US EPA

1050799 

Journal Article 

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

Morin, TJ; Wanniarachchi, S; Gwengo, C; Makura, V; Tatlock, HM; Lindeman, SV; Bennett, B; Long, GJ; Grandjean, F; Gardinier, JR 

2011 

Yes 

Dalton Transactions (Online)
ISSN: 1477-9234 

40 

31 

8024-8034 

English 

21720641 

10.1039/c1dt10712g 

A series of iron(II) chloride complexes of pentadentate ligands related to α,α,α',α'-tetra(pyrazolyl)-2,6-lutidine, pz(4)lut, 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**(4)lut, 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)(4)lut)]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.