Coordination chemistry of 1,4-bis(carboxymethyl)-1,4,7-triazacyclononane: Synthesis and characterization of mononuclear and binuclear μ-oxo-bridged iron(III) complexes, and a 1D-helical copper(II) chain

The syntheses of the pentadentate ligand 1,4-bis(carboxymethyl)-1,4,7-triazacyclononane (LH2) and its use in the preparation of [LHCu]ClO4 (1), and a mononuclear iron(III) complex ([LFeCl] (2)) are reported. The hydrolysis of 2 in the presence of an excess of NaClO4 resulted in the crystallization of a binuclear complex, [Fe2(μ-O)L2] · (NaClO4)3 · CH3OH · 3H2O (3). The crystal structures of 1–3 have been determined by single-crystal X-ray crystallography. In complex 1, the Cu(II) centre is in square based pyramidal environment, with two nitrogen atoms from the tacn ring and two oxygen atoms from two different carboxylate groups lying in the basal plane and the third nitrogen atom occupying the apical position. One pendant acetic acid group is protonated and, instead of coordinating to the copper(II) centre, participates in hydrogen bonding interactions with the perchlorate counter-ion. The coordinated carboxylate group forms a bridge to the copper atom of an adjacent [LHCu]+ molecule, thus generating 1D-helical chains. The compound exhibits weak ferromagnetic coupling probably due to weak interactions between [LHCu]+ molecules. In complex 2, the iron(III) centre is in a distorted octahedral geometry, with the fac-coordinated triamine ring, two carboxylate groups and one chloride ligand occupying the coordination sphere. In the binuclear complex 3, two iron(III) centres are bridged by one oxygen atom to form a μ-oxo-diiron(III) complex with an Fe⋯Fe distance of 3.423(3) Å and a non-linear Fe–O–Fe angle of 144.4°. This binuclear complex features strong antiferromagnetic coupling between the two iron(III) centres.

A pentadentate derivative of 1,4,7-triazacyclononane has been used to prepare a carboxylate bridged copper(II) 1D-chain, a mononuclear iron(III) complex and an antiferromagnetic oxo-bridged binuclear iron(III) complex; the binuclear complex co-crystallized with three molecules of sodium perchlorate which form 1D-chains along the y axis.Figure optionsDownload as PowerPoint slide