Novel copper(II) complexes with diazamesocyclic ligands functionalized by additional donor group(s): syntheses, crystal structures and magnetic properties

Abstract

Copper(II) complexes with three diazamesocyclic ligands based on l,5-diazacyclooctane (DACO) bearing additional imidazole or phenol functional donor groups, 1,5-bis(imidazol-4-ylmethyl)- (L¹11), 1-(imidazol-4-ylmethyl)- (L²22), and 1-(2-hydroxybenzyl)-1,5-diazacyclooctane (HL³33), have been newly synthesized and characterized, and their structures determined by X-ray diffraction analyses. It has been revealed that with Cu(ClO₄)₂·6H₂O L¹11 forms a mononuclear complex [CuL¹11Cl]ClO₄·H₂O 1, L²22 forms a μ-Cl⁻ bridged binuclear complex [CuL²22Cl]₂[ClO₄]₂2, whereas HL³33 forms a phenoxo-bridged binuclear complex [CuL³3(H₂O)]₂[ClO₄]₂3. Each Cu^II in the three complexes is five-coordinated in a distorted square-pyramidal environment. For the mononuclear complex 1 the Cl⁻ anion is at the apical site, whereas for the μ-Cl⁻-bridged binuclear complex 2 the two bridging Cl⁻ anions occupy both the axial and one equatorial position with Cu–Cl–Cu angle 88.81(5)° and intramolecular Cu ⋯ Cu separation 3.494(8) Å. In the phenoxo-bridged binuclear complex 3 the Cu–O–Cu bridging angle is 100.80(12)° and the intramolecular Cu ⋯ Cu distance is 3.0324(9) Å. Variable-temperature magnetic susceptibility measurements on the two binuclear complexes 2 and 3 in the range 4.2–300 K indicate a quite different magnetic intramolecular coupling between the binuclear copper(II) centers, from a weak ferromagnetic to a very strong antiferromagnetic coupling, with 2J = 1.16 (for 2) vs. −574 cm⁻¹ (for 3), and the magneto-structural correlations are discussed in detail. The solution behaviors of the complexes have been further studied by UV/Vis and ESR techniques.