Voltammetric data have been obtained for 2,2'-dipyridyl (dip) complexes of rhodium in acetonitrile. A reaction sequence is proposed based on analysis of electrochemical and luminescence data. For [Rh(dip)3I3+, the first one-electron reduction is followed by moderately fast elimination of one dip ligand. A second, apparently reversible, one-electron transfer which produces a Rh(1) species is also followed by a chemical reaction. Two more stepwise, reversible one-electron transfers yield [Rh(dip)z]O and [Rh(dip)z] -successively. Reactions for [Rh(dip)zClz]+ exactly parallel those found for the tris dip complex except chloride is eliminated following the first electron transfer. Preparation and cyclic voltammetry of (dipH)[Rh(dip)Cla(OH)].H20, [Rh(dip)z]C104.3HzO, and [Rh(dip)&l]2(C104)2.4Hz0 confirm the above sequence.

Electron spin resonance data for [VOCl5]3— and [MoOCl5]2— in dilute single crystals are reported and and analyzed to give the spin Hamiltonian parameters for these complexes. A molecular orbital formulation is given for the spin Hamiltonian parameters, and terms dependent on spin—orbit interactions near ligand nuclei are found. This formulation is applied to the experimental results by means of an empirical method including radial expansion effects, and estimates of certain LACO—MO coefficients are obtained. The bonding in [VOCl5]3—, [VO(H2O)5]2+, and [MlOCl5]2— is discussed in terms of these LCAO—MO coefficients.

50) The question of "What is the radius of an ion In solution?", is a vexed one; and not only because of the difficulty of precise definition and the uncertainty of the exact meaning of any value calculated from experimental data, or otherwise. There is also the problem of selecting the value that is most appropriate for a particular application. In the present context, the distance of closest approach of a nonpolar nonelectrolyte to an ion seems best defined In terms of the size of an ion plus the very small number of tightly bound water molecules which could be described as "having lost their own degrees of translation freedom and have those of the Ion".45 Bockris and Saluja42•45 define this number of water molecules of the solvation number of an ion. A set of radii of hydrated ions approximately corresponding to this extent of hydration have been used.

Cyclic voltammetry data have been obtained for the bis-, bisesquis-, and tris(2,2'-bipyridine) (bpy) complexes of iridium(II1) in acetonitrile. A reaction mechanism is proposed based on analysis of electrochemical and luminescence data. For the bisesquis and tris complexes the mechanism involves successive one electron transfers producing stable species on an electrochemical time scale. For [Ir(bpy),Clz]+ the electron transfer sequence is interrupted at several steps by the elimination of a chloride. These elimination reactions are time dependent and can be resolved by the variation of the scan rate. The classification of the redox orbitals as localized or delocalized is also discussed.

No abstract