CO Coordination Research Articles

Complexes with functional phosphines. Part 8. Interconversion study of [RuCl2{Ph2PCH2C(O)OEt}L2], [RuCl2(CO){Ph2PCH2C(O)OEt}L], and [RuCl2(CO)2L2][L = Ph2PCH2C(O)OEt] under CO. Synthesis and X-ray structure of mer-[RuCl3{Ph2PCH2C(O)OEt}L

The complex trans-[[graphic omitted]O)OEt}L2](1)[L = Ph2PCH2C(O)OEt] undergoes a reversible one-electron oxidation at +0.77 V vs. a saturated calomel electrode (s.c.e.) on a Pt electrode in 1,2-dichloroethane containing 0.1 mol dm–3 NBu4ClO4. A cyclic voltammetric study establishes that under a CO atmosphere, (1) is quantitatively converted into trans,trans,trans-[RuCl2(CO)2L2](3)(E½=+1.65V)via trans-[[graphic omitted])OEt}L](2)(E½= 1.35 V). Complex (2) interconverts with (3)via reversible CO co-ordination. Regeneration of (1) from (3) requires u.v. irradiation in the presence of excess L. The reversible one-electron reduction of mer,trans-[[graphic omitted])OEt}L](4) occurs at –0.22 V. The structure of complex (4) was established by a single-crystal X-ray diffraction study. Crystals are orthorhombic, space group P212121(no. 1 9), with Z= 4 in a unit cell of dimensions a= 9.1 04(2), b= 15.511(2), and c= 24.1 90(2)Å. The structure has been refined to R 0.034 (R′ 0.046). The Ru atom has a distorted octahedral environment with the three chlorine atoms in a mer relationship. The chelating ligand is characterized by a Ru–P(2) distance of 2.368(2)Å and a relatively short Ru–O(3) distance of 2.1 43(5)Å. The distance between Ru and the chlorine atom [Cl(1)]trans to the co-ordinated ester oxygen is 2.31 2(2)Å whereas Ru–Cl(2) and Ru–Cl(3) are 2.323(2) and 2.362(2)Å, respectively.

Selective conversion of CO into methanol at ordinary temperature. Part 4. Activation by iron(II), iron(III), and chromium(III) complexes

The conversion of carbon monoxide into methanol has been performed at a platinum electrode modified with K2FeII[FeII(CN)6]. This reaction was activated by catalytic systems consisting of a primary alcohol and a series of iron(II), iron(III), or chromium(III) complexes. The current–time curves at a constant potential showed an oscillation, the period, induction time, and amplitude of which are a function of temperature, applied potential, and the nature and concentration of the metal complex or alcohol added. The pseudo-rate constant, the current efficiency, and the activation energy for the methanol formation have been determined. The current efficiency was almost 100% except in the presence of pentachlorochromate(III) and pentafluoroferrate(II), and the activation energy was 2.9–5.8 kcal mol–1 Infrared spectra of the metal complex isolated from the catalyst solution indicated that the reduction of CO takes place via methyl formate as an intermediate. These results are suggestive of a mechanism in which co-ordination of CO to the central metal in the form of methyl formate is a key step, and the diffusion of the co-ordinated species toward the modified electrode is rate determining.

Crystal structure of a platinum carbonyl phosphine cluster Pt4(CO)5[P(C2H5)3]4 and the IR bands of CO groups with different coordination to the metal atoms

The crystal structure of Pt4(CO)5(PEt3)4 was determined and the IR spectra of this compound in the VCO region characteristic for such clusters were studied. Four models for the interaction of CO with metals upon adsorption were proposed on the basis of the geometrical parameters obtained for the coordination of CO in this and other clusters. Calculation of the frequencies and shape of the vibrations of all four models showed that we must independently evaluate the force constants of the interaction of the CO groups with the remaining part of the complex in order to develop reliable spectral indicators for the specific type of CO coordination.

