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

1.4.3 Coordination Complexes of Thiazyl and Selenazyl Radical Ligands
Quite a few examples of coordination complexes for nitronyl nitroxide (I-2) 135,136
and verdazyl (I-8) 136,137 radicals have been demonstrated, however of particular interest
to the present work are thiazyl based coordination complexes.
For this reason the
primary focus of this section will be on these types of molecular systems.
A very interesting thiazyl based complex came from the coordination of TTTA (I-
14a) to Cu 2+ with ancillary hexafluoroacetylacetonato (hfac) ligands (I-21). 138 The
radical coordinated in a monodendate fashion and bridged neighbouring copper nuclei via
coordination of one of the nitrogen atoms from the 1,2,5-TDA ring and the nitrogen atom
from 1,3,2-DTA ring (where the majority of the spin density associated with the radical
character resided) such that copper atoms were arranged at an angle of approximately 90°
to one another. The two radical moieties attached to each copper atom are trans to one
another such that the hfac ligands make up the equatorial sites of the distorted octahedral
geometry. A Cu 2+
ion has 9 d-electrons and is therefore sensitive to a Jahn-Teller
2
distortion resulting in the d 2 x -y orbital being higher in energy than the other d-orbitals
and would therefore be the only half full orbital. Therefore this orbital would be the only
one available to interact with the SOMO of the radical, predicting a ferromagnetic
relationship based on the model proposed in Figure 1-16. However this only holds true
for the radical coordinated via the nitrogen atom of the 1,3,2-DTA ring. Since the second
radical is perpendicular to the equatorial plane of the metal center defined by the hfac
ligands, there is an electrostatic interaction between a sulfur atom from the 1,3,2-DTA
ring and one of the equatorial oxygen positions. Shown in Figure 1-16a, this interaction
40