Molecular Crystals and Liquid Crystals, Vol.481, 34-55, 2008
Mesomorphism of four-coordinated four-chained metal complexes based on pyrazolylpyridine derivatives
A homologous series of four-chained silver(I) and zinc(II) metal complexes based on the coordination of two NN '-bidentate ligands pz(R2)py 2-[3,5-bis(4-alkyloxy)phenyl]-pyrazol-1-yl]pyridine (R = C6H4OCnH2n+1, n = 16, 18) have been synthesised. All compounds [M(pz(R2)py)(2)][A](m) (M = Ag, m = 1, n = 16, 18, A = PF6-(1,2), SbF6- (3,4), CF3SO3- (OTf-) (5,6), NO3- (7,8); M = Zn, m = 2, n = 16, 18, A = NO3- (9,10)) exhibit liquid crystal properties showing enantiotropic SmA phases, independently of the starting pzR2py ligands (non-mesomorphism for n = 18 or monotropic liquid crystal for n = 16), as well as the coordination geometry. The silver(I) derivatives [Ag(pz(R2)py)(2)](+) containing PF6- and SbF6- as counteranions (1-4) are four-coordinated cationic complexes, but those containing OTf-and NO3- (5-8) exhibit a five-coordinated metal environment with distorted base-square pyramidal/trigonal bipyramidal geometry involving the counteranion. For the zinc(II) related compounds [Zn(pz(R2)py)(2)][NO3](2) (9-10), the tetrahedral metal environment is also distorted by the presence of coordinative interactions with the NO3- groups. Neutral tetrahedral compounds [ZnCl2(pz(R2)py)] (R = C6H4OCnH2n+1, n = 16 (11), 18 (12), 1 (13)) have also been investigated. Crystal structure of the first member of this series with n = 1, [ZnCl2 (pz(An2)py)] (13), has been characterised by single crystal X-ray diffraction. The molecules adopt the tetrahedral coordination environment with a planar ZnNNCN core. That structure for the related compounds containing longer alkyloxy chains (11-12) suggests a rod-like molecular shape in agreement with their observed liquid crystal lamellar phases.
Keywords:four-chained complexes;four-coordinated silver and zinc complexes;pyrazolylpyridine ligands;smectic mesophases;XRD studies