Chemistry of organopalladium and nickel complexes relevant to catalysis

Abstract

Synthesis and spectroscopic characterization of a new class of heterotetranuclear compounds with thiocyanate groups as bridging ligands. The X-ray structure of bis-(μ-tetrakis(thiocyanato- S)mercury(II)- N,N′)diaquahexakis(5.7-dimethyl[1,2,4] triazolo[1,5- a] pyrimidine- N3) dicobalt(II)

The synthesis and characterization of a novel type of heterotetranuclear compounds of general formula [MHg(dmtp) 3(SCN) 4(H 2O)] 2 [M = Mn, Co, Ni(II) and dmtp = 5,7-dimethyl[1,2,4] triazolo[1,5-a] pyrimidine] are described. Infrared spectra show the presence of both S-coordinating and N,S-bridging thiocyanate ligands. Ligand-field spectra indicate an ocahedral coordination geometry for the transition-metal ions. The structure of one of the three, mutually isomorphous, compounds was determined by X-ray diffraction methods. Crystals of [CoHg(dmtp) 3(SCN) 4(H 2O)] 2 are triclinic, space groups P 1 with a = 11.481(9), b = 13.975(11), c = 11.479(8) Å, α = 101.08(6), β = 90.11(7), γ = 77.24(6)°, Z = 1. The structure was solved from diffractometer data by Patterson and Fourier methods and refined by full-matrix least-squares to R = 0.038 for 2392 independent observed reflections. The structure consists of centrosymmetric heterotetranuclear complexes formed by thiocyanate groups bridging heterometals. Mercury is tetrahedrally coordinated by sulphur atoms from thiocyanate groups (HgS bonds ranging from 2.457 to 2.601 Å), two of which bridge two centrosymmetric Co atoms. Three N atoms from dmtp ligands and one oxygen from a water molecule complete the octahedral coordination of Co (CoN bonds: 2.11, 2.14 and 2.18 Å; CoO w bond: 2.08 Å). Intramolecular hydrogen bonds between water hydrogens and N atom sfrom a dmtp molecule and a non-bridging thiocyanate group respectively stabilize the tetranuclear species. Magnetic suspectibility studies indicate that the magnetic exchange between the metal ions is very weak.

Reactions of carbon monoxide with Fe(II) diethyldithiocarbamate and Fe(II) ethylxanthate

Reactions of carbon monoxide with iron(II) diethyldithiocarbamate and iron(II) ethylxanthate were followed using solution IR spectroscopy. In DMF and CH 3CN solutions, the only Fe—dithiocarbamate—carbon monoxide complex observed was cis-[Fe(CO) 2(dedtc) 2]. This complex formed rapidly and appeared to be very stable, resisting displacement of the coordinated CO molecules by other ligands. Fe(exa) 2 showed very little coordination of CO in DMF solution, but in CH 3CN solution formed the complex cis-[Fe(CO) 2(exa) 2] rapidly via the monocarbonyl intermediate [Fe(CO)(exa) 2CH 3CN]. In CHCl 3 solution, in the presence of CO and added bases, a series of complexes, [Fe(CO)(exa) 2L], where L = pyridine, pyrrolidine, diethylamine and triphenylphosphine, was formed. However, with the exception of [Fe(CO)(exa) 2(ø 3P)], these monocarbonyl complexes were unstable with respect to disproportionation to cis-[Fe(CO) 2(exa) 2] and [Fe(exa) 2L 2]. No mixed-ligand monocarbonyl complexes were observed with Fe(dedtc) 2.

The coordination of Co 2+ions in Co substituted magnetites, Fe 3−xCo xO 4, with x⩽0.04

57Fe Mössbauer spectra at room temperature, both with and without external magnetic field, indicate that Co 2+ ions in Co xFe 3−xO 4spinels ( x⩽0.04) are situated on the octahedral B sites. The Mössbauer parameters are listed and the existence of unpaired Fe 3+ ions is evidenced.

