Large magnetic anisotropy of chromium(III) ions in a bis(ethylenedithio)tetrathiafulvalenium salt of chromium bis(dicarbollide), (ET)2[3,3'-Cr(1,2-C2B9H11)2]

The synthesis of a radical-cation salt based on a derivative of tetrathiafulvalene, (ET)(2)[3,3'-Cr(1,2-C2B9H11)(2)] (ET = bis(ethylenedithio)tetrathiafulvalenium), was accomplished by electrochemical anodic oxidation of ET in the presence of (Me4N)[3,3A '-Cr(1,2-C2B9H11)(2)] in the galvanostatic regime. An electric conductivity sigma (293 K) = 7 x 10(-3) Ohm(-1) cm(-1) with semiconductor activation energy E-a congruent to 0.1 eV in the range of 127-300 K was observed. The crystal structure of (ET)(2)[3,3'-Cr(1,2-C2B9H11)(2)] was determined by X-ray diffraction at 173 K, revealing the presence of structural tetramers in radical-cation stacks. The magnetic properties of the complex were investigated in the temperature range 1.8-300 K using magnetometry and EPR, showing that the magnetic structure of (ET)(2)[3,3'-Cr(1,2-C2B9H11)(2)] consists of two independent magnetic subsystems. Cation radicals form a rectangular magnetic lattice in the ab-plane with significant antiferromagnetic exchange interactions. The chromium bis(dicarbollide) anions are characterized by unusually strong positive zero-field splitting of the Cr(III) ions, which was confirmed by ab initio calculations.