Synthesis, Crystal Structure and Thermal Reactivity of [ZnX2(2‐chloropyrazine)] (X = Cl, Br, I) Coordination Compounds

Abstract

AbstractReaction of zinc(II) halides with 2‐chloropyrazine in different solvents leads to the formation of five new coordination compounds that contain either only 2‐chloropyrazine or additional water molecules as donor ligands. In the ligand‐rich 1:2 compound catena[bis(2‐chloropyrazine‐N)]di‐μ‐chlorozinc(II) (1) the zinc atom is coordinated by two 2‐chloropyrazine ligands and four chlorine atoms in an octahedral fashion. The zinc atoms are connected by the chloride atoms forming linear chains. In the isotypic ligand‐rich 1:2 compounds bis(2‐chloropyrazine‐N)dibromozinc(II) (2) and bis(2‐chloropyrazine‐N)diiodozinc(II) (3) discrete complexes are found in which each zinc atom is coordinated by two 2‐chloropyrazine ligands and two halide atoms within distorted tetrahedra. The 1:1 compounds aqua‐(2‐chloropyrazine‐N)dibromozinc(II) (4) and aqua‐(2‐chloropyrazine‐N)diiodozinc(II) (5) are also isotypic and form discrete complexes in which the zinc atoms are surrounded by two halide atoms, one 2‐chloropyrazine ligand and one water molecule. Upon heating, compounds 1–5 form ligand‐deficient 1:1 and 2:1 compounds of composition [ZnX2(2‐chloropyrazine)] (X = halide) and [(ZnX2)2(2‐chloropyrazine)]. X‐ray powder diffraction shows that identical ligand‐deficient intermediates are obtained on decomposition of either [ZnX2L2] (L = 2‐chloropyrazine) or the [ZnX2L(H2O)] complexes. DFT calculations suggest that the formation of the [ZnX2L(H2O)] complex is energetically favoured for the heavier halide anions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)