Reaction of N, N-diethyldithiocarbamate and other bidentate ligands with Zn, Co and Cu bovine carbonic anhydrases : Inhibition of the enzyme activity and evidence for stable ternary enzyme-metal-ligand complexes

The reactions with N, N-diethyldithiocarbamate (DDC) of zinc, cobalt and copper carbonic anhydrase from bovine erythrocytes were investigated. The native zinc enzyme was inhibited by DDC, but no removal of zinc could be detected even at a very high [ligand]/[protein] ratio. At identical pH values a larger inhibitory effect was found for the cobalt enzyme. The metal was removed by DDC from the protein at pH < 7.0. No cobalt removal occurred at pH 10, where a stable ternary complex with the enzyme-bound Co(II) was detected. Its optical and EPR spectra are indicative of five-coordinate Co(II). The reaction of the Cu(II) enzyme with stoichiometric chelating agent was marked by the appearance of an electronic transition at 390 nm ( ε = 4300 M −1·cm −1). Metal removal from the copper enzyme readily occurred as the ligand was in excess over the metal, with parallel appearance of a band at 440 nm, which was attributed to the free Cu(II)-DDC complex. Also, in the case of the copper enzyme an alkaline pH was found to stabilize the ternary adduct with the diagnostic 3900 nm band. EPR spectra showed that the ternary adduct is a mixture of two species, both characterized by the presence in the EPR spectrum of a superhyperfine structure from two protein nitrogens and by a low g | value, indicative of coordination to sulfur ligands. It is suggested that the two species contain the metal as penta- and hexacoordinated, respectively. Measurements of the longitudinal relaxation time, T 1, of the water protons suggested that water coordination is retained in the latter case. Hexacoordination with retention of water is also proposed for the Cu(II) derivatives with the bidentate oxalate and bicarbonate anions, unlike the corresponding Co(II) derivatives, which are pentacoordinated. Different coordination of Co(II) and Cu(II) adducts may be relevant to the difference of activity of the two substituted enzymes.

X-ray investigation of CoCl bonding in a concentrated aqueous solution of CoCl 2 and LiCl

A concentrated CO(II) solution with a Cl −/Co 2+ ratio of≈4 was examined by X-ray diffraction. The Fourier-transformed scattering data indicated inner complex formation between Co 2+ and Cl −ions. The overall coordination of Co 2+ ions is very close to 6 and the average number of bonded Cl − ions per cobalt atom was found to be nearly 1. The similarity of this result to the one obtained from a solution of NiCl 2 of equal concentration is discussed. This result was also checked through EXAFS measurements.

Catalysis by supported clusters: two examples of catalytic reactions that involve a molecular cluster frame

Two examples of catalysis by supported clusters are given that involve a molecular cluster frame during the catalytic cycle. (H)Os 3 (CO) 10 (OSi^) is able to hydrogenate ethylene between 343 and 373 K. The mechanism of this reaction, which involves the molecular cluster frame, requires the opening of the bridging three-electron oxygen ligand as the key step of the catalytic process. Rh 6 (CO) 16 adsorbed on alumina is a catalyst for the water-gas shift reaction carried out between 293 and 393 K. The mechanism of this reaction involves three steps: (i) electrophilic attack by surface protons on the metallic frame with formation of Rh I (CO) 2 and Rh III (H) (H) species; (ii) reductive elimination of H 2 favoured by CO coordination to the Rh III (H) (H) species; (iii) nucleophilic attack by molecular water on CO coordinated to Rh I with regeneration of the starting cluster, release of CO 2 and surface protons.

An angle resolved photoemission determination of the coordination of CO on the ZnO(0001) surface

Angle resolved ultraviolet photoemission spectroscopy employing polarized He ii resonance radiation has been used to determine the bonding geometry of CO to ZnO(0001) at 80 K. Bound CO molecules are oriented perpendicular to the zinc-terminated surface forming a linear Zn–C–O complex. This result, along with earlier work on the ZnO(101̄0) surface, is explained by a concise and coherent model for CO chemisorption on ZnO surfaces. The role of defect sites for CO chemisorption is considered.

