Carbonyl Cluster Anions Research Articles

Spectroscopic characterization of heteronuclear iron-chromium carbonyl cluster anions.

Infrared photodissociation spectroscopy has been used to investigate CrFe(CO)n- (n = 4-9) clusters in the gas phase. Comparison of the observed spectra in the carbonyl stretching frequency region with those predicted for low-lying isomers by DFT calculations showed that the observed CrFe(CO)n- (n = 4-8) clusters could be characterized to have Cr-Fe bonded (OC)4Fe-Cr(CO)n-4 structures. The coexistence of isomers with the (OC)Fe-Cr(CO)5 and (OC)3Fe-Cr(CO)4 structures was also observed for CrFe(CO)6- and CrFe(CO)7- anions, respectively. The CrFe(CO)n- (n = 4-8) complexes were strongly bonded systems. The CrFe(CO)8- complex was a coordination-saturated cluster, and the CrFe(CO)9- anion was characterized to contain a CrFe(CO)8- core tagged by one CO molecule. Bonding analysis revealed that the Cr-Fe bonds in the CrFe(CO)n- (n = 4-8) clusters were predominantly σ-type single bonds. The iron center in the Fe(CO)4 moiety and the chromium center in the Cr(CO)5 moiety fulfilled the 18-electron configuration for the CrFe(CO)n- (n = 4-6) clusters. As in the CrFe(CO)n- (n = 7, 8) complexes, the iron center in the Fe(CO)4 moiety exhibited a 17-electron configuration, while the chromium center in the Cr(CO)4 moiety exhibited a 16-electron configuration. These findings provide valuable insights into the structure and bonding mechanism of heterometallic carbonyl clusters.

Infrared Photodissociation Spectroscopy of Heteronuclear Arsenic-Iron Carbonyl Cluster Anions.

Heteronuclear arsenic-iron carbonyl cluster anions AsmFe(CO)n- (m, n = 2, 3) have been generated in the gas phase and investigated by mass-selected infrared photodissociation spectroscopy and density functional theory calculations at the B3LYP/BP86/TPSS levels. All the AsmFe(CO)n- (m, n = 2, 3) cluster anions are determined to contain Fe(CO)n- fragments, which can be regarded as being formed by replacing one arsenic atom of the arsenic clusters Asm+1 with the Fe(CO)n- group. Bonding analyses indicated that each As2Fe(CO)n- (n = 2, 3) cluster anion involves two Fe-As single bonds and one As-As double bond. Each As3Fe(CO)n- (n = 2, 3) cluster anion has three Fe-As single bonds and three As-As single bonds. The Fe(CO)3- group with a 15-electron configuration is valence isoelectronic to the As atom and can serve as a building block for forming heteronuclear arsenic-iron carbonyl clusters.

Infrared Spectra, Structures and Bonding of Binuclear Transition Metal Carbonyl Cluster Ions

Binuclear transition metal carbonyl clusters serve as the simplest models in understanding metal-metal and ligand bonding that are important organometallic chemistry catalysis. Binuclear first row transition metal carbonyl ions are produced via a pulsed laser vaporization/supersonic expansion cluster ion source in the gas phase. These ions are studied by mass-selected infrared photodissociation spectroscopy in the carbonyl stretching frequency region. Density functional theory calculations have been performed on the geometric structures and vibrational spectra of the carbonyl ions. Their geometric and electronic structures are determined by comparison of the experimental IR spectra with the simulated spectra. The structure and the metal-metal and metal-CO bonding of both saturated and unsaturated homonuclear as well as heteronuclear carbonyl cluster cations and anions are discussed.

Sequential bonding of CO molecules to a titanium dimer: A photoelectron velocity-map imaging spectroscopic and theoretical study of Ti2(CO)n- (n = 1-9).

