Quartz crystal microbalance (QCM) in high-pressure carbon dioxide (CO2): experimental aspects of QCM theory and CO2 adsorption

The quartz crystal microbalance (QCM) technique has been developed into a powerful tool for the study of solid-fluid interfaces. This study focuses on the applications of QCM in high-pressure carbon dioxide (CO2) systems. Frequency responses of six QCM crystals with different electrode materials (silver or gold) and roughness values were determined in helium, nitrogen, and carbon dioxide at 35-40 degrees C and at elevated pressures up to 3200 psi. The goal is to experimentally examine the applicability of the traditional QCM theory in high-pressure systems and determine the adsorption of CO2 on the metal surfaces. A new QCM calculation approach was formulated to consider the surface roughness contribution to the frequency shift. It was found that the frequency-roughness correlation factor, Cr, in the new model was critical to the accurate calculation of mass changes on the crystal surface. Experiments and calculations demonstrated that the adsorption (or condensation) of gaseous and supercritical CO2 onto the silver and gold surfaces was as high as 3.6 microg cm(-2) at 40 degrees C when the CO2 densities are lower than 0.85 g cm(-3). The utilization of QCM crystals with different roughness in determining the adsorption of CO2 is also discussed.     

Synthesis and characterization of chromium and tungsten tetracarbonyl bound to the bridging ligand 2,3-bis(2-pyridyl)pyrazine (dpp)

The synthesis, electronic absorption, infrared and ¹³C NMR spectra, and electrochemistry of [Cr(CO)₄]dpp and [W(CO)₄]dpp (dpp = 2,3-bis(2-pyridyl)pyrazine) are reported. Electronic absorption spectra in different solvents show solvatochromic behavior and indicate the metal to ligand charge transfer (MLCT) excited state is lower in energy than the ligand field (LF) excited state. Electrochemical results show the [Cr(CO)₄]dpp complex undergoes semi-reversible one electron oxidation, while [W(CO)₄]dpp undergoes irreversible one electron oxidation. ¹³C NMR spectra of both complexes show all carbons in the metal-bound dpp ring shift downfield. The amount of downfield shift for the series [M(CO)₄]dpp (M = Cr, Mo, W) is interpreted as indicating better M dπ → dpp pπ backbonding occurs for Mo and W than for Cr.     

Photonic and electrochemical properties of adsorbed [Ru(dpp)2(Qbpy)]2+ luminophores

Dense monolayers of [Ru(dpp)2Qbpy]2+, where dpp is 4,4'-diphenylphenanthroline and Qbpy is 2,2':4,4' ':4'4' '-quarterpyridyl, have been formed by spontaneous adsorption onto clean platinum microelectrodes. The cyclic voltammetry of these monolayers is nearly ideal, and three redox states are accessible over the potential range of +/-1.3 V. Chronoamperometry conducted on the microsecond time scale has been used to probe the dynamics of heterogeneous electron transfer and indicates that the standard heterogeneous electron-transfer rate constant, k degrees , is approximately 106 s-1. The metal complex emits at approximately 600 nm in fluid and solid solution as well as when bound to a platinum electrode surface within a dense monolayer. In the case of the monolayers, it appears that the excited states are not completely deactivated by radiationless energy transfer to the metal because electronic coupling between the adsorbates and the electrode is weak. The dynamics of lateral electron transfer between the electronically excited Ru2+* and ground-state Ru3+ species has been explored by measuring the luminescence intensity after defined quantities of Ru3+ have been produced electrochemically within the monolayer. The rate of lateral electron transfer is between 8 x 106 and 3 x 108 M-1 s-1, indicating efficient electron transfer between adsorbates in close-packed assemblies. Voltammetry conducted at megavolt per second scan rates has been used to directly probe the redox properties of the electronically excited species.     

