Synthesis, structure, and liquid crystal properties of a series of platinum(II) complexes containing chiral 4-(4-alkoxyphenylethynyl) phenylisocyanide ligands

Several platinum(II) isocyanide complexes of the type PtI₂ (CNC₆H₂-2,6-R₂-4-CC-(C₆ H₂-3,5-R′₂-4-(R or S )-OCHMeC_n-1 (H_2(n-1)CH₃))₂ have been prepared and their mesomorphic properties have been investigated. The complexes with R=Me, R′=H, and n=4-7 exhibit a broader N* phase than the corresponding complexes with R=R′=H, indicating that the methyl substituents on the phenylisocyanide group improve the liquid crystal properties by creating a smooth transition between the bulky PtI₂ center and the more slender organic units. The complexes with R=Me and R′=Me exhibit a SmA phase. The presence of methyl groups in the R′-positions in addition to the methyl groups in the R-positions increases the melting point, but does not significantly change the clearing temperature. For the complexes with R=Me and R′=H the temperature-dependent pitches of the N* phase range from 350 to 400 nm.