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Compounds of Co, Rh, and Ir

Cluster Compounds of Co, Rh, and Ir. In addition to the above-mentioned neutral cluster compounds, there is a large number of anionic carbonyl clusters and metal carbonyl carbides. Carbonyl carbides are formed when the interstice inside the metal cluster is sufficiently large to accommodate the carbon atom. Carbonyl carbides possessing at least four metal atoms are known. The most thoroughly investigated carbides are those of rhodium because they are very stable and resist air oxidation. Carbonyl clusters of group 9 elements containing even more than 20 metal atoms are now known [M6(CO)i5] - (M = Co, Rh, Ir), lM CO)uT. [M6(CO)i5C] -(M = Co,Rh), [Co8(CO),sC] -, [Rh,(CO)i,] -, [Rh8(CO)i,C], [Ir8(CO)22] -, [Pg.89]

The cobalt carbonyls are prepared by the disproportionation reaction of [Co2(CO)g] in the presence of Lewis bases or by the reduction of cluster cobalt carbonyls with the alkali metals. The iridium compounds are obtained during reduction of [Ir4(CO)i2] with sodium in ether solution. The rhodium carbonyls are usually synthesized by reduction of [Rh2Cl2(CO)4] or [RhClg] with carbon monoxide in basic medium or by nucleophilic attack of bases on the carbonyl group of carbonyl clusters (see preparation of [M4(CO)i2] and [M6(CO)i6]). [Pg.89]

The reaction between [Rh4(CO)i2] and [Co2(CO)g] affords [CoRh(CO)7] from which other different heterometallic carbonyls may be prepared. [CoRh(CO)7] is also obtained by the reaction of Na[Co(CO)4] with Rh2Cl2(CO)4. [Pg.89]

Cobalt exhibits a characteristic tendency to form clusters of the formula RCCo3(CO)9, which have trigonal-pyramidal structures. The cobalt atoms occupy the three positions at the base of the pyramid, and the carbon group lies at its top vertex. These cobalt-carbon clusters are prepared by reactions of RCX3 with Co2(CO)8 or NaCo(CO)4 in the presence of Lewis bases  [Pg.89]

Cobalt carbonyl halides, in contrast to rhodium and iridium carbonyl halides, are very unstable, and only few have been prepared and investigated [CoX(CO)4] is [Pg.89]


The process has been established for a series of pentaamminemetal(III) compounds (of Co, Rh, or Ir) with bridging imidazolate (21). The (jl-pyrazine mixed decaammine diruthenium(II)/(III) dimer has also been prepared (180), in addition to a diruthenium compound with a 1,4-dicyanobicyclo[2.2.2]octane bridging ligand and a mixed ruthe-nium(III)/cobalt(III) compound with the same bridging ligand (8). Osmium(III) dimers have also been reported (192). [Pg.186]

The magnetic properties were studied in the temperature range of 2-1100 K (Hiebl et al. 1987). The compounds in which the transition-metal component is from the same column of the Periodic Table display a similar behaviour. A temperature-independent exchange-enhanced susceptibility was observed for T = Fe, Ru, and Os. In the case of Co, Rh, and Ir, the molar susceptibility is somewhat lower, but a broad maximum in the temperature dependence of x around 600 K, observed in all three compounds, is reminiscent of spin fluctuators. Antiferromagnetic ordering, indicated for T = Ni, Pd, and Pt by sharp cusps in the x versus T curves, was confirmed by the observation of linear magnetization curves at low temperatures. MCW behaviour is found above the antiferromagnetic transition. [Pg.461]

The title compounds are part of a series of four-coordinate complexes of the (MNO) group (M = Co, Rh, and Ir). Until recently, these complexes... [Pg.32]

Examples of S-bonded thiophene complexes are known for a wide variety of metals, viz. Mn, Re, Cr, Mo, W, Fe, Ru, Co, Rh and Ir, as shown in Table 2.1 the procedures used to synthesize such compounds are usually straightforward, involving addition of the thiophene to an unsaturated metal precursor or displacement of a labile ligand. This type of binding has generally turned out to be weak, resulting in rather unstable compounds the stability increases along the trend thiophenes < benzothiophenes < dibenzothiophenes. [Pg.38]

A study of the irreversible reduction of several Co ", Rh" and Ir" complexes revealed no correlation between the polarographic Ey and several spectroscopic parameters but, interestingly, it was found that a linear correlation existed for several of the Co " complexes between the y, and In where was the rate constant for homogeneous electron transfer, when [Ru(NH3)6] was used as reductant. The theoretical foundation for this relationship is that Ey is linearly related to In (the heterogeneous rate constant for electrochemical reduction) and, from the theories of Marcus and Hush, the ratio of k for a series of compounds is the same as the ratio of the rate constants k for a constant reductant provided both pathways are outer sphere. The mechanistic implication of the relationship is not clear it may simply mean that both pathways proceed via an outer sphere mechanism as no correlation was found between y, and the values of kgx for reduction by which can undergo homogeneous electron transfer by an inner sphere mechanism. [Pg.500]

