Spin behavior of iron(II) complexes of new 2,6-di(1H-pyrazol-1-yl)pyridine-derived ligands and iron(II) coordination onto 2,6-di(1H-pyrazol-1-yl)pyridine-functionalized carboxylic acid monolayers

Suhad Omar, Technische Universität Berlin, Andreas Grohmann
Tridentate ligands of the 2,6-di(1H-pyrazol-1-yl)pyridine-functionalized carboxylic acid type have received intense attention, for the promise their iron(II) complexes hold with respect to the creation of spin-switchable molecules, with potential application in the fields of data storage, sensors, devices, and molecular electronics. In this thesis, the formation of self-assembled monolayers (SAMs) of such molecules at surfaces has been studied, in the context of potential nano-scale
more » ... , with a view to bringing metal ions to coordinate onto pre-existing layers, or to anchor organic ligand/transition metal complexes directly on surfaces. 4-(2,6-Di(1H-pyrazol-1-yl)pyridin-4-yl)benzoic acid (L1), 4'-(2,6-di(1H-pyrazol-1-yl)pyridin-4-yl)-[1,1'-biphenyl]-4-carboxylic acid (L2) and their iron(II) complexes have been successfully prepared and characterized. These ligands and complexes had been hitherto unknown. [Fe(L2)2](OTf)2 and [Fe(L1)2](OTf)2 complexes have shown incomplete spin crossover, where a limited number of molecules switch their spin state from high spin (HS) to low spin (LS) upon cooling, and vice versa. [Fe(L1)2](OTf)2 has afforded two types of crystals from the same solution (polymorphism). While one of the two crystalline forms can be expected to show reversible SCO, this could not be verified as the species determined at 150 K to be LS had weathered to a HS-form at ambient temperature, due to sequential loss of acetonitrile solvate molecules. This change in the crystal lattice affected the inner coordination sphere and lead to structural changes in the coordination geometry. By solid-liquid interface-based preparation, L2 molecules were successfully self-assembled on a silver-modified gold surface (Ag(1×1)/Au(111)), in both pristine and "diluted" (mixed) states, producing SAMs arranged in zigzag rows of Y-shaped molecules containing the N3 donor set in a transoid arrangement. Only layers admixed with 4-(pyridin-4-yl)benzoic acid (PBA) have shown the ability for FeII metal ion deposition. It wa [...]
doi:10.14279/depositonce-16028 fatcat:qi5owqpdejd2fj322apte3zz4m