Figure 5. Energy diagram of the [Fe(azp)(qsal-Me)] molecules optimized at the B3LYP* functional in a gas phase at
298 K. The Gibbs energy of the LS isomer is set to zero.
In summary, we demonstrated the synthesis, crystal
structures, physical measurements, and theoretical calculations of the methyl-substituted neutral heteroleptic
Fe(III) complex 2 from the azobenzene ligand. The ligand orientational disorder, the HS-to-LS relaxation, and
computed TS energies revealed that the SCO transition
from the LS to HS state would be coupled to the pedallike motion of the azobenzene ligand, resulting in linkage isomerization in complex 2. This SCO-induced linkage isomerization indicates that the spin-state of a transition metal complex can switch not only the molecular
motion of a coordinated ligand but also the bonding and
dissociation of a coordination bond. The former leads to
the possibility of the on-off switch of motion for
molecular machines and actuators, the latter may lead to
the elucidation of a chemical reaction mechanism involved in metal complex catalysts and bioinorganic molecular functional systems having potential SCO metal
centers. Further investigations from the point of view of
intermolecular interactions are needed to clarify the
mechanisms of the unidirectional relaxation to the OR
isomer and the change in SCO transition.
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