Chloride complexation of the group-4 elements Zr and Hf in 8.011.9M HCl is investigated by extended X-ray absorption fine structure (EXAFS) spectroscopy to characterize chloro complexes of the transactinide element, rutherfordium (Rf). The complexes of Zr and Hf successively vary with the concentration of HCl from a hydrated complex [M(H 2O) 8] 4+ at 8.0M to a hexachloro complex [MCl 6] 2- at 11.9M (M = Zr and Hf). The present structural changes of the Zr and Hf complexes well reflect the previously studied anion-exchange behavior of Zr and Hf in HCl. From both the EXAFS and anion-exchange results, we suggest that Rf forms the same complexes as those of Zr and Hf in HCl, and that the complexation strength of the hexachloro complexes of the group-4 elements, [MCl 6] 2- (M = Zr, Hf, and Rf), is in the sequence of Rf > Zr > Hf.
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