P), one of the photolysis products of NO2, with ethylene have been identified using FT-IR and a Gaussian 98W simulation program. These products include oxirane, acetaldehyde, ethyl nitrite radical, and ketene. The temperature effect in the range of 10-30 K on the products formed has also been investigated. The reaction mechanisms are discussed and the viability of the solid Ar matrix being a low temperature microreactor to examine reaction mechanisms of mobile oxygen atoms is elaborated.

Synthesis, Characterization, and Photochemical and Computational Investigations of Ru(II) Heterocyclic Complexes Containing 2,6-dimethylphenylisocyanide (CNx) Ligand

The isocyanide ligand forms complexes with ruthenium(II) bis-bipyridine of the type [Ru(bpy)(2)(CNx)Cl](CF(3)SO(3)) (1), [Ru(bpy)(2)(CNx)(py)](PF(6))(2) (2), and [Ru(bpy)(2)(CNx)(2)](PF(6))(2) (3) (bpy = 2,2'-bipyridine, py = pyridine, and CNx = 2,6-dimethylphenylisocyanide). The redox potentials shift positively as the number of CNx ligands increases. The metal-to-ligand charge-transfer (MLCT) bands of the complexes are located at higher energy than 450 nm and blue shift in proportion to the number of CNx ligands. The complexes are not emissive at room temperature but exhibit intense structured emission bands at 77 K with emission lifetimes as high as 25 micros. Geometry optimization of the complexes in the singlet ground and lowest-lying triplet states performed using density functional theory (DFT) provides information about the orbital heritage and correlates with X-ray and electrochemical results. The lowest-lying triplet-state energies correlate well with the 77 K emission energies for the three complexes. Singlet excited states calculated in ethanol using time-dependent density functional theory (TDDFT) and the conductor-like polarizable continuum model (CPCM) provide information that correlates favorably with the experimental absorption spectra in ethanol.

Infrared Multiphoton Dissociation Spectroscopy of Gas-Phase Mass-Selected Hydrocarbon−Fe+ Complexes

Infrared spectra in the mid-infrared region (800-1600 cm(-1)) of highly unsaturated Fe(+)-hydrocarbon complexes isolated in the gas phase are presented. These organometallic complexes were selectively prepared by ion-molecule reactions in a Fourier transform ion cycloton mass spectrometer (FTICR-MS). The infrared multiphoton dissociation (IRMPD) technique has been employed using the free electron laser facility CLIO (Orsay, France) to record the infrared spectra of the mass selected complexes. The experimental IRMPD spectra present the main features of the corresponding IR absorption spectra calculated ab initio. As predicted by these calculations, the experimental spectra of three selectively prepared isomers of Fe+(butene) present differences in the 800-1100 cm(-1) range. On the basis of the comparison with calculated IR spectra, the IRMPD spectrum of Fe(butadiene)(+) suggests that the ligand presents the s-trans isomeric form. This study further confirms the potentialities of IRMPD spectroscopy for the structural characterization of organometallic ionic highly reactive intermediates in the gas phase. In conjunction with soft ionization techniques such as electrospray, this opens the door to the gas-phase characterization of reactive intermediates associated with condensed phase catalysts.

Persistent Photo-Reversible Transition-Metal Methylidene System Generated from Reaction of Methyl Fluoride with Laser-Ablated Zirconium Atoms and Isolated in a Solid Argon Matrix

A photoreversible transition-metal methylidene system has been formed for the first time by reaction of methyl fluoride and laser-ablated Zr atoms, isolated in solid argon, and investigated by means of infrared spectroscopy. Four different groups of absorptions are characterized on the basis of behaviors upon broad-band irradiation and sample annealing. Growth of Group I is accompanied by demise of Group II on irradiation with visible light (lambda > 530 nm) and vice versa with UV light (240 < lambda < 380 nm). The methylidene complex CH(2)=ZrHF is responsible for Groups I and II either in different singlet-triplet spin states or argon matrix packing configurations. The ground singlet state is stabilized by an agostic interaction. On the other hand, Group III, which arises from the Grignard type compound CH(3)-ZrF, disappears upon irradiation of UV light (lambda > 380 nm), increasing the concentration of CH(2)=ZrHF by alpha-H elimination. Fragments of methyl fluoride such as the CH(2)F radical comprise Group IV. Theoretical calculations are carried out for the alkylidene complex and other plausible products, and the results are compared with the experimental frequencies.

The low-lying electronic excited states of NiCO

Highly correlated coupled cluster methods with single and double excitations (CSSD) and CCSD with perturbative triple excitations were used to predict molecular structures and harmonic vibrational frequencies for the electronic ground state X 1Sigma+, and for the 3Delta, 3Sigma+, 3Phi, 1 3Pi, 2 3Pi, 1Sigma+, 1Delta, and 1Pi excited states of NiCO. The X 1Sigma+ ground state's geometry is for the first time compared with the recently determined experimental structure. The adiabatic excitation energies, vertical excitation energies, and dissociation energies of these excited states are predicted. The importance of pi and sigma bonding for the Ni-C bond is discussed based on the structures of excited states.

Quantitative vibrational dynamics of iron in nitrosyl porphyrins

We use quantitative experimental and theoretical approaches to characterize the vibrational dynamics of the Fe atom in porphyrins designed to model heme protein active sites. Nuclear resonance vibrational spectroscopy (NRVS) yields frequencies, amplitudes, and directions for 57Fe vibrations in a series of ferrous nitrosyl porphyrins, which provide a benchmark for evaluation of quantum chemical vibrational calculations. Detailed normal mode predictions result from DFT calculations on ferrous nitrosyl tetraphenylporphyrin Fe(TPP)(NO), its cation [Fe(TPP)(NO)]+, and ferrous nitrosyl porphine Fe(P)(NO). Differing functionals lead to significant variability in the predicted Fe-NO bond length and frequency for Fe(TPP)(NO). Otherwise, quantitative comparison of calculated and measured Fe dynamics on an absolute scale reveals good overall agreement, suggesting that DFT calculations provide a reliable guide to the character of observed Fe vibrational modes. These include a series of modes involving Fe motion in the plane of the porphyrin, which are rarely identified using infrared and Raman spectroscopies. The NO binding geometry breaks the four-fold symmetry of the Fe environment, and the resulting frequency splittings of the in-plane modes predicted for Fe(TPP)(NO) agree with observations. In contrast to expectations of a simple three-body model, mode energy remains localized on the FeNO fragment for only two modes, an N-O stretch and a mode with mixed Fe-NO stretch and FeNO bend character. Bending of the FeNO unit also contributes to several of the in-plane modes, but no primary FeNO bending mode is identified for Fe(TPP)(NO). Vibrations associated with hindered rotation of the NO and heme doming are predicted at low frequencies, where Fe motion perpendicular to the heme is identified experimentally at 73 and 128 cm-1. Identification of the latter two modes is a crucial first step toward quantifying the reactive energetics of Fe porphyrins and heme proteins.