Abstract. K2(CsHs).(CH3OCH2CH2)20, (K2COT.diglyme), orthorhombic, Pnma, a = 7.689 (3), b = 15.376 (5), c= 13.703 (5) A (from diffractometer data), Z=4, Dx= 1.30 g cm -3. The packing of the K + and COT 2-ions may be described as a zigzag chain of K2COT units. This chain is in the direction of the a axis and is embedded in a diglyme environment. Only one potassium ion of each K2COT unit is coordinated by the complexing ether, diglyme.Introduction. The crystals were prepared under exclusion of air and water by slowly adding a mixture of diglyme and tetrahydrofuran (THF) (1:2) to a 0.8 mol K2COT solution in THF. After one day single crystals separated out. The results of an elementary analysis are K, 24"60 (24"71), C, 52"82 (53.12) and H, 7.07 (7-01)%. (Values in parentheses are the calculated ones.) The crystals are very sensitive to air. Therefore they were mounted in paraffin (m.p. 42-44°C) in thin-walled glass capillaries under a He atmosphere. Unit-cell dimensions and intensities were obtained from a crystal of approximate dimensions 0.4 × 0-3 × 0.2 ram, with a computer-controlled Nonius CAD-3 diffractometer (Cu Ks radiation, Ni-filtered, 0-20 scan). Systematic