Binuclear titanium carbonyl cluster anions, Ti2(CO)n- (n = 4-6), are produced via a laser vaporization supersonic cluster source and characterized by mass-selected photoelectron velocity-map imaging spectroscopy. Quantum chemical calculations are carried out for Ti2(CO)n- (n = 1-9) to explore the trend of sequential bonding of CO molecules to a titanium dimer. It has been found that the CO molecules bind to Ti2 in a side-on fashion and form a stable Ti2[η2(μ2-C, O)]3 structure at n = 3, the motif of which retains up to n = 5. Starting at n = 6, a new building block of two CO groups side-on-bonded to Ti2 is favored, the structure of which persists up to n = 9. In the larger clusters (n = 6-9), the side-on-bonded CO molecule can be stabilized via the removal of two electrons from an anionic titanium carbonyl, which is different from the effect of charge on CO binding in rhodium carbonyls where bridge-bonded CO molecules are selectively destabilized by the removal of an electron from a neutral rhodium carbonyl. The present study provides a stepwise picture for molecular-level understanding of CO bonding on transition-metal clusters, which is directly relevant to the elementary processes of CO at metal catalysts.

Infrared photodissociation spectroscopy of mass-selected heteronuclear iron-copper carbonyl cluster anions in the gas phase.

Mass-selected heteronuclear iron-copper carbonyl cluster anions CuFe(CO)n(-) (n = 4-7) are studied by infrared photodissociation spectroscopy in the carbonyl stretching frequency region in the gas phase. The cluster anions are produced via a laser vaporization supersonic cluster ion source. Their geometric structures are determined by comparison of the experimental spectra with those calculated by density functional theory. The experimentally observed CuFe(CO)n(-) (n = 4-7) cluster anions are characterized to have (OC)4Fe-Cu(CO)n-4 structures, each involving a C3v symmetry Fe(CO)4(-) building block. Bonding analysis indicates that the Fe-Cu bond in the CuFe(CO)n(-) (n = 4-7) cluster anions is a σ type single bond with the iron center possessing the most favored 18-electron configuration. The results provide important new insight into the structure and bonding of hetronuclear transition metal carbonyl cluster anions.

Infrared photodissociation spectra of mass selected homoleptic dinuclear iron carbonyl cluster anions in the gas phase

Infrared spectra of mass-selected homoleptic dinuclear iron carbonyl cluster anions Fe2(CO)n− (n = 4–9) are measured via infrared photodissociation spectroscopy in the carbonyl stretching frequency region. The cluster anions are produced via a laser vaporization supersonic cluster source. Density functional calculations have been performed and the calculated vibrational spectra are compared to the experimental data to identify the gas-phase structures of the cluster anions. The experimentally observed Fe2(CO)n− (n = 4–7) cluster anions are characterized to have unusual asymmetric (OC)4Fe–Fe(CO)n−4 structures, which also correspond to the computed lowest energy structures. The experimentally observed Fe2(CO)8− cluster anion is determined to have an unbridged structure instead of the previously reported dibridged structure. The Fe2(CO)9− cluster anion is determined to involve a Fe2(CO)8− core anion that is solvated by an external CO molecule. Bonding analysis indicates that these anions each have a Fe–Fe single bond to satisfy the 18-electron configuration of one iron center. The results provide important new insight into the structure and bonding mechanisms of transition-metal carbonyl clusters.

ChemInform Abstract: Synthesis and Characterization of Heterometallic Carbonyl Cluster Anions

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Oxygen reduction reaction activity of monodispersed Pt nanoparticles-loaded carbon black catalyst prepared with a Pt carbonyl cluster anion

Pt nanoparticles-loaded carbon black (CB) was prepared from Pt carbonyl cluster complexes, and had much narrower size distribution than commercial Pt nanoparticles/CB. In the former the monodispersed Pt nanoparticles were highly dispersed on CB without aggregation even at high Pt loading of 80 wt.%. Hydrodynamic voltammograms in O2-saturated 0.05 M H2SO4 solution at 30 °C showed that the onset potential of oxygen reduction reaction (ORR) current for the monodispersed Pt nanoparticles/CB electrode was more positive than that for a polycrystalline Pt electrode and similar to that for the commercial Pt nanoparticles/CB electrode. Moreover, the mass activity for ORR for the monodispersed Pt nanoparticles/CB electrode was ca. 4.9 times higher than that for the commercial Pt nanoparticles/CB electrode, clearly indicating that the control of size distribution of Pt nanoparticles is meaningful for reducing the Pt consumption.

