Synthesis and Crystal Structure of Potassium Crown Ether Tetrathiosquarate

Slow diffusion of diethylether into a concentrated solution of K2C4S4·H2O and two equivalents of 18-crown-6 in pyridine affords dark orange crystals of bis(potassium{18-crown-6})(3-cyclobutene-1,2-dithione-3,4-dithiolate) (K(C12H24O6))2(C4S4). The crystal structure determination (monoclinic, P 21/n, a = 12.2095(8) A, b = 11.3263(8) A, c = 14.0552(7) A, β = 101.032(3)°, Z = 2) shows the presence of C4S4 2 ions with almost undistorted D4h symmetry having C-C bond lengths of 1.442(10) A and 1.478(8) A and C-S bond lengths of 1.651(8) A and 1.664(7) A. Since the K + ions are shielded in a half-spherical way by the crown ether ligands, the crystal structures is built of centrosymmetric molecular entities ((18-crown-6)K(C4S4)K(18-crown-6)). The K + ions have eight of coordination number, C4S4 2 acts as a chelating and bridging ligand towards two K + with K-S distances of 3.434(2) A and 3.380(2) A.