Dithiophene-TTF Salts; New Ladder Structures and Spin-Ladder Behavior

(α-DT-TTF)2[Au­(i-mnt)2] and (α-DT-TTF)2[Co­(mnt)2] are two new
salts of the donor α-dithiophene-tetrathiafulvalene with stable
diamagnetic anions, both presenting a ladder structure of the donors
organized in paired segregated stacks. The first one is isostructural
with previously reported closely related compounds and presents a
magnetic spin-ladder behavior with J∥= 83.5 K and J⊥ = 110.3 K as estimated
from spin susceptibility data in single crystals. (α-DT-TTF)2[Co­(mnt)2] presents a new structural type with
a different arrangement of pairs of donor stacks, alternating with
stacks of dimerized [Co­(mnt)2] anions which are however
arranged in an uncorrelated fashion perpendicular to the stacking
axis. Due to the strong coupling between the disordered anion chains
and the donor chains, this compound does not present a magnetic spin-ladder
behavior. The low temperature superstructure of (DT-TTF)2[Cu­(mnt)2] below the transition at 235 K, previously known
to be associated with a lattice doubling along the stacking axis,
was solved by synchrotron radiation diffraction in small single crystals.
It is found that this dimerization is due to donor charge localization
with the spin carriers being associated with fully oxidized donor
species alternating with neutral donors.