Pyridine-based complexes of copper(II) chloride and bromide: ligand conformation effects on crystal structure. Synthesis, structure and magnetic behavior of Cu(2-Cl-3-X′py)₂X₂ [X, X′ = Cl, Br]

Reaction of copper(II) chloride or bromide with 2-chloro-3-bromopyridine or 2,3-dichloropyridine generates a family of compounds of the general formula L₂CuX₂ (1–4). X-ray crystallography shows that the bromide complexes (3-bromo-2-chloropyridine)dibromidocopper(II) (1) and (2,3-dichloropyridine)dibromidocopper(II) (3) are particularly unusual in that they crystallize with both the syn- and anti-conformation structures in the same crystal. A review of the literature on complexes of the formula (substituted-pyridine)₂CuX₂ suggests that these are the first examples of such complexes. The members of the family show a variety of magnetic behaviors and variable temperature magnetic susceptibility data indicate that 1 is essentially paramagnetic (θ = −0.9(1) K) while 3 is weakly ferromagnetic (J = 2.9(1) K). Compound 2 [(3-bromo-2-chloropyridine)dichloridocopper(II)] is fit by the uniform 1-D antiferromagnetic model (J = −19.6(1) K), while 4 [(2,3-dichloropyridine)dichloridocopper(II)] exhibits weak anti-ferromagnetic interactions (J = −3.68(3) K).