Structural characterization of a bridged 99Tc-Sn-dimethylglyoxime complex: implications for the chemistry of 99mTc-radiopharmaceuticals prepared by the Sn (II) reduction of pertechnetate.

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Abstract
Reduction of pertechnetate by Sn(II) in the presence of dimethylglyoxime is shown, by single crystal X-ray analysis, to yield a Tc-Sn-dimethylglyoxime complex in which Sn and Tc are intimately connected by a triple bridging arrangement. One bridge consists of a single O atom and it is hypothesized that this bridge arises from the inner sphere reduction of Tc by Sn(II), the electrons being transferred through a Tc yl O which eventually becomes the bridging atom. Two additional bridges arise from 2 dimethylglyoxime ligands that function as bidentate N donors towards Tc and monodentate O donors towards Sn. The Sn atom can thus be viewed as providing a 3-pronged cap on 1 end of the Tc-dimethylglyoxime complex. The additional coordination sites around Tc are occupied by the 2 N of a 3rd dimethylglyoxime ligand, making the Tc 7-coordinate. The additional coordination sites around Sn are occupied by 3 Cl anions, giving the Sn a fac octahedral coordination environment. From indirect evidence the oxidation states of Sn and Tc are tentatively assigned to be IV and V, respectively. Since most 99mTc-radiopharmaceuticals are synthesized by the Sn(II) reduction of pertechnetate, it is likely that the Sn-O-Tc linkage is an important feature of the chemistry of these species. This linkage also provides a ready rationale for the close association of Sn and Tc observed in many 99mTc-radiopharmaceuticals.