Coordination of trivalent lanthanum and cerium, and tetravalent cerium and actinides (An = Th(iv), U(iv), Np(iv)) by a 4-phosphoryl 1H-pyrazol-5-olate ligand in solution and the solid state??

Dalton Transactions Pub Date: 2021-02-12 DOI: 10.1039/D1DT00365H

Abstract

Structural investigations of three actinide(IV) 4-phosphoryl 1H-pyrazol-5-olate complexes (An = Th(IV), U(IV), Np(IV)) and their cerium(IV) analogue display the same metal coordination in the solid state. The mononuclear complexes show the metal centre in a square antiprismatic coordination geometry composed by the two O-donor atoms of four deprotonated ligands. Detailed solid state analysis of the U(IV) complex shows that dependent on the solvent used altered arrangements are observable, resulting in a change in the coordination polyhedron of the U(IV) metal centre to bi-capped trigonal prismatic. Further, single crystal analyses of the La(III) and Ce(III) complexes show that the ligand can also act as a neutral ligand by protonation of the pyrazolyl moiety. All complexes were comprehensively characterized by NMR, IR and Raman spectroscopy. A single resonance in each of the 31P NMR spectra for the La(III), Ce(III), Ce(IV), Th(IV) and Np(IV) complex indicates the formation of highly symmetric complex species in solution. Extended X-ray absorption fine structure (EXAFS) investigations provide evidence for the same local structure of the U(IV) and Np(IV) complex in toluene solution, confirming the observations made in the solid state.

Graphical abstract: Coordination of trivalent lanthanum and cerium, and tetravalent cerium and actinides (An = Th(iv), U(iv), Np(iv)) by a 4-phosphoryl 1H-pyrazol-5-olate ligand in solution and the solid state
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