4 years ago

Expanding the Family of Pyrazole-Bridged Mixed-Spin and Mixed-Valence Tetranuclear [2 × 2] Iron Grid Complexes

Expanding the Family of Pyrazole-Bridged Mixed-Spin and Mixed-Valence Tetranuclear [2 × 2] Iron Grid Complexes
Jin Tong, Serhiy Demeshko, Franc Meyer, Sebastian Dechert
The new bis(tridentate) compartmental proligand 3,5-bis[6-(1-methyl-1H-imidazole-2-yl)pyrid-2-yl]pyrazole (HLim) was synthesized and used for the self-assembly of a rugged tetranuclear [2 × 2] Fe4 grid complex [FeII4Lim4](ClO4)4 (1), which readily forms upon reaction of HLim with Fe(ClO4)2·6H2O in the presence of a base (NaOtBu). According to cyclic voltammetry, all-ferrous 1 can be sequentially oxidized in four steps, with pronounced stability of the twice-oxidized dimixed-valent form [FeII2FeIII2Lim4]6+. Treatment of 1 with the oxidant AgClO4 yielded the dimixed-valent molecular grid [FeII2FeIII2Lim4](ClO4)6 (2) and an unusual heterometallic grid [FeIII2(AgI2)2Lim4](ClO4)6. (3), depending on reaction conditions. 3 can also be synthesized via the intermediate “corner complex“ [FeII(HLim)2](ClO4)2. Complexes 1, 2 and 3 were characterized by single-crystal X-ray diffraction analysis as well as by SQUID magnetometry and Mössbauer spectroscopy. 1 is shown to adopt a dimixed-spin trans-[HS-LS-HS-LS] configuration (HS: high-spin; LS: low-spin) while 2 features ferromagnetic coupling in a trans-[FeIII(LS)-FeII(HS)-FeIII(LS)-FeII(HS)] configuration. Correlations between structural parameters and magnetic properties are analyzed and discussed in comparison with previously reported Fe4 grids based on related pyrazole-bridged ligands. A new pyrazole-based bis(tridentate) ligand has been synthesized and used for the self-assembly of an all-ferrous Fe4 [2 × 2] grid complex, which can be oxidized twice to its dimixed-valent congener. Trans dimixed-spin configurations for both grids were established by a combination of crystallographic, magnetic and Mössbauer studies.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/ejic.201700733

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