Molecular Polyselenide Anions Sandwiched between Cationic Extended Metal Hydroxides: Synthesis and Structures of [Sr 2 Sn(OH) 6 (H 2 O) 6 ]Se 4 and [Sr 2 Sn(OH) 6 (H 2 O) 5 ]Se 3 ·H 2 O

Two new strontium tin hydroxy polyselenides [Sr 2 Sn(OH) 6 (H 2 O) 6 ]Se 4 ( 1 ) and [Sr 2 Sn(OH) 6 (H 2 O) 5 ]Se 3 · H 2 O ( 2 ) were synthesized from hydrothermal reactions. Their structures were determined from single‐crystal X‐ray data measured at 218 K. Compound 1 crystallized in the space group P $\bar{1}$ with a = 5.935(1), b = 8.440(1), c = 9.464(2) Å, α = 97.292(2)°, β = 104.957(2)°, γ = 110.328(2)°. Compound 2 crystallized also in the space group P $\bar{1}$ with a = 10.658(2), b = 11.082(2), c = 15.797(2) Å, α = 73.303(4)°, β = 74.942(4)°, γ = 64.627(3)°. Both compounds have structures containing infinite cationic layers of hydrated metal hydroxides built from Sn(OH) 6 octahedra and Sr(OH, H 2 O) n polyhedra. Molecular Se 4 2– and Se 3 2– anions are located in the interlayer spaces of 1 and 2 , respectively. The Se 4 2– anions of 1 adopt a flat zigzag conformation with a torsion angle of 0°.