Silver and gold trinuclear complexes based on 3-substituted or 3,5-disubstituted pyrazolato ligands. X-ray crystal structure of cyclo-tris{mu-[3,5-bis(4-phenoxyphenyl)-1H-pyrazolato-kappa N-1 :kappa N-2]}trigold dichloromethane ([Au(mu-pz(pp2))](3) c

摘要

Ten new silver and gold trimeric complexes of the type [M-3(mu-pz')(3)] (M = Au, Ag), where pz' indicate pyrazolato ligands derived from mesogenic 3.5-disubstituted 1H-pyrazoles Hpz(R2) or non-mesogenic 3-substituted 1H-pyrazoles Hpz(R) (R = C6H4OCnH2n+1), were synthesized and characterized. The gold and silver complexes 7,8, 10, and 11 containing symmetric pyrazolato ligands as bridging groups (pz(R2); R = C6H4OCnH2n+1, n = 4 (pz(bp2)) and 8 (pz(op2))) exhibited a trigonal symmetric structure. The same results were obtained for the related silver derivatives 16-18 with 3-substituted pyrazolato ligands (pz(R); R = C6H4OCnH2n+1, n = 4 (pz(bp)), 12 (pz(ddp)), and 18 (pz(odp))). By contrast the 3-substituted pyrazolato-gold compounds 13-15 adopted an asymmetric molecular structure related to the position of the substituents on the trinuclear core. The thermal behavior of these complexes was investigated by differential scanning calorimetry and polarized-light microscopy. The mesomorphism of the parent 3,5-disubstituted pyrazoles is avoided in their corresponding trinuclear complexes 7. 8, 10, and 11. However, the metal derivatives 14 and 17 containing the asymmetric 3-[4-(dodecyloxy)phenyl]pyrazolato ligand were found to have liquid-crystal properties. These compounds exhibited monotropic behavior with columnar mesophases that could be related to the disc-like shape of the molecular core and the appropriate length of the alkyloxy chain. For comparative purposes, the X-ray structure of the related gold complex [Au-3(mu-pz(pp2))(3)] (9) having phenoxyphenyl substituents at the 3- and 5-positions of the pyrazolato ligand is also described. ne molecular structure is formed by a non-planar (Au-N-N)(3) core, containing three Au-atoms bridged by three pyrazolato ligands. The molecular packing is described as a columnar organization, the shortest Au (...) Au distance being 4.639(1) Angstrom between consecutive trimers. [References: 38]