Fluoridonitrosyl complexes of technetium(I) and technetium(II). synthesis, characterization, reactions, and DFT calculations

A mixture of [Tc(NO)F₅]^2- and [Tc(NO)(NH ₃)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)F ₅]^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)(NH ₃)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)F ₅]^2-, [Tc(NO)(py)₄F]⁺, [Tc(NO)(NH₃)₄F]⁺, and [Tc(NO)(NH ₃)₄F]²⁺.