We present our attempts to prepare lamellar SnP 2 S 6 and CuInP 2 S 6 by metathesis reactions in aqueous media. Use of a SnCl 4 precursor unexpectedly led to the formation of the three-dimensional compound Sn II 2 P 2 S 6 rather than Sn IV P 2 S 6 . The crystallites thus obtained were about 65 nm in size, i.e., much larger than those previously synthesized from SnCl 2 . We correlate this with the smaller Sn/P ratio ( (1), which implies fewer nucleation sites and probably enhanced particle growth in the present case. The product tested positive for second-harmonic generation (SHG) at room temperature (RT). Initial 31 P NMR-MAS spectroscopy data indicate that this material is in an intermediate state between the ferroelectric and paraelectric phases of crystalline Sn 2 P 2 S 6 . An analogous solution method readily yielded CuInP 2 S 6 , the first quaternary thiophosphate prepared via this soft-chemistry route. A rather small coherence length + +27A > , equivalent to four layers, is found for this product; band broadening is also observed in the Raman spectrum. SHG measurements likewise revealed a signal for this material at RT; a non polar macroscopic state may, however, not be precluded, given the known order-disorder nature of the ferroelectric-paraelectric transition in crystalline CuInP 2 S 6 .