Synthesis and molecular structure of a lantern dimer, (AsPh sub 4 ) sub 2 (Tc sub 2 O sub 2 (SCH sub 2 CONHCH sub 2 CH sub 2 NHCOCH sub 2 S) sub 4 )

Reaction of (Bu{sub 4}N)(TcOCl{sub 4}) with a 5-fold excess of N,N{prime}-ethylenebis(2-mercaptoacetamide) (H{sub 4}ema) in methanolic sodium methoxide yielded a blue precipitate which was metathesized to give (AsPh{sub 4}){sub 2}(Tc{sub 2}O{sub 2}(H{sub 2}ema){sub 4}) (1). Complex 1 crystallized as a hexahydrate and was structurally characterized by single-crystal x-ray crystallography. The structure of the dianion showed a centrosymmetric dianion with two square-pyramidal OTcS{sub 4}cores bridged 4-fold by the (H{sub 2}ema{sup 2{minus}}) dithiolate ligands. The metal-oxo groups are oriented into the center of the cage created by the bridging ligands, giving what is referred to as a lantern structure. The intramolecular Tc-Tc* distance was 7.175 (4) {angstrom}, and the distance between the two metal oxo ligands, O1-O1*, was 3.96(2) {angstrom}. The six water molecules per dimer were found to be hydrogen-bonded to each other and to the amide NH and CO groups on the ligands. Compound 1 was converted to (AsPh{sub 4})(TcO(ema)) when heated in solution or when reacted with aqueous base. 19 refs., 3 figs., 5 tabs.