Cation–Cation Interactions in Neptunium(V,VI)-diglycolamide System

The SC-XRD structure and Raman spectra of two new mixed-valence Np(V)-Np(VI) compounds with cation-cation interactions (CCIs) using TEDGA (tetraethyldiglycolamide, belonging to the diglycolamide family) as a ligand are reported: a trimeric species, [NpVO2(TEDGA)2]2[NpVIO2(NO3)2](NO3)2 (1), which is the first neptunium representative of a linear actinide trimer with CCIs, and a dimeric species, [NpVO2(TEDGA)2][NpVIO2(NO3)3]·CH3CN (2). These two structures were prepared thanks to controlled and reproducible syntheses, based on the mixing of the two monomer solutions in an inert solvent: a Np(V)-TEDGA monomer solution mixed with a dinitrate or trinitrate Np(VI) solution. To better understand the impact of the CCIs on the actinyl cation electronic properties, these structures were compared to the constituent monomers, [NpVO2(TEDGA)2]+ (3), which was also synthesized, and NpVIO2(NO3)2(H2O)2. To complete the series, the [NpVIO2(TEDGA)2]2+ (4) monomer is also reported. In addition, DFT calculations were performed to aid in interpreting the Raman experimental data, to characterize the bonding in such polynuclear species, and to identify the main parameters influencing the stability of cation-cation structures, such as the nature of counterions, the influence of alkyl chains and the presence of weak intra- or intermolecular interactions.