Fast removal and recovery of Cr(VI) using surface-modified jacobsite (MnFe2O4) nanoparticles

In this work, the effectiveness of surface-modified jacobsite (MnFe2O4) nanoparticles was investigated for the removal and recovery of Cr(VI) from synthetic wastewater. Ten nanometer modified MnFe2O4 nanoparticles were produced to be a new adsorbent using a co-precipitation method followed by a surface redox reaction. The equilibrium time for Cr(VI) adsorption onto modified MnFe2O4 nanoparticles was as short as 5 min, and the adsorption data fit the Langmuir model well. The maximum uptake of 31.5 mg of Cr(VI)/g of modified MnFe2O4 was obtained at pH 2, which was comparable with other common adsorbents such as activated carbon and sawdust. The effects of ligands (EDTA, SO4(2-), NH4+) and ionic strength were studied in a pH range of 2-10. EDTA and SO4(2-) inhibited the adsorption of Cr(VI) over the entire pH range studied, whereas NH4+ enhanced the uptake of Cr(VI) at pH greater than 6.5. The mechanisms leading to Cr(VI) adsorption by modified MnFe2O4 nanoparticles were determined by X-ray diffraction and X-ray photoelectron spectroscopy to be a combination of electrostatic interaction and ion exchange. Regeneration studies indicated the potential reuse of the modified MnFe2O4 nanoparticles without sacrificing adsorption capacity and the possible recycling of Cr(VI) without changing the valence.     

Evidence of CO(2) molecule acting as an electron acceptor on a nanoporous metal-organic-framework MIL-53 or Cr(3+)(OH)(O(2)C-C(6)H(4)-CO(2))

The adsorption mode of CO(2) at low coverage in the nanoporous metal benzenedicarboxylate MIL-53(Cr) or Cr(3+)(OH)(O(2)C-C(6)H(4)-CO(2)) has been identified using IR spectroscopy; the red shift of the nu(3) band and the splitting of the nu(2) mode of CO(2) in addition to the shifts of the nu(OH) and delta(OH) bands of the MIL-53(Cr) hydroxyl groups provide evidence that CO(2) interacts with the oxygen atoms of framework OH groups as an electron-acceptor via its carbon atom; this is the first example of such an interaction between CO(2) and bridged OH groups in a solid.     

Electronic and Geometric Structure of Bimetallic Clusters: Density Functional Calculations on [M(4){Fe(CO)(4)}(4)](4-) (M = Cu, Ag, Au) and [Ag(13){Fe(CO)(4)}(8)](n)(-) (n = 0-5)

The results of all-electron density functional calculations on the bimetallic cluster compounds [M(4){Fe(CO)(4)}(4)](4-) (M = Cu, Ag, Au) and on the corresponding naked species M(4)Fe(4) are reported. The trends within the triad have been investigated. The bare metal clusters exhibit a strong magnetization which is quenched on addition of CO ligands. The bonding in the bare clusters is different for the silver derivative compared to that of copper and gold, resulting in comparatively weaker Ag-Fe and Ag-Ag bonds. This can be rationalized in terms of the different d-sp mixing, which for Cu and Au is larger than for Ag. Relativistic effects act to increase the 4d-5s mixing in Ag and to strengthen the intermetallic bond with Fe. In the carbonylated clusters a charge transfer from the metal M (M = Cu, Ag, or Au) to the Fe(CO)(4) groups occurs so that the atoms M can be considered in a formal +I oxidation state, rationalizing the nearly square-planar geometry of the metal frame. In fact, the local coordination of the M atoms is almost linear, as expected for complexes of M(I). The addition of extra electrons results in a stabilization of the clusters, indicating the electron-deficient nature of these compounds. Similar features have been found for the largest cluster synthesized so far for this class of compounds, [Ag(13){Fe(CO)(4)}(8)](n)(-), (n = 0-5). The nature and localization of the unpaired electron in the tetraanion is also discussed.     

Adsorption of Cr(VI) and Se(IV) from their aqueous solutions onto Zr4+-substituted ZnAl/MgAl-layered double hydroxides: effect of Zr4+ substitution in the layer

Hydrotalcite-like compounds (layered double hydroxides, LDHs) containing varying amounts of Al(3+), Zr(4+), and Zn(2+) or Mg(2+) in the metal hydroxide layer have been synthesized and characterized by various physicochemical methods. The adsorption behavior of uncalcined (as-synthesized) and calcined LDHs have been investigated for Cr(2)O(7)(2-) and SeO(3)(2-). The mixed oxides, obtained on calcination at 450 degrees C, exhibit high adsorption capacities for Cr(2)O(7)(2-) (1.6-2.7 meq/g) and SeO(3)(2-) (1.1-1.5 meq/g), where adsorption occurs through rehydration. Substitution of Zr(4+) in the LDHs, for either M(2+) or Al(3+) ions, increases the adsorption capacity up to 20%, thus providing an alternative way to enhance the adsorption capacity of this type of material. The high adsorption capacity of these materials could be successfully used for removal of undesirable anions from water and also for synthesis of intercalated materials with tailored acidobasicity.     

