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Helical dinuclear 3d metal complexes with bis(bidentate) [S,N] ligands: synthesis, structural and computational
Jamie Allen1, Jörg Saßmannshausen2, Kuldip Singh1
1School of Chemistry, University of Leicester, University Road, Leicester, LE1 7RH, UK. sandy.kilpatrick@leicester.ac.uk.
Abstract:
A diprotic bis(β-thioketoimine) ligand precursor featuring a flexible 4,4'-methylbis(aniline) linker, H22, was synthesised via treatment of the corresponding bis(β-ketoimine) with Lawesson's reagent. Lithiation of H22 and coordination with one equivalent of d-block metal(II) chlorides MCl2(THF) (M = Fe, Co and Zn) yielded a corresponding series of homoleptic dinuclear complexes, [M2(μ-2)2]. X-ray diffraction analysis reveals a tetrahedral geometry for the two metals and a double-stranded helicate structure arising from inter-strand face-face π-stacking. These interactions create a helical 'twist' of ca. 70°. Utilising a bulky mononucleating β-thioketoiminate ligand, [3]-, the analogous series of homoleptic monometallic complexes, [M(3)2] (M = Fe, Co and Zn), were prepared and characterised by spectroscopic and analytical techniques. A comprehensive DFT study of all complexes reveals a stronger M-S bonding compared to M-N due to a higher degree of covalency. Solution magnetic studies and natural bonding orbital calculations on the mono- and dinuclear iron and cobalt complexes are consistent with high-spin tetrahedral Fe(II) and Co(II) centres, and cyclic voltammetry reveals both oxidation and reduction processes are accessible.
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