EXAFS as a probe of local coordination environments of transition metal ions in polycrystalline zeolite catalysts. Co(i i) in hydrated zeolite –A and –Y

Synthetic zeolites exchanged with transition metal or rare earth ions are of immense importance in catalysis, both commercially and in basic research; however, difficulty in growing single crystals and problems of long range disorder make crystallographic studies formidable tasks. In this study, extended x-ray absorption fine structure (EXAFS) spectroscopy has been successfully applied to characterize the local coordination of Co(ii) ions in polycrystalline zeolite –A and –Y, thereby establishing the utility of this technique for structural study of intrazeolitic complexes. The Co(ii) ions in Co18.2Na20.7–Y⋅xH2O are found to be ’’solutionlike’’, six-coordinate with Co–O bond distances of 2.06(1) Å, but in Co4.3Na3.4–A⋅xH2O and Co5.5Na1.0–A⋅xH2O, they are five coordinate with Co–O distances of 2.07(1) Å. The latter result is compatible with several published spectroscopic measurements, but is in conflict with a previous single crystal x-ray diffraction study; this discrepancy has been critically analyzed. The experimental data were collected for ∼17 h per sample on an ’’in house’’ EXAFS facility employing a standard 1 kW Mo x-ray tube and focussing optics. Hence, EXAFS appears to be a powerful tool for investigating short range order even in materials as complex as zeolites.

Chemical and spectroscopic conformation of an exogenous ligand bridge in half met hemocyanin

Half met-N 3 − hemocyanin is shown to undergo a unique change at the Cu(II)⋯Cu(I) active site with temperature, exhibiting class II mixed valent properties at low temperature (The appearance of an intense near IR intervalence-transfer transition and a delocalized EPR spectrum). This requires a Cu(II)NNNCu(I) bridging geometry. The effects of CO coordination to half met-N 3 − , combined with the presence of a low energy N 3 − → Cu(II) charge transfer transition, demonstrate that azide is also bridging at room temperature. Finally, half met-N 3 − is found to be capable of coordination of a second N 3 − at the copper(II) site.

Reactivity of Ni(CO)[P(C 6H 5) 2(CH 2) 4P(C 6H 5) 2] 2 with (π-acidic) Lewis bases. An example of reversible coordination of carbon monoxide to nickel(0)

The tetracoordinate nickel(0) complex Ni(CO)(DPB) 2 (DPB = 1,4 bis(diphenylphosphino) butane), I, reacts readily with tetracyanoethylene (TCNE) even in 1 : 1 molar ratio with displacement of CO and formation of the known π-olefinic complex Ni(DPB)(TCNE). Complex I reacts with fumaronitrile (FN) in a two step reaction, the final products being Ni(CO) 2(DPB) and Ni(DPB)(FN); the initial product is the tetracoordinate species Ni(CO)(DPB-P)(FN), which provides an example of reversible coordination of CO to nickel(0). Complex I reacts easily with P(OR) 3 (R = CH 3 C 2H 5, C 6H 5, o-C 6H 4-CH 3) with complete and controllable substitution of one DPB molecule per nickel atom. The rate depends markedly on the nature of the entering group. The complex does not react with propio- or benzo-nitrile or with alkynes under ambient conditions.

An infrared study of nitric oxide adsorbed on rhodium-alumina catalyst

Infrared spectroscopic study was made of NO and CO and their mixture adsorbed on rhodium metals supported on γ-alumina. When NO is adsorbed on rhodium, two surface species are identified: cationic one (M NO+) produced by donation of an electron antibonding (π2pz*) of NO to d orbital of the metal to strengthen the NO bond, and anionic one (M NO−) produced by transfer of a d electron of the metal to an antibonding π2pz* orbital of NO to weaken the NO bond. Cis-type coordination of NO and CO to one rhodium atom was found. When NO is first adsorbed and CO is introduced to react with the adsorbed NO, M NCO (isocyanate) is formed which is stable up to 400 °C under vacuum.

Influence of conformational changes of co(III)–poly‐N‐vinyl‐2‐methylimidazole complexes on electron‐transfer reactions of the complexes

