Synthesis and Characterization of Homo- and Heteroleptic Neptunium(IV) Heteroarylalkenolate Complexes

Heteroleptic An^IV (An = U, Np) chlorido-ketoenaminate complexes of the type [AnCl₂(TFB-<i>t</i>BuA)₂(THF)] (<b>An-1</b> type: <b>U-1</b>, <b>Np-1</b>; TFB-<i>t</i>BuA = 4-(<i>tert</i>-butylamino)-1,1,1-trifluorobut-3-en-2-one) and the homoleptic Np^IV heteroarylalkenolate complexes [Np(PyTFP)₄] (<b>Np-2</b>, PyTFP = 1-(pyridin-2-yl)-3,3,3-trifluoroprop-1-en-2-ol) and [Np(DMOTFP)₄] (<b>Np-3</b>, DMOTFP = 1-(4,5-dimethyloxazol-2-yl)-3,3,3-trifluoroprop-1-en-2-ol) were synthesized and characterized (SC-XRD, NMR, Vis-NIR, MS). While their solid-state structures compare well to those of their uranium analogues, the behavior in solution showed significant differences. The binding motif of the DMOTFP ligand in complex <b>Np-3</b> can change to form two different complex isomers, as seen by paramagnetic chemical shifts in NMR experiments. Furthermore, the flexibility and the influence of the steric effects at the <i>N</i>-side of the ligands are discussed and compared with its uranium counterpart.