Platinum complexes bipyridyl

Fig. 5 Estimates of the energies of the low-lying triplet ligand-centred (ji-ji ), charge-transfer (MLCT) and metal-centred (d-d) excited states of three platinum(II) bipyridyl complexes. Reproduced from data in [10] with permission. (1993) American Chemical Society...

Excitation to the LC states may also result in population of the CT-excited states, especially the LLCT states. These phenomena are frequently encountered in complexes containing both rc-acceptor (eg 1,10-phenantroline or 2,2 -bipyridyl) and 7r-donor ligands (eg aromatic thiols). Then the LC excitation can induce charge transfer between these ligands through central atom (LLCT) that leads to a photoredox reaction. Such reactions were reported in the case of heteroleptic organometallic compound [Rh CylLXCsHs)]3 [37], heteroleptic Re1 complex fac-[Re (L)(CO)3(bpy)]n+ [46] and metal-carbon-bonded platinum complexes [47]. 

The phthalocyanine containing polymer films were electrochemically investigated for their electrochromic reductions and reoxidations [406,411]. Under irradiation the reduction of O2 to water was studied in photoelectrochemical cells [407,409,412]. Especially Zn(II)-phthalocyanine in poly(vinylidene fluoride) shows high cathodic photocurrents. Also the electrochemical carbox dioxide and proton reduction by Co(II)-phthalocyanines in a low concentration monomolecular in a polyvinylpyridine matrix were investigated as part of a photoenergy systems [413,414]. As an active catalyst for proton reduction also a bipyridyl platinum complex in a polymer Nafion membrane was found [415]. In order to construct such a photochemical energy conversion system, the research in this field was extended for the electrocatalytic water oxidation to O2 [416-419]. The Ru-complexes cj5-[Ru(bpy)2Cl2] and especially Ru-red ([(NHsjs Ru >-Ru(NH3)4-0-Ru(NH3)5] ) are active as electrocatalysts. 

Supramolecular systems assembled by peripheral and axial coordination were also thoroughly described. For example, heteroarrays held by axial coordination, particularly of zinc, nickel, ruthenium, tin, silicon, etc. porphyrins and phthalo-cyanines to peripheral pyridyl and 4,4-bipyridyl groups were described. Another interesting class of compounds are porphyrin dimers prepared by coordinative assembly of cw- icso-(4-pyridyl)porphyrins with PdCla forming two [PtCl2(pyP)2] complexes, and more complex tesselated structures by substitution of the platinum complex chloro ligands by 2,3-diamine(azaporphyrins), as depicted in Fig. 12. 

The dimethylplatinum(II) complexes having chelate nitrogen ligands, [PtMe2(N-N)] (N-N = 2,2 -bipyridyl or 1,10-phenanthroline) (46) reacted with alcohols (ROH, R = Me, Et, Pr) to give hygroscopic and basic platinum(IV) complexes. 

Rate and equilibrium constant data, including substituent and isotope effects, for the reaction of [Pt(bpy)2]2+ with hydroxide, are all consistent with, and interpreted in terms of, reversible addition of the hydroxide to the coordinated 2,2 -bipyridyl (397). Equilibrium constants for addition of hydroxide to a series of platinum(II)-diimine cations [Pt(diimine)2]2+, the diimines being 2,2 -bipyridyl, 2,2 -bipyrazine, 3,3 -bipyridazine, and 2,2 -bipyrimidine, suggest that hydroxide adds at the 6 position of the coordinated ligand (398). Support for this covalent hydration mechanism for hydroxide attack at coordinated diimines comes from crystal structure determinations of binuclear mixed valence copper(I)/copper(II) complexes of 2-hydroxylated 1,10-phenanthroline and 2,2 -bipyridyl (399). 

Abruna, HD, Meyer, T3, Murray, RW, Chemical and Electrochemical Properties of 2,2 —bipyridyl Complexes of Ruthenium Covalently Bound to Platinum Oxide Electrodes. 

