Liquid Crystalline Octahedral Iron(III) Complexes with 1,4,7-Tris[3,4-bis(decyloxy)benzyl]-1,4,7-triazacyclononane: Thermal Characterization and Mössbauer Investigations of Bridging and Redox Behavior

Abstract

The complexation of iron(iii) chloride with 1,4,7-tris[3,4-bis(decyloxy)-benzyl]-1,4,7-triazacyclononane leads to a liquid crystalline product, which forms a second mesophase after thermal treatment at around 70 8C above the first clearing temperature. Polarizing microscopy, DSC, and UV observations reveal a transformation, which was further investigated by Mössbauer spectroscopy. In different temperature ranges, various octahedral, binuclear iron(iii) complexes are present along with a monomeric species. In the presence of water and oxygen, the iron(iii) center participates in a redox equilibrium.

Design of High Coordination Number Metallomesogens by Decoupling of the Complex-Forming and Mesogenic Groups: Nematic and Lamello-Columnar Mesophases

“…Due to the stronger geometrical constraints, it is even more difficult to obtain metallomesogens with a coordination number of six or even higher . The first metallomesogens with an octahedral coordination sphere were the 1,4,7-triazacyclononane tricarbonyl and trichloro metal complexes (ML(CO) 3 , with M = W, Cr, and Mo, and FeLCl 3 ) described by Lattermann and co-workers . Bruce and co-workers prepared the first octahedral metallomesogens with a calamitic shape .…”

Spin Cross-Over (SCO) Complex Based on Unsymmetrical Functionalized Triazacyclononane Ligand: Structural Characterization and Magnetic Properties

“…From the design point of view, a recent strategy consists in preparing SCO systems with the use of systems with the use of polydentate ligands with a large potential denticity, such as cyclam and cyclen, which are known to form very stable complexes with transition metal ions [22]. However, even their remarkable reactivity toward transition metal ions, the limited number of the appropriate donor atoms that are involved in their corresponding macrocycle units, disallows some polydentate coordination modes, such as pentadentate or hexadentate coordination [22][23][24][25][26][27][28][29][30][31][32].…”

Pressure-Induced Phase Transitions on a Liquid Crystalline Europium(III) Complex

“…[9][10][11][12] The first metallomesogens with an octahedral coordination sphere were the 1,4,7-triazacyclononane tricarbonyl and trichlorometal metal complexes. [13][14][15] Bruce and co-workers prepared octahedrally coordinated metallomesogens with a rod-like shape. [16][17][18] It is even more difficult to obtain metallomesogens with coordination numbers higher than six.…”

“…Because of the desire to combine the properties of liquid crystals and metal complexes, a substantial amount of effort has been devoted in the last two decades to the design of liquid crystalline−metal complexes (metallomesogens). − The first discovered classes of metallomesogens were designed in such a way that they mimicked the shape of organic liquid crystals, such as linear complexes (Ag + and Hg 2+ ) and square-planar complexes (Cu 2+ , Ni 2+ , Pd 2+ , and Pt 2+ ). Because of strong geometrical constraints, it is a challenge to design metallomesogens with coordination geometries other than linear or square-planar orientations. − The first metallomesogens with an octahedral coordination sphere were the 1,4,7-triazacyclononane tricarbonyl and trichlorometal metal complexes. − Bruce and co-workers prepared octahedrally coordinated metallomesogens with a rod-like shape. − It is even more difficult to obtain metallomesogens with coordination numbers higher than six. The driving forces for the development of new metallomesogens with high coordination numbers are not only the desire to build molecular edifices with geometries that are impossible to achieve by all-organic liquid−crystals but also the unique luminescence and magnetic properties of lanthanide ions .…”