Fluoridonitrosyl Complexes of Technetium(I) and Technetium(II). Synthesis, Characterization, Reactions, and DFT Calculations

A mixture of [Tc­(NO)­F₅]^2– and [Tc­(NO)­(NH₃)₄F]⁺ is formed during the reaction of pertechnetate with acetohydroxamic acid (Haha) in aqueous HF. The blue pentafluoridonitrosyltechnetate­(II) has been isolated in crystalline form as potassium and rubidium salts, while the orange-red ammine complex crystallizes as bifluoride or PF₆^– salts. Reactions of [Tc­(NO)­F₅]^2– salts with HCl give the corresponding [Tc­(NO)­Cl_4/5]^−/2– complexes, while reflux in neat pyridine (py) results in the formation of the technetium­(I) cation [Tc­(NO)­(py)₄F]⁺, which can be crystallized as hexafluoridophosphate. The same compound can be synthesized directly from pertechnetate, Haha, HF, and py or by a ligand-exchange procedure starting from [Tc­(NO)­(NH₃)₄F]­(HF₂). The technetium­(I) cation [Tc­(NO)­(NH₃)₄F]⁺ can be oxidized electrochemically or by the reaction with Ce­(SO₄)₂ to give the corresponding Tc­(II) compound [Tc­(NO)­(NH₃)₄F]²⁺. The fluorido ligand in [Tc­(NO)­(NH₃)₄F]⁺ can be replaced by CF₃COO^–, leaving the “[Tc­(NO)­(NH₃)₄]²⁺ core” untouched. The experimental results are confirmed by density functional theory calculations on [Tc­(NO)­F₅]^2–, [Tc­(NO)­(py)₄F]⁺, [Tc­(NO)­(NH₃)₄F]⁺, and [Tc­(NO)­(NH₃)₄F]<sup>2+