High-yield syntheses of [Rh 7(CO) 16] 3− and [Rh 14(CO) 25] 4− working in ethylene glycol solution under 1 atm of CO

The anionic rhodium carbonyl clusters [Rh 7(CO) 16] 3− and [Rh 14(CO) 25] 4− can be easily prepared by a new simple and high yield one-pot synthesis starting from RhCl 3· nH 2O dissolved in ethylene glycol and involving two steps: (i) treatment of RhCl 3· nH 2O under 1 atm of CO at 50 °C to give [Rh(CO) 2Cl 2] −; (ii) addition of a base (CH 3CO 2Na or Na 2CO 3) followed by reductive carbonylation under 1 atm of CO at an adequate temperature (50 °C for [Rh 7(CO) 16] 3−; 150 °C for [Rh 14(CO) 25] 4−). These new syntheses are more convenient than those previously reported, especially since such clusters are not accessible via silica surface-mediated reactions. This different behavior is due to the particular stabilization on the silica surface and under 1 atm of CO of an anionic carbonyl cluster, called A, which does not allow the formation of a higher nuclearity carbonyl cluster, called B, which was shown to be the key-intermediate in the synthesis of [Rh 14(CO) 25] 4− working in ethylene glycol solution. Although it was not possible to isolate crystals of A and B suitable for X-ray structural determination, a combination of cyclovoltammetry, one of the few examples so far available of the use of this technique for anionic rhodium carbonyl clusters, infrared spectroscopy and elemental analyses suggest that A and B are probably the never reported [Rh 7(CO) 14] − and [Rh 15(CO) 28] 3− clusters, respectively. In particular the tentative formulation of the two clusters was carried out by a non-conventional method based on the existence of a linear correlation between carbonyl frequencies of the main band and the [(charge/Rh atoms)/CO number] ratio.

The problems of detecting hydrides in metal carbonyl clusters by 1H NMR: the case study of [H4−nNi22(C2)4(CO)28(CdBr)2]n− (n = 2–4)

The new tetra-acetylide carbonyl clusters [H(4-n)Ni(22)(C(2))(4)(CO)(28)(CdBr)(2)](n-) (n = 2-4) have been prepared by reacting [Ni(10)C(2)(CO)(15)](2-) with a large excess of CdBr(2).xH(2)O and the molecular structure of the di-anion [H(2)Ni(22)(C(2))(4)(CO)(28)(CdBr)(2)](2-) has been fully elucidated by means of X-ray crystallography. The corresponding [HNi(22)(C(2))(4)(CO)(28)(CdBr)(2)](3-) and [Ni(22)(C(2))(4)(CO)(28)(CdBr)(2)](4-) conjugated bases are quantitatively obtained upon dissolution of [H(2)Ni(22)(C(2))(4)(CO)(28)(CdBr)(2)](2-) salts in more basic solvents such as acetonitrile and DMSO, respectively. The hydride nature of both [H(2)Ni(22)(C(2))(4)(CO)(28)(CdBr)(2)](2-) and [HNi(22)(C(2))(4)(CO)(28)(CdBr)(2)](3-) has been directly proved by (1)H NMR spectroscopy. Their resonances are very broad under all experimental conditions and their chemical shift greatly depends on solvent as well as temperature. Observation of the hydride resonances in [H(4-n)Ni(22)(C(2))(4)(CO)(28)(CdBr)(2)](n-) (n = 2, 3) makes these clusters a case study of the phenomena behind the loss of any NMR signal in higher-nuclearity metal carbonyl cluster anions (MCCA). In the attempt to obtain a better insight on this experimental spectroscopic behaviour, solutions of [NMe(4)](3)[HNi(22)(C(2))(4)(CO)(28)(CdBr)(2)] have been investigated by dynamic light scattering (DLS) at various concentrations. The DLS experiments point out the presence in solution of a distribution of particles with nominal hydrodynamic diameters enormously greater than those of the free cluster ions resulting, probably, from aggregation in solution. This could formally justify the observed NMR behaviour, even if the present observations are preliminary and their quantitative assessment requires further systematic studies on MCCA aggregation in solution.

