Synthese, FIR-Spektren und Kristallstrukturen der Pentaselenide K2Se5 und [Na(15-Krone-5)l2Se5 Syntheses, FIR Spectra, and Crystal Structures of the Pentaselenides K 2Se5 and [Na( 15-crown-5)]2Se5

K 2 Se5 has been prepared by crystallization from a potassium polyselenide solution in DM F. In a similar way [Na(15-crown-5)]2Se5 can be prepared by crystallization from a sodium poly­ selenide solution in D M F in the presence o f 15-crown-5. Both compounds were characterized by FIR spectroscopy as well as by X-ray structure determinations. K 2 Se5: Space group P 2,2,2,, Z 4, 1659 observed independent reflections, R = 0.061. Lat­ tice dimensions at -9 0 °C; a = 671.5(5), b = 694.9(5), c = 1776.4(9) pm. The compound crys­ tallizes with the K 2 S5 type structure. [Na(15-crown-5)]2Se5: Space group P 1, Z = 2, 3026 observed indenpendent reflections, R = 0.140. Lattice dimensions at -1 0 0 °C: a = 853.7(5), b = 1042.8(10), c = 2011.0(10) pm; a = 88.95(5)°, ß = 79.42(5)°, y = 66.15(5)°. The compound forms an ion triple, in which the sodium ions are coordinated by the five oxygen atoms o f the crown ether molecules as well as by the terminal selenium atoms o f the pentaselenide chain. The rather high R value is a result o f the disordered crown ether molecules.