Flux Growth of [NaK<sub>6</sub>F][(UO<sub>2</sub>)<sub>3</sub>(Si<sub>2</sub>O<sub>7</sub>)<sub>2</sub>] and [KK<sub>6</sub>Cl][(UO<sub>2</sub>)<sub>3</sub>(Si<sub>2</sub>O<sub>7</sub>)<sub>2</sub>]: The Effect of Surface Area to Volume Ratios on Reaction Products

2016-02-02T00:00:00Z (GMT) by Gregory Morrison Hans-Conrad zur Loye
Single crystals of two new salt-inclusion uranium­(VI) silicates, [NaK<sub>6</sub>F]­[(UO<sub>2</sub>)<sub>3</sub>(Si<sub>2</sub>O<sub>7</sub>)<sub>2</sub>] and [KK<sub>6</sub>Cl]­[(UO<sub>2</sub>)<sub>3</sub>(Si<sub>2</sub>O<sub>7</sub>)<sub>2</sub>], were grown from mixed alkali halide salt fluxes. Both compounds crystallize in the [NaRb<sub>6</sub>F]­[(UO<sub>2</sub>)<sub>3</sub>(Si<sub>2</sub>O<sub>7</sub>)<sub>2</sub>] structure type in the orthorhombic space group <i>Pnnm</i> with lattice parameters <i>a</i> = 11.0819(5) Å, <i>b</i> = 13.1149(6) Å, and <i>c</i> = 7.8418(4) Å ([NaK<sub>6</sub>F]) and <i>a</i> = 11.0830(7) Å, <i>b</i> = 13.5850(4) Å, and <i>c</i> = 7.8693(5) Å ([KK<sub>6</sub>Cl]). The surface area to volume (sa/vol) ratio of the reaction, controlled by the reaction vessel dimensions, has a strong influence on the reaction products with small sa/vol ratios favoring the growth of the salt-inclusion phases. Both compounds exhibit the typical luminescence of the uranyl group with the luminescence of [KK<sub>6</sub>Cl]­[(UO<sub>2</sub>)<sub>3</sub>(Si<sub>2</sub>O<sub>7</sub>)<sub>2</sub>] being less intense than [NaK<sub>6</sub>F]­[(UO<sub>2</sub>)<sub>3</sub>(Si<sub>2</sub>O<sub>7</sub>)<sub>2</sub>], likely due to quenching by the Cl<sup>–</sup> ions.