A water soluble nanostructured platinum (0) metal catalyst from platinum carbonyl molecular clusters: Synthesis, characterization and application in the selective hydrogenations of olefins, ketones and aldehydes

High nuclearity platinum carbonyl cluster anions (Chini's clusters) have been used as precursors to prepare a platinum nanocatalyst. The ionic polyelectrolyte poly(diallyldimethylammonium chloride) has been used as the support material for anchoring [Pt 30(CO) 60] 2− via ion-pairing and subsequent stabilization of the nanoparticles. The polymer-supported material has been studied by spectroscopy (NIR, 13C NMR, and IR) and TEM before and after its use as a water soluble hydrogenation catalyst. The nanocatalyst is found to be effective for the chemoselective hydrogenation of olefinic, aldehydic and ketonic double bonds. For most of the substrates isolation of the product and reuse of the catalyst are extremely easy due to the automatic phase separation of the products from the catalyst. The spectral features of the fresh catalyst show retention of the carbonyl ligands and molecular identity of the parent cluster, but after use the carbonyl ligands appear to be lost. TEM of the supported material before and after use as a catalyst shows the presence of platinum nanoparticles with majority (≥70%) of the particles in the range of 2–6 nm. Smaller particles are dominant in the used catalyst and this observation is rationalized on the basis of the known reactivity of Chini's clusters with dihydrogen.

Kinetic investigations of the mechanism of dihydrogen driven catalytic reduction of methylene blue, safranine O, methyl viologen and ferricyanide using platinum carbonyl cluster anions (Chini-clusters) as catalyst

[Bu 4N] 2[Pt 12(CO) 24] ( 1) catalyses the selective reduction of electron acceptors ( S), methylene blue (MB +), safranine O (Saf +), methyl viologen (MV 2+) and ferricyanide by dihydrogen. Macroscopic rate investigations for the cationic substrates in DMF, and for ferricyanide in DMSO have been carried out. In all cases, k obs is given by k 1 [ S] + k 2, indicating that there are two catalytic cycles. In one of them, the formation of a complex between S and [Pt 12(CO) 24] 2− in the rate determining step (rate constant k 1) is followed by electron transfer and/or other fast steps. In the other catalytic cycle, the rate determining step (rate constant k 2) involves formation of the solvated cluster anion [Pt 12(CO) 24] 2−. The solvated cluster then undergoes fast reduction by dihydrogen and other reactions. The relative contributions of these two cycles depend on the substrate, and for MB +, Saf +, MV 2+ and [Fe(CN) 6] 3− the contribution of the second cycle is about 99%, 55%, 77% and 97%, respectively. Both k 1 and k 2 of ferricyanide are about three orders of magnitude smaller than those of the cationic electron acceptors. The rates of reduction of MB + and Saf + have also been studied in the presence of added water. Rates increase as the presence of water provides an additional pathway for the reduction of [Pt 12(CO) 24] 2− to [Pt 9(CO) 18] 2−.

