Polynuclear manganese amino acid complexes

Abstract

The reaction of MnCl₂·4H₂O with DL-valine (Val) in MeOH in the presence of Et-saoH₂ (2-hydroxypropiophenone oxime) and NEt₄OH forms the complex [Mn^III₃Mn^IV₂O₂(CH₃O)(Et-sao)₆(Val)]·Val·1.5H₂O (1·Val·1.5H₂O) in very good yields. A similar reaction of MnCl₂·4H₂O with Glycine (Gly) in MeOH in the presence of saoH₂ (salicylaldoxime) and Ca(OH)₂ yields the complex [Mn^III₃O(sao)₃(Gly)Cl(MeOH)₃]·1.87 MeOH·0.13H₂O (2·1.87 MeOH·0.13H₂O). Replacing saoH₂ with Me–saoH₂ (2-hydroxyethanone oxime) and Gly with HPABA (para-aminobenzoic acid) in the presence of CH₃ONa in MeOH forms the complex [Mn₆O₂(PABA)₂(Me-sao)₆(MeOH)₄(H₂O)₂]·2[Mn₆O₂(PABA)₂(Me-sao)₆(MeOH)₂]·11 MeOH (3·11 MeOH) in moderate yields. Magnetic studies for 1 and 2 reveal the presence of both ferromagnetic and antiferromagnetic interactions, leading to S = 2 ground states for both complexes. Complexes 1 and 2 represent the first examples of polynuclear manganese complexes with any naturally occurring α-amino acid, while 3 is the first structurally characterised example of a manganese para-aminobenzoate complex.