AbstractIn order to study the effect of conformational changes in electron‐transfer reactions of Co(III)–polymer complexes, cis‐[Co(III)(en)2LCl]Cl2, where the ligand L is PVI(poly‐N‐vinyl‐2‐methylimidazole) or NEI (N‐ethylimidazole), was prepared. Electrontransfer reactions with ferrous sulfate or FeEDTA2− were examined mainly with respect to the effects of the degree of coordination, ionic strength, composition of reaction solvent, in relation to the conformational changes. In the reduction by FeEDTA2−, an increase in the degree of coordination of Co(III)–PVI brought about an extreme increase in its reactivity, while it was almost unity in the reduction by ferrous sulfate. With an increase in the ionic strength, the reactivity decreased due to the electrostatic shielding in the reduction by FeEDTA2−. It was noticed that the reaction of Co(III)–PVI was much more enthalpically disadvantageous due to the shrinkage of the polymer chain than that of Co(III)–NEI, when neutral salts were added. In an aqueous alcoholic solvent, an increase in the alcohol concentration accelerated the reaction with FeEDTA2−, and especially in the reaction of Co(III)‐PVI, the maximum and minimum points of the reactivity were observed. On increasing the reaction temperature, the maximum and minimum points shifted to lower alcohol concentration. These phenomena are discussed in regard to the conformational changes of Co(III)–PVI.

Members of the series IrX(CO)(PPh3)2 with various anionic ligands and their dioxygen complexes

Acetonitrile is displaced from [Ir(CO)(CH3CN)(PPh3)2]+ by the co-ordinating anions, F–, OH–, NCO–, NCS–, O2CH–, O2CCF3–, SH–, CCPh–,P-toluenesulphinate, and CN– to yield four-co-ordinate analogues of IrCl(CO)-(PPh3)2 except for the cyanide which is five-co-ordinate, IrCN (CO)(PPh3)3. The comparative uptake of dioxygen by these compounds to form dioxygen complexes has been studied. The sulphinate, Ir(P-toluenesulphinate)-(CO)(PPh3)2is O-bound but upon further co-ordination of CO or O2 the sulphinate changes to S-bound although addition of methyl iodide produces an O-bound iridum(III) compound.

Ab initiomolecular orbital calculations of transition metal complexes

The bonding in Ni(CN)4 2- and Ni(C5H5)NO is discussed by means of all-electron ab initio SCF-MO calculations. In the square-planar cyanide the metal-carbon bonds are predominantly of σ character, whilst in Ni(C5H5)NO the Ni-NO bond is of π character and the Ni-C5H5 bond mainly ionic. The mode of co-ordination of the ligands CO, NO, CN- and C5H5 is compared.

Pair Formation and Tetrahedral Coordination of Co2+ in AgCl and AgBr

AbstractThe analysis of the optical absorption spectra (measured at 20 °K) of Co‐doped (&lt; 800 ppm), quenched AgCl and AgBr crystals shows that in addition to octahedrally coordinated Co2+ (incorporated on cation sites) there are also tetrahedrally coordinated Co2+ ions. Tetrahedrally coordinated Co2+ arises from pairs of Co2+ ions on cation sites in which one of both Co2+ jumps on an interstitial site when both the charge compensating cation vacancies are situated in the neighbourhood of the pair. The concentration of pairs is determined by the probability to find a Co2+ ion in the neighbourhood of another one. In Co‐doped crystals additionally doped with other divalent cations the Co2+ ion jumps on an interstitial site also in that pairs in which the second cation is not Co2+. This leads to an enhancement of the concentration of tetrahedral Co2+ centres related to crystals without additional doping. The investigation of this enhancement as a function of the cation concentrations provides the spatial arrangements of the cations in the pair leading to tetrahedral Co2+ centres in the different cases.

Diphenyl sulphoxide complexes of some divalent metal ions

Diphenyl sulphoxide (DPSO) complexes of some divalent metal perchlorates and chlorides are prepared The perchlorates of Mn, Co, Ni, Zn and Cd have the general formula [M(DPSO) 6](CIO 4) 2. The Cu(II) complex is found to have the composition [Cu(DPSO) 4] (CIO 4 2. The chloro complex having the formula ZnCl 2. 2DPSO, CdCl 2.DPSO, HgCl 2. DPSO and PdCl 2. 2 DPSO have also been obtained. Infrared spectra indicate that the DPSO complexes of Mn, Co, Ni, Cu and Zn are oxygen-bonded while those of Cd, Hg and Pd are sulphur-bonded. The magnetic susceptibility and the optical spectral data reveal octahedral coordination for Mn, Co and Ni complexes. From the electronic spectra of Co and NI complexes, the ligand field parameters, Dq and β, are calculated.