Energy-dependent Electrospray Ionisation Mass Spectrometry of Carbonyl Clusters

The electrospray ionisation mass spectra (EDESI-MS) of Ru6C(CO)16(PPh3) and Ir4(CO)11(PR3) (PR3=PPh3, P(p-C6H4OMe)3, P(p-C6H4NMe2)3, P(p-C6H4Cl)3, P(OPh)3, P(OMe)3, PO3C5H9) are described and the relative importance of carbonyl loss versus phosphine loss as a fragmentation pathway is assessed. Qualitatively, the phosphine ligands bind more strongly to Ir4(CO)11 clusters than to Ru6C(CO)16. The influence on the collision cell pressure on MS/MS spectra of transition metal carbonyl cluster anions is also explored showing that a greater, simultaneous, distribution of fragment ions is produced as the collision cell pressure is increased.

Studies on the Reactions of Dihydrogen with Salts of Platinum Carbonyl Cluster Anions (Chini Clusters) and Redox Active Countercations

Reactions of An[Pt12(CO)24] (A = methylene blue (MB+), safranine O (Saf+), nicotinamide benzyl chloride (BNA+), n = 2; A = methylviologen (MV2+), n = 1) with dihydrogen in DMF and DMSO have been st...

New high-nuclearity Ni-Pt carbonyl clusters: synthesis and X-ray structure of the ordered [HNi24Pt17(CO)46]5- and the substitutionally Ni/Pt disordered [Ni32Pt24(CO)56]6- cluster anions.

Condensation between preformed Ni-Pt and Pt carbonyl clusters leads to the new [H(6-n)Ni(24)Pt(17)(CO)(46)](n-)(n= 5, 6) and the substitutionally Ni/Pt disordered [Ni(24)(Ni(12-x)Pt(x))Pt(20)(CO)(56)](6-) (x = 4) carbonyl clusters, the latter of which represents the highest nuclearity homoleptic carbonyl cluster anion so far reported.

Fragmentation of transition metal carbonyl cluster anions: structural insights from mass spectrometry.

The anionic clusters [HOs(5)(CO)(15)](-), [PtRu(5)C(CO)(15)](2-), [Os(10)C(CO)(24)](2-), [Os(17)(CO)(36)](2-), [Os(20)(CO)(40)](3-), [Co(6)C(CO)(15)](2-), [Pt(3)Ru(10)C(2)(CO)(32)](2-) and [Pd(6)Ru(6)(CO)(24)](2-) have been analysed by energy-dependent electrospray ionisation mass spectrometry (EDESI-MS). Three main features have emerged. Firstly, carbonyl ligands are fragmented from clusters with compact metal cores in an orderly fashion, with each of the ions generated by CO loss having approximately equal intensity. Secondly, electron autodetachment takes place in multiply charged anionic clusters, but only after elimination of a large proportion of their carbonyl ligands. Thirdly, clusters with open metal cores do not undergo CO loss in an orderly fashion, but certain peaks are considerably less intense. The appearance of these low-intensity peaks is believed to signify polyhedral core rearrangements, with open clusters folding to form more compact geometries. In some cases, the gas-phase transformations observed by EDESI-MS mirror those that are known to take place in solution.

Collision-induced dissociation and photodetachment of singly and doubly charged anionic polynuclear transition metal carbonyl clusters: Ru3Co(CO)13−, Ru6C(CO)162−, and Ru6(CO)182−