Electropolyraerization is useful and has been successfully applied to 4-vinylpyridine complexes and to 4-methyl-4 -vinyl-2,2 -bipyridyl.52 Vinylferrocene (vide infra) has been polymerized on to platinum, glassy carbon and titanium dioxide electrodes by introduction to a radiofrequency argon plasma discharge. Electropolymerization and plasma polymerization are likely to be of value to produce copolymers on electrode surfaces. 

A number of polymer films related to PVP are known. An obvious variation is polybipyridyl. Thus the complex cation tris(4-vinyl-4 -methyl-2,2 -bipyridyl)ruthenium(II) may be electroreduced in acetonitrile solution to give a polymer film on a platinum electrode. Pulsing of the electrode at 0.5 Hz between +1.5 and —1.5 V (vj. SCE) gives an orange emission (eel) arising from annihilation between RuII and Ru1 centres.59... 

Metal complexes like lanthanide chelates (mainly europium or terbium), ruthenium phenanthrolines or bipyridyls, and platinum porphyrins can be used as fluorescent labels for biomolecules. Their long decay times are perfectly suited for a detection by time-resolved imaging, and the labeled target molecules can be used for the determination of intracellular recognition processes or for the screening of DNA and protein arrays. Ratiometric lifetime-based imaging methods in combination with sophisticated data acquisition and evaluation tools can substantially contribute to the development... 

Spontaneously adsorbed monolayers of the dimeric complex (Figure 5.11) [(pOp) Os(bpy)2 (4-tet) Os(bpy)2 Cl]3+, where pOp is 4,4 -bipyridyl, bpy is 2,2/-bipyridyl and 4-tet is 3,6-bis(4-pyridyl)-l,2,4,5-tetrazine, have been assembled on platinum microelectrodes in an attempt to address these issues [33]. Significantly, as illustrated in Figure 5.11, the voltammetric response associated with the Osn/m reaction is unusually ideal for both metal centers. Studies using mononuclear model compounds reveal that the redox responses centered at approximately 0.620 and 0.300 V correspond to the inner [(pOp) Os(bpy)2 (4-tet)]2+ and outer [(4-tet) Os(bpy)2 Cl]+ moieties, respectively. The observation of two well-defined voltammetric waves indicates that electron transfer can occur across the [(pOp) Os(bpy)2 (4-tet)]2+ bridge to the outer [Os(bpy)2 Cl]+ moiety, i.e. charge trapping does not occur. 

Sulfato(bipyridyl)platinum(II) is yellow, unlike (pyridine)2PtSO4 which is reported to be black (286). It is not possible to introduce A,A,A, A -tetramethylethylenediamine directly into a platinum(II) complex. An indirect route involving the in situ synthesis of the ligand is available bipyridyl is present in the molecule (725-727). Other mixed... 

The crystal structure of bis(NN-di-isobutyldithiocarbamato)nickel(ii). [Ni(S2-CNBu 2)2], shows that nickel is approximately square planar and co-ordinated by two symmetric bidentate ligands (Ni—S = 2.20 A) the ligand symmetry approximates to 2- The reduction mechanism of a series of nickel(ii) dithiocarbamates has been investigated in DMSO at the mercury electrode it is claimed to involve a dissociation to a nickel species which is more easily reduced than the nickel(ii) dithiocarbamate. An e.p.r. study of the reversible electrochemical reduction of nickel(ii) diethyldithio-carbamates in the presence of 2,2 -bipyridyl show that a bipy radical anion is formed initially. Ligand alkylation occurs when ao -dibromo-o-xylene is added to bis-(NiV-diethyldithiocarbamato)nickel(ii). The electron-transfer properties of 16 nickel(ii) dithiocarbamate complexes have been studied in acetone at a platinum electrode. Their oxidation is difficult and irreversible the overall process is ... 

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