Monomeric and dimeric manganese(II) complexes of N,N,N',N'-tetrakis [(2-benzimidazolyl)-methyl]-1,2-ethanediamine and its derivatives

Abstract

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 characterized. 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 ⁵⁵Mn with a coupling constant IAI =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)](CIO₄)₂), 5.88, ([Mn(Me-EDTB)] (ClO₄) and 5.46 ([Mn(Et-EDTB)] (CIO₄)₂) per Mn(II) atom are in the-range found for <i>d</i>⁵ 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<img src='http://www.niscair.res.in/jinfo/Subscript4.gif' border=0>) makes it easy to bind only one metal ion.