One-step synthesis of core(Cr)/shell(gamma-Fe(2)O(3)) nanoparticles

Core(Cr)/shell(gamma-Fe(2)O(3)) nanoparticles were synthesized by mixing Fe(CO)(5) and Cr(CO)(6) in the 9:1 ratio. These particles exhibit narrow size distribution with 13.5 nm as mean diameter and uniform spherical shape. The TEM image, which is in good agreement with the synchrotron powder XRD pattern, reveals the heterogeneous nature (core/shell structure). The analysis of the pattern reveals gamma-Fe(2)O(3) structure and a metal crystal structure. Mossbauer spectra, which support the superparamagnetic behavior determined by H-M measurement, do not show any traceable amount of Fe(0). This suggests that the metal component is Cr. EELS analysis and iron mapping suggest controlled stoichiometry and also confirm a core made of Cr and a shell made of gamma-Fe(2)O(3).     

CO adsorption on Ag(100) and Ag/MgO(100)

Theoretical studies of CO adsorption on a two-layer Ag(100) film and on a two-layer Ag film on a MgO(100) support are reported. Ab initio calculations are carried at the configuration interaction level of theory using embedding methods to treat the metal-adsorbate region and the extended ionic solid. The metal overlayer is considered in two different structures: where Ag-Ag distances are equal to the value in the bulk solid, and for a slightly expanded lattice in which the Ag-Ag distances are equal to the O-O distance on the MgO(100) surface. The calculated adsorption energy of Ag(100) on MgO(100) is 0.58 eV per Ag interfacial atom; the Ag-O distance is 2.28 A. A small transfer of electrons from MgO to Ag occurs on deposition of the silver overlayer. CO adsorption at an atop Ag site is found to be the most stable for adsorption on the two-layer Ag film and also for adsorption on Ag deposited on the oxide; CO adsorption energies range from 0.12 to 0.19 eV. The CO adsorption energy is reduced for the Ag/MgO system compared to adsorption on the unsupported metal film thereby providing evidence for a direct electronic effect of the oxide support at the metal overlayer surface. Expansion of the Ag-Ag distance in the two-layer system also reduces the adsorption energy.     

Adsorption of cations onto the surfaces of silver nanoparticles

The effects of cations on the absorption spectra of silver sols have been investigated by the UV-vis spectrometry and TEM. Experiments showed that injection of certain amounts of transition metal cations into silver sols resulted not only in the aggregation of silver nanoparticles but also in the appearance of a new band centered near 510 nm in the absorption spectra of silver sols. However, the new band was not observed in the presence of alkaline earth metal cations or the Mv2+ cations. The peak position of the new band depends on the nature as well as the concentration of metal cations used. Comparing the peak positions of the new bands, it was found that the new band induced by the injection of Cr3+ was red-shifted with respect to those induced by Cu2+, Zn2+, or the Cd2+ cations. It is reasonable that this band near 510 nm should be attributed to the coeffects of the adsorption of metal cations onto the surfaces of silver nanoparticles and the aggregation of silver nanoparticles.     

Ionic liquids of bis(alkylethylenediamine)silver(I) salts and the formation of silver(0) nanoparticles from the ionic liquid system

We have prepared novel ionic liquids of bis(N-2-ethylhexylethylenediamine)silver(I) nitrate ([Ag(eth-hex-en)(2)]NO(3) and bis(N-hexylethylenediamine)silver(I) hexafluorophosphate ([Ag(hex-en)(2)]PF(6)), which have transition points at -54 and -6 degrees C, respectively. Below these transition temperatures, both the silver complexes assume amorphous states, in which the extent of the vitrification is larger for the eth-hex-en complex than for the hex-en complex. The diffusion coefficients of both the complex cations, measured between 30 (or 35) and 70 degrees C, are largely dependent on temperature; the dependence is particularly large in the case of the eth-hex-en complex cation below 40 degrees C. Small-angle X-ray scattering studies showed that the bilayer structure of the metal complex is formed in the liquid state for both the silver complexes. A direct observation of the yellowish [Ag(eth-hex-en)(2)]NO(3) liquid by transmission electron microscopy (TEM) indicates the presence of nanostructures, as a microemulsion, of less than 5 nm. Such structures were not clearly observed in the [Ag(hex-en)(2)]PF(6) liquid. Although the [Ag(eth-hex-en)(2)]NO(3) liquid is sparingly soluble in bulk water, it readily incorporates a small amount of water up to [water]/[metal complex] = 7:1. Homogeneous and uniformly sized silver(0) nanoparticles in water were created by the reduction of the [Ag(eth-hex-en)(2)]NO(3) liquid with aqueous NaBH(4), whereas silver(0) nanoparticles were not formed from the [Ag(hex-en)(2)]PF(6) liquid in the same way.     

