The effect of coordinated water on the connectivity of uranium(IV) sulfate x-hydrate: [U(SO4)2(H2O)5]•H2O and [U(SO4)2(H2O)6]•2H2O, and a comparison with other known structures

Two new solid-state uranium(IV) sulfate x-hydrate complexes (where x is the total number of coordinated plus solvent waters), namely catena-poly[[pentaaquauranium(IV)]-di-mu-sulfato-kappa O-4:O'] monohydrate], {[U(SO4)(2)(H2O)(5)]center dot H2O}(n), and hexaaquabis(sulfato-kappa O-2,O') uranium(IV) dihydrate, [U(SO4)(2)(H2O)(6)]center dot 2H(2)O, have been synthesized, structurally characterized by single-crystal X-ray diffraction and analyzed by vibrational (IR and Raman) spectroscopy. By comparing these structures with those of four other known uranium(IV) sulfate x-hydrates, the effect of additional coordinated water molecules on their structures has been elucidated. As the number of coordinated water molecules increases, the sulfate bonds are displaced, thus changing the binding mode of the sulfate ligands to the uranium centre. As a result, uranium(IV) sulfate x-hydrate changes from being fully crosslinked in three dimensions in the anhydrous compound, through sheet and chain linking in the tetra-and hexahydrates, to fully unlinked molecules in the octa-and nonahydrates. It can be concluded that coordinated waters play an important role in determining the structure and connectivity of U-IV sulfate complexes.