Structural and Functional Evolution of Gold Essay

Figure 2.12 below showed the reaction pathway in synthesizing the trinuclear gold(I) pyrazolate complexes. Complexes 1 and 2, which have a heptyl and octyl group, at 4 position of each pyrazole ring were the complexes that behave as an mesophase at the range of 99 to 112C upon heating and 85 to 61 C upon cooling, respectively. Liquid crystalline gold(I) isocyanide complexes have been synthesized and their liquid crystalline behavior were investigated by Fujisawa and his co-workers [30]. Simple ligands such as an ethynylbenzene group conjugated to various lengths of alkoxy chains and n-alkyl isocyanide were utilized in order to prevent steric hindrance and facilitated a strong intermolecular aurophilic interaction. These resulted in highly efficient of photoluminescence. It was found that the complexes easily formed dimers in the crystalline, liquid crystalline, and isotropic phases due to strong interaction between the gold atoms of neighbouring molecules, and that these dimers acted as unit mesogens in the liquid crystalline phase. The thermodynamics of Au(I) complexes were studied using POM, DSC, and XRD. The liquid crystal phase was identified as nematic (N) or smectic (Sm) by POM, based on their optical textures. Their optical textures of Au(I) complexes are shown as in Figure 2.14. Mohamed Benouazzane et al. [31] also reported that they succeccsully synthesized and study the liquid crystalline behavior of ionic gold(I) isocyanide complexes of type [Au(CNR)2]Y (R = C6H4OCnH2n+1, C6H4C6H4OCnH2n+1, C6H2(3,4,5-OCnH2n+1)3 Y = NO3-, PF6-, BF4-). Irrespective of the isocyanide used, all the gold nitrate derivatives prepared are not liquid crystals whereas the phenyl and biphenyl gold derivatives show smectic A phases and 3,4,5-trialkoxyphenyl isocyanide complexes of gold show hexagonal columnar mesophases. These showed that metal atom, anion and the isocyanide on mesogenic behavior gave effect in the liquid crystal structure of the complexes formed. Reported by R. Bayn and his co-workers [32], rodlike gold(I) complexes, [Au(C6F4OCmH2m+1)(CNC6H4C6H4OCnH2n+1)] (m = 2, n = 4, 10 m = 6, n = 10 m = 10, n = 6, 10), display interesting features. They were liquid crystals and showed photoluminescence in the mesophase, as well as in the solid state and in solution. The single-crystal, XRD structure of [Au(C6F4OC2H5)(CNC6H4C6H4OC4H9)] confirms its rodlike structure, with a linear coordination around the gold atom, and reveals the absence of any AuAu interactions (interactions that often present in luminescent gold complexes). POM textural images (x 100) observed for gold(I) complexes are shown in Figure 2.16. Moreover, Kishimura et al. [16] reported that a trinuclear gold(I) pyrazolate complex bearing long C18 alkyl chains in hexane self-assembles via Au(I)-Au(I) metallophilic interaction, to form a red luminescent organogel upon excitation at 284 nm and showed luminescence centered at 640 nm at ambient temperature. In the same year, this research group have synthesized dendritic copper(I) pyrazolate complexes carrying long alkyl chains, (Cu[Cn]Lmpz (n = 12, 18, m = 2,3 Lm = the number (m) of dendritic layers, pz = pyrazolate). They found that luminescent solid Cu[C18]L2pz was dichroic at room temperature that emitted a red luminescence centred at 650 nm.