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)­Cl4/5]−/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]2+.