Exchange interactions in tropylium bis(1,2-dicyanoethylene dithiolato) nickelate (III)

The compound tropylium bis[l,2-dicyanoethylenedithiolato] nickelate (III), i.e., (C7H7)+[Ni(mnt)2]-, has been prepared and its crystal structure determined; the space group is P 21/c, Z=2, the unit cell axes are a=6.364, b=7.458, c=17.991 Å, and β= 91.22 °. The Ni(mnt)2-_ and C 7H7+ ions form segregated stacks in the direction of the b axis. This is in contrast with the structure of the analogous thiete complex (C7H7)+ [NiS2C 2(CF3)2]-, in which crystals alternating stacks of cations and anions are present. The susceptibility appears to be dominated by a strong one-dimensional, isotropic, antiferromagnetic exchange coupling (J0=-4.4 cm-1). However, the angular dependence of the EPR linewidth at room temperature has to be explained with an additional anisotropic exchange interaction of 0.26 cm-1. Furthermore, Q-band EPR measurements in the ab plane reveal a very small interstack exchange interaction (0.015 cm-1 at room temperature) which increases by a factor of 4 upon lowering the temperature to 8 K and which might be responsible for a possible long range order at low temperature. © 1981 American Institute of Physics.