Self-assembled Transition Metal Coordination Frameworks of ...

Chapter 5
Broad signals above g=2, due to the S =5/2 ZFS has been reported for
distorted mononuclear octahedral Mn(H) [38] and dimanganese(Il) complexes [39].
So, here the presence of dinuclear species is hard to prove, as the same broad EPR
features may also arise from ZF S of mononuclear species [3]. Alternatively, partial
decomposition of the dimer to mononuclear species by the coordinating solvent may
give same result [3].
The spectra of 21 and 22 are more close to Mn(H) monomeric species, due to
possible decomposition to monomeric units, and similar to each other. The six line
manganese hyperfine pattem centered at g =l.995 for both compounds are in
accordance with the Mn(H) ions in an environment close to octahedral symmetry and
is known to arise from the transition between the energy levels of the lower doublet.
This is usually observed with complexes of weak field ligands, which give only one
g value close to 2.0023, the fiee electron g value.
The magnitude of the hyperfine splitting A estimated to be approximately
264 MHz (94.5 G) for complex 21 and 265 MHz (94.9 G) for 22 are consistent with
octahedral coordination [36]. It is seen that the Am values are somewhat lower than
those of the pure ionic compounds. The average separations of the forbidden
hyperfine lines lying between each of the two main hyperfine lines in the spectra are
approximately 55.8 MHz (20 G) for both compounds. For both the compounds, a D
value of 400 MHZ (1.3343>