Solution and solid state electron spin resonance properties of some dihydrido paramagnetic Ir(IV) complexes.

The ESR behaviour of [Ir(IV)(H)2(CI)2(P-i-Pr3)2] and [Ir(IV)(H)2(CI)2(PCy3)2], both in frozen solution and in the solid state is reported. At 1 10 K the frozen solution spectra of these highly distorted octahedral complexes permit the observation of weak, rhombic ESR signals with parameters close to the free electron g-value. In agreement with previous NMR data, these signals are ascribed to the low concentration of Ir(IV) present in solution. In the solid state the Ir(IV) complexes are responsible for a broad, featureless ESR line, whereas superimposed signals represent the initial stage of photoreaction involving reductive elimination of HCI and formation of a square-planar Ir(II) species.