Abstract
We report herein on five new Fe(II) complexes of general formula [Fe(L)2(NCCH3)2](BF4)2•xCH3CN (L = substituted 2-pyridylimine-based ligands). The influence of proximally located electron withdrawing groups (e.g., NO2, CN, CF3, Cl, Br) bound to coordinated pyridylimine ligands has been studied for the effect on spin crossover in their Fe(II) complexes. Variable-temperature UV-visible spectroscopic studies performed on complexes with more strongly electronegative ligand substituents revealed spin crossover (SCO) in the solution, and thermodynamic parameters associated with the spin crossover were estimated.
Highlights
Spin crossover (SCO) [1,2,3] describes the phenomenon of spin state switching in some 3d4 –3d7 transition metal complexes
Our work focused on the incorporation of bidentate 2-pyridylimine-based ligands into mononuclear Fe(II)
We speculate that the poor σ-donating ability of the imine N-donor was a potential cause for preferred coordination of NCCH3, and not steric ability of the imine N-donor was a potential cause for preferred coordination of NCCH3, and not congestion about the Fe(II) node; literature reports of a [Fe(L)2 (NCCH3 )2 ] analogue, where X = H
Summary
Spin crossover (SCO) [1,2,3] describes the phenomenon of spin state switching in some 3d4 –3d7 transition metal complexes. Octahedral Fe(II) complexes are the most widely studied, because the interconversion between the diamagnetic low-spin (LS) state (S = 0) and paramagnetic high-spin (HS) state (S = 2) is accompanied by striking associated changes in structural and optical properties [7,8]. The presence and nature of SCO are related to two main features intrinsic to the compounds: (i) The electronic properties (including the ligand field strength); [13] and, (ii) cooperative supramolecular or covalent pathways between spin switching centres [14]. The study of SCO in the solution state has been offered as a means to investigate magnetic properties, whereby the intermolecular interactions found in the solid state are mitigated, allowing for rationalisation of the molecular magnetic character of the isolated complexes [19]
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