Mesogenic Enaminoketone Ni(II) Complexes of Phenazine and Quinoxaline Derivatives

Discotic Liquid Crystals

“…It was proposed that the spin interactions leading to ferromagnetism are enhanced by bridging the metal complexes along the columns due to chelation of the metal ions by atoms of neighboring molecules (Scheme , right). For structurally related enaminoketone complexes with fluorinated side chains Krzyczkowska et al found that the number of fluorinated side chains determines whether SmA or Col h phases are observed . It was rationalized that the preferred formation of the Col h phase with increased degree of fluorination is due to the stiffer structure of the perfluorinated chains compared to hydrocarbon chains, broadening the molecular core.…”

“…In addition, dipole–dipole interactions and C s symmetry favors the formation of Col h phases, as was published by Krówczyński et al for a series of similar enamino complexes . Instead of the 1,2-phenylenediamine unit in the chelate ligand also diaminophenazines and -quinoxalines could be used for such Cu­(II) and Ni­(II) metallomesogens . Quinoxaline-salicylaldimine conjugates were also suitable ligands for planar Cu­(II), Pd­(II) complexes showing Col h phases, whereas the correponding tetrahedral Zn­(II) complexes were nonmesomorphic .…”

“…For structurally related enaminoketone complexes with fluorinated side chains Krzyczkowska et al found that the number of fluorinated side chains determines whether SmA or Col h phases are observed. 578 It was rationalized that the preferred formation of the Col h phase with increased degree of fluorination is due to the stiffer structure of the perfluorinated chains compared to hydrocarbon chains, broadening the molecular core. A reentrant isotropic phase was found below the columnar phase because of the competing tendency to form columnar and lamellar structures over a specific temperature range.…”

“…579 Instead of the 1,2-phenylenediamine unit in the chelate ligand also diaminophenazines and -quinoxalines could be used for such Cu(II) and Ni(II) metallomesogens. 578 Quinoxaline-salicylaldimine conjugates were also suitable ligands for planar Cu(II), Pd(II) complexes showing Col h phases, whereas the correponding tetrahedral Zn(II) complexes were nonmesomorphic. 580 Scissor-shaped tetradentate enaminoketones yielded H-bonded Pd(II) complexes with Col h phases.…”