STRUCTURE, EPR AND UV-VIS AND IR SPECTROELECTROCHEMISTRY OF REVERSIBLY REDUCIBLE COMPOUNDS [(C(5)ME(5))IRCL(L)](PF6), L=1,3-DIMETHYLLUMAZINE OR 1,3-DIMETHYLALLOXAZINE

In an attempt to model possible metal-pterin or metaI-flavin ligand in teractions the title compounds have been prepared and their structure, spectroscopy and spectroelectrochemistry (EPR, IR, UV-VIS) compared w ith results for the corresponding rhodium analogues. The X-ray crystal structure of [(C(5)Me(5))IrCl(DML)](PF6), DML = 1,3-dimethyllumazine, shows O-4/N-5 chelate coordination of iridium with a shorter bond to the nitrogen centre [2.103(4) vs. 2.186(3) Angstrom], a slightly more unsymmetrical situation than that found in the rhodium analogue. Elect rochemical studies (cyclic voltammetry, polarography) showed largely r eversible one-electron reduction processes to radical species [(C(5)Me (5))IrCl(L)](.) which allowed us to investigate the EPR, IR and UV-VIS response to the reduction. Although the EPR spectra of the iridium co mpounds remained unresolved, the low g factors (g < 2) and particular line shapes revealed small but significant contributions from the heav y-metal centre. Long-wavelength absorptions at ca. 600 nm and low-ener gy shifts of the carbonyl stretching bands confirm the formulation [(C (5)Me(5))(IrCl)-Cl-III(L(-1))](.) for the electronic situation.