Copper ion salts of arylthiotetrathiafulvalenes: synthesis, structure diversity and magnetic properties

The combination of CuBr(2) and arylthio-substituted tetrathiafulvalene derivatives (1–7) results in a series of charge-transfer (CT) complexes. Crystallographic studies indicate that the anions in the complexes, which are derived from CuBr(2), show diverse configurations including linear [Cu(I)Br(2)](–), tetrahedral [Cu(II)Br(4)](2–), planar [Cu(II)(2)Br(6)](2–), and coexistence of planar [Cu(II)Br(4)](2–) and tetrahedral [Cu(II)Br(3)](–) ions. On the other hand, the TTFs show either radical cation or dication states that depend on their redox potentials. The central TTF framework on most of TTFs is nearly planar despite the charge on them, whereas the two dithiole rings on molecule 4 in complex 4·CuBr(4) are significantly twisted with a dihedral angle of 38.3°. The magnetic properties of the complexes were elucidated. The temperature-dependent magnetic susceptibility of complex 5·Cu(2)Br(6) shows the singlet–triplet transition with coupling constant J = −248 K, and that of 3·(CuBr(4))(0.5)·CuBr(3)·THF shows the abrupt change at 270 K caused by the modulation of intermolecular interactions. The thermo variation of magnetic susceptibility for the other complexes follows the Curie–Weiss law, indicating the weak antiferromagnetic interaction at low temperature.