Mononuclear complexes, absorption

Further examples of emissive cyclometallated gold(III) complexes are [Au(L)Cl] (L = tridentate carbanion of 4 -(4-methoxyphenyl)-6 -phenyl-2,2 -bipyridine) [53], as well as mono- and binuclear bis-cyclometallated gold(III) complexes, namely [Au (C N C )L ]" (C N C = tridentate dicarbanion of 2,6-diphenylpyridine L = depro-tonated 2-mercaptopyridine (2-pyS ), n = 0 L = PPh3 or 1-methylimidazole, n = 1) and [Au2(C N C )2(P P)](C104)2 (P P = dppm, dppe) respectively [54]. The crystal structures of the binuclear derivatives show intramolecular interplanar separations of 3.4 A between the [Au(C N C)] moieties, implying the presence of weak n-n interactions. The mononuclear complexes show absorption with vibronic structure at 380-405 nm (e > 10 cm ), attributed to metal-perturbed intraligand transition. 

In recent years a variety of spectroscopic and other techniques have been employed to investigate and monitor hydrosilylation reactions. The techniques include multinuclear NMR, transmission electron microscopy, extended X-ray absorption fine structure (EXAFS), etc. Results from these experiments indicate that depending on the precatalyst, colloids and/or mononuclear complexes take part as catalytic intermediates. 

Reactions of the dichloro-bridged rhodium(ni) and iridium(III) dimers with diimine ligands resulted iu the formation of the luminescent mononuclear complexes [M(N C)2(N N)]+ (M = Ir, Rh = ppy, bzq N N = bpy, phen). The electronic absorption and emission spectra of these complexes are shown in Figure 8. The rhodium(III) complexes displayed very long-lived emission in... 

All these polymers, A (39), B (40), C (41,42), D (43), showed distinctive absorption and emission due to the MLCT transition of the rhenium(I) diimine complexes. Among these rhenium-containing polymers, polymer C has the most notable emission properties, with an emission quantum yield and a lifetime ( e = 0.132, Te = 2019ns in a deaerated CH2CI2 solution) comparable to those of the corresponding mononuclear complex (0e = O.181, Te = 2200 ns) (43). 

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]. 

Mononuclear complexes, [Ru(NH3)5(LH)]2+, where LH = Me2dicydl I, dicydl I and Cl2dicydH, have been prepared and characterized by electronic absorption spectroscopy and cyclic voltammetry.40 When deprotonated, the complexes oxidize to the Ru17 oxidation state and this allowed a spectroscopic analysis the RuIV-cyanamide chromophore. Only [Ru(NH3)5(Me2dicyd)]2+ could be isolated with sufficient purity to permit NMR studies, which suggested the metal ion was diamagnetic RuIv. 

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