Syntheses, Structures, and Mesomorphism of a Series of Cu(II) Salen Complexes with 4-Substituted Long Alkoxy Chains

Abstract

A series of copper(II) salen complexes containing 4-substituted alkoxy chains of aromatic rings [Cu((4-C _n H_2n+1O)₂salen)] (n = 3 ( 1 ), 4 ( 2 ), 6 ( 3 ), 8 ( 4 ), 10 ( 5 ), 12 ( 6 ), 14 ( 7 ), 16 ( 8 ), 18 ( 9 ), and 20 ( 10 ) and salen (N,N'-ethylenebis(salicylideneiminato)) has been prepared, and single-crystal structures of 2  · H₂O, 4 , and 6 by an X-ray crystallographic analysis have been revealed. Complexes 4 and 6 form tetrahedrally distorted square planer structure with one-dimensional polymeric stacking by van der Waals interaction between the dramatically distorted salen moieties. Complexes 1 – 3 did not exhibit any mesophases, but complexes 4 – 10 with longer alkoxy chains of n = 8–20 showed the metallomesogen of a lamello-columnar (ColL) mesophase in the smectic layers with the nearly constant stacking distances, irrespective of the variation of the alkoxy chain lengths by the X-ray diffraction measurements, which show similar behaviors to the corresponding Ni(II) complexes of n = 14–20. The molecular assemblies and mesomorphic properties in relation to the single-crystal structures of 4 and 6 with the liquid crystals at higher temperature are discussed.

Keywords:

• crystal structure
• Cu(II) complexes
• metallomesogen
• salen ligand with 4-substituted long alkoxy chains

ACKNOWLEDGMENTS

We are grateful to the Nara Women's University Intramural Grant for Project Research.

Notes

^a DMF was used.

^b Scan speed: 100 mV/s.

^a Phase nomenclature: K = crystal, M = mesophase, and I.L. = isotropic liquid.

#: Halo of the melton alkoxy chains.