Structural Polarity Induced by Cooperative Hydrogen Bonding and Lone-Pair Alignment in the Molecular Uranyl Iodate Na<sub>2</sub>[UO<sub>2</sub>(IO<sub>3</sub>)<sub>4</sub>(H<sub>2</sub>O)]
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Na2[UO2(IO3)4(H2O)] has been synthesized under mild hydrothermal conditions. Its structure consists of Na+ cations and [UO2(IO3)4(H2O)]2- anions. The [UO2(IO3)4(H2O)]2- anions are formed from the coordination of a nearly linear uranyl, UO22+, cation by four monodentate IO3- anions and a coordinating water molecule to yield a pentagonal bipyramidal environment around the uranium center. The water molecules form intermolecular hydrogen bonds with the terminal oxo atoms of neighboring [UO2(IO3)4(H2O)]2- anions to yield one-dimensional chains that extend down the b axis. There are two crystallographically unique iodate anions in the structure of Na2[UO2(IO3)4(H2O)]. One of these anions is aligned so that the lone-pair of electrons is also directed along the b axis. The overall structure is therefore polar, owing to the cooperative alignment of both the hydrogen bonds and the lone-pair of electrons on iodate. The polarity of the monoclinic space group C2 (a = 11.3810(12) Å, b = 8.0547(8) Å, c = 7.6515(8) Å, β = 90.102(2)°, Z = 2, T = 193 K) found for this compound is consistent with the structure. Second-harmonic generation of 532 nm light from a 1064 nm laser source yields a response of approximately 16× α-SiO2.
