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⊂(Cu2L(3)2)3, 4, adopting a double helicate form, whereas the analogous copper(II) bromide complexes 2Br⊂(Cu2L(3)2)2, 5, and 2Br⊂(Cu2L(3)2)2, 6, both adopt 2 + 2 "box" structural configurations. Spectroscopic analysis has shown an enhancement in the binding strength of ClO4(-) over the anions SO4(2-) 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.