MONOMERIC AND DIMERIC MANGANESE(II) COMPLEXES OF N,N,N',N'-TETRAKIS[(2-BENZIMIDAZOLYL)-METHYL]-1,2-ETHANEDIAMINE AND ITS DERIVATIVES

Two types of manganese(II) complexes of N, N, N', N'-tetrakis[(2-benzimidazolyl)-methyl]1, 2-ethanediamine (EDTB) and its N-methyl (Me-EDTB) and N-ethyl (Et-EDTB) derivatives have been synthesized and characterised. Solution EPR of the [Mn2(EDTB) (OAc)4] in methanol at 142 K indicates that there are the equivalent Mn(II) ions coupled by an exchange interaction, fostered by bridging acetates. This is evidenced by a nearly isotropic 11-line hyperfine structure for Mn-55 with a coupling constant \A\ = 45 +/- 5 G. The room temperature magnetic moment of 4.86 B.M. per Mn atom indicates a clear quenching of the magnetic moment below that of a monomeric Mn(II) ion. The [Mn(L)] (ClO4)2 type complexes show EPR spectra typical of monomeric Mn(II) complexes, in a trigonal prismatic environment; their room temperature magnetic moments of 5.99, ([Mn(EDTB)] (ClO4)2), 5.88, ([Mn(Me-EDTB)] (ClO4)) and 5.46 ([Mn(Et-EDTB)] (ClO4)2 per Mn(II) atom are in the range found for d5 monomeric Mn(II) complexes. Thus a bridging inner sphere anion-like acetate makes it difficult for the ligand to coordinate to a metal ion with all its six donor atoms, and hence a second metal ion is coordinated by the ligand, whilst a weakly coordinating anion-like perchlorate (ClO-4) makes it easy to bind only one metal ion.