Chemistry of trans-aquonitrosyltetraamminetechnetium(I) and related studies

Article abstract of DOI:10.1021/ic50162a031

Attempts to reduce Tc(VII) or Tc(IV) in strongly acidic solutions containing noncomplexing anions indicate that reduction to Tc(II) is possible, but the species of lower oxidation state are unstable and there is no assurance that they are mononuclear This instability contrasts markedly with that of a compound reported by Eakins et al.² as containing [Tc(NH₂OH)₂-(NH₃)₃H ₂O]²⁺. Structure determination by Radonovich and Hoard on the chloride salt of the cation shows it to be trans-[Tc(NH₃)₄(H₂O)NO]²⁺, rather than that formulated by Eakins. The nitrosyl ion shows a stretch in the ir spectrum at 1680 cm^-1, the low frequency indicating great stabilization by Tc^I→(NO)^I back-bonding. The species is remarkably inert to substitution, as is the nitrosyl group to nucleophilic attack. At low pH, the trans-[Tc(NH₃)₄(H₂O)NO]^3+/2+ couple is reversible, E_f against NHE being 0.80 V. The ion of higher oxidation state undergoes substitution more readily than does that of charge 2+ and is unstable at higher pH. The values of pK_a for the 2+ and 3+ species have been measured as 7.3 and ca. 2.0, respectively. Modification of the Eakins method of preparation leads to other derivatives but of these only [Tc(1,10-phen)₂(NH₃)NO]²⁺ has been at all well characterized.