Stephan Schlamp

Influence of the alkyl chain length on the self-assembly of amphiphilic iron complexes: an analysis of X-ray structures.

Several new amphiphilic iron complexes were synthesised and characterised by single crystal X-ray structure analysis. The Schiff-base-like equatorial ligands contain long alkyl chains in their outer periphery with chain lengths of 8, 12, 16 and 22 carbon atoms. As axial ligands methanol, pyridine, 4-aminopyridine, 4-(dimethylamino)pyridine and 1,2-bis(4-pyridyl)ethane were used. X-ray structure analysis of the products reveals different coordination numbers, depending on the combination of equatorial and axial ligand. The driving force for this is the self-assembly to lipid-layer-like arrangements. This can be controlled through the chain lengths and the dimension of the axial ligands in a crystal-engineering-like approach. For this an empirical rule is introduced concerning the crystallisation behaviour of the complexes. The efficacy of this rule is confirmed with the crystallisation of an octahedral complex with two docosyl (C22) chains in the outer periphery. The rule is also applied to other ligand systems.

Amphiphilic iron(II) complexes with short alkyl chains – crystal packing and spin transition properties

An amphiphilic iron(II) spin crossover complex with relatively short octyl chains was synthesised and the crystal structures of the high spin and the low spin state could be determined. In further reactions, a second modification of the hexa-coordinated complex and two different penta-coordinated complexes could be obtained and characterised by X-ray structure analysis. The examples demonstrate an influence of the alkyl chains on the stoichiometry of the final product. Different arrangements of the alkyl chains were observed in the crystal packing. Despite those differences, the spin transition of the hexa-coordinated complexes is always gradual and comparable to that observed in solution.

A ladder type iron(II) coordination polymer with cooperative spin transition.

Ladder type 1D coordination polymers were synthesised with the aim to improve the spin crossover properties of the iron(II) complexes following the concepts of crystal engineering. A wide hysteresis loop (34 K) was observed if rigid linkers were used. The first X-ray structure for a 1D iron(II) ladder is reported.

Water channels and zipper structures in Schiff base-like Cu(II) and Ni(II) mononuclear complexes

The crystal structures of four Cu(ii) complexes and one Ni(ii) complex bearing a square planar N2O2 coordination sphere are discussed. In all cases a distorted square planar coordination sphere is observed that is independent of the metal centre and the ligand and is only influenced by the packing of the molecules in the crystal. For the less distorted copper complexes metal-aromatic interactions are observed, while no significant intermolecular interactions are found for the nickel complexes. This can be explained by the different electronic character of Cu(ii) and Ni(ii) and is also reflected in the differences in the solvatochromism of these complexes.