Mononuclear complexes, absorption spectra

The UV-vis spectra of the trinuclear aza- and nitro-capped aminoethanethiol cobalt sarcophaginates are very similar to those for the initial [Co(Co(aet)3)2] cation and intermediate hexaimine complex. The absorption band at 18 180 cm- is due to the ig— d-d transition for a cobalt(III) ion in octahedral symmetry, and another one at 23 260 cm- was observed. These broad asymmetric bands have more than one contributing component, consistent with a deviation from octahedral symmetry and with an overlap of both terminal C0N3S3 and central CoSe chromophore transitions. The UV bands for these complexes are much more intense than the visible ones and were attributed to CT from ligand (sulphur atoms) to terminal and central cobalt(III) ions. The band at 28 570 cm- was assigned to the CT transition from the bridged sulphur to cobalt ion, because this one is not observed in the spectrum of the mononuclear complex [129]. 

The magnetic moment arising from the ground A term is expected to be close to the spin-only value of 3.87 BM and independent of temperature. In practice, providing the compounds are mononuclear, these expectations are realized remarkably well apart from the fact that, as was noted for octahedral complexes of vanadium(lll), the third high-energy band in the spectrum is usually wholly or panially obscured by more intense chaige-transfer absorption. 

Infrared spectra in the range 1400 - 850 K have been recorded for several metal sulphates in aqueous solution. For this purpose 8,8 /i thick cells with IRTRAN - 2 windows have been used. In the frequency region mentioned the free sulphate ion absorbs radiation at 1104 K corresponding to the asymmetric S-0 vibration From solid state investigations (1) it is known that in the spectrum of sulphato complexes this absorption peak is split into two or three new peaks depending upon whether the symmetry of the sulphate ion is decreased to C3Y or C2v This corresponds to a mononuclear, unidentate complex and a polynuclear or possibly a mononuclear bidentate complex, respectively. Furthermore, the symmetric S-0 vibration (i ), which is infrared inactive for the free ion, becomes apparent in the spectra of sulphato complexes. 

The situation is different for the deposit trinuclear Ru hexaacetate complex without M-M bonds. The IR spectrum of this complex contains no characteristic absorption bands of carboxyl groups. In the range of the carrier s stretching vibrations, we observe the same changes as described above for immobilized binuclear Ru tetraacetate. Thus, in contrast to binuclear complexes with the M-M bond, we may suppose that heterogenization of the trinuclear acetate complex without Ru-Ru bonds is accompanied by decomposition the initial complex turns into a mononuclear one, and the acetate groups are substituted by the carrier s amino groups. 

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