Mesomorphism of Four-Coordinated Four-Chained Metal Complexes Based on Pyrazolylpyridine Derivatives

Abstract

A homologous series of four-chained silver(I) and zinc(II) metal complexes based on the coordination of two NN 0 -bidentate ligands pz R2 py 2-[3,5-bis(4-alkyloxy)phenyl]-pyrazol-1-yl]pyridine (R ¼ C 6 H 4 OC n H 2nþ1 , n ¼ 16, 18) have been synthesised. All(9,10)) exhibit liquid crystal properties showing enantiotropic SmA phases, independently of the starting pz R2 py ligands (non-mesomorphism for n ¼ 18 or monotropic liquid crystal for n ¼ 16), as well as the coordination geometry.The silver(I) derivatives [Ag(pz R2 py) 2 ] þ containing PF À 6 and SbF À 6 as counteranions (1-4) are four-coordinated cationic complexes, but those containing OTf À and NO À 3 (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 ][NO 3 ] 2 (9-10), the tetrahedral metal environment is also distorted by the presence of coordinative interactions with the NO À 3 groups. Neutral tetrahedral compounds [ZnCl 2 (pz R2 py)] (R ¼ C 6 H 4 OC n H 2nþ1 , n ¼ 16 (11), 18 (12), 1 (13)) have also been investigated. Crystal structure of the first member of this series with n ¼ 1, [ZnCl 2 (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.

Coordination behaviour of new dipyridylpyrazole ligands towards ZnCl2and PdCl2fragments. Crystalline structural characterization and multinuclear NMR studies as evidence of linkage and conformational isomers

“…For the rest of compounds 1 H-NMR spectra were performed at room temperature on a Bruker DPX-300 spectrophotometer (NMR Service of Complutense University) from solutions in DMSO-d 6 or CDCl 3 . 1 H Chemical shis (d) are listed relative to Me 4 Si using the signal of the deuterated solvent as reference (2.50 and 7.26 ppm, respectively), and coupling constants J are in hertz.…”

“…For compound (6), aer rening, the presence of solvent residual electron density was detected as disordered atomic groups located in the void regions, and centered in sites among the molecule. The solvent molecule could not be modeled properly in none of the crystals, due to the poor spectra quality.…”

“…were recorded in solutions of CDCl 3 and DMSO-d 6 (HMQC and HMBC) and in the solid state (CPMAS) (Tables 3 and 4).…”

“…In particular in our research group, many metallomesogens containing mesogenic or promesogenic pyrazole type ligands have been prepared. [3][4][5][6] In addition, we have found that the introduction of a polar group like pyridine on the molecular periphery appears to be determinant to achieve and/or to improve the mesomorphic properties of the metal complexes. 7 So it was interesting to note that Ag(I) and Pd(II) metallomesogens with pyridylpyrazole type ligands pypz R(n) and Hpz R(n)py (R(n) ¼ C 6 H 4 OC n H 2n+1 , n ¼ 1, 12-18) [3][4][5][6] exhibited lower melting points and a wider mesophase range than the related ones with ligands not containing pyridine groups.…”

“…[3][4][5][6] In addition, we have found that the introduction of a polar group like pyridine on the molecular periphery appears to be determinant to achieve and/or to improve the mesomorphic properties of the metal complexes. 7 So it was interesting to note that Ag(I) and Pd(II) metallomesogens with pyridylpyrazole type ligands pypz R(n) and Hpz R(n)py (R(n) ¼ C 6 H 4 OC n H 2n+1 , n ¼ 1, 12-18) [3][4][5][6] exhibited lower melting points and a wider mesophase range than the related ones with ligands not containing pyridine groups. 4,7 On the other hand dipyridylpyrazole ligands have been recently proved as candidates to stabilize polymeric structures through strong chelation.…”