On the site symmetry of uranyl crown compounds in solution

Abstract

The spectroscopic properties of two uranyl crown ether complexes, [UO₂(18-crown-6)]²⁺ and [UO₂(dicyclohexano-18-crown-6)]²⁺, dissolved in acetonitrile and propylene carbonate were studied. UV/VIS and magnetic circular dichroism (MCD) spectra were recorded, as well as emission and excitation spectra. The inclusion complexes formed, have a distorted D_3d symmetry, which is common for a crown ether ring, coordinated with a central metal ion. The electronic transitions and vibrational progressions are identified in a D_∞h, D_3d and D₃ distortion scheme. Relaxation of the selection rules by vibronic coupling with the fundamental vibrations of uranyl is discussed.