Cobalt complexes infrared spectra

The cw-azidobis(ethylenediaminc)sulfitocobalt(III) exhibits an absorption maximum at 502 nm. The infrared spectrum shows expected bands for the sulfito and azido groups. Polarographic analysis indicates a cobalt/sulfite ratio of 1. The assignment of the cis configuration is tentative, based on the generally complex infrared spectrum.s... 

This complex is analogous in all ways to the cobalt complex (XXIV), and the proposed structure is supported by its infrared spectrum which shows bands due to the ir-cyclopentadienyl-metal grouping, a methylene group, and conjugated double bonds co-ordinated to the metal atom (at 1451 cm-1). 

Under the same conditions, cobalt acetylacetonate afforded a mixture of four products the mono-, di-, and triacetylated chelates (XVII, XVIII, and XIX), along with the starting material. In contrast to the chromium chelates, the mixture of cobalt complexes was cleanly separated by chromatography. The identity of each of these products was established by an NMR spectrum. The presence of uncoordinated carbonyl groups was revealed by infrared absorption at 1675 cm.-1... 

Hydridobis[ s-vinylenebis(diphenylphosphine)] cobalt(l) is a red crystalline solid that is unstable in air both in the solid state and in solution. The complex is soluble in tetrahydrofuran (9.2 X 10-3 mole/L, at 20°), toluene (10.2 X 10 3 mole/L), chloroform (6.3 X 10-3 mole/L), dichloromethane (1.6 X 10-3 mole/ L), and benzene (8.4 X 10-3 mole/L). It is insoluble in ethanol, diethyl ether, acetone, and pentane. The infrared spectrum in Nujol mull shows a band at 1885 (m) cm-1, attributable to the Co-H stretching vibration. 

The cobalt(III) complex [Co(2,3-Me2[14]-l,3-diene-l,4,8,l l-N4)Br2] Br is six-coordinate and diamagnetic. Analysis of the visible spectrum (absorptions occur near 15.8 and 26.2 kK) leads to a value for Dq of 2630 cm" . The NMR spectrum in dimethyl sulfoxide shows a methyl singlet at 3.32 ppm. The infrared spectrum is very similar to that given for the nickel(II) complexes. A wide variety of cobalt(lll) complexes has been prepared by metathetical reactions on the dibromo and dichloro complexes. The imine functions can be hydrogenated, producing cobalt(III) complexes of 2,3-Me2 [14] ane-1,4,8,11-N4 or 2,3-Me2-[14]-l-ene-l,4,8,ll-N4. ... 

Chlorodiphenylacetonitrile formed tetraphenylsuccinonitrile as well as a diflFerent type of complex. The infrared spectrum of the latter contained no nitrile absorption band (2210 cm." ) but exhibited a cyanide stretch at 2130 cm. S characteristic of inorganic pentacyanocobaltate(III) complexes 14,22), and a carbonyl band at 1575 cm. Its PMR spectrum indicated the presence of the (C6H5).)CH group. Diphenylacetamide precipitated on heating an aqueous solution of the complex. Apparently the resonance-stabilized radical initially formed in the reaction of this a-halonitrile with pentacyanocobaltate(II) may either dimerize or combine with pentacyanocobaltate(II) to form an N-keteniminocobalt complex. The latter is unstable in water, being converted to an N-amido-cobalt complex, which may be further hydrolyzed to the free amide (Reaction 23, paths d and e). Presumably the radical cannot add penta-... 

The complex is a yellow, crystalline solid soluble in organic solvents, including hexane. The solid is unstable and decomposes slowly at room temperature and rapidly in solution. It can be stored indefinitely at - 20° under nitrogen. Melting point 36°. TTie infrared spectrum shows v(CO) at 2125(s), 2060(vs), and 2040(vs) (hexane). The complex serves as a useful reagent for the preparation of carbonyl phosphine cobalt(I) complexes, as one or two CO groups can be readily displaced at room temperature by different ligands. 

A yellow, air-stable complex [7r-CgHioCo(CO)2]2 is obtained from the reaction of the triene mixture with cobalt carbonyl (60). The infrared spectrum was interpreted to show the presence of the 1,3,6-isomer in the complex. 

Figure 12 Infrared spectrum of the hexammine cobalt complex [C0(NH3)6]Cl2.

Other examples are shown on pp. 107,108 and 121. An interesting feature of unsubstituted-cyclopentadiene complexes, e.g. 3.17, is that their infrared spectra show a broad, intense C-H stretch at the unusually low frequency of 27C0 cm i. For the cobalt complex, 3.17, the assignment is confirmed by the spectrum of the deuterated analogue the anomalous C-H stretch is absent and a corresponding C-D band appears [15]. 

PMR spectra cannot indicate the presence of amide hydrogen because of rapid exchange of the proton with deuterium oxide solvent. We have found that nitrogen-cobalt bonded complexes with infrared absorptions at 1575 cm. may be formed when N-bromo primary amides react with pentacyanocobaltate(II). Comparison with the spectrum of a complex formed from an N-bromo secondary amide, in which no acidic hydrogen would be present, should help resolve this problem. 

Triamminetrinitrocobalt(III)> tCo(N02)j(NH3)3], was first prepar in 1866 by Erdmann, later by Werner and Jorgensen, who prepared the complex by the air-oxidation of ammoniacal cobalt(II) salt solutions containing sodiiun nitrite and a large amount of ammonium chloride. In 1938, Duval examined the products obtained from several different procedures by absorption and infrared spectroscopy, refractive index of aqueous solutions, conductivity, and X-ray powder diffraction. He recognized two products in the Werner s preparation and the Jorgensen s preparation. In that year, Sueda reported an isomeric complex from the reaction of the [Co(N03)j(NH3)3] complex with sodium nitrite in a cold aqueous solution, which was assumed to be cis-cis isomer on the basis of the absorption spectrum. 

Azide ion, both free and bound to metal-ion complexes, also absorbs strongly in this range. A comparison between the infrared spectra of azide bound to diethylene-triamine Zn(II) and Co(II) complexes or to the cobalt-enzyme and the corresponding spectrum for the native enzyme showed that the azide ion is coordinate to the Zn(II) atom of the native enzyme. Examination of the difference spectra in the presence of both azide and CO2 showed that the bound azide sterically interferes with the binding of CO2 in the hydrophobic cavity adjacent to the Zn(ll). 

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