Trinuclear Gold(I) Pyrazolate Complexes Exhibiting Hexagonal Columnar Mesophases with only Three Side Chains

Reaction of long-chain alkyl-substituted pyrazoles with AuCl(SMe₂) yields trinuclear gold-(I) pyrazolate complexes, two of which exhibit monotropic mesophases. Optical microscopy and/or X-ray diffraction studies show that these compounds form hexagonal columnar mesophases. They are only the third examples of discotic mesogens possessing only three aliphatic side chains. The X-ray crystal structure of one compound reveals that two molecules form a "dimer" mainly through intermolecular Au-Au interactions. The "dimers" are stacked in a tilted fashion to form columns along the b axis in the crystal phase, which are presumably rearranged to the hexagonal columnar structure in the mesophase.