Syntheses, structures, and mesomorphism of a series of Ni(II) salen complexes with 4-substituted long alkoxy chains

Abstract

A series of nickel(II) salen complexes containing 4-substituted alkoxy chains of aromatic rings, [Ni((4-C n H 2 n + 1 O) 2salen)] ( n = 3 ( 1), 4 ( 2), 6 ( 3), 8 ( 4), 10 ( 5), 12 ( 6), 14 ( 7), 16 ( 8), 18 ( 9), and 20 ( 10)), and their parent complex, [Ni((4-HO) 2salen)] ( 11) (salen = N, N′-ethylenebis(salicylideneiminato)), have been prepared and mesomorphic properties have been investigated. An X-ray crystallographic analysis revealed that complex 11 · 2DMF has one-dimensional stacking structure supported by the π–π interaction between the six-membered chelate and aromatic rings with the Ni Ni distances of alternatively 3.3957 and 3.7224 Å and that complex 3 is formed by one-dimensional stacking by weak C H⋯O type hydrogen bonded interaction between the five-membered chelate ring and phenoxo atoms of the dramatically distorted salen moieties with the Ni Ni distance of 5.994 Å. Complexes 1– 6 did not exhibit any mesophases. On the other hand, complexes 7– 10 with longer alkoxy chains of n = 14–20 showed an unusual metallomesogen of a lamello-columnar mesophase within the smectic layers with an interlamellar distance of 31.1 Å (7), 33.6 Å ( 8), 37.1 Å ( 9), and 39.5 Å ( 10) and nearly constant stacking distance of 6.19–6.24 Å between the inter-dimers, irrespective of the variation of the alkoxy chain lengths by the X-ray diffraction measurements of the liquid crystal. The relationship between molecular assemblies and mesomorphic properties is discussed.