Technetium(V)–nitrido complexes of dithiocarbazic acid derivatives. Reactivity of [TcN]2+ core towards Schiff bases derived from S-methyl dithiocarbazate. Crystal structures of [S-methyl 3-(2-hydroxyphenylmethylene)dithiocarbazato]nitrido(triphenylphosphine)technetium(V) and bis(S-methyl 3-isopropylidenedithiocarbazato)nitridotechnetium(V)

Abstract

New technetium(V)–nitrido complexes with bi- and tri-dentate Schiff bases, derived from the condensation of various aldehydes and acetone with the methyl ester of dithiocarbazic acid, NH₂NHC(S)SCH₃, were prepared by substitution or substitution–reduction reactions on the square-pyramidal complexes [Tc^VNCl₂(PPh₃)₂] and [Tc^VINCl₄]^–. The final complexes all maintain the square-pyramidal geometry of the starting compounds with the TcN group in an apical position. The bidentate ligands give rise to mono- and di-substituted complexes, in which they are co-ordinated to the metal through the β-nitrogen atom and the thiol sulphur atom; in monosubstituted complexes, the remaining two positions in the plane of the square pyramid are occupied by triphenylphosphine (PPh₃) and Cl^– groups. The tridentate Schiff bases co-ordinate to the metal, in the basal plane, as doubly negatively charged ligands through the phenolic oxygen atom, the β-nitrogen atom, and the thiol sulphur atom, the fourth position being occupied by the phosphorus atom of a PPh₃ group. The crystal structures of [TcNL¹(PPh₃)](1)[H₂L¹=S-methyl 3-(2-hydroxyphenylmethylene)dithiocarbazate] and [TcN(L¹²)₂](2)(HL¹²=S-methyl 3-isopropylidenedithiocarbazate) have been determined. Relevant crystal data for (1) are: refined from 5 008 reflections with I 3σ(I) to a final R of 0.029, crystals are triclinic, space group P, with unit-cell dimensions a= 8.309(1), b= 12.294(1), c= 13.308(3)Å, α= 96.22(1), β= 95.07(1), γ= 101.34(1), and Z= 2; for (2): refined from 1 756 reflections with I 3σ(I) to a final R of 0.023, crystals are monoclinic, space group I2/a, with unit-cell dimensions a= 16.707(3), b= 8.838(1), c= 12.514(2)Å, β= 106.85(1)°, and Z= 4. In both complexes, the co-ordination around Tc is distorted square pyramidal with an apical multiply bonded nitrogen atom [TcN 1.611(3)Å in (1) and 1.613(3)Å in (2)] and the basal ligands bent away from the nitrido group.