Fluoridonitrosyl Complexes of Technetium(I) and Technetium(II).
Synthesis, Characterization, Reactions, and DFT Calculations
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Abstract
A mixture of [Tc(NO)F<sub>5</sub>]<sup>2–</sup> and [Tc(NO)(NH<sub>3</sub>)<sub>4</sub>F]<sup>+</sup> 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 PF<sub>6</sub><sup>–</sup> salts. Reactions of [Tc(NO)F<sub>5</sub>]<sup>2–</sup> salts
with HCl give the corresponding [Tc(NO)Cl<sub>4/5</sub>]<sup>−/2–</sup> complexes, while reflux in neat pyridine (py) results in the formation
of the technetium(I) cation [Tc(NO)(py)<sub>4</sub>F]<sup>+</sup>,
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)(NH<sub>3</sub>)<sub>4</sub>F](HF<sub>2</sub>). The technetium(I) cation
[Tc(NO)(NH<sub>3</sub>)<sub>4</sub>F]<sup>+</sup> can be oxidized
electrochemically or by the reaction with Ce(SO<sub>4</sub>)<sub>2</sub> to give the corresponding Tc(II) compound [Tc(NO)(NH<sub>3</sub>)<sub>4</sub>F]<sup>2+</sup>. The fluorido ligand in [Tc(NO)(NH<sub>3</sub>)<sub>4</sub>F]<sup>+</sup> can be replaced by CF<sub>3</sub>COO<sup>–</sup>, leaving the “[Tc(NO)(NH<sub>3</sub>)<sub>4</sub>]<sup>2+</sup> core” untouched. The experimental
results are confirmed by density functional theory calculations on
[Tc(NO)F<sub>5</sub>]<sup>2–</sup>, [Tc(NO)(py)<sub>4</sub>F]<sup>+</sup>, [Tc(NO)(NH<sub>3</sub>)<sub>4</sub>F]<sup>+</sup>, and [Tc(NO)(NH<sub>3</sub>)<sub>4</sub>F]<sup>2+</sup>