The co-ordination of small molecules by manganese(II) phosphine complexes. Part 10. The reversible binding of nitric oxide by [MnX2(PR3)](X = Cl, Br, I; R3= Prn3, Bun3, PhMe2, PhEt2) in the solid state and in tetrahydrofuran solution. The effect of the nature of the halogen and the phosphine on stability and reversibility

Abstract

The complexes [MnX₂(PR₃)](X = Cl, Br, or I; PR₃= PPrⁿ₃, PBuⁿ₃, PPhMe₂, or PPhEt₂) have been shown to react with nitric oxide (NO) both in the solid state and in tetrahydrofuran (thf) solution. For X = Cl or Br, the reaction is reversible and [MnX₂(PR₃)(NO)] species are formed. For X = I the reaction is irreversible even at low temperatures, the phosphine ligand being oxidised. For the reversible reaction in the solid state the complexes have ν(NO)ca. 1 600 cm^–1; the magnetic moment and e.s.r. data indicate that the [MnX₂(PR₃)(NO)] species have four unpaired electrons and are formulated as Mn^III–NO^– moieties. In thf solution the formation of 1 : 1 Mn : NO adducts has been confirmed by quantitative gas absorption measurements. These adducts are also highly coloured and NO-binding isotherms have been constructed. Cycling experiments have shown the adducts to be more stable at lower temperatures. The decomposition product has been studied with phosphine oxides being formed both in solid-state and solution decomposition. It is postulated that NO oxidation of the PR₃ ligand occurs at higher temperature.