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ELECTRON-DENSITY DISTRIBUTIONS IN SELECTED FERROCENYL-PYRAZOLYL LATE TRANSITION-METAL COMPLEXES

Abstract

57Fe Mössbauer spectroscopy has been used to study electronic dispersions in complexes of Fe, Co, Ni and Pd anchored on 3-ferrocenyl-5-methylpyrazolylmethylenepyridine and 3-ferrocenylpyrazolylmethylenepyridine ligands. Mössbauer spectroscopy shows that pyrazolyl-derivatizing of ferrocene increases the electron-density at the Fe-centre as well as facilitating the Fe-to-cyclopentadienyl ring back-donation of electron-density. The coordination of the ferrocenyl-pyrazolyl ligand to transition metals such as Fe, Co, Ni and Pd, reduces the electron-density at the Fe-centre of the ferrocenyl moiety while increasing the electron-density at the coordinated metal centre, especially in the Fe complexes. The electron-density change at the coordination metal centre is inversely proportional to the electronegativity of the halide substituent. Furthermore, the type of substituent (Me or H) at position 5 on the pyrazolyl moiety has influence on the electron density at the ferrocenyl-Fe and the coordinated metal centre. The methyl group as a substituent reduces the π-acceptor ability of the pyrazolyl and therefore increases the electron-density at the ferrocenyl-Fe centre. However, when the substituent is hydrogen, the electron-density at the coordination metal centre increases. Similarly, for other metals (i.e., Co, Ni and Pd) the electron density at the ferrocenyl-Fe is also significantly reduced upon coordination of the ligand to the metal. Additionally, Mössbauer experiments reveal a trivalent Fe species in the synthesized complexes which is not discerned by X-ray and elemental analysis. The species has been identified as the oxidative product [Fe(III)X4]- where X = Cl or Br. The study also highlights and cautions on the possibility of photo-oxidation processes involving both ferrocene and the coordinating Fe-halides under standard lighting conditions with possible contributions from aerated solvents.

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Publication details

The article was accepted on 27 Mar 2018 and first published on 27 Mar 2018


Article type: Paper
DOI: 10.1039/C8CP01135D
Citation: Phys. Chem. Chem. Phys., 2018, Accepted Manuscript
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    ELECTRON-DENSITY DISTRIBUTIONS IN SELECTED FERROCENYL-PYRAZOLYL LATE TRANSITION-METAL COMPLEXES

    M. A. Peck, C. Obuah, G. Hearne and J. Darkwa, Phys. Chem. Chem. Phys., 2018, Accepted Manuscript , DOI: 10.1039/C8CP01135D

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