Orientational order in liquid crystal complexes based on lanthanides

In this study, we have for the first time determined the degree of an orientational order $S$ for a series of liquid-crystal complexes based on lanthanides (Eu$^{+3}$, Gd$^{+3}$, Tb$^{+3}$, Dy$^{+3}$) with the same ligand composition in the temperature range of existence of the nematic phase by using experimental refractometry results. We have also found an even-odd alternative $S$ as number of protons in the ions complexing agent has consecutively increased. The obtained values of $S$ have been compared with the corresponding degrees of order of the calamite organic liquid crystals.