Syntheses, crystal structures, and spectroscopic properties of copper(II) complexes with 3,14-diethyl-2,6,13,17-tetraazatricyclo(16.4.0.0^7,12)docosane

Abstract

[Cu(L)(NO₃)₂] (1) and [Cu(L)(H₂O)₂](SCN)₂ (2) [L = 3,14-diethyl-2,6,13,17-tetraazatricyclo(16.4.0.0^7,12)docosane] have been prepared and structurally characterized by single-crystal X-ray diffraction at 100 K. For these constrained macrocycle complexes, copper(II) exists in a tetragonally distorted octahedral environment with the four nitrogen atoms of the macrocyclic ligands and two oxygen atoms from either nitrate or water in axial positions. The macrocyclic ligands in both complexes adopt the most stable trans-III conformation. The Cu–N distances are 2.021(2)–2.047(2) Å and typical but the axial ligands are weakly coordinating, with Cu–O bond lengths, 2.506(2) Å for 1 and 2.569(2) Å for 2, due to the pseudo Jahn–Teller effect. The crystals are stabilized by a 3-D network by intra and intermolecular hydrogen bonds that are formed among the secondary nitrogen hydrogen atoms and nitrate in 1, and intermolecular hydrogen bonds are formed by water and thiocyanates in 2. The electronic absorption and IR spectral properties are also discussed.

Keywords:

• Crystal structure
• Spectroscopic properties
• Copper(II)
• Macrocyclic ligand
• trans-III Conformation

Acknowledgments

We thank the Ministry of Higher Education of Malaysia (grant no. UM.C/HIR/MOHE/SC/12) for supporting this study. M.A. Subhan thanks the NRF of Korea for a postdoctoral fellowship grant 2010.