PRESSURE-INDUCED TEMPERATURE-DEPENDENCE OF A WEAK EXCHANGE COUPLING IN CHLOROBIS(1-PHENYL-3,5-DIMETHYLPYRAZOLE)COPPER(II) CRYSTALS

X-band EPR temperature and pressure (up to 450 MPa) measurements of th e chlorobis(1-phenyl-3,5-dimethylpyrazole)copper(II) crystal show that exchange coupling between Cu(II) ions is very weak with Absolute valu e of J = 0.003 86 cm-1 at room temperature. This coupling is temperatu re independent but decreases under pressure. Moreover, when pressure i s applied to the crystal, the J-value becomes temperature dependent an d decreases on cooling. Also the g(z)-factor and the line width value are affected by temperature and pressure. These effects are discussed and explained as a result of a decrease of the tilt angle between the pyrazole ring and Cu(II) coordination plane under pressure and a short ening of the Cu-N bond on cooling. Exchange coupling is suggested to b e ferromagnetic at normal conditions with an antiferromagnetic contrib ution appearing under pressure.