Self-assembled Transition Metal Coordination Frameworks of ...

Chapter 5
lower than cubic. However, in eqn. (1) we can ignore the terms of the spin-spin
interactions, NZ interaction and the quadrupole interactions between pairs of nuclear
spins, since their magnitudes are very small compared to the other terms and the usual
linewidths observed in paramagnetic complexes. Therefore the Hamiltonian takes the
form,
F1, = /2,§,gs+D[sf-s(s+1)/3]+E(sj -sj)+ZI*'A,1, (2)
k—l
The construction of a proper model for the simulation is very hard, especially
in the lack of X-ray crystal structure data and fragmentation in DMF. However, the
Mn(II) systems were simulated by considering eqn. (2), as the taken spectra resembles
a possible fragmentation of all complexes to monomeric species, to get the magnetic
parameters.
In the zero field splitting terms, D is the axial zero field splitting term and E
is the rhombic zero field splitting parameter. If D and E are very small compared to
electron Zeem_an term, five ESR transitions corresponding to Ams= :|:l are expected.
But if D is very large, then only transition between |+ |— with a g value
of ~2 will be observed. However, for the case where D or E is very large, the
lowest doublet has effective g values of g"~2, g L ~6 for D¢0 and E=0, but for
D =0 and E #0 the middle Kramer’s doublet has an isotropic g value of 4.29 [30,
31]. Depending upon the values of D and A , the number of lines appear in the
spectra will be 30 or 24 or six [32].
In the present study, X-band EPR spectra of all the complexes in DMF at 77
K were recorded in a cw EPR spectrometer. The numerical data of these frozen
solution spectra were calculated by using EasySpin [33,34] written in MATLAB, and
allows fitting of the experimental spectra by simulations by variation of the
independent parameters including g , hyperfine coupling constant A , ZF S parameters
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