The existence of [Rh2( 0)8] under normal conditions has not been confirmed, although its synthesis from dispersed metal under pressure (28 MPa) and at 473 K had been reported. However, it was shown that [Rh2( 0)8] exists in solutions only at high pressures and at low temperatures.[Rh2(CO)8] and [Ir2( 0)8] were also prepared by reactions of atomic Rh and Ir with carbon monoxide in 0 matrices. During condensation at 10 K, [Rh( 0)4] or [Ir( 0)4] are formed first, and subsequently at 50 K react to give [M2( 0)8] compounds. At 223 K, the dinuclear carbonyls are transformed into [M4( 0)i2]. This means that with respect to tetranuclear compounds, the dinuclear complexes are thermodynamically unstable. [Rh2( 0)8] in solutions as well as in the matrix and [Ir2( 0)8] in the matrix have bridging carbonyl groups (Table 2.26). [Pg.85]

Co, Rh and Ir Stable paramagnetic butadiene sandwich compounds [Co(ti -C4H4Bu 2)2] have been prepared by co-condensation of cobalt atoms with 1,4-tertbutylbuta-1,3-diene. Reduction of the product with potassium metal in the presence of a crown ether afforded the salt [K(18-crown-6)(THF)2]" tCo(Ti -C4H4Bu 2)2]. the crystal struture of which was reported. The anion represents the first structurally characterised homoleptic butadiene sandwich compound. [Pg.347]

Table 5.46. The highest melting points (°C) observed in the alloys of the central elements of the iron and platinum metals families (that is of Co, Rh, Ir) with compound-forming elements of the 4th and 6th rows of the Periodic Table. [Pg.437]

The hydrides HM(PF3)4, M = Co, Rh, Ir, possess a structure simUar to that of HCo(CO)4. In C3v skeletal symmetry the filled metal orbitals are of symmetry e(2), the Rh-H a bond transforms as a, and the metal-phosphorus a bonds span the irreducible representations a,(2) + e. Three low-energy peaks (Table XXIX) (169, 227) have been detected in the UPS of HCo(PF3)4, and overlapping of ionization occurs with the Rh and Ir compounds (Fig. 28). While the assignments cannot be regarded as definitive at the present time, the first two peaks in the UPS of HCo(PF3)4 probably correspond to the two 2E ionic states of predominant metal character. [Pg.110]

In previous sections some organometallic compounds of Rh and Ir in high oxidation states, III-V as well as some CO compounds have been described. There is a vast chemistry for both elements involving cyclopentadienyl or substituted cyclopenta-... [Pg.1059]

As noted, various simple carbonyls have molecular structures in solution diiferent from those in the solid state. The structure of the molecules in the vapor state may be different again. It has been found that the infrared spectrum in the CO-stretching region of [C5H5Ni(CO)]2 in solution contains two bands, but there is only one band in the gas-phase spectrum (142, 235). Furthermore, mass spectroscopic studies have shown various anomalies between structures of certain compounds in the gas phase and in solution. Infrared spectroscopic studies are now in progress to ascertain the structure of the compounds [C6H5M(CO)3]2 (M = Cr, Mo, or W), [C5HbM (CO)2]2 (M = Fe, Ru, or Os), M"3(CO)i2 (M" = Fe, Ru, Os), and M" 4(CO)i2 (M " = Co, Rh, or Ir) in the vapor state (159). [Pg.69]


See other pages where Compounds of Co, Rh, and Ir is mentioned: [Pg.189]    [Pg.205]    [Pg.835]    [Pg.851]    [Pg.189]    [Pg.205]    [Pg.835]    [Pg.851]    [Pg.602]    [Pg.95]    [Pg.1137]    [Pg.176]    [Pg.1248]    [Pg.303]    [Pg.171]    [Pg.5]    [Pg.110]    [Pg.104]    [Pg.1687]    [Pg.99]    [Pg.1686]    [Pg.765]    [Pg.279]    [Pg.291]    [Pg.30]    [Pg.60]    [Pg.286]    [Pg.291]    [Pg.295]    [Pg.1134]    [Pg.1039]    [Pg.18]    [Pg.241]    [Pg.440]    [Pg.719]    [Pg.372]    [Pg.380]    [Pg.6]    [Pg.8]    [Pg.117]    [Pg.1063]    [Pg.219]   


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