SYNTHESIS AND PROPERTIES OF (+-)-TRANS-(ETA-2-ALKENE)(4-ALKYLOXY-4'-STILBAZOLE)DICHLOROPLATINUM - A REMARKABLE FAMILY OF LOW-MELTING METALLOMESOGENS

A novel series of low-melting metallomesogens (metal-containing liquid crystals) has been prepared and characterised. Reaction of Zeise's salt K[PtCl3 (eta2-CH2=CH2)] with the 4-n-alkyloxy-4'-stilbazole ligands (L = CnH2n+1OC6H4CH=CHC5H4N; n = 3-12) yielded trans- [PtCl2(eta2-CH2=CH2)L] 1, which react with alk-1-enes (CH2=CHCmH2m+1; m = 1-8, 10 or 12) to give trans-[PtCl2(CH2=CHCmH2m+1)L] 2. The complexes where (m + n) greater-than-or-equal-to ca. 8 are generally liquid crystalline (smectic A mesophases); those with shorter tails [(m + n) = 8 to ca. 13] show monotropic mesophases, while those with longer tails [(m + n) > ca. 1 3] show enantiotropic behaviour. The melting temperatures are lower than would be anticipated for metallomesogens of this size, reflecting the non-centrosymmetric molecular structures which make the crystal packing less easy. A 70:30 mixture of the complexes 2 (n = 12, m = 3; K --> S(A) at 61-degrees-C) and (n = 12, m = 6; K --> S(A) at 70-degrees-C) shows the transition into the mesophase, K --> S(A), at 45-degrees-C, an unusually low temperature. The mesophase to isotropic (S(A) --> 1) transition temperatures remain rather constant at 92 +/- 4-degrees-C for all compositions.