Liquid-crystalline mono- and dinuclear (perhalophenyl)gold(I) isocyanide complexes

Rodlike gold(I) and gold(III) complexes [AuR(C drop N(C6H4)(m)OCnH2n+1-p)] (m = 1, n = 10, R = C6F5; m = 2, n = 4, 6, 8, 10, 12, R = C6F5, C6F4Br-o, C6F4Br-p), [(mu-4,4'-C6F4C6F4){AuC drop N(C6H4)(m)OCnH2n+1}(2)] (m = 1, 2; n = 4, 6, 8, 10, 12), [AuRI2(C drop NC6H4C6H4OCnH2+1-p)] (R = C6F5, n = 8; R = C6F4Br-o, n = 10), and [(mu-4,4'-C6F4C6F4){AuX2C drop N(C6H4)(m)OCmH2n+1}(2)] (m = 1, 2; n = 4, 6, 8, 10, 12) have been prepared and their liquid crystal behavior has been studied. The gold(III) compounds are not mesomorphic, but all the perhalo-gold(I) derivatives described are liquid crystals except the phenyl isocyanide gold(I) derivative [Au(C6F5)(C drop NC6H4-OC10H21-p)]. The mononuclear derivatives show only a nematic (N) phase when the isocyanides have a short tail (n = 4), N and smectic A phases (S-A) when the isocyanides have an intermediate tail (n = 6, 8), and only S-A phases for longer chains. Their thermal stability is high, even in the isotropic state. The variation in transition temperatures is as follows: C6F4Br-p greater than or equal to C6F5 > C6F4Br-o when n less than or equal to 6 and C6F4Br-p > C6F4Br-o > C6F5 for n greater than or equal to 8. This behavior is understood on the basis of electronic and steric factors. The dinuclear compounds [(mu-4,4'-C6F4C6F4){AuC drop N(C6H4)(m)OCnH2n+1}(2) display only N mesophases and all the biphenylisocyanide derivatives and phenyl isocyanide compounds with n less than or equal to 6 undergo some decomposition upon reaching the clearing point to the isotropic state.