Dicobalt(II) complexes of a macrocyclic ligand containing hydroxo-, alkoxo-, phenoxo-, thiolato-, halogeno-, and pseudohalogeno-bridges: structures and magnetic exchange interactions

Abstract

Two families of dicobalt(II) complex of a binucleating macrocyclic ligand (L), C₁₈H₂₀N₄O₂, derived from a cyclic [2 + 2] condensation of 2,5-diformylfuran with 1,3-diaminopropane, have been synthesised and characterised by analytical, spectroscopic, magnetic, and X-ray diffraction methods. They differ in the co-ordination geometry of the cobalt(II) ions (tetrahedral or trigonal bipyramidal) but are alike in that the metal ions are intramolecularly linked via two bridging ligands which may be the same or different. The co-ordination number of the metal ions is determined by the nature of the bridging groups which include OH^–, OMe^–, OEt^–, OPr^n–, OPr^i–, OBu^t–, OPh^–, SEt^–, SPh^–, Cl^–, Br^–, 1,1-N₃^–, and nitrogen atom-only NCS^– and NCSe^–. Crystals of [CO₂L(OEt)(NCS)₃](1) are monoclinic with a= 9.03(1), b= 10.73(1), c= 14.64(1)Å, β= 99.0(1)°, Z= 2, and space group P2₁/c. Crystals of [CO₂L(OMe)(N₃)₃](2) are monoclinic with a= 8.381 (7), b= 10,09(1), c= 14.185(11)Å, β= 96.1(1)°, Z= 2, and space group P2₁/n. For (1) and (2), 692 and 700 reflections above background were measured by diffractometer and refined by Fourier methods to R 0.099 and 0.115, respectively. In both structures each cobalt(II) ion has a distorted trigonal-bipyramidal environment, being bonded to two nitrogen atoms of the macrocycle and a disordered N/O bridge atom in the equatorial plane. The two axial sites are occupied by a nitrogen atom of a terminal anion [NCS^– in (1), N₃^– in (2)] and the other disordered N/O bridge atom. The Co ⋯ Co separations are 3.119(6) and 3.195(6)Å, respectively. The structures are compared to those of other metal complexes of the same macrocycle. The magnetic moments of the five-co-ordinate complexes show little dependence on temperature although a small ferromagnetic interaction is apparent for the µ-azido-µ-methoxo-complex. All the tetrahedral complexes exhibit antiferromagnetic superexchange, the coupling constants J(in H=–2JS₁S₂) ranging from –5.5 cm^–1 for the di-µ-bromo-complex to –90.5 cm^–1 for the di-µ-thiophenolato-complex.