Experimental and quantum mechanical characterization of an oxygen‐bridged plutonium(IV) dimer

We report the synthesis and characterization of K 4 {[PuCl 2 (NO 3 ) 3 ] 2 (mu 2 -O)}.H 2 O, which contains the first known mu 2 -oxo bridge between two Pu IV metal centers. Adding to its uniqueness is the Pu-(mu 2 -O) bond length of 2.04 A, which is the shortest of other analogous compounds. The Pu-(mu 2 -O)-Pu bridge is characterized by the mixing of s -, d -, and p -orbitals from Pu with the p -orbitals of O; the 5 f -orbitals do not participate in bonding. Natural bond orbital analysis indicates that Pu and O interact through one 3c-2e sigma Pu-O-Pu and two 3c-2e pi Pu-O-Pu bonding orbitals and that the electron density is highly polarized on the mu 2 -O. Bond topology properties analysis indicates that the Pu-(mu 2 -O) bond shares both ionic and covalent character. Quantum mechanical calculations also show that the dimer has multiconfigurational ground states, where the nonet, septet, quintet, triplet, and singlet are close in energy. This work demonstrates the interplay between experimental and computational efforts that is required to understand the chemical bonding of Pu compounds.