Studies of technetium complexes. Part 6. The preparation, characterisation, and electron spin resonance spectra of salts of tetrachloro- and tetrabromo-nitridotechnetate(VI): crystal structure of tetraphenylarsonium tetrachloronitridotechnetate(VI)

Abstract

The air-stable compounds R[TcNCl₄] and R[TcNBr₄](R =[AsPh₄]⁺ or [NBuⁿ₄]⁺) have been prepared by the reaction of [NH₄][TcO₄] with NaN₃ in the presence of concentrated HCl or of HBr. The e.s.r. spectra of [TcNCl₄]^– and [TcNBr₄]^– are typical of ions with a 4d¹ electronic configuration and the unpaired electron in an orbital with substantial 4d_xy character. The crystal structure of [AsPh₄][TcNCl₄] has been determined by single-crystal X-ray diffraction methods at 21 °C. Crystals are tetragonal, space group P4/n, with a= 12.707(2), c= 7.793(1)Å, and Z= 2. Full-matrix least-squares refinement gave a final R value of 0.031 for 1 079 independent reflections. The compound is isostructural with the series [AsPh₄][MNCl₄](M = Mo, W, Re, Ru, or Os) and with [AsPh₄][MOCl₄](M = Mo or Re). The [TcNCl₄]^– anion in [AsPh₄][TcNCl₄] possesses C_4v symmetry with Cl–Tc–Cl bond angles of 86.95(1) and 153.33(6)° and NTc–Cl bond angles of 103.34(3)°. The TcN bond distance is 1.581 (5)Å and the Tc–Cl distances are 2.3220(9)Å.