Mixed oxidation state trinuclear cobalt complexes with bridging sulphito and Schiff-base ligands. Part 1. Preparation of the complexes [CoII(µ-SO3)2(µ-L)2COIII2(ROH)2](L = Schiff base anion, R = alkyl) and structure determination of [CoII(µ-SO3)2(µ-α,α′-Me2-salpd)2CoIII2(PrnOH)2]·2PrnOH

Abstract

Mixed-valence complexes of the type [Co^II(µ-SO₃)₂(µ-L)₂Co^III₂(H₂O)_n(ROH)_2–n](n= 0, 1, or 2; R = Me or Prⁿ) have been prepared and characterized, where the deprotonated Schiff-base ligands L^2– are either symmetrical, such as N,N′-ethylenebis(salicylideneiminate)(salen), N,N′-ethylenebis(α-methylsalicylideneiminate)(α,α′-Me₂-salen), propane-1,3-diylbis(salicylideneiminate)(salpd), and propane-1,3-diylbis(α-methylsalicylideneiminate)(α,α′-Me₂-salpd), or unsymmetrical such as propane-1,3-diyl(α-methylsalicylideneiminate)(salicylideneiminate)(α-Me-salpd). An X-ray structure determination of [CO^II(µ-SO₃)₂(µ-α,α′Me₂-salpd)₂Co^III₂(PrⁿOH)₂]·2PrⁿOH showed the presence of bridging phenolic oxygens and sulphite ions. The mixed-valence state Co^III(S= 0)–Co^II(S=)–Co^III(S= 0) in these trinuclear complexes has been demonstrated by cryomagnetic measurements because the effective magnetic moments (4.40–5.00) at room temperature correspond to the monomeric complex of a cobalt(II) ion in a high-spin state. Down to 77 K, no spin-exchange interaction was observed between the cobalt(III) and cobalt(II) ions. I.r. spectra and thermal gravimetric-differential thermal analysis data have been obtained and discussed with regard to the co-ordination modes of the solvent molecules water, methanol, ethanol, and propan-1-ol.