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

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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)2L1 2]·2H2O 2, [Fe(H2L1)(H2O)2][ClO4]3·H2O 3, [Fe2(µ-OH)2(H2L2)2]-[ClO4]4·2H2O 4, [Fe2(µ-OH)2L2 2]·2H2O 5 and [Fe2(µ-OH)2L3 2]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.

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