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

half a unit cell length. The distance between neighbouring molecules in this column can
be approximated by measuring the distance between consecutive antimony atoms giving
alternating values of 10.775(3) and 11.143(3) Å. The Sb2 and Sb3 containing molecules
by contrast do not pack in regular columnar arrays, but are actually stacked in mixed
molecular pairs, the distances between antimony atoms in one of these pairs is
comparable to that observed in the columns investigated thus far with a distance of
10.813(3) Å.
Polymorphs IV-2a and IV-2b both pack in noncentrosymmetric space groups
consistent with the columns observed. IV-2b shows head-to-tail orientation of the phenyl
rings of neighbouring columns, whereas IV-2a has these rings oriented in a head-to-head
fashion. Polymorph IV-2d has examples of both of these orientations and the direction
changes mid-unit cell as this polymorph packs in a centrosymmetric space group.
Recent studies indicate that polymorphism is quite common in organic chemistry 14
and organometallic chemistry 15
and is of significant importance within the
pharmaceutical industry. 16
IV-2 provides an example of an organometallic compound
which exists in several different polymorphic forms and shows some conformational
polymorphism related to relative positions of the phenyl rings. There is also evidence to
suggest that there is some degree of control associated with isolation of any of the
different polymorphs. The simplest packing arrangement seems to be obtained for the
thermodynamically preferred polymorph and can therefore be selected by growing the
crystals rather slowly. The phenyl rings in this polymorph can be likened to a propeller
type arrangement. If the crystals are grown more quickly, the molecules arrange
themselves in less symmetrical configurations associated with two of the other
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