title: The Many Aspects Of Amphiphilic Complexes
Creators: name: Weihermüller, Johannes
Publisher: name: University of Bayreuth
Year: 2019
Subjects: subject: Amphiphilic Complexes
subject: Metallomesogens
subject: Self-Assembly
subject: Fe
subject: Cu
subject: Ni
subject: Magnetism
subject: 540

description: In this work, metallomesogenic complexes were synthesised and their properties were investigated. For this, a selection of alkyl chains with different lengths was attached to an equatorial Schiff base-like ligand to obtain an amphiphilic system. The reaction with Fe(II) acetate, Cu(II) acetate, or Ni(II) acetate yielded the corresponding complexes. The amphiphilicity resulted in an interesting order in the solid phase, in the melt, and in solution. A variation of the axial ligands and the metal centres gave rise to further remarkable attributes. In the first part, an Fe(II) system with C12 alkyl chains attached to the tetradentate equatorial ligand was studied. The reaction with dmap or bipy as axial ligands resulted in monomeric or polymeric octahedral complexes, respectively. Crystallographic data of the monomeric [FeL(12)(dmap)2] complex, a partially converted [FeL(12)(dmap)(MeOH)] complex, and also an oxidised Fe(III) species [µ O {FeL(12)}2(dmap)] were obtained. [FeL(12)(dmap)(MeOH)] and [µ O {FeL(12)}2(dmap)] showed a lipid layer-like arrangement in the crystal packing due to van der Waals interactions between the alkyl chains. This is in consistency with the sap of around 1.00 from previous work. [FeL(12)(dmap)2] displayed a lipid layer-like arrangement which was slightly disarranged due to a relatively high sap value of 1.12. It was suggested that this value is on the border for the formation of those structures. The magnetic measurements of [FeL(12)(dmap)2] and [FeL(12)bipy]n revealed SCO properties with hysteretic behaviour for both complexes. TIESST measurements showed that the HS species of both complexes could be trapped in a metastable state by rapid cooling. Heating up resulted in a TTIESST of 121 K for [FeL(12)(dmap)2] and 101 K for [FeL(12)bipy]n. The width of the hysteresis was strongly depending on the scan rate of the measurement which was confirmed for [FeL(12)bipy]n by kinetic measurements in the region of the SCO. As a result, a hysteresis without kinetic effects was obtained. In the next part, the influence of the length of the alkyl chains on the SCO properties was investigated. Fe(II) complexes with C16, C18, C20, and C22 alkyl chains attached to the equatorial ligand were synthesised. Bridging bismonodentate axial ligands were used to form more stable coordination polymers. The rigidity of the coordination polymers was varied for the complexes with a C22 chain by using axial ligands with a single (bpea), a double (bpee), or a triple bond (bpey) as a bridge. For comparison purpose the four corresponding Fe(III) µ-O-complexes were synthesised and characterised, as well. Crystallographic data was obtained for [FeL(22)bpea]n, [FeL(22)bpey]n, and the precursor complex [FeL(20)(MeOH)2]. Lipid layer-like arrangements were again observed in the crystal packing which were in agreement with the sap values. The PXRD measurements confirmed a similar crystal packing for the six Fe(II) coordination polymers. Magnetic measurements showed an abrupt irreversible SCO above room temperature for all Fe(II) complexes. A second reversible SCO around 220 K was observed for the Fe(II) complexes with bpey as axial ligand. Temperature dependent PXRD, DSC and POM measurements showed that the SCO was related to a phase transition which was triggered by a reorientation of the alkyl chains in the crystal packing. In addition, birefringent structures were observed after crystallisation from the melt in the POM measurements. These were correlated with a liquid crystalline phase in the solid. Furthermore, the film formation behaviour was tested with [µ-O-{FeL(16)}2] which was a first step towards the application as a multifunctional sensor. Homogenous films with a thickness of 15 and 30 nm were obtained by spin coating. A delamination procedure of the crystalline powder of [FeL(22)bpey]n was tested, too, and resulted in small platelets with a thickness roughly between 75 and 260 nm. In the last part, the ligand system was modified to bear branched alkyl chains. It was expected that switching to a conical complex shape would reduce the phase transition temperatures and bring them closer to room temperature. Additionally, the conical shape ought to be advantageous for the formation of micelles. Cu(II) and Ni(II) complexes were synthesised first to investigate their behaviour in solution and their phase transition properties as they were easier to handle under air than an Fe(II) system. In n-hexane both complexes formed micelles with the addition of MeOH and NaCN which was confirmed by DLS and TEM. UV-Vis and 1H-NMR studies showed a CISSS for [NiL(27)] in CHCl3/CDCl3 with the stepwise addition of the coordinating solvent pyridine/pyridine-d5. Preliminary test demonstrated that micelle formation and a CISSS can be obtained at the same time. DSC and POM measurements revealed a melting process over a broad temperature range for both complexes and the formation of birefringent spherulitic structures when the samples were cooled from the melt. Moreover, [CuL(27)] formed a second phase of well-defined six armed stars which has to be further investigated.