Dimormorphism and Cocrystal Formation of 3-(Chloroacetamido)pyrazole

3-(Chloroacetamido)pyrazole (4) crystallizes in two different forms. Crystallization with chloroacetic
acid reveals a cocrystal. In the two polymorphs (4α and 4β), all hydrogen acceptors and hydrogen donors take part
in the formation of hydrogen bonds. In both structures, the molecules formed dimers through hydrogen bonds; in 4α
the site symmetry of the dimer is the 2-fold axis, and it has a bowl shape. The site symmetry of the dimer in (4β)
is inversion center, and it is planar. The 2-fold symmetry (in 4α) imposed on the four molecules that are hydrogen
bonded to the dimer a propeller-like arrangement with the molecules up and down alternately with regards to the
plane of the dimer. When inversion symmetry is present (in 4β), two molecules are up and two molecules are down
with respect to the plane of the dimer. In the cocrystal, a molecular compound is formed between a molecule of
3-(chloroacetamido)pyrazole (4) and chloroacetic acid. 3-(Chloroacetamido)pyrazole is also hydrogen bonded to two
other molecules of the same kind to form an infinite layered ribbon.