Fourteen membered hexaaza copper macrocycle: Synthesis, characterization, crystal structures and the consequence of anion coordination

Fourteen membered hexaaza macrocyclic complexes of the type [CuLX2] (where L = 3,10-bis(benzyl)1,3,5,8,10,12-hexaazacyclotetradecane and X=ClO4-, SCN−) and [CuL(CH3CN)2](PF6)2(CH3CN)2 have been synthesized by template assisted condensation reaction. They have been characterized by spectral and X-ray crystallographic techniques. It was of interest to investigate the effect of anions on the gross geometry and chemical properties of Cu(II) ion. The crystal structure of all the complexes show axially elongated octahedral geometry with weakly coordinated anions. The macrocyclic ring adopts the trans-III configuration with six- and five-membered chelate rings in chair and gauche conformation, respectively. The IR and other spectral properties are consistent with the result of X-ray diffraction. It was observed that in the solid state the arrangement of the coordination sphere is distorted octahedral whereas in solution, a square-planar structure is predominant. The molar conductivity of the complexes indicates that the axially bonded anions are almost entirely dissociated in acetonitrile solution. The EPR spectra of complexes 1–3 are axial and consistent with a dx2-y2dx2-y2 ground state.

Graphical abstractFourteen-membered hexaaza macrocycle [CuL(X)2] (where X = ClO4−, SCN− and CH3CN) have been synthesized and characterized by spectral and X-ray crystallographic techniques. It was observed that in the solid state the arrangement of the coordination sphere is distorted octahedral whereas in solution, the square-planar one is prevailed. The molar conductance of the complexes indicates that the axially bonded anions are almost entirely dissociated in acetonitrile solution.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Investigating the effect of the anions on the gross geometry of Cu(II) ion. ► Axially elongated octahedral geometry. ► Anions are weakly coordinated to the metal ion. ► In the solid state the arrangement of the coordination sphere is distorted octahedral. ► In solution coordination sphere is the square-planar.