Cation–Cation\nInteraction in Np(V) Perchlorates\nand Their Electronic Absorption Spectra

Four new Np(V) perchlorate complexes of the composition\n[NpO<sub>2</sub>(H<sub>2</sub>O)<sub>4</sub>]ClO<sub>4</sub> (orthorhombic)\n(<b>1</b>), [(NpO<sub>2</sub>)<sub>2</sub>(ClO<sub>4</sub>)(H<sub>2</sub>O)<sub>4</sub>]ClO<sub>4</sub>·H<sub>2</sub>O (<b>3</b>), [(NpO<sub>2</sub>)(UO<sub>2</sub>)(H<sub>2</sub>O)<sub>8</sub>](ClO<sub>4</sub>)<sub>3</sub> (<b>4</b>), and [(NpO<sub>2</sub>)<sub>2</sub>Cl(H<sub>2</sub>O)<sub>4</sub>]ClO<sub>4</sub>·2H<sub>2</sub>O (<b>5</b>) have been synthesized and\nstructurally characterized. The structure of previously known monoclinic\nmodification of NpO<sub>2</sub>ClO<sub>4</sub>·4H<sub>2</sub>O (<b>2</b>) has been determined at 100 K. The coordination\nenvironment of Np and U atoms in compounds <b>1</b>–<b>5</b> is pentagonal bipyramids. A cation–cation (CC) interaction\nwas found in structures <b>1</b>–<b>5</b>, in which\nthe NpO<sub>2</sub><sup>+</sup> ion manifests itself as a monodentate\n(<b>1</b>, <b>2</b>) or bidentate (<b>3</b>–<b>5</b>) ligand. CC bonds play a fundamental role in the crystal\nstructures of compounds <b>1</b>, <b>2</b>, and <b>4</b>. They are the main structure-forming bonds that form the\ncrystal package as a whole. The spectra of all compounds in the visible-near-IR\nrange were measured.