Pyrazolyl methyls prescribe the electronic properties of iron(ii) tetra(pyrazolyl)lutidine chloride complexes

Tyler J. Morin, Sarath Wanniarachchi, Chengeto Gwengo, Vitales Makura, Heidi M. Tatlock, Sergey V. Lindeman, Brian Bennett, Gary J. Long, Fernande Grandjean, James R. Gardinier

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14 Scopus citations


A series of iron(ii) chloride complexes of pentadentate ligands related to α,α,α′,α′-tetra(pyrazolyl)-2,6-lutidine, pz 4lut, has been prepared to evaluate whether pyrazolyl substitution has any systematic impact on the electronic properties of the complexes. For this purpose, the new tetrakis(3,4,5-trimethylpyrazolyl)lutidine ligand, pz** 4lut, was prepared via a CoCl 2-catalyzed rearrangement reaction. The equimolar combination of ligand and FeCl 2 in methanol gives the appropriate 1:1 complexes [FeCl(pz R 4lut)]Cl that are each isolated in the solid state as a hygroscopic solvate. In solution, the iron(ii) complexes have been fully characterized by several spectroscopic methods and cyclic voltammetry. In the solid state, the complexes have been characterized by X-ray diffraction, and, in some cases, by Mössbauer spectroscopy. The Mössbauer studies show that the complexes remain high spin to 4 K and exclude spin-state changes as the cause of the surprising solid-state thermochromic properties of the complexes. Non-intuitive results of spectroscopic and structural studies showed that methyl substitution at the 3- and 5- positions of the pyrazolyl rings reduces the ligand field strength through steric effects whereas methyl substitution at the 4-position of the pyrazolyl rings increases the ligand field strength through inductive effects.

Original languageEnglish (US)
Pages (from-to)8024-8034
Number of pages11
JournalDalton Transactions
Issue number31
StatePublished - Aug 21 2011


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