Progressive Transformation between Two Magnetic Ground States for One Crystal Structure of a Chiral Molecular Magnet

We report the exceptional observation
of two different magnetic ground states (MGS), spin glass (SG, TB = 7 K) and ferrimagnet (FI, TC = 18 K), for one crystal structure of [{MnII(D/L-NH2ala)}3{MnIII(CN)6}]·3H2O obtained
from [Mn­(CN)6]3– and D/L-aminoalanine, in contrast to one MGS for [{MnII(L-NH2ala)}3{CrIII(CN)6}]·3H2O. They consist of
three Mn­(NH2ala) helical chains bridged by MIII(CN)6 to give the framework with disordered water molecules
in channels and between the MIII(CN)6. Both
MGS are characterized by a negative Weiss constant, bifurcation in
ZFC-FC magnetizations, blocking of the moments, both components of
the ac susceptibilities, and hysteresis. They differ
in the critical temperatures, absolute magnetization for 5 Oe FC (lack
of spontaneous magnetization for the SG), and the shapes of the hysteresis
and coercive fields. While isotropic pressure increases both Tcrit and the magnetizations linearly and reversibly
in each case, dehydration progressively transforms the FI into the
SG as followed by concerted in situ magnetic measurements and single-crystal
diffraction. The relative strengths of the two moderate MnIII–CN–MnII antiferromagnetic (J1 and J2), the weak MnII–OCO–MnII (J3), and Dzyaloshinkii–Moriya antisymmetric (DM) interactions
generate the two sets of characters. Examination of the bond lengths
and angles for several crystals and their corresponding magnetic properties
reveals a correlation between the distortion of MnIII(CN)6 and the MGS. SG is favored by higher magnetic anisotropy
by less distorted MnIII(CN)6 in good accordance
with the Mn–Cr system. This conclusion is also born out of
the magnetization measurements on orientated single crystals with
fields parallel and perpendicular to the unique c axis of the hexagonal space group.