Metal carbonyls absorption spectra

The intermediate cyclooctene complex appears to be more reactive with respect to CS coordination and more sensitive to oxidation when the arene ring bears electron-withdrawing groups (e.g., C02CH3). Dicarbonyl(methyl rj6-benzoate)-thiocarbonyl)chromium is air stable in the solid state and reasonably stable in solution.9 The infrared spectrum exhibits metal carbonyl absorptions at 1980 and 1935 cm"1 and a metal thiocarbonyl stretch at 1215 cm"1 (Nujol) (these occur at 1978, 1932, and 1912 cm"1 in CH2C12 solution).10 Irradiation of the compound in the presence of phosphite or phosphine leads to slow substitution of CO by these ligands, whereas the CS ligand remains inert to substitution. The crystal structure has been published."... 

The bands due to Fe(CO)4 are shown in Fig. 8. This spectrum (68) was particularly important because it showed that in the gas phase Fe(CO)4 had at least two vq—o vibrations. Although metal carbonyls have broad vC—o absorptions in the gas phase, much more overlapped than in solution or in a matrix, the presence of the two Vc—o bands of Fe(CO)4 was clear. These two bands show that in the gas phase Fe(CO)4 has a distorted non-tetrahedral structure. The frequencies of these bands were close to those of Fe(CO)4 isolated in a Ne matrix at 4 K (86). Previous matrix, isolation experiments (15) (see Section I,A) has shown that Fe(CO)4 in the matrix had a distorted C2v structure (Scheme 1) and a paramagnetic ground state. This conclusion has since been supported by both approximate (17,18) and ab initio (19) molecular orbital calculations for Fe(CO)4 with a 3B2 ground state. The observation of a distorted structure for Fe(CO)4 in the gas phase proved that the distortion of matrix-isolated Fe(CO)4 was not an artifact introduced by the solid state. 

A kinetic trace for a particular metal carbonyl intermediate is recorded at a specific wavelength obtained from the time-resolved infrared absorption spectrum. Suitable data analysis allows determination of the kinetics of the decay of the intermediate. 

The compound [PPN][Mn2(/i-PPh2)(CO)8] is an orange, air-stable solid. It is soluble in tetrahydrofuran, acetone, and chlorinated solvents, moderately soluble in alcohols and toluene and insoluble in water and hydrocarbon solvents. Solutions of [PPN][Mn2(ju-PPh2)(CO)8] are surprisingly stable as compared to most other transition metal carbonyl anions, decomposing only slowly (days) on exposure to air and/or moisture. The carbonyl IR spectrum of the anion in dichloromethane shows absorptions at 2037 (m), 1947 (s), 1941 (vs), 1914(w), 1888(m), and 1872(m).3... 

The increase in A(J caused by tt bonding is substantial enough in many cases that the absorption maximum for the h -to-ejj electronic transition is blue-shifted out of the visible region into the ultraviolet portion of the electromagnetic spectrum, with the result that the complexes are colorless. This is the case for the metal carbonyls, for example. 

As an example, both monofunctional and multifunctional polymeric mercapto-esters were deposited onto optically smooth silicon wafers coated with vapor-deposited copper. The copper had been oxidized to Cu20, as verified by XPS. Infrared reflectance (RAIRS) at 81° (4 cm-1 resolution, 2000 scans) using an MCT detector yielded information on both the nature and the durability of the mercaptoester bond to the metal oxide film. A 16 cm l shift (1740— 1724 cm-1) was observed in the carbonyl absorption of stearyl thioglycolate (STG) deposited onto the Cu20 mirror. The absorption spectrum of the carbonyl region is illustrated in Fig. 11, both for the pure STG and the reacted monolayer. 

Finally, 1-electron oxidation of [Fe2Rc(CO)i23 with tropilium bromide has been reported to give a neutral mixed-metal cluster formulated as [Fe2Re(CO)i2]2 on the basis of elemental analyses (67) however, its IR spectrum, which shows carbonyl absorptions quite similar to those of the starting material, is inconsistent with such a formulation. 

Formula II shows one trans-double bond which is shared with the nickel atom. Furthermore, there are six carbon atoms which are in the state of an -hybridization. Each C atom shares one r-electron with the nickel. (The complex shows the correct molecular weight for NiCi2Hig, and there is no absorption in the infrared spectrum characteristic of double bonds.) This formulation has some relationship to structures which have been recently proposed by different authors (2, 4) for various allylic groups bonded to transition metal carbonyls. 

Recrystallization from pentane gave attractive yellow crystals. The structure of 2 could be determined by X-ray diffraction analysis (Figure 2). The NMR spectroscopic results were consistent with the assigned structure (Table 1). The IR spectrum shows three v(CO absorptions at 1965, 1991 and 2044 cm. This behavior is typical for metal carbonylates of the type c/s-L2M(CO)3 Compound 2 is more stable than the previosly described (ri -C5H5)M(CO)3SiMe2SiMe2Br (M=W, Mo) [5], Complex 2 decomposes thermally below 150°C and is stable against light. Decomposition under the influence of donor solvents was not observed. 

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