Aryl-Linked Salicylaldoxime-Based Copper(II) Helicates and “Boxes”: Synthesis, X‑ray Analysis, and Anion Influence on Complex Structure

The synthesis and spectroscopic analysis
of both “metal-only”
and anion encapsulated salicylaldoxime-based complexes utilizing a
new 1,3-xylyl strap are described. X-ray crystallographic analysis
reveals that the aromatic spacer restricts the confirmation flexibility
of the resulting complexes leading to dicopper­(II) double helicate
and dicopper­(II) 2 + 2 “box” structural forms. The choice
of the structural motif is influenced by the anion present, with the
copper­(II) nitrate-containing complex [NO3⊂(Cu2L32)]­(NO3)3, 4, adopting a double helicate
form, whereas the analogous copper­(II) bromide complexes [2Br⊂(Cu2L32)]­(Br)2, 5, and [2Br⊂(Cu2L32)]­(BF4)2, 6, both adopt 2 + 2 “box” structural
configurations. Spectroscopic analysis has shown an enhancement in
the binding strength of ClO4– over the
anions SO42– and NO3–. The enhanced rigidity caused by the use of the 1,3-xylyl spacer
in this series of complexes has favored the formation of the “double
loaded” dibromide complex.