Design of Neutral Metallomesogens from 5,5-Dimethyldipyrromethane: Metal Ion Mediated Control of Folding and Hairpin Structures

New ligands derived from 5,5-dimethyldipyrromethane and their corresponding neutral complexes with Zn-II and Pd-II are described. The ligands incorporate either a hexacatenar [H2(1(n)), n = 1, 10, 12, 14 and 16], tetracatenar [H-2(2(n)), n = 1 and 16] or an extended dicatenar structure [H-2(3(n)), n = 1 and 16]. Single-crystal X-ray structure determinations of [Zn-2(1(1))(2)] and [Zn-2(3(1))(2)] confirm a distorted tetrahedral geometry at Zn-II to afford double-stranded helical structures, while the Pd-II species [Pd(3(1))] shows a distorted square-planar geometry with the ligand adopting an alternative hairpin conformation. The metal-free hexacatenar ligands H-2(1(n)) (n = 10, 12, 14, 16) and the corresponding complexes [Zn-2(1(16))(2)] and [Pd(1(n))] (n = 12, 14, 16) are not mesomorphic. However, the tetracatenar complex [Zn-2(2(16))(2)] generates a smectic mesophase, as confirmed by X-ray diffraction, while [Pd(2(16))] and the metal-free ligand H-2(2(16)) show no mesomorphic behaviour. Two of the extended dicatenar compounds, H-2(3(16)) and [Zn-2(3(16))(2)] are non-mesomorphic, while [Pd(3(16))] displays a smectic A phase. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)