Synthesis and Characterization of Novel Tc(V) and Re(V) Complexes with Water-Soluble Tetraaza Diamido Dipyridino Ligands: Single-Crystal X-ray Structural Investigations of Mono- and Dinuclear Complexes

Rhenium and technetium are known for their useful applications in nuclear medicine with similar properties. In this study, new diamido dipyridino (N4) water-soluble ligands (2-0510100)201, 1 (UH2), (24100)201, 2, and -CsNO-CINHOOCI, 3, were synthesized. Reaction of UH2 with ReOCl3(PPh3)2 resulted in the novel six-coordinated rhenium(V) complex, trans-ReO(U)(OEt), 4. The complex was characterized by spectroscopic methods, and its X-ray crystallographic analysis revealed that rhenium is coordinated to four nitrogen atoms of the ligand and to two oxygen atoms from the deprotonated ethanol and the oxo group respectively in a distorted octahedral geometry. In solution, complex 4 was transformed to a new complex 5, which was proved to be the dinuclear complex -oxo [ReOd-O. Reaction of 1 with -Bu4N][ReOCl4] resulted in the neutral complex 6, trans-[ReO(U)]CI. Similarly, when ligand 1 was reacted with [n-Bu4N][TcOCl4], the neutral s-[TcO(U)]CI complex 7 was formed, which upon dissolution transformed into a cationic complex 8, ans-[TcO(L)(OH2)CI. The single-crystal X-ray structure of 8 reveals that the coordination sphere about technetium is a distorted octahedron with four nitrogen atoms in the equitorial plane, while doubly bonded oxygen and coordinated water occupy the apical positions. Further dissolution of 8 resulted in the formation of dinuclear -oxo [TcOO, 9. This study shows that Tc and Re have similar metal core structures in solution for diamido dipyridino systems, besides similarity in geometrical structure, proved by the X-ray structures on the same ligands.