Disk-like liquid crystals of transition metal complexes Part 21.‡—Critical molecular structure change from columnar to lamellarliquid crystal in bis(diphenylglyoximato)nickel(II)-based complexes

Abstract

The critical molecular structure change from columnar to lamellar mesophases in bis(diphenylglyoximato)nickel(ii)-based complexes has been investigated. When the number of the long chains surrounding the core complex part was reduced from eight to four, the mesophase changes its structure from columnar Col_hd to novel disk-like lamellar D_L.rec(P2₁2₁). When the length of the four chains at the p-positions was fixed and the remaining four chains at m-positions were gradually made shorter, each of the complexes shows a columnar Col_ho mesophase. Surprisingly, even when the substituents at m-positions are methoxy or methyl groups, a columnar Col_ho mesophase is still observed. When the substituents at m-positions were OH groups, another novel disk-like lamellar D_L.rec(P2₁1) mesophase is observed. Hence, it can be shown that the critical molecular structure change from the columnar to lamellar mesophase occurs between methoxy and hydroxy groups at the m-position. In both of the two novel D_L.rec mesophases in the present study, the core complex parts are parallel to the layers and the long chains are normal to both the layers and the core complex planes. Such a unique mesophase structure has not been previously observed. The synthesis of these complexes and the temperature-dependent X-ray structural analyses of the unique mesophases are reported.