Aspects of the co-ordination chemistry of some transition metals

Abstract

The work reported in his thesis is divided into three parts. Part A is concerned with studies on stable complexes of dinitrogen, and related ligands, Part B details studies on the rhenium (V) oxo-complex Cs₂ReOCl₅, and part C outlines general experimental details. Part A. Some reactions of the dinitrogen complex [Ru(NH₃)₅(N₂)]Cl₂ have been investigated and the oxidation potential of the [Ru(NH₃)₅(N)₂]²⁺ ion in neutral conditions has been found to be approximately -0.95 volts. The reactions have demonstrated that [Ru(NH₃)₅(N₂)]Cl₂ prepared using hydrazine hydrate is impure, the impurity is probably [Ru(NH₃)₅(N₂H₄)]Cl₂. The dinitrogen of purified [Ru(NH₃)₅(N₂)]Cl₂ has not yet been reduced in aqueous conditions, contrary to a previous report. The reactions of some ruthenium, osmium, iridium and rhodium complexes with hydrazine hydrate and with metal reductants (e.g. Zn) in concentrated ammonia were investigated. A number of products including [M(NH₃)₅(CO)]²⁺, [M(NH₃)₄(N₂)₂]²⁺, [M(NH₃)₅(CO)]²⁺ (M=Os, Ru), [Ir(NH₃)₄(CO)Cl]²⁺ and [Rh(NH₃)₅H]²⁺, together with hydrazine containing products, were formed. Possible mechanisms for some of these products are suggested. The cystal structure of the osmium complex [Os(NH₃)₅(N₂)]Cl₂ has been determined by X-ray diffraction methods. The crystal belongs to the orthorhombic space group Pnma with a = 1357.5, b = 1046.5, c = 687.5pm and z = 4. The cations lie on crystallographic mirror planes and the interatomic distances within the cation are Os-N₂ (184pm); N≡N (112pm) and Os-NH3 (212-215pm). The ruthenium complex [Ru(NH₃)₅(N₂)]Cl₂ was found to form solid solutions with [Ru(NH₃)₅(N₂)]Cl₂ which are isomorphous with the above osmium complex. This corresponds to a change of crystal system for the ruthenium dinitrogen complex. The energy if the (NN) absorption in the solid solutions is up to 50 cm-1 lower than pure [Ru(NH₃)₅(N₂)]Cl₂, and it is suggested that this observation is caused by steric interactions in the solid state. Low frequency infrared spectra of a number of ammine complexes have been recorded. These spectra show coupling effects between vibration modes, and also that the two metals, osmium and iridium, form stronger bonds to halide and ammonia, than do the corresponding second row metals ruthenium and rhodium. Part B. The reported paramagnetic rhenium (V) ions such as ReOCl²⁻₅ were studied in this section. This complex ion is reported as being different from most rhenium (V) complexes which are diamagnetic. The present study has demonstrated that Cs₂ReOCl₅ is, infact, only slightly paramagnetic, presumably due to temperature independent paramagnetism. The reason for the high paramagnetism reported previously has been shown to be due to the presence of paramagnetic Cs₂ReCl₆ in samples of Cs₂ReOCl₅, owing to an equilibrium reaction. 3ReOCl²⁻₅ + H₂O ⇌ ReO⁻₄ + 2ReCl₆²⁻ + 2H⁺ + 3Cl⁻ occurring during the preparative procedures.