Technetium
Simple hydride and halide complexes

Technetium forms the complex TcH. The potassium salt is isostructural with ReH. At high pressure formation of TcH1,3 from elements was also reported.

The following binary (containing only two elements) technetium halides are known: TcF, TcF, TcCl, TcBr, TcBr, α-TcCl, β-TcCl, TcI, α-TcCl, and β-TcCl. The oxidation states range from Tc(VI) to Tc(II). Technetium halides exhibit different structure types, such as molecular octahedral complexes, extended chains, layered sheets, and metal clusters arranged in a three-dimensional network. These compounds are produced by combining the metal and halogen or by less direct reactions.

TcCl is obtained by chlorination of Tc metal or Tc O Upon heating, TcCl gives the corresponding Tc(III) and Tc(II) chlorides.

The structure of TcCl is composed of infinite zigzag chains of edge-sharing TcCl octahedra. It is isomorphous to transition metal tetrachlorides of zirconium, hafnium, and platinum.

Two polymorphs of technetium trichloride exist, α- and β-TcCl. The α polymorph is also denoted as Tc Cl. It adopts a confacial bioctahedral structure. It is prepared by treating the chloro-acetate Tc (O CCH) Cl with HCl. Like Re Cl, the structure of the α-polymorph consists of triangles with short M-M distances. β-TcCl features octahedral Tc centers, which are organized in pairs, as seen also for molybdenum trichloride. TcBr does not adopt the structure of either trichloride phase. Instead it has the structure of molybdenum tribromide, consisting of chains of confacial octahedra with alternating short and long Tc—Tc contacts. TcI has the same structure as the high temperature phase of TiI, featuring chains of confacial octahedra with equal Tc—Tc contacts.

Several anionic technetium halides are known. The binary tetrahalides can be converted to the hexahalides (X = F, Cl, Br, I), which adopt octahedral molecular geometry. More reduced halides form anionic clusters with Tc–Tc bonds. The situation is similar for the related elements of Mo, W, Re. These clusters have the nuclearity Tc, Tc, Tc, and Tc. The more stable Tc and Tc clusters have prism shapes where vertical pairs of Tc atoms are connected by triple bonds and the planar atoms by single bonds. Every technetium atom makes six bonds, and the remaining valence electrons can be saturated by one axial and two bridging ligand halogen atoms such as chlorine or bromine.
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