Uranyl

The uranyl ion is an oxycation of uranium in the oxidation state +6, with the chemical formula UO2+
2. It has a linear structure with short U–O bonds, indicative of the presence of multiple bonds between uranium and oxygen. Four or more ligands may be bound to the uranyl ion in an equatorial plane. The uranyl ion forms many complexes, particularly with ligands that have oxygen donor atoms. Complexes of the uranyl ion are important in the extraction of uranium from its ores and in nuclear fuel reprocessing.

The uranyl ion is linear and symmetrical, with both U–O bond lengths of about 180 pm. The bond lengths are indicative of the presence of multiple bonding between the uranium and oxygen atoms. Since uranium(VI) has the electronic configuration [ radon ], the electrons used in forming the U-O bonds are supplied by the oxygen atoms. The electrons are donated into empty atomic orbitals on the uranium atom. The empty orbitals of lowest energy are 7s, 5f and 6d. In terms of valence bond theory the sigma bonds may be formed using d_z² and f_z³ to construct sd, sf and df hybrid orbitals (the z-axis passes through the oxygen atoms). (d_xz, d_yz) and (f_xz² and f_yz²) may be used to form pi bonds. Since the pair of d or f orbitals used in bonding are doubly degenerate this equates to an overall bond order of three.

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