TETRACYANOQUINODIMETHANE SALTS OF TRANSITION-METAL COMPLEXES .2. SINGLE-CRYSTAL ELECTRON-PARAMAGNETIC RESONANCE OF TRIS(1,10-PHENANTHROLINE)ZINC(II) BIS(TETRACYANOQUINODIMETHANIDE) AND TRIS(1,10-PHENANTHROLINE)COPPER(II) BIS(TETRACYANOQUINODIMETHANIDE)

The single-crystal and polycrystalline powder EPR spectra of the compounds Zn(phen)3(TCNQ)2 and Cu(phen)3(TCNQ)2 have been recorded at the X-band frequency in the temperature range 300-4.2 K. In the Zn derivative, a Frankel-type excitonic spectrum was observed attributed to one of the two magnetically nonequivalent TCNQ-ions seen in the crystal structure. The triplet exciton spectra were interpreted with a dipolar zero field splitting tensor with \D1\ = 66 (2) x 10(-4) cm-1 and \E1/D1\ = 0.12 (1). These values nicely agree with the spin density distribution computed with the X-alpha-SW method. Less intense features seen in the crystal spectra at temperatures lower than 20 K were assigned to a S = 2 state arising from exciton-exciton interactions. The zero field splitting of the S = 2 state was measured to be \D2\ = 35 (2) x 10(-4) cm-1 and \E2/D2\ = 0.07 (1). The EPR spectra of Cu(phen)3(TCNQ)2 showed only resonances due to one unpaired electron localized on a copper(II) center. The spectra have been found to be temperature dependent, the principal g values being g(x) = 2.037 (3), g(y) = 2.052 (3), and g(z) = 2.104 (3) and g(x) = 2.052 (3), g(y) = 2.057 (3), g(z) = 2.180 (3) at 290 and 4.2 K, respectively. This temperature dependence has been attributed to interactions of the copper(II) ion unpaired electron with the mobile triplet excitons of TCNQ-.