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

Abstract

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+).

The Reaction of Cs2[Tc(NO)F5] with BF3 in Acetonitrile: Formation and Structure of [{Tc(NO)(CH3CN)4}2(μ‐F)](BF4)3

“…Cs 2 [Tc(NO)F 5 ] crystallizes from aqueous HF (48 %) as monohydrate in the orthorhombic space group Cmcm . Thus, it is isostructural with the corresponding potassium and rubidium salts of the same complex and related ruthenium and osmium complexes , . The technetium atom is coordinated in a slightly distorted octahedral environment (Figure a).…”

“…Depending on the degree of symmetry lowering, this can lead to an observable splitting of the E modes. Additionally, in the crystal class D 2 h , a weak splitting of the normal modes may occur due to a coupling of the normal modes of the four anions of the unit cell ,…”

“…The fluorido ligands in Cs 2 [Tc(NO)F 5 ] can be replaced by Cl – or Br – by dissolution of the salt in aqueous HCl or HBr, whereas the dissolution in water results in the formation of a diamagnetic, probably dimeric fluorido compound with a Tc–O–Tc bond , . Attempts to undertake ongoing ligand exchange reactions particularly with organic ligands failed due to the low solubility of the alkaline metal salts in organic solvents.…”

“…Nitrosyl complexes of technetium with fluorido ligands are rare and only a few of them have been studied by X‐ray diffraction and spectroscopic methods , . Although M 2 [Tc(NO)F 5 ] and [Tc(NO)(NH 3 ) 4 F]( A ) salts ( M + = K + , Rb + ; A – = HF 2 – , PF 6 – ) can be prepared from pertechnetate, HF, and acetohydroxamic acid in satisfactory yields and high purity,, these materials are not suitable as precursors for ongoing ligand exchange reactions due to their insolubility in organic solvents and/or the inertness of their ligands. Hitherto, only one nitrosyltechnetium complex with an organic ligand could be prepared from them, namely the cationic [Tc(NO)(py) 4 F] + , which is formed after prolonged heating of the fluorido or ammine complexes in neat pyridine …”

Exploring EPR Parameters of 99Tc Complexes for Designing New MRI Probes: Coordination Environment, Solvent, and Thermal Effects on the Spectroscopic Properties

“…The EPR parameters of a set of Tc(II) nitrosyl complexes were reported in the previous studies in the literature [20].…”