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New unusual magnetic complexes: synthesis, electronic and magnetic properties

Fachliche Zuordnung Experimentelle Physik der kondensierten Materie
Förderung Förderung von 2013 bis 2019
Projektkennung Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 213590445
 
Erstellungsjahr 2017

Zusammenfassung der Projektergebnisse

A series of transition metal complexes with phosphorus containing ligands were obtained, their structural, magnetic and spectroscopic properties were studied by vibrational spectroscopy, ESR spectroscopy, and X-ray single crystal diffraction. The bis-(µ:η1,η1-3,4,5-triaryl-1,2-diphosphacyclopentadienyl)bis(tetracarbonyl manganese) (aryl = C6H5 (2a), p-FC6H4 (2b), p-ClC6H4 (2c)) undergo non-reversible rearrangement to form mononuclear 3,4,5-triaryl-1,2-diphosphacymantrene (3a-c) with a good yield. According to quantum-chemical calculations, binuclear complexes 2 can be considered as a product of kinetic control and mononuclear species 3 are the thermodynamically favorable compounds. The anti-ferromagnetic intramolecular interaction observed for complexes 2 can be effectively tuned by substituents in para-position of the arene ring, whereas mononuclear 1,2-diphosphacymantrenes (3) are diamagnetic. Secondly, a flexible porous coordination polymer based on phosphinic acid was synthesized, which demonstrates reversible crystal structure transformation and is able to exist in two different stable forms: hydrated Mn(H2O)2(Fc(PHOO)2)·2H2O and dehydrated Mn(Fc(PHOO)2). The stability of the hydrated sample is provided by multiple hydrogen bond interactions with participation of phosphinate groups and lattice and coordinated water molecules, all water molecules are leaving the coordination polymer in one step upon heating. The two dimensional coordination network is preserved upon dehydration, as it is evident from IR spectroscopy and powder X-ray diffraction. The dehydrated compound can absorb H 2O molecules selectively over other possible adsorptives such as methanol, ethanol, acetone, and tetrahydrofuran at 298 K. The dehydrated framework is also not accessible for nitrogen and hydrogen at 77 K. The structural transformations are also reflected in magnetic properties of the coordination polymer. A possibility to reversibly tune the structure enables a controllable switching of the magnetism in terms of changing the spatial dimensionality of magnetic interactions, which can be considered as a potentially useful magnetic functionality of such a class of coordination polymers. Using crystal growth procedures from solution and vapor phase, new CT complexes of picene and coronene with F4TCNQ and with different stoichiometry were obtained. Their crystal structure and its interconnection with charge transfer and electrochemical properties, donor and acceptor mobility were analyzed with the original methodology including a combination of X-ray diffraction and electrochemistry in solid state, and in time resolved manner in solution. The latter makes it possible to clarify the nucleation of CT complexes in solution. It was shown that the mobility of coronene molecules in crystal is more affected by the asymmetry of its surrounding than by the composition and degree of charge transfer and interstack interactions. Finally, we have successfully prepared novel charge transfer compounds based upon transition metal phthalocyanines. We could show that the fluorinated F16CoPc is a very good electron acceptor, and that charge transfer at organic interfaces also results in a reduction of the Co center and an associated spin change. For the system MnPc/F4TCNQ, our results demonstrate the oxidation of MnPc, whereas the electron is removed from Mn 3d orbitals, which again is accompanied by a spin change.

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