Rhodium/1 complexes absorption spectra

Immediately after addition of 1-octene, the strong absorption band indicative of aldehyde formation (1734 cm ) appeared in the IR spectrum, proving that the hy-droformylation reaction had started. The amount of 18b dropped considerably upon addition of 1-octene, but it did not disappear completely during the hydrofor-mylation reaction. Seven new absorptions appeared in the terminal carbonyl region indicating that complex 18b was converted (in part) to several new carbonyl-containing rhodium complexes. 

Rhodium complex was loaded onto the quatemised polymer support by the reaction with [Rh(CO)2I]2 in hexane (Eq 2). The resulting polymer beads or films showed the characteristic yellow colour of [Rh(CO)2I2] . An infrared spectrum of the powdered beads (KBr disk) showed two weak v(CO) absorptions of similar intensity at 2056 and 1984 cm 1, consistent with the presence of the cis-dicarbonyl complex, [Rh(CO)2I2]" (2059, 1988 cm 1 in CH2C12). Spectra of a much higher quality and intensity were obtained from polymer films loaded with rhodium complex. These observations of polymer supported [Rh(CO),I,r match those reported in the original study of Drago et al. 

Crystalline-state photochromism usually proceeds with considerably lower interconversion ratios of less than 15% because the light penetration into the bulk crystal is prohibited by the absorption of the photo-generated isomer (inner-filter effects) [3,4]. The fully reversible crystalline-state photochromism of 1 can be partly attributed to its photochromic property. The rhodium dithionite complex 1 belongs to a unique class of photochromic compounds, which exhibits a unimolecular type T inverse photochromism [13]. The type T inverse photochromism means that the back reaction occurs thermally and the A.max of the absorption spectrum of 1 is longer than that of 2. If the back reaction occurs photochemically and the XmaK of the initial absorption spectrum is shorter than that of the photo-generated isomer, it is called type P positive photochromism and is known as a common photochromic system. 

The dpp-bridged Ru(II)-Rh(III) complex displays typical absorptions for ruthenium and rhodium polyazine complexes in the UV and visible regions. The UV region in the electronic absorption spectrum of [(bpy)2Ru(dpp)Rh(bpy)2] in acetonitrile reveals two bands at = 312... 

The absorption spectra of tris-polypyridyl Rhodium(III) complexes are characterised by several intense Ligand Centered (LC) absorption bands in the UV. Neither MC absorption bands, nor CT bands are observed in the visible region of the spectrum in contrast to their Ruthenium analogues. This makes tris(polypyridyl)Rh(III) complexes formed with bpy and phen practically colorless [1]. 

In the example discussed above, the heterotriad consists of a photosensitizer and an electron donor. In the following example, a ruthenium polypyridyl sensitizer is combined with an electron acceptor, in this case a rhodium(lll) polypyridyl center [15]. The structure of this dyad is shown in Figure 6.21 above. The absorption characteristics of the dyad are such that only the ruthenium moiety absorbs in the visible part of the spectrum. Irradiation of a solution containing this ruthenium complex with visible light results in selective excitation of the Ru(ll) center and in an emission with a A.max of 620 nm. This emission occurs from the ruthenium-polypyridyl-based triplet MLCT level, the lifetime of which is about 30 ns. This lifetime is very short when compared with the value of 700 ns obtained for the model compound [Ru(dcbpy)2dmbpy)], which does not contain a rhodium center. Detailed solution studies have shown that this rather short lifetime can be explained by fast oxidative quenching by the Rh center as shown in the following equation ... 

Under syn gas pressure the rhodium acac precursors were converted to the catalytically active hydride complexes HRh(CO)2(L-L). The complexes are generally assmned to have a trigonal bipyramidal structure and two isomeric structures of these complexes are possible, containing the diphosphite coordinated in a bisequatorial (ee) or an equatorial-apical (ea) fashion. The structure of the complexes can be elucidated by (high pressure) IR and NMR data (Table 3). In the carbonyl region of the infrared spectrum the vibrations of the ee and ea complex can be easily distinguished. The ee complexes typically show absorptions around 20 15 and 2075 cm [24, 26,... 

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