Gels of Bis[1,2-bis(3,4-di-n-alkoxyphenyl)ethanedione dioximato]palladium(II) Complexes

Bis[1,2-bis(3,4-di-n-alkoxyphenyl)ethanedione dioximato]palladium(II) complexes (abbreviated as [Pd{(CnO)4dpg}2]; n = 7—12) form gels in an over-concentrated n-hexane solution. We have developed a specific cell for X-ray diffraction in order to determine the gel structure. The gel has a two-dimensional hexagonal structure which is similar to the inverted hexagonal phase of lyotropic liquid crystals. The electronic spectra were measured for the gel and for a chloroform solution, which dose not form a gel. As a result, it has become apparent that a 4dz2–5pz intermolecular charge-transfer transition between the neighboring palladium ions is the main driving force of the gel formation. The circular dichroism and magnetic circular dichroism of the gel suggested that this complex has a stack of left-handed helicity. The complex also has a thermotropic liquid-crystalline state, as previously reported. Hence, these three kinds of states are closely related to each other in terms of the formation of molecular aggregates.