Coordination chemistry of neptunyl(V) compounds by means of Mossbauer spectroscopy

Five neptunyl(V) compounds were synthesized and studied by Np-237 Mossbauer Spectroscopy The isomer shifts (delta) of the Mossbauer spectra ranged from -18.6 to -19.0 mm s(-1) for the compounds with Np atoms surrounded by seven oxygen atoms. Interlaced two sets of hyperfine splitting were observed in the spectra for the acetate and the benzoate, delta's of one set with larger magnetic splitting were -19.4 and -19.5 mm s(-1), respectively, but those of the other set with smaller magnetic splitting were -13.2 and -10.8 mm s(-1), respectively. From the comparison of the present results with those reported on neptunyl(V) and (VI) compounds, it is concluded that there are two neptunium sites in the acetate and the benzoate in their structure, one is the site with the coordination number (CN) of 7 and the other is that with CN of 8. (C) 1998 Elsevier Science S.A.