Structure and properties of ET charge transfer salts with cobalt(II)/zinc(II) anion networks templated by urea

Abstract New compounds (ET)5[MIICl4][MIICl3(u)](u)2, MII = Co (1), Zn (2) and α-(ET)2[(u)2(H)]ZnCl4 (3) have been prepared and characterized. Urea (u) was used as a template for creating anionic layers in ET-based layered charge transfer salts, ET = bis(ethylenedithio)tetrathiafulvalene. In the anion layers of 1 and 2, urea molecules form chains, in the channels between which there are chains of tetrahedral anions [MIICl4]2‾ and [MIICl3(u)]‾, these chains being parallel to the ribbons of ET radical cations from cation layers. In the anion layers of 3, the [ZnCl4]2- anions and the [(u)2(H)]+ cations alternate in a checkerboard pattern and form hydrogen-bonded chains parallel to the ET stacking direction in cation layers. Electrical transport studies reveals that 1 and 2 behave as metals down to 75 and 65 K, respectively, and 3 is a semiconductor with activation energy of 0.1 eV. Magnetic susceptibility of 1 defined mainly by cobalt(II) anions follows the Curie-Weiss law. The Weiss temperature value (+0.6 K in the 10-300 K range) indicates weak magnetic coupling between the cobalt(II) spins. In the EPR spectrum of 1, one signal attributed to the ET radical cation is detected down to 60 K, and wide signals from cobalt are superimposed below this temperature.