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Abstract
The reactivity of zinc complexes with N,S-donor molecules may be of relevance to the study of Zn-metalloproteins and -metalloenzymes. In this context, the zinc complex [Zn(MeImSH)2I2] was synthesised by the reaction of zinc powder with the 1 : 1 iodine adduct of the drug methimazole [(MeImSH)·I2]. The molecular structure of the complex, elucidated by X-ray diffraction analysis, showed a tetrahedral zinc(II) centre coordinated by two neutral methimazole units (through the sulfur atoms) and two iodides. From the reaction of MeImSH and Zn powder, the complex [Zn(MeImSH)(MeImS)2] (MeImS = deprotonated form of methimazole) was separated and characterised. An analysis of the crystal packing of the neutral complexes [Zn(MeImSH)2X2] (X = I, Br and Cl) and the ionic complex [Zn(MeImSH)3I]I showed that in all of the complexes the sulfur atom, in addition to binding to the metal centre, contributes to the formation of 1-D chains built via C(4)–H⋯S and N–H⋯X interactions in the neutral complexes, and via C(4)–H⋯S and N–CH3⋯S interactions in the ionic complex [Zn(MeImSH)3I]I. The deprotonation/protonation of the coordinated methimazole units can modulate the coordination environment at the Zn core. From the reaction of complex [Zn(MeImSH)3I]I with a strong non-coordinating organic base, we have shown that, as a consequence of the NH deprotonation of methimazole S-coordinated to zinc(II), the ligand coordination mode changes from S-monodentate to N,S-bridging. Correspondingly, in the complex [Zn(MeImSH)(MeImS)2], the MeImS that displays the N,S-bridging mode at zinc can be N-protonated and thereby changes to the S-monodentate coordination.
Highlights
DSI2 M0 E t12 O 14o rdCay Hs/2rC .tL. 2 oxidized/complexed metal (1) AdductaMetal Solvent Main product/s Ref
It is noteworthy that Fujisawa et al.8 were not able to synthesise this complex by reacting ZnI2 with MeImSH in MeOH, the unexpected ionic complex of stoichiometry [Zn(MeImSH)3I]I was instead obtained
The crystal packing highlights the formation of 1-D chains built via weak interactions of C(4)–H⋯S and N–H⋯halogen
Summary
The experimental data show that the adduct (MeImSH)·I2 in CH2Cl2 can successfully oxidize zinc powder to Zn(II) by a twoelectron transfer process according to the overall reaction (2). Similar to the observations for the complex [Zn(MeImSH)2I2] (Fig. 4a), for all of the structures, it is possible to identify 1-D chains built via weak interactions of C(4)–H⋯S (Fig. 6a–d) involving C–H adjacent to the MeImSH N–H group (C–H⋯S distances lie in the range 2.8–3.2 Å).
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