Formation, structure, and optical properties of PuO22 + complexes with N,N,N′,N′-tetramethyl-3-oxa-glutaramide

Abstract

SynopsisPu atom is at the inversion center of the PuO2L2(ClO4)2 complex where L stands for N,N,N’,N’-tetrtametryl-3-oxa-glutaramide (TMOGA). Due to the forbiddance of the f-f transitions, PuO2L2(ClO4)2 in solution is “silent” in near IR optical absorption and PuO2L2(ClO4)2 in solid does not have significant diffuse reflectance bands.The variation of the absorption spectra of Pu(VI) in the presence of a tridentate organic ligand, N,N,N′,N′-tetramethyl-3-oxa-glutaramide (TMOGA denoted as L), was interpreted with the assumption that the 1:2 complex, PuO2L2(ClO4)2, is “silent” in optical absorption of the near IR region because the f–f transitions of Pu(VI) are forbidden due to the high symmetry of the complex. To test the assumption and demonstrate the validity of the Laporte's rule that governs the probability of f–f transitions, crystals of the PuO2L2(ClO4)2 complex were synthesized from the aqueous solution and characterized with single-crystal X-ray diffraction and diffuse reflectance spectra. The structural data, showing that the square-based prism salt crystallized in a highly symmetrical tetragonal space group, I4/mcm, and the plutonium atom is on a center of inversion at the intersection of three perpendicular mirror planes, support the above assumption. The diffuse reflectance spectra of the solid PuO2L2(ClO4)2 also showed no significant bands in the near IR region, consistent with the “silent” feature in the absorption spectra of this complex in solution.