Three polynuclear transition metal carbonyl cluster anions, Ru3Co(CO)13−, Ru6C(CO)162−, and Ru6(CO)182− have been studied using energy-dependent electrospray ionization mass spectrometry (EDESI–MS) and photodetachment photoelectron spectroscopy (PES). EDESI–MS maps show a simple collision-induced dissociation (CID) process for Ru3Co(CO)n− by stripping CO down to the metal core. For the doubly charged species, two competing CID channels were observed, viz. loss of neutral CO and loss of CO+e−. It was found that the parent dianions first lose neutral CO down to n=9, producing a series of dianions, Ru6C(CO)n2− (n=9–16) and Ru6(CO)n2− (n=9–18). For n<9, the dianions become electronically unstable against autodetachment, and singly charged anions, Ru6C(CO)n− and Ru6(CO)n− (n=0–9), were observed. The PES spectra of the dianions show the electron binding energies decrease monotonically as n decreases and become ∼0.0 eV for n=9, in exact agreement with the CID patterns that reflect the electronic instability of the doubly charged metal complexes with n<9. All of the PES spectra show congested features, indicating very high density of low-lying electronic states for the transition metal carbonyl clusters. The electron binding energies of Ru3Co(CO)n− are similar for n=4–13, but decrease sharply from n=4 to 0. The intramolecular Coulomb repulsion in the dianions was observed to increase with loss of CO, ranging from ∼1.8 eV for Ru6C(CO)162− to ∼2.4 eV for Ru6C(CO)92−.

Synthesis and structural characterization of the [[Rh(5)(CO)(14)]-(H(2)N(CH(2))(4)NH(2))-[Rh(5)(CO)(14)])](2-) and [Rh(5)(CO)(13)(H(2)N(CH(2))(2)NH(2))](-) anions (as [PPh(4)](+) salts): an unprecedented example of carbonyl substitution by alkylamines in a homoleptic metal carbonyl cluster anion.

The substitution of one or two carbonyls by many different primary and secondary alkylamines and -diamines has been established for the first time in a homoleptic carbonyl cluster anion, the trigonal bipyramidal [Rh(5)(CO)(15)](-). Two derivatives, the bis-monosubstituted [[Rh(5)(CO)(14)]-(H(2)N(CH(2))(4)NH(2))-[Rh(5)(CO)(14)]](2-) dianion (1) and the disubstituted chelated [Rh(5)(CO)(13)(H(2)N(CH(2))(2)NH(2))](-) monoanion (2), have been structurally characterized, both in the solid state (as [PPh(4)](+) salts) and in solution, revealing that the sites of the substitution are the cluster apexes. (13)C NMR spectra of 2 revealed localized fluxionality of the CO ligands over the temperature range 298-183 K.

Mass Spectrometric Method for the Rapid Characterization of Transition Metal Carbonyl Cluster Reaction Mixtures

Energy-dependent electrospray ionization mass spectrometry (EDESI-MS) has been applied to the characterization of reaction products that contain a mixture of metal carbonyl cluster anions. The technique allows rapid identification of the components and provides molecular weight (parent ion), ion composition (isotope pattern), and structural information (fragmentation pattern). The spectra are presented as a two-dimensional map of cone voltage versus mass-to-charge ratio which resolves each component of the reaction product. The EDESI-MS technique is illustrated using the reaction products obtained from the reaction of [Ru6C(CO)17] and [PPN][M(CO)4] where M = Co or Ir. The anions identified from these reactions are [Ru5CoC(CO)16]-, [Ru3Co(CO)13]-, [RuCo3(CO)12]-, [HRu4Co2C(CO)15]-, [Ru5IrC(CO)16]-, [Ru3Ir(CO)13]-, and [RuIr3(CO)12]-. All the compounds have been fully characterized as their [PPN]+ salts by EDESI-MS together with other methods including single-crystal X-ray diffraction for [PPN][Ru5CoC(CO)16].

Laser Desorption Ionization Versus Electrospray Ionization Mass Spectrometry: Applications in the Analysis of Cluster Anions

Mass spectra of transition metal carbonyl cluster anions were recorded using laser desorption ionization time-of-flight (LDI-TOF) and electrospray ionization (ESI) techniques. The LDI spectra generally contain peaks corresponding the intact cluster together with extensive CO loss fragments ions whereas the ESI spectra exhibit peaks corresponding the intact cluster together with few (if any) CO loss fragment ions. The parameters of both techniques can be modified to vary the extent of fragmentation. In all cases no fragmentation of the metal core is observed. Overall, ESI is a more informative method for the analysis of these types of cluster anions.