6 Molecular and Crystal Structures of Polymorphic …
245
Fig. 6.13 1D column
structures (upper) and their
arrangements for the four
polymorphs of the o-Br
pyrazine dye: a Y-form
(KELGEO02), b YO-form
(KELGEO03), c RO-form
(KELGEO01) and d R-form
(KELGEO)
(a) Y
(b) YO
a
b
O
c
a
b
O
c
(c) RO
(d) R
a
b
O
c
a
b
O
c
terminal Cl atoms to form a 3D column arrangement. Conversely, in the YO form
of the o-Br derivative, one molecule forms two complementary Br–N interactions
between two neighbouring molecules to form the column arrangement along the
b-axis. This structural difference is considered to arise from the substituted position
of the halogen atom. Unlike the YO form of the o-Br derivative, the YO form of the