A trigonal-prismatic hexanuclear technetium(II) bromide cluster: solid-state synthesis and crystallographic and electronic structure

The compound Na{[Tc6Br12]2Br} has been obtained from the decomposition of TcBr4 under vacuum in a Pyrex ampule at 450 °C. The stoichiometry of the compound has been confirmed by energy-dispersive X-ray spectroscopy and its structure determined by single-crystal X-ray diffraction. The compound contains a trigonal-prismatic hexanuclear [Tc6Br12] cluster. The cluster is composed of two triangular Tc3Br6 units linked by multiple Tc-Tc bonds. In the Tc3Br6 unit, the average Tc-Tc distance [2.6845(5) Å] is characteristic of Tc-Tc single bonds, while the average Tc-Tc distance between the two triangular units [2.1735(5) Å] is characteristic of Tc≡Tc triple bonds. The electronic structure of the [Tc6Br12] cluster was studied by first-principles calculations, which confirm the presence of single and triple Tc-Tc bonds in the cluster.

Multi-configurational quantum chemical studies of the Tc2X8(n-) (X = Cl, Br; n = 2, 3) anions. Crystallographic structure of octabromoditechnetate(3-)

The [Cs((2 + x))][H(3)O((1 - x))]Tc(2)Br(8)·4.6H(2)O (x = 0.221) salt has been synthesized and characterized by single crystal XRD. Multi-configurational quantum chemical calculations on Tc(2)X(8)(n-) (X = Cl, Br; n = 2, 3) have been performed and indicate the π component in the Tc-Tc bond to be stronger for n = 3.

Tc(IV) chemistry in mixed chloride/sulphate acidic media. Formation of polyoxopolymetallic species

The substitution of the Cl- ions of TcCl6 2- in various media (Cl-, SO4 2-, TFMS-) at various pH or the electroreduction of TcO4 - in the same media led to a common Tc(IV) species characterized by an UV-visible absorption band at 500nm. This band was present in the spectra of Tc(IV) in all the media investigated, except in chloride at low pH. The analysis of the spectroscopic data showed that it can be attributed to a Tc(IV) oxopolymeric species.The data fits better with a trimeric species Tc3O4 4+ which reminds the Mo3O4·9H2O4+ clusters known for Mo(IV). The stability of 3×10-5M Tc3O4 4+ solutions has been investigated as a function of pH with respect to the formation of Cl- complexes at low pH, and precipitation of TcO2 at pH, higher than 3. The anions of the media interact with Tc3O4 4+ clusters as shown by small changes in their UV-visible spectra. We observed that the affinity of Tc3O4 4+ for these ions is in the order: SO4 2->Cl->TFMS-. Neutral species Tc3O4(SO4)2 are observed in 0.1M sulphate solutions.