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An EGTA complex of the incomplete cubane-type, trinuclear tungsten sulfur cluster, [W3S4], was prepared and investigated as a possible candidate for a new generation of X-ray contrast agents for medical diagnostic imaging. The aqua ion, [W3S4(H2O)9]4+ (I) was prepared through an improvement of the literature method to facilitate scale-up. Reaction of I with EGTA in refluxing DMF produced a mixture of (W3S4)x(EGTA)y (x,y ≥ 1) cluster complexes. A 2:3(W3S4:ligand) complex, [(W3S4)2(EGTA)3]4− (II), was isolated via size-exclusion chromatography in 25–40% yield. Cluster complex II was fully characterized by X-ray crystallography in addition to routine techniques. It is soluble in H2O and stable in the pH range 2 to 10. Animal studies of II indicated a low acute toxicity and a pharmacokinetic profile similar to that of an existing heavy metal cluster complex with a known extracellular biodistribution. |
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