Stabilization of Sn2+ in K10Sn3(P2Se6)4 and Cs2SnP2Se6 Derived from a Basic Flux

K10Sn3(P2Se6)4 and Cs2SnP2Se6 stabilize the lower oxidation state of Sn2+. K10Sn3(P2Se6)4 crystallizes in the trigonal space group R3̅ with a = b = 24.1184(7) Å and c = 7.6482(2) Å at 100 K. Cs2SnP2Se6 crystallizes in P21/c with a = 10.1160(4) Å, b = 12.7867(5) Å, c = 11.0828(5) Å, and β = 94.463(3)° at 100(2) K. Electronic absorption spectra revealed band gaps of 1.82 eV for K10Sn3(P2Se6)4 and 2.06 eV for Cs2SnP2Se6. Solid-state magic-angle-spinning 31P NMR, UV−vis, Raman, and IR spectroscopy and thermal analysis studies of the compounds are reported.