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Inorganics 2018, 6(2), 51; https://doi.org/10.3390/inorganics6020051

[2 × 2] Molecular Grids of Ni(II) and Zn(II) with Redox-Active 1,4-Pyrazine-Bis(thiosemicarbazone) Ligands

1
Department für Chemie, Institut für Anorganische Chemie, Universität zu Köln, Greinstraße 6, D-50939 Köln, Germany
2
Department für Chemie, Institut für Biochemie, Universität zu Köln, Otto-Fischer-Str. 12-14, D-50674 Köln, Germany
3
Department für Chemie, Zentrum für Massenspektrometrie, Institut für Organische Chemie, Universität zu Köln Greinstraße 4, D-50939 Köln, Germany
4
Department für Chemie, Institut für Physikalische Chemie, Universität zu Köln, Luxemburger Str. 116, 50939 Köln, Germany
*
Author to whom correspondence should be addressed.
Received: 19 April 2018 / Revised: 15 May 2018 / Accepted: 17 May 2018 / Published: 21 May 2018
(This article belongs to the Special Issue First-Row Transition Metal Complexes)
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Abstract

Tetranuclear complexes [M4(LR)4] with M = Ni(II) or Zn(II), with a [2 × 2] grid-type structure, were assembled in good yields and purity from the easily accessible but unprecedented pyrazine-bridged bis(thiosemicarbazone) protoligands (ligand precursors) H2LR (1,4-pyrazine-2,5-bis(R-carbaldehyde-thiosemicarbazone); R = Me, Et, iPr, or Ph). The complexes were characterised in solution by NMR, MS, IR, and UV-Vis absorption spectroscopy and (spectro)electrochemical methods. HR-MS spectra unequivocally reveal that the tetranuclear species are very stable in solution and any measurements represent these species. Only at higher temperatures (fragmentation in solution: MS and in the solid: TG-DTA) or upon the addition of protons (acidic UV-Vis titrations) can the tetrameric entities be decomposed. Single crystal XRD measurement remained preliminary. Rapid loss of co-crystallised solvent molecules within the [2 × 2] grid-type structures resulted in crystals of very poor quality, but the results were qualitatively in line with spectroscopy, electrochemistry, and quantum chemical (DFT) calculations. IR and NMR spectroscopy point clearly to a thiolate coordination of dianionic (deprotonated) ligands. The electrochemistry reveals four electronically coupled and reversible one-electron reductions centred largely at the pyrazine bridges. EPR and UV-Vis spectroelectrochemical measurements in combination with DFT calculation support the assignment. View Full-Text
Keywords: bis(thiosemicarbazone); 1,4-pyrazine; supramolecular chemistry; mass spectrometry; electrochemistry bis(thiosemicarbazone); 1,4-pyrazine; supramolecular chemistry; mass spectrometry; electrochemistry
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Arefyeva, N.; Sandleben, A.; Krest, A.; Baumann, U.; Schäfer, M.; Kempf, M.; Klein, A. [2 × 2] Molecular Grids of Ni(II) and Zn(II) with Redox-Active 1,4-Pyrazine-Bis(thiosemicarbazone) Ligands. Inorganics 2018, 6, 51.

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