X‐ray Crystallographic and First‐Principles Theoretical Studies of K₂[TcOCl₅] and UV/Vis Investigation of the [TcOCl₅]^2– and [TcOCl₄]^– Ions

Abstract

Dipotassium pentachloridooxidotechnetate, K 2 [TcOCl 5 ], has been isolated as green single crystals by the dissolution of (NH 4 )TcO 4 in 12 M HCl at 0°C and careful precipitation with KCl. The structure of this compound was determined by single-crystal X-ray diffraction analysis [a = 13.0815(9), b = 9.8982(6), c = 6.7623(4) Å; V = 875.605 Å 3 , orthorhombic, Pnma, Z = 4] and compared with the corresponding molybd- IntroductionPentachloridooxidometallate(V) [MOCl 5 ] 2complex anions are formed with the transition metals V, Nb, Ta, Cr, Mo, W, Tc, and Re. They can also be precipitated as crystalline salts with the heavier alkali metals (i.e., K, Rb, and Cs) or other small monocationic counter ions, such as NH 4 + . [1][2][3][4] When precipitated as the caesium salt, these compounds crystallize in the cubic lattice with space group Fm3m, whereas with K + , Rb + , or NH 4 + , the orthorhombic Pnma structure is observed. Both the cubic and orthorhombic structures are based on close-packing of the [MOCl 5 ] 2anions with the cations located in the tetrahedral holes. [1] The combination of the strong M=O interactions and readily exchangeable chlorido ligands makes these six-coordinate compounds important precursors to a variety of polyatomic oxido-containing metal complexes. Technetium (Z = 43) is a transition-metal element of particular interest, primarily due to the synergy of its radiolytic properties and [a] 1097 enum and rhenium analogues. The structure of K 2 [TcOCl 5 ] was also investigated by density functional theory, and the results are in agreement with the crystallographic data. The oscillator strengths of the electronic transitions in the C 4v complex anions [TcOCl 5 ] 2and [TcOCl 4 ]were also calculated by using time-dependent density functional theory and compared with the experimental UV/Vis spectra.

Speciation and Oxidative Stability of Alkaline Soluble, Non-Pertechnetate Technetium

“…Development of the Tc EPR method was initiated using the methylene chloride mother liquor solution produced in the synthesis of the [TcOCl 4 ]compound as described in Section 5.1.1. The reduction of pertechnetate with HCl generates two equilibrium forms of Tc(V), namely [TcOCl 4 ]and [TcOCl 5 ] 2- (Johnstone et al 2013). The presence of the reductive Tc(VI) intermediate [TcOCl 5 ]in the reaction mixture has been suggested, and its EPR spectrum and corresponding magnetic parameters reported (Kirmse et al 1985).…”