Conformational characterization of square planar nickel(II) tetraaza macrocyclic complexes by proton NMR. Crystal structure of [Ni(13aneN4)]ZnCl4 |
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Authors: | E. Joseph Billo Peter J. Connolly Dennis J. Sardella Jerry P. Jasinski Ray J. Butcher |
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Affiliation: | a Department of Chemistry, Boston College, Chestnut Hill, MA 02167, USA b Department of Chemistry, Keene State College, Keene, NH 03431, USA c Department of Chemistry, Howard University, Washington, DC 20059, USA |
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Abