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-C 2 B 9 H 11 ) 2 ] (ET = bis(ethylenedithio)tetrathiafulvalenium), was accomplished by electrochemical anodic oxidation of ET in the presence of (Me 4 N)[3,3´-Cr(1,2-C 2 B 9 H 11 ) 2 ] in the galvanostatic regime. An electric conductivity σ (293 K) = 7 × 10 −3 Ohm −1 cm −1 with semiconductor activation energy E a ≅ 0.1 eV in the range of 127–300 K was observed. The crystal structure of (ET) 2 [3,3′-Cr(1,2-C 2 B 9 H 11 ) 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-C 2 B 9 H 11 ) 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.