A correlation between isomer shifts of Np-237 Mossbauer spectra and coordination numbers of Np atoms in neptunyl(V) compounds

Five neputnyl(V) compounds were synthesized and studied by Np-237 Mossbauer spectroscopy. The isomer shifts (delta) of the Mossbauer spectra ranged fr om -18.6 to -19.1 mm/s for the compounds with Np atoms surrounded by 7 oxyg en atoms (coordination number (CN) 7). On the other hand, the larger value of delta was obtained for the compound with CN 8. From the comparison of th e present results with those reported on neptunyl(V) and (VI) compounds, it is concluded that there is a correlation between the delta and the CN for neptunyl(V) compounds, and the distribution of delta is narrower for neptun yl(V) compounds than that of neptunyl(VI) compounds.