Pyrazine and Pyrazole Complexes

An example of a bridged 1,4-pyrazine system is the dimeric Ru(n)/Cu(II) complex (NH3)5Ru°( -l,4-pyrazine)Cu°. Upon flash photolysis, electron transfer occurs from Ru(II) to Cu(II), and the product is the thermodynamically unstable Ru(III)/Cu(I) complex  

No reaction is observed when nonreducible metal ions such as or Rh are used in place of Cu(II). Both the excited state bleaching and the back reaction with these complexes are very fast. These systems can be extended to ones using 

2-Pyrazole has been used as a bridging ligand for metal centers. Complexes prepared with these ligands have the metal centers held in close proximity. An example of such a complex is [IrOM-pz)(l,5-COD)]2 (pz = 1,2-pyrazole) which has an Ir(I)-Ir(I) separation of 3.216(1) A. The absorption spectrum of this complex in acetonitrile solvent shows bands at 498 nm (e = 9100 cm ) and 585 nm (a 

This triplet state is a powerful reductant, and the excited state redox reactions are summarized in Fig. 4.23. 

Electrogenerated chemiluminescence is observed in the complex [Ir( -pz)(l, 5-C0D)]2. This chemiluminescence is produced by the sequential generation of It2 and lii by pulsing the potential of a platinum working electrode between the anodic and cathodic potentials. The emission is characteristic of the excited state previously observed in the photoluminescence of these complexes.  

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