Technetium complexes with thioether ligands—III. Synthesis and structural characterization of cationic nitridotechnetium(V) complexes with thiacrown ethers

The first representative of a new class of TcN complexes with thiacrown ethers have been prepared by ligand exchange reaction of NBu₄[TcNCl₄] with 1,4,8,11-tetrathiacyclotetradecane (14S4), 1,5,9,13-tetrathiacyclohexadecane (16S4), 1,5,9,13-tetrathiacyclohexadecane-3,11-diole (16S4-(OH)₂) and 1,4,7,10,13,16-hexathiacyclooctadecane (18S6). The crystal structure of [TcNCl(14S4)]TcNCl₄ 1) consists of couples of independent cations with the metal in the oxidation state + 5 and hexavalent TcNCl₄⁻ anions. In the complex cation the metal is six-coordinated in a rather distorted octahedral geometry, being directly bound to four sulphur atoms from the macrocyclic ligand in the equatorial plane and to the nitrido atom and to one chlorine atom in the axial positions. The strong trans influence of the nitrido ligand causes an extreme lengthening of the Tc---Cl bond distance to 2.718 Å. The octahedral molecular structure of [TcNCl(18S6)]TcNCl₄ (3) is comparable with that of 1, but only four sulphur atoms of the thiacrown ether form the equatorial plane, two sulphur atoms remain non-coordinated, and the nitrido and Cl⁻ ligands are in axial positions. The most interesting feature in the structure of [TcNCl(16S4-(OH)₂)]Cl (5) is the observation of an exceptionally long Tc---N distance of 1.95 Å.