Sorption of palladium(II), rhodium(III), and platinum(IV) on Fe(3)O(4) nanoparticles

The adsorption of palladium(II), rhodium(III), and platinum(IV) from diluted hydrochloric acid solutions onto Fe(3)O(4) nanoparticles has been investigated. The parameters studied include the contact time and the concentrations of metals and other solutes such as H(+) and chloride. The equilibrium time was reached in less than 20 min for all metals. The maximum loading capacity of Fe(3)O(4) nanoparticles for Pd(II), Rh(III), and Pt(IV) was determined to be 0.103, 0.149, and 0.068 mmol g(-1), respectively. A sorption mechanism for Pd(II), Rh(III), and Pt(IV) has been proposed and their conditional adsorption equilibrium constants have been determined to be logK=1.72, 1.69, and 1.84, respectively. Different compositions of eluting solution were tested for the recovery of Pt(IV), Pd(II), and Rh(III) from Fe(3)O(4) nanoparticles. It was found that 0.5 mol L(-1) HNO(3) can elute all of the metal ions simultaneously, while 1 mol L(-1) NaHSO(3) was an effective eluting solution for Rh(III), and 0.5 mol L(-1) NaClO(4) for Pt(IV). In competitive adsorption, the nanoparticles showed stronger affinity for Rh(III) than for Pd(II) and Pt(IV).     

One electron oxidation of chromium N,N-bis(diarylphosphino)amine and bis(diarylphosphino)methane complexes relevant to ethene trimerisation and tetramerisation

Complexes of the type [(diphosphine)Cr(CO)(4)] (diphosphine = Ph(2)PN(iPr)PPh(2), Ar(2)PN(Me)PAr(2) or Ar(2)PCH(2)PAr(2) (Ar = 2-C(6)H(4)(MeO)) have been synthesised. In the solid state, these complexes show tight phosphine bite angles in the range 67.82(4) degrees to 71.52(5) degrees and the nitrogen atom in N,N-bis(diarylphophino)amine ligands adopts an almost planar (sp(2)) geometry. All of the complexes are readily oxidised electrochemically or chemically to corresponding Cr(i) species. There is no evidence for coordination of the pendant ether group in derivatives with Ar = 2-MeO-C(6)H(4) in either Cr(0) or Cr(i) species. Treatment of the [(diphosphine)Cr(CO)(4)] complexes with [NO]BF(4) yields [(diphosphine)Cr(NO)(CO)(3)]BF(4). Removal of CO ligands to generate an oligomerisation-active species is not observed with amine oxides but triethyl aluminium is effective in this role, and active catalysts can be produced. The use of weakly coordinating anions seems crucial in achieving oligomerisation catalysis.     

Modeling Pb(II) adsorption onto sandy loam soil

The adsorption of Pb(II) onto hydrous sandy loam soil was investigated with batch equilibrium adsorption experiments. Results show that the amount of Pb(II) adsorbed increases with increasing pH and surface loading. It was demonstrated that the surface acidity of the soil could be determined using electrophoretic mobility measurements. The surface acidity constants, pK(a1)(int) and pK(a2)(int), were 1.57 and 3.43, respectively. A surface complex formation model (SCFM) was employed to describe the adsorption. The intrinsic stability constants, pK(i)(s), for the surface reaction between the Pb species and the ionized soil surface hydroxyl groups were determined from SCFM fitting. The adsorption free energy of Pb2+ and Pb(OH)+ ions ranges from -5.74 to -6.48 kcal/mol and from -9.68 to -10.00 kcal/mol, respectively, for surface loadings between 1.21 x 10(-5) and 2.41 x 10(-4) mol/g. The adsorption binding calculation indicated that the specific chemical interaction is the major mechanism responsible for the adsorption process.     

