Axial Bonds in Copper(II) Cyclam with DMF Ligands

Upon recrystallization of [Cu(L)](PF₆)₂ from DMF/H₂O, we obtained the DMF coordinated complex as purple plates. The crystals of retain their transparency for several weeks in a refrigerator, but they slowly decompose upon exposure to the atmosphere as evidenced by elemental analysis. The infrared spectrum and microanalysis for clearly support the structure determined by the X-ray diffraction studies as described in the Experimental Section. There have been many examples of copper(II) tetraazamacrocycles, where the axial donors interact with copper(II) ions. However, the complexes reported usually show considerably long Cu-axial donor distances with weak interactions between metal centers and axial donors. Even such weak interactions, it appears that the presence of hydrogen-bonding chelate rings comprised of axial donors, suitable anions and solvents, and secondary amines of the macrocycle is requisite for the stabilization of axial ligands to the central copper(II) ions. In the present work, we describe the preparation and structure of trans-[Cu(L)-(DMF)₂](PF₆)₂, where the complex shows fairly strong copper-axial donor interactions without the support of hydrogen-bonding chelate rings