Characterization of the 1:1 Charge-Transfer Reaction between Decamethylferrocene and 2,3-Dichloro-5,6-dicyanoquinone (DDQ): Structure of the DDQH- Anion

Article abstract of DOI:10.1021/ja00380a015

The 1:1 charge-transfer reaction of decamethylferrocene (DMeFc) and 2,3-dichloro-5,6-dicyanoquinone (DDQ) results in a heterosoric stacked complex of +*>-> composition where the DDQH^- anion has a structure intermediate between the quinoid and benzenoid states.The crystal structure of the 1:1 complex +*>-> has been determined by single-crystal X-ray diffraction.The material crystallizes in the orthorhombic space group, Pbna, with unit cell parameters a = 17.027 (3) Angstroem, b = 14.497 (4) Angstroem, c = 10.616 (1) Angstroem, V = 2620.4 (14) Angstroem³, Z = 4, ρ = 1.40 g cm^-3.The data were collected on a four-circle Syntex P2₁ diffractometer, and the structure was solved by direct methods and refined with Fourier and full-matrix least-squares techniques.The final R_F was 0.054 for 2409 independent reflections where F²_obsd > ?F²_calcd.The crystal structure consists of heterosoric stacks of alternating DMeFc⁺* and DDQH^- ions along the c axis.Each ion has C₂ symmetry, the DDQH^- ion being disordered.The planar DDQH^- anion and C5Me5 rings of the DMeFc⁺* ion are separated by 3.564 Angstroem.The angle between the C⁵ and DDQH^- plane is 3.33 grad.The structure of the DDQH^- ion is intermediate between the quinoid and benzenoid states with C=C bond distances of 1.368 (5) and 1.384 (4) Angstroem and C-C bond distances of 1.454 (3) and 1.445 (3) Angstroem.The C=O, C-Cl, and C<*>N distances are 1.237 (3), 1.732 (2), and 1.101 (3) Angstroem, respectively.The DMeFc⁺* is ordered, and the C5Me5 rings are staggered by 26 grad with the methyl groups directed away from the Fe atom and out of the C5Me5 plane by 0.30-0.74 Angstroem.The average Fe-C, C-C, and C-Me bond distances are 2.096 (2), 1.422 (3), and 1.505 (3) Angstroem, respectively.The spin susceptibility at room temperature is 5.00 * 10^-3 emu/mol or 3.5 μ_B for fully oriented samples (g₁ of DMeFc⁺* parallel to the magnetic field).This is consistent with a S = 1/2 DMeFc⁺*, which possesses g_<*> = 1.92 and g_<*> = 4.002.The magnetic susceptibility fits the Brillouin function for all temperatures studied (>/- 1.80 K) and for magnetic fields up to 8 T.There is no evidence for exchange coupling among the DMeFc⁺* spins, in contrast to the behavior observed for (DMeFc⁺*)(TCNQ^-*).Comparison of the magnetic properties of these two compounds demonstrates the important role of the presence of a spin on the acceptor molecule in mediating the exchange interaction between DMeFc⁺* units.