Synthesis and structure of crystalline complexes of Np(V) with 1,10-phenanthroline-2,9-dicarboxylic acid. Complexation in solution and spectral studies

Complexes of Np(V) with 1,10-phenanthroline-2,9-dicarboxylic acid, C 12H6N2(COOH)2 (H2PDA), of the compositions [(NpO2)2(PDA)(H2O) 3]·H2O (I), (NH4)2[NpO 2(PDA)]2·3H2O (II), and [C(NH 2)3]2[NpO2·(PDA)] 2·4H2O (III) were synthesized. The Np atoms in the crystal lattices of all the compounds have the pentagonal bipyramidal coordination surrounding, with the [C12H6N 2(COO)2]2- anions acting as chelate-bridging N,O-donor ligands. In the structure of I, two crystallographically independent NpO 2 + dioxocations participate in the cation-cation interaction leading to the formation of tetrameric cation-cation complexes. The nonequivalence of the Np atoms is manifested in splitting of the main absorption band of Np(V) in the electronic spectrum of solid compound I. The structures of II and III are based on dimeric anionic complexes [NpO2(C 12H6N2(COO)2)] 2 2-. Only one kind of complexes, NpO2(PDA)-, was detected in the solution, and high value of the concentration stability constant β, ∼1012 L mol-1, is due to tetradentate coordination of the ligand. © 2014 Pleiades Publishing, Inc.