Manganese(II) and iron(III) complexes of the tridentate ligands bis(benzimidazol-2-ylmethyl)-amine (L1) and -methylamine (L2). Crystal structures of [MnL1(CH3CO2)2], [FeL2Cl3], and [Fe2L12(µ-O){µ-(CH3)3CCO2}2][ClO4]2

Abstract

The preparation and characterisation of [MnL¹(CH₃CO₂)₂](1), [Mn₆(µ₄-O)₂(C₆H₅CO₂)₁₀(H₂O)₄](9), [FeL¹Cl₃](10), [FeL²Cl₃](2), and [Fe₂L¹₂(µ-O){µ-(CH₃)₃CCO₂}₂][ClO₄]₂(3) are reported where L¹ and L² are bis(benzimidazol-2-ylmethyl)amine and bis(benzimidazol-2-ylmethyl)methylamine. The molecular structures of (1), (2), and (3) were determined by X-ray diffraction. Complex (1) exists as a discrete, neutral, mononuclear species in the solid state. The manganese(II) ion is five-co-ordinate with the tridentate ligand bound in a meridional manner. Both acetates are monodentate with Mn–O distances of 2.076(5) and 2.158(5)Å. Complex (9) contains a [Mn₆(µ-O)₂]¹⁰⁺ core, formally 4Mn^II :2Mn^III. Complex (2) is neutral, mononuclear, distorted octahedral. The ligand co-ordinates in a similar manner to that seen in (1) and the chlorides occupy the three remaining meridional sites, with Fe–Cl(equatorial) 2.318(5)Å and Fe–Cl(axial) 2.322(5) and 2.433(5)Å. The Mössbauer spectrum of (10) at room temperature comprises a quadrupole doublet: δ= 0.40(1), ΔE_Q= 0.33(2) mm s^–1. Complex (3) is a dinuclear iron(III) species containing the triply bridged [Fe₂(µ-O)(µ-RCO₂)₂]²⁺ core. The Fe ⋯ Fe distance is 3.075(5)Å and the Fe–O(oxo)–Fe angle is 117.0(6)°. The high-spin iron(III) centres are antiferromagnetically coupled with J=–116 cm^–1. The Mössbauer spectra of (3) at room temperature and 70 K consist of doublets with δ= 0.44(1), ΔE_Q= 1.37(2), and δ= 0.55(1), ΔE_Q= 1.30(2) mm s^–1 respectively.