1,2,3-Dithiazolyl and 1,2,35-Dithiadiazolyl Radicals as Spin-Bearing ...

single molecular unit. Upon closer inspection of the crystallographic data it was noted
that there were close contacts between the sulfur atom of the DTDA ring and an oxygen
atom of one of the ancillary hfac ligands of a neighbouring molecule which were within
the sum of the van der Waals radii of the two nuclei. This interaction which can be seen
in Figure 2-13 resulted in an additional antiferromagnetic exchange term between the
radical from one molecule and the metal center of another. The outcome was that the
spin vectors for the two manganese ions were oriented the same direction for a total spin
of S = 5. The antiferromagnetic coupling interaction resulted in the two radical units
having the opposite spin reducing the ground state spin to S = 4 for the two-molecule
system.
Calculations were carried out on II-12 and it was determined that the sulfur atom had
substantial positive spin density and the oxygen which it was close to, possessed negative
spin density. The shape of the molecular orbitals located at the positions of the atoms in
question was such that a non-orthogonal overlap would be expected to give rise to the
observed antiferromagnetic coupling.
This was important as it provided insight to the pathway of the intermolecular
communication for II-6 and II-9 that had previously been missing. These same close S-O
(or in the case of II-6, Se-O) contacts were present as depicted in Figure 2-7. However
another important feature of this data was the presence of the disorder of the radical
ligand. Figure 2-7 a shows that the pyramidal ring is super-imposed on the DSDA and
vice versa indicating that throughout the crystal lattice there is no preferred orientation of
the radical ligand. There are two differently oriented molecules within the unit cell of II-
6, and Molecule 1, as defined in Figure 2-7a, has no substantial close contacts with
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