The electron spin resonance g factor, linewidth and spin susceptibilit
y of single crystals of a fully deuterated bis(ethylenedithio)tetrathi
afulvalene (D8-ET) based conductor with Hg(SCN)2Cl- anions are present
ed. The spin susceptibility of the salt is thermally activated with an
omalies near the metal-insulator phase transition and a maximum of the
electrical conductivity. A discussion of the ESR parameters is given.