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

4.3 Discussion
Prior to the discovery of IV-2a, there were three different polymorphs known. The
first was structurally characterized in 1966 (IV-2b) 9 and shown to be in the space group
P2 1 2 1 2 1 . This initial report confirmed the 5-coordinate trigonal bipyramidal geometry
with chlorine atoms in the apical positions and the phenyl groups in the equatorial sites.
The structure was later refined by a different group with a reassignment of cell axes. 10
This latter group previously reported an attempt to isolate the mixed halide complex
SbPh 3 ClF, but instead revealed a different polymorph of IV-2 (IV-2c). 11
This polymorph
was also found to inhabit the P2 1 2 1 2 1 space group, however there were two molecules in
the asymmetric unit instead of the one observed in IV-2b. The molecular formula for IV-
2c was actually found to be Sb(C 6 H 5 )Cl 1.8 F 0.2 , which may account for the doubling of the
unit cell volume observed. A third polymorph with four crystallographically unique
molecules in the unit cell was also discovered to exist in the space group Pbca. This
polymorph (IV-2d) was thought to be a decomposition product of the a metal complex
with the molecular formula: [Os IV 2(μ-O)(μ-O 2 CCH 3 ) 2 Cl 4 (SbPh 3 ) 2 ]. 12 The crystallographic
data for each of these polymorphs have been summarized in table 4-1.
Several small-scale crystal growth experiments were performed on commercially
obtained IV-2. It was found that when a solution of the compound in methylene chloride
or acetonitrile was slowly concentrated to dryness in the atmosphere, polymorph
IV-2b was obtained exclusively. By contrast, it was found that when the solvent was
flash distilled from an acetonitrile solution, clear, colourless crystalline needles, rods and
plates were formed. The majority of the sample was found to be the colourless needles
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