Solvothermal Synthesis and Structure of a New Selenium-Rich Selenophosphate K3PSe4·2Se6

The compound K3PSe4·2Se6 was synthesized at 110 °C via solventothermal techniques from binary starting materials and Se in acetonitrile. The compound crystallizes in the space group Fd3̄ of the cubic system with eight formula units in a cell with a dimension of a = 16.415(2) Å at T = 193 K. The structure contains an unusual intermixing of ionic and uncharged species. The selenophosphate tetrahedral trianions PSe4 3- are surrounded by potassium cations; other potassium cations in the structure are coordinated to 12 selenium atoms from four Se6 rings in a tetrahedral arrangement. There are no short contacts between adjacent selenium rings. Heating the same reaction mixture to 160 °C results in the formation of only needles of trigonal selenium.