Hydroxide-bridged diiron(III) complexes of tetraaminodiphenol macrocyclic ligands: structure and properties

Abstract

Some dinuclear iron(III) complexes derived from two tetraaminodiphenol macrocyclic ligands, one (H₂L¹) contains two -NH(CH₂)₃NH- and the other (H₂L²) one -NH(CH₂)₃NH- and one -NH(CH₂)₂NH- units, and an acyclic tetradentate ligand {H₂L³N,N'-bis(2-hydroxybenzyl)-1,3-diaminopropane} have been synthesised and studied. In all of the macrocyclic complexes [Fe₂(µ-OH)₂(HL¹)₂][ClO₄]₂1, [Fe₂(µ-OH)₂L¹₂]·2H₂O 2, [Fe(H₂L¹)(H₂O)₂][ClO₄]₃·H₂O 3, [Fe₂(µ-OH)₂(H₂L²)₂]-[ClO₄]₄·2H₂O 4, [Fe₂(µ-OH)₂L²₂]·2H₂O 5 and [Fe₂(µ-OH)₂L³₂]6 only N₂O₂ donation to the metal centres occurs, while the two unco-ordinated amino nitrogens either remain singly protonated (2 and 5) or one (1) or both of these (3 and 4) is doubly protonated. Variable-temperature magnetic susceptibility data for 1, 4 and 6 indicate weak antiferromagnetic-exchange interactions in each case with J values of: -5.5 (1), -7.3 (4) and -11.8 cm^-1(6). The isomer-shift and quadrupole-splitting values for 1 at 77 K are 0.46 and 0.43 mm s^-1, respectively. The redox chemistry of 1 has been studied by cyclic voltammetry and its crystal structure has been determined: monoclinic, space group P2₁/c, a= 13.448(1), b= 14.847(1), c= 13.442(1)Å, β= 91.48(1)°, Z= 2, R= 0.048 and R'= 0.050. The two edge-sharing FeO₄N₂ octahedra are distorted and connected by a centre of inversion.