Columnar metallomesogens derived from unsymmetrical pyrazoles

The synthesis and mesomorphism for two series of unsymmetrical pyrazoles and their nickel(II) complexes were described. This is the first example of nickel complexes exhibiting columnar phase. The derivatives with two alkoxy chains exhibited smectic A or smectic C phases; however, all derivatives with four alkoxy chains formed hexagonal columnar phases. In contrast, all nickel(II) complexes 1a formed hexagonal columnar phases. The crystal and molecular structures of 1-(4-propyloxyphenyl)-2-(3-(4-propyloxyphenyl)-1H-pyrazol-5-yl)ethanone were determined, and it crystallizes in the triclinic space group P-1. The overall molecular shape is considered as rod-shaped. The pyrazole and one phenyl ring were coplanar, however, they were not coplanar with other phenyl ring by a dihedral angle of ca. 66.2°. A dimeric structure formed by an intermolecular H-bond (2.11 Å) and a weak π–π interaction (3.51 Å) was observed, which was probably attributed to the formation of the mesophase. The XRD experiments confirmed their structures of the mesophases.

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