Single crystal EPR spectra

No information concerning the distribution of the unpaired electron on the chelate ligands of four-coordinated low-spin Co(II) Schiff base complexes is available from single crystal EPR spectra. In particular, no nitrogen hf interaction, which is sensitive to the ground state configurations, is observed. 

In most paramagnetic sandwich complexes the proton hf structure is not resolved in low temperature powder or single crystal EPR spectra. In vanadium dibenzene, a typical example of this type of compound, the poor resolution is due to the fact that the aromatic rings are rigidly frozen at T < 50 K and thus the proton hfs tensors of the benzene rings are no longer magnetically equivalent. 

The transition-metal component of [Pt(bipy)2][TCNQ]3 is also diamagnetic. The structure86 consists of stacks of trimers, [T CNQ], surrounded by non-interacting Pt(bipy)2+ cations. Adjacent trimers are closely spaced with an interplanar separation of only 3.33 A as compared with 3.23 A within the trimer. The magnetic properties of this system have been studied much less extensively than those of [TMPD]2[Ni(mnt)2]. Single crystal EPR spectra do show, however, that spins are interacting along the TCNQ stacks. Structurally, this compound is very different from the 1 2 compound [Pt(bipy)2][TCNQ]258> (Sect. 2) which forms Da stacks with the two TCNQ moieties <7-bonded to each other.. ... 

Computer simulation of randomly oriented or single-crystal EPR spectra from isolated or coupled paramagnetic centers is required to accurately determine the spin Hamiltonian parameters (Eqs. (1) and (2)) and the electronic and geometric structure of the paramagnetic center. The simulation of randomly oriented EPR spectra is performed in frequency space through the following integration [1,26] ... 

Since single-crystal epr spectra contain information about electron spin distribution it is necessary to know how the electron spin is distributed about the nuclear framework of a radical in order to infer how the radical is oriented. When the spin distributions of isolated radicals are known from index>endent sources, epr gives detailed information about the arramgement of the radicals in pairs. Naturally knowing this arrangement cam be uniquely helpful in detemining the factors which influence reactions of organic solids. 

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