Scandium Selenophosphates: Structure and Properties of K4Sc2(PSe4)2(P2Se6)

The new compound K4Sc2P4Se14 was synthesized via the polychalcogenide flux method. It crystallizes in the space group C2/c, and the structure is composed of 1/∞[Sc2P4Se144–] chains that are separated by K+ cations. The structural motif features two [PSe4]3– units and one [P2Se6]4– unit bridging the Sc centers and has not been reported for any other compound. The 1/∞[Sc2P4Se144–] chains pack in a crosshatched pattern perpendicular to the c axis of the crystal, forming channels for half of the K+ atoms while the other half occupy empty space between the chains. The orange-yellow crystals of K4Sc2P4Se14 are air-sensitive and gradually turn red over the course of a couple hours. The band gap of the phase is 2.25(2) eV, and Raman spectroscopy shows the symmetric stretches of the selenophosphate groups to be at 231 and 216 cm–1 for the [PSe4]3– and [P2Se6]4– units, respectively. Solid-state 31P MAS NMR of K4Sc2P4Se14 shows two prominent peaks at 11.31 and −23.07 ppm and one minor peak at −106.36 ppm, most likely due to degradation of the product or an unknown second phase.