Hydroflux Crystal Growth of Platinum Group Metal Hydroxides: Sr<sub>6</sub>NaPd<sub>2</sub>(OH)<sub>17</sub>, Li<sub>2</sub>Pt(OH)<sub>6</sub>, Na<sub>2</sub>Pt(OH)<sub>6</sub>, Sr<sub>2</sub>Pt(OH)<sub>8</sub>, and Ba<sub>2</sub>Pt(OH)<sub>8</sub>

Crystals of five complex metal hydroxides containing platinum group metals were grown by a novel low-temperature hydroflux technique, a hybrid approach between the aqueous hydrothermal and the molten hydroxide flux techniques. Sr<sub>6</sub>NaPd<sub>2</sub>(OH)<sub>17</sub> (<b>1</b>) crystallizes in orthorhombic space group <i>Pbcn</i> with lattice parameters <i>a</i> = 19.577(4) Å, <i>b</i> = 13.521(3) Å, and <i>c</i> = 6.885(1) Å. This compound has a three-dimensional framework structure with Sr­(OH)<sub><i>n</i></sub> polyhedra, Na­(OH)<sub>6</sub> octahedra, and Pd­(OH)<sub>4</sub> square planes. Isostructural phases Li<sub>2</sub>Pt­(OH)<sub>6</sub> (<b>2</b>) and Na<sub>2</sub>Pt­(OH)<sub>6</sub> (<b>3</b>) crystallize in trigonal space group <i>P</i>-3 with lattice parameters of <i>a</i> = 5.3406(8) Å and <i>c</i> = 4.5684(9) Å and <i>a</i> = 5.7984(8) Å and <i>c</i> = 4.6755(9) Å, respectively. Structures of these materials consist of layers of A­(OH)<sub>6</sub> (A = Li (<b>2</b>), Na (<b>3</b>)) and Pt­(OH)<sub>6</sub> octahedra. Sr<sub>2</sub>Pt­(OH)<sub>8</sub> (<b>4</b>) crystallizes in monoclinic space group <i>P</i>2<sub>1</sub>/<i>c</i> with lattice parameters <i>a</i> = 5.9717(6) Å, <i>b</i> = 10.997(1) Å, <i>c</i> = 6.0158(6) Å, and β = 113.155(2)°, while Ba<sub>2</sub>Pt­(OH)<sub>8</sub> (<b>5</b>) crystallizes in orthorhombic space group <i>Pbca</i> with lattice parameters <i>a</i> = 8.574(2) Å, <i>b</i> = 8.673(2) Å, and <i>c</i> = 10.276(2) Å. Both of these compounds have three-dimensional structures composed of Pt­(OH)<sub>6</sub> octahedra surrounded by either Sr­(OH)<sub>8</sub> or Ba­(OH)<sub>9</sub> polyhedra. Decomposition of these materials into condensed metal oxides, which is of importance to possible catalytic applications, was monitored via thermogravimetric analysis. For example, Na<sub>2</sub>Pt­(OH)<sub>6</sub> (<b>3</b>) converts cleanly via dehydration into α-Na<sub>2</sub>PtO<sub>3</sub>.