1,4-Pyrazine complexes

Bortoluzzi, M., De Faveri, E., Daniele, S. and Pitteri, B. (2006) Synthesis of a new tetrakis(2-pyridinyl)pyrazine complex of gold(III) and its computational. 

Pyrazine, bridged supramolecular complexes, 46 206-213, 240-243 p-Pyrazine complexes, osmium, 37 307 Pyrazolates, ligand with rhodium complex, 44 278 Pyrazoles... 

Scheme 13. Preparation of p.-pyrazine complexes. Reprinted with permission from Inorganic Chemistry, Ref. 80. Copyright 1988, American Chemical Society.

Silver(I) complexes of pyrazine were first reported in 1895." Since then there have been numerous reports on the preparation and properties of pyrazine complexes of silver(I).85 Thermodynamic data for some of these complexes are given in Table 18. 

Table 18 Thermodynamic Data for the Formation of some Silver(I) Pyrazine Complexes (0.1 M KN03, 25 Q100...

The structure of the pyrazine complex was suggested to contain polymeric square planar cations with bridging pyrazines and the magnetic properties (300-80K) were interpreted in terms of an antiferromagnetic exchange interaction. A Curie-Weiss constant of 84 K was calculated. At room temperature, the magnetic moment was found to be 1.61 BM. 

Fig. 20. Absorption spectra of PdLCl and the interfacial aggregates of ternary PdL-Dz complexes measured by the CLM method. [PdLCl]in t = 5.6 x 10 5M, [pyridazine] = 2.0 x 10 4M, [pyrimidine] = 8.0 x 10 3M, [pyrazine] = 8.0 x 10 5M, [C104 ] = 0.1 M, [Cl ] = 0M, pH 2.0. The left structure shows a probable unit of the membrane-like aggregate formed in pyrazine complexes.

A number of these have been isolated, including species with mixed oxidation states and heteronu-clear species with ruthenium. In their general chemistry these remarkable complexes show clear analogies with bridging pyrazine complexes (p. 536) ... 

In spite of the fact that pyrazine has the lowest stability among Dz isomers in the formation of PdL complex at the toluene/water interface, the stability for the formation of the interfacial aggregate was the highest for the pyrazine complex. This result indicates that the formation of the interfacial aggregate of PdL-Dz isomers was governed by the geometric structure of Dz, not by its basicity. 

Such large enhancement factors for localized and isolated hot spots from few atom Ag clusters arising from only the chemical enhancement under certain conditions are supported by calculations. Zhao working with Jensen and Schatz used time-dependent density functional theory (TDDFT) to investigate the adsorption and Raman response of pyrazine molecules [21]. Figure 10.6 shows the Raman response of (a) isolated pyrazine compared to that of pyrazine complexed to the vertex of a (b) one and (c) two 20 Ag atom clusters with enhancements of 10 and 10 predicted, respectively. Small clusters of Ag atoms have little or no plasmon response, suggesting that the chemical enhancement can be quite significant and certainly may allow for enhancement hot spots. 

Substitution reactions of cis-Ru(bipy)2X2 (X = F, Cl, or Br) with methyl-substituted pyridines have been studied in various non-aqueous solvents and the results indicate a dissociative mechanism via [Ru(bipy)2X] as the intermediate. The outer-sphere electron transfer between [Ru(NH3)g] and [(NH3)5Co02Co(NH3)s] has been monitored. Flash photolysis at the intense metal-to-ligand CT band (508 nm) of the pyrazine complex [(NH3)5Ru"(pyr)Cu"] causes an intramolecular electron transfer to [(NH3)5Ru (pyr)Cu ]. This allowed the unimolecular reverse electron-transfer process to be monitored. 

Group V Donors. The force constant of the Rh—N bond in [Rh(NH3)g] has been determined as 210 Nm" and is thus higher than for the ruthenium analogue. Electronic spectra of rhodium pyrazine complexes, e.g. [Rh(NH3)5(pyr)], have been recorded N-protonation causes a red shift in the n- n pyrazine transition. The use of n.m.r. to differentiate cis- and trans-isomers of [Rh(en)2X2]Y (X = Cl or Br) has been discussed. At room temperature, spectra are, to a greater or less extent, exchange-simplified and thus unreliable. Equilibrium (7) and isomerization of both species was monitored. A dissociative mechanism was proposed for the isomerizations. 

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