Discotic liquid crystals of transition metal complexes 41: influence of rare-earth metal ions on clearing points of sandwich-type bis[octakis(3,4-didodecyloxyphenoxy)phthalocyaninato]lanthanoid(III) complexes

It has long been believed that the phase transition behavior and clearing points (c.p.s.) of phthalocyanine-based metallomesogens scarcely change regardless of the kind of central metal. In this work, we have synthesized a series of novel sandwich-type phthalocyanine-based lanthanoid complexes, bis[2,3,9,10,16,17,23,24-octakis(3,4-didodecyloxyphenoxy)phthalocyaninato]lanthanoid(III) (abbreviated as {[(C12O)2PhO]8Pc}2M, M = La, Ce, Eu, Gd, Tb, Yb and Lu : 1–7). Their mesomorphic properties were investigated by polarization microscope, DSC and temperature-dependent X-ray diffraction techniques to compare with the phase transition behavior and c.p.s. of the complexes. Very interestingly, the c.p.s. of these seven rare-earth metal complexes increased in an order of La (1) → Ce (2) → Eu (3), reached to a maximum for Gd (4), and decreased in an order of Tb (5) → Yb (6) → Lu (7). We have noticed that their rise and fall of c.p.s. correspond to the values of total spin quantum number (S) of the central rare-earth metal ions. Thus, it was found, for the first time in metallomesogens, that the S values of central rare-earth metal ions strongly influence their c.p.s.