Study of complexation behavior of a hexadentate bispidine derivative towards neptunium T. Suzuki1, G. Geipel, A. Rossberg, H.Stephan2, S. Juran2, P. Comba3 1The University of Kitakyusyu, Fukuoka, Japan; 2Insitute of Bioinorganic and Radiopharmaceutical Chemistry, Dresden, Germany ; 3Department of Inorganic Chemistry, Heidelberg, Germany
ABSTRACT. EXAFS measurements on Np-bispidine Fig. 3. The results support the suggestion on strong com- complexes were carried out at BM20 at the ESRF. The plex formation between actinyl ions and bispidone. EXAFS spectra of the three samples (5.0x10-4 mol/L) were measured in fluorescence mode with a 13- REFERENCES element Ge solid-state detector. [1] Bleiholder, C. et al. (2005) Inorg. Chem., in press. 3 Hexadentate bispidine ligands N2Py4 (Fig. 1) having Experiment Fit amine and pyridine nitrogen as donor atoms show inter- 15 Residual esting complexation behavior [1]. Such ligands seem to be very promising in view of lanthanides/actinides separa- Np4-01 tion. In this nexus, it is desirable to have the information 10 2 about the binding pattern formed for lanthanides and 3 actinides. Here, we want to report the complexation be- (k)*k FT havior of the hexadentate bispidine ligand N2Py4 towards χ 5 Np4-02 neptunium. 1
0 Np4-03
0 -5 4 6 8 10 12 14 0123456 -1 k [Å ] R + ∆ [Å] Fig. 2: EXAFS Spectra and FT’s including the adjustment and residuals of the studied Np-(N2Py4)-complexes.
Tab. 2: EXAFS structural parameters for the fit in Fig. 2. Fig.1: Structure of hexadentate bispidone (N2Py4). Sample Np-Oaxial Np-Atomequatorial EXPERIMENTAL. The metal:ligand ratios and pH R [Å] Atom N R [Å] values of the studied samples are summarized in Table 1. pH 4 1.824(2) N 4.9(6) 2.525(6) The concentration of the metal was adjusted to pH 3 1.829(2) N 4.7(5) 2.520(5) 5.0x10-4 mol/L. The measurements were performed at the ROBL Beamline at the ESRF. For EXAFS the fluores- pH 2 1.824(2) N 3.3(4) 2.528(5) 2.8-14 C 3(1) 3.49(2) cence signal at the Np-LIII edge was used. 1 C2 5(2) 3.69(1) Tab. 1: Metal:ligand ratio and pH of the samples. pH 4 1.825(3) N 5.7(6) 2.515(6) Sample Np Ligand (N2Py4) pH Np 1 4.86(1) Np4-01 1 2 4 Np4-02 1 1 3 Np4-03 1 2 2
RESULTS AND DISCUSSION. The EXAFS spectra and the corresponding Fourier transformations (FT) are shown in Fig. 2. The resulting structural parameters are summarized in Table 2. In the samples at pH 4 and pH 3 a residual was found which can be interpreted as a radial Np–O distance at 2.15 ± 0.02 Å. For the sample at pH 4 an additional peak at 4.6 Å arises in the FT. This backscatter contribution was not found in the other two samples. The structural parameters of this sample were fitted again and the signal is assigned to a Np–Np interaction with a distance of 4.86 ± 0.02 Å (Table 2 last line). For the complex formed at pH 4 a Fig. 3: Structural fragment of a hypothetical mononuclear Np- polynuclear complex is suggested. complex as found for sample at pH 2. Atoms of minor The formed complexes in the samples at pH 2 and 3 are relevance to the ligand are not shown. assigned to be a mononuclear. For the sample at pH 2 the fit could be improved by inclusion of two carbon atoms (Table 3). For this sample and possibly also for pH 3 the proposed structure of the formed complex is shown in
22 FZR – IRC Annual Report 2004