Investigation of the synthesis, activation, and isosteric heats of CO2 adsorption of the isostructural series of metal-organic frameworks M3(BTC)2 (M = Cr, Fe, Ni, Cu, Mo, Ru)

The synthesis, activation, and heats of CO(2) adsorption for the known members of the M(3)(BTC)(2) (HKUST-1) isostructural series (M = Cr, Fe, Ni, Zn, Ni, Cu, Mo) were investigated to gain insight into the impact of CO(2)-metal interactions for CO(2) storage/separation applications. With the use of modified syntheses and activation procedures, improved BET surface areas were obtained for M = Ni, Mo, and Ru. The zero-coverage isosteric heats of CO(2) adsorption were measured for the Cu, Cr, Ni, Mo, and Ru analogues and gave values consistent with those reported for MOFs containing coordinatively unsaturated metal sites, but lower than for amine functionalized materials. Notably, the Ni and Ru congeners exhibited the highest CO(2) affinities in the studied series. These behaviors were attributed to the presence of residual guest molecules in the case of Ni(3)(BTC)(2)(Me(2)NH)(2)(H(2)O) and the increased charge of the dimetal secondary building unit in [Ru(3)(BTC)(2)][BTC](0.5).     

Betaine-induced assembly of neutral infinite columns and chains of linked silver(I) polyhedra with embedded acetylenediide

Ten polymeric silver(I) double salts containing embedded acetylenediide: [(Ag2C2)2(AgCF3CO2)9(L1)3] (1), [(Ag2C2)2(AgCF3CO2)10(L2)3]H2O (2), [(Ag2C2)(AgCF3CO2)4(L3)(H2O)]0.75 H2O (3), [(Ag2C2)(1.5)(AgCF3CO2)7(L4)2] (4), [(Ag2C2)(AgCF3CO2)7(L5)2(H2O)] (5), [(Ag2C2) (AgC2F5CO2)7(L1)3(H2O)] (6), [(Ag2C2)(AgCF3CO2)7(L1)3(H2O)]2 H2O (7), [(Ag2C2)(AgC2F5CO2)6(L3)2] (8), [(Ag2C2)2(AgC2F5CO2)12(L4)2(H2O)4]H2O (9), and [(Ag2C2)(AgCF3CO2)6(L3)2(H2O)]H2O (10) have been isolated by varying the types of betaines, the perfluorocarboxylate ligands employed, and the reaction conditions. Single-crystal X-ray analysis has shown that 1-4 all have a columnar structure composed of fused silver(I) double cages, with C2(2-) species embedded in its stem and an exterior coat comprising anionic and zwitterionic carboxylates. For 5 and 6, single silver(I) cages are linked into a beaded chain through both types of carboxylate ligands. In 7, two different coordination modes of L1 connect the silver(I) polyhedra into a chain. For 8, the mu(2)-O,O' coordination mode of L3 connects the silver(I) double cages into a chain. Compound 9 exhibits a two-dimensional architecture generated from the cross-linkage of double cages by C2F5CO2-, L4, and [Ag2(C2F5CO2)2] units. Similar to 9, 10 is also a two-dimensional structure, which is formed by connecting the chains of linked double cages through [Ag2(CF3CO2)2] bridging.     

Ab initio studies of the electronic structure of L-cysteine adsorbed on Ag(111)

We have performed ab initio calculations for the adsorption of L-cysteine on Ag(111) using density functional theory. We have focused on two possible adsorbed species: the L-cysteine radical (?S-CH(2)-CH-NH(2)-COOH) adsorbed almost flat at a bridge site, slightly displaced toward an fcc location, and the zwitterionic radical Z-cysteine (?S-CH(2)-CH-NH(3)(+)-COO(-)) adsorbed at a bridge site, shifted to a hcp site forming a (4 × 4) unit cell (θ = 0.06) and a (√3 × √3) R 30° unit cell (θ = 0.33), respectively. Special attention has been paid to the electronic structure of the system. The adsorbate-silver bond formation has been exhaustively investigated by analyzing the density of states projected onto the different atoms of the molecule, and by charge density difference calculations. A complicated interplay between sp and d states of silver in the formation of bonds between the adsorbates and the surface has been found. The role of the carboxyl group in the interaction with the surface has been also analyzed.     

Experimental X-ray charge density studies on the binary carbonyls Cr(CO)6, Fe(CO)5, and Ni(CO)4

The experimental charge densities in the binary carbonyls Cr(CO)(6) (1), Fe(CO)(5) (2), and Ni(CO)(4) (3) have been investigated on the basis of high-resolution X-ray diffraction data collected at 100 K. The nature of the metal-ligand interactions has been studied by means of deformation densities and by topological analyses using the Atoms in Molecules (AIM) approach of Bader. A detailed comparison between the experimental results and theoretical results from previous work and from gas-phase and periodic DFT/B3LYP calculations shows excellent agreement, both on a qualitative and quantitative level. An examination of the kappa-restricted multipole model (KRMM) for Cr(CO)(6), using theoretically derived structure factors, showed it to provide a somewhat worse fit than a model with freely refined kappa' values. The experimental atomic graphs for the metal atoms in 2 and 3 were found to be dependent on the multipole model used for that atom. In the case of compound 2, restriction of the multipole populations according to idealized site symmetry of D(3h) gave an atomic graph in essential agreement with the theoretical gas-phase study. For compound 3, all multipole models fail to reproduce the atomic graph obtained from the theoretical gas-phase study. The atomic quadrupole moments for the C atoms in all compounds were consistent with significant pi back-donation from the metal atoms.     

Dinuclear oxidative addition of N-H and S-H bonds at chromium. Reaction of (*)Cr(CO)(3)(C(5)Me(5)) with [o-(HA)C(6)H(4)S-Cr(CO)(3)(C(5)Me(5))] (A = S,NH) yielding [eta(2)-o-(mu-A)C(6)H(4)S-Cr(C(5)Me(5))](2) and H-Cr(CO)(3)(C(5)Me(5))

Reaction of the 17-electron radical (*)Cr(CO)(3)Cp* (Cp* = C(5)Me(5)) with 0.5 equiv of 2-aminophenyl disulfide [(o-H(2)NC(6)H(4))(2)S(2)] results in rapid oxidative addition to form the initial product (o-H(2)N)C(6)H(4)S-Cr(CO)(3)Cp*. Addition of a second equivalent of (*)Cr(CO)(3)Cp* to this solution results in the formation of H-Cr(CO)(3)Cp* as well as (1)/(2)[[eta(2)-o-(mu-NH)C(6)H(4)S]CrCp*](2). Spectroscopic data show that (o-H(2)N)C(6)H(4)S-Cr(CO)(3)Cp* loses CO to form [eta(2)-(o-H(2)N)C(6)H(4)S]Cr(CO)(2)Cp*. Attack on the N-H bond of the coordinated amine by (*)Cr(CO)(3)Cp* provides a reasonable mechanism consistent with the observation that both chelate formation and oxidative addition of the N-H bond are faster under argon than under CO atmosphere. The N-H bonds of uncoordinated aniline do not react with (*)Cr(CO)(3)Cp*. Reaction of the 2 mol of (*)Cr(CO)(3)Cp* with 1,2-benzene dithiol [1,2-C(6)H(4)(SH)(2)] yields the initial product (o-HS)C(6)H(4)S-Cr(CO)(3)Cp and 1 mol of H-Cr(CO)(3)Cp*. Addition of 1 equiv more of (*)Cr(CO)(3)Cp to this solution also results in the formation of 1 equiv of H-Cr(CO)(3)Cp*, as well as the dimeric product (1)/(2)[[eta(2)-o-(mu-S)C(6)H(4)S]CrCp*](2). This reaction also occurs more rapidly under Ar than under CO, consistent with intramolecular coordination of the second thiol group prior to oxidative addition. The crystal structures of [[eta(2)-o-(mu-NH)C(6)H(4)S]CrCp*](2) and [[eta(2)-o-(mu-S)C(6)H(4)S]CrCp*](2) are reported.     

Structural similarities and differences among mixed-metal clusters containing a single M(PPh3) (M = Cu, Ag or Au) fragment

The heteronuclear metal clusters [H₃MRu₄(CO)₁₂(PPh₃)] and [MFe₃(μ-COMe)(CO)₁₀(PPh₃)] (M = Cu, Ag or Au) have been prepared; the gold-tetraruthenium cluster has a different metal core geometry to that adopted by the copper and silver analogues, whereas all three iron-Group IB mixed-metal clusters have the same geometry.