NEUTRAL OXO AND NITRIDO COMPLEXES OF TECHNETIUM(V) AND RHENIUM(V) WITH AN UNSATURATED TETRADENTATE (N2S2) LIGAND - CRYSTAL-STRUCTURE OF [N,N'-ETHYLENEBIS(THIOACETYL-ACETONYLIDENEIMINATO)(2-)-S,S',N,N']NITRIDOTECHNETIUM(V)

Ligand-exchange reactions of the tetradentate unsaturated N2S2 Schiff-base ligand N,N'-ethylenebis-(thioacetylacetonylideneimine) (H2L) with labile monooxo-technetium(v) and -rhenium(v) compounds ([NBu4][TcOCl4]; [NBu4][ReOCl4] or [ReOCl3(PPh3)2]) gave two types of neutral six-co-ordinated species [MO(L)Cl] and [{MO(L)}2O] (M = Tc or Re). The monooxo monomeric complexes rearrange to the mu-oxo dimeric species via a charged labile intermediate in wet organic solvents or when solutions are kept in contact with air. Reaction of H2L with [NBu4][Tc(VI)NCl4] follows a reduction-substitution route to give another neutral, but five-co-ordinated species, [TcN(L)] which contains the [Tc(V) = N]2+ nitrido core. All complexes have been characterized by means of standard spectroscopic techniques. The influence of the metal on ligand H-1 NMR chemical shifts is discussed. The technetium centre shifts all the ligand protons more downfield than does rhenium. This behaviour is in general agreement with the stronger acidity of the [TcO]3+ core with respect to [ReO]3+. The five-co-ordination of the nitrido complex [TcN(L)] is confirmed by its X-ray structure determination: monoclinic, space group P2(1)/n, a = 14.654(7), b = 12.62(5), c = 7.819(4) angstrom, beta = 92.60(3)-degrees and Z = 4. The co-ordination sphere around the Tc centre is nearly square pyramidal with an apical multiply bonded nitrogen atom [Tc = N 1.621(8) angstrom].