10.1021/cg060889g.s001
Gaurav Bhosekar
Gaurav
Bhosekar
Inke Jess
Inke
Jess
Zdenek Havlas
Zdenek
Havlas
Christian Näther
Christian
Näther
Structures and Properties of Three Polymorphic Modifications based on Tetrahedral Building Blocks of Dichlorobis(pyridazine-N) Zinc(II)
American Chemical Society
2007
space group Pna 21.
form III
Theoretical calculations show
DSC
Tetrahedral Building Blocks
space group Cc
tetrahedral building blocks
form III crystallizes
form II
2007-12-05 00:00:00
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Structures_and_Properties_of_Three_Polymorphic_Modifications_based_on_Tetrahedral_Building_Blocks_of_Dichlorobis_pyridazine_N_Zinc_II_/2970631
Reaction of zinc(II) chloride with pyridazine under different conditions leads to the formation of three polymorphic modifications of dichlorobis(pyridazine-N) zinc(II). Forms <b>I</b> and <b>II</b> crystallize monoclinic in space group <i>Cc</i> (<b>I</b>) and <i>P</i>2<sub>1</sub>/<i>c</i> (<b>II</b>), respectively, whereas form <b>III</b> crystallizes orthorhombic in space group <i>Pna</i>2<sub>1</sub>. In all three forms, the zinc atoms are surrounded by two chloro atoms and two pyridazine ligands within distorted tetrahedra, and the orientations of the pyridazine rings within these tetrahedra are different. In the crystal structure, the tetrahedral building blocks are packed differently and are connected by intermolecular C–H···Cl and C–H···N interactions. Crystallization experiments clearly show that form <b>I</b> represents the thermodynamically most stable form at room temperature, whereas forms <b>II</b> and <b>III</b> are metastable. Theoretical calculations show that in form <b>II</b> the most stable molecular structure is found, whereas the molecular structure in form <b>III</b> is less stable by only 8 kJ/mol. Differential thermoanalysis and thermogravimetry measurements reveal that all forms decompose into a new ligand-deficient compound [ZnCl<sub>2</sub>(pyridazine)], which can also be prepared in solution. Form <b>I</b> can be transformed into form <b>II</b>, which is more stable at higher temperatures as evidenced by differential scanning calorimetry (DSC) measurements. On some of the DSC measurements, form <b>I</b> decomposes without further transformation into form <b>II</b>. Both forms <b>I</b> and <b>II</b> behave enantiotropic. The DSC thermogram of form <b>III</b> gave no indication of a polymorphic transformation.