Self-assembled Transition Metal Coordination Frameworks of ...

Manganese(II) complexes
D and E , etc. The g values other than that at ~2 of 19 and 20 were calculated from
the spectra without simulations. For all complexes, EPR spectral simulation was done
by considering them as mononuclear Mn(II) systems, i.e. under the investigation
conditions. The simulations of 19 (Fig. 5.7) and 20 (Fig. 5.8) are not matching well
with mononuclear Mn(H) models, as they doesn’t show g values other than at ~2;
however, the simulation at the hyperfine sextet could yield precise values of g and
A , though the D -term might be unreliable, due to wrong model usage. However, the
simulations of 21 (Fig. 5.9) and 22 (Fig. 5.10) are in well agreement with
experimental spectra and suggesting the possible decomposition of these complexes in
DMF.
All manganese complexes, except 23, exhibit a resonance at g '~“- 2, show a six
line hyperfine structure, which is due to the interaction of electron spin of manganese
ions with its own nuclear spin [=5/2. The g value for the hyperfine splitting is
indicative of the nature of bonding in the matrix. The strength of the hyperfine
splitting depends on the matrix into which the ion is dissolved and is mainly
determined by the electronegativety of the neighbors. This means a qualitative
measure of the covalency of the bonding in the matrix that can be determined from the
value of A ; the smaller the splitting, the more covalent the bonding of the anion. In
the spectra of all the complexes additional forbidden lines are observed in between
each of the two lines of the central hyperfine sextet. These lines are arising by the
violation of Am|= :k() of allowed transitions (Am,= il, Am|= :l:0).
The EPR spectrum of 19 exhibits a well-defined hyperfine sextet at g =1 .995.
Several additional features can be observed including five other ESR resonances at
g=7.l6l, g=4.002, g=3.239, g= 2.473 and g=l.582 as small disturbances. A
similar, but along with two sets of eleven lines are reported for a dinuclear Mn(H)
system in X-band frozen solution spectrum [35]. The hyperfine coupling constant
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