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Structural and 99Tc NMR Investigations of Complexes with fac-[Tc(CO)3]+ Moieties and Macrocyclic Thioethers of Various Ring Sizes:  Synthesis and X-ray Structure of the Complexes fac-[Tc(9-ane-S3)(CO)3]Br, fac-[Tc2(tosylate)2(18-ane-S6)(CO)6], and fac-[Tc2(20-ane-S6-OH)(CO)6][tosylate]2

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journal contribution
posted on 23.06.1998, 00:00 by Roger Schibli, Roger Alberto, Ulrich Abram, Sonja Abram, André Egli, P. August Schubiger, Thomas A. Kaden
Starting originally from the organometallic precursor [NEt4]2[TcBr3(CO)3] (1b), substitution reactions were performed with the macrocyclic thioethers 1,4,7-trithiacyclononane (9-ane-S3), 1,4,7,10,13,16-hexathiacyclooctadecane (18-ane-S6), and 3,6,9,13,16,19-hexathiacycloicosanol (20-ane-S6-OH). The corresponding complexes fac-[Tc(9-ane-S3)(CO)3]Br (2), fac-[Tc2(tosylate)2(18-ane-S6)(CO)6] (3), and fac-[Tc2(20-ane-S6-OH)(CO)6][tosylate]2 (5) were isolated in good yields and characterized spectroscopically by IR, 1H, 99Tc NMR, and X-ray diffraction methods. In the case of 18-ane-S6 and 20-ane-S6-OH the formation of the 1:2 as well as the 1:1 complex could be observed in the 99Tc NMR experiment, depending on the ligand to metal ratio. Complex 2 crystallizes in the monoclinic space group P21/c, a = 14.79(2) Å, b = 11.691(2) Å, c = 16.94(2) Å, β = 94.88(6)°, Z = 8. The tripodal ligand is coordinated through the sulfur atoms to the metal center, forming three favorable five-membered chelate rings. Complex 3 crystallizes in the monoclinic space group C2/c, a = 26.073(4) Å, b = 9.288(1) Å, c = 17.898(3) Å, β = 99.84(1)°, Z = 4. The binuclear unit is formed by two fac-[Tc(tosylate)(CO)3] moieties which are trans, bidentate coordinated to the macrocyclic ligand. Compound 5 crystallizes in the monoclinic space group Pc, a = 25.737(4) Å, b = 14.009(1) Å, c = 26.479(3) Å, β = 149.56(2)°, Z = 4. In the case of the dicationic compound 5, the two Tc(I) centers are tripodal, cis coordinated toward the thia crown ether. A detailed analysis of the ring conformation in the solid state structure explained to a certain extent the formation of only one isomer (trans in the case of 3 and cis in the case of 5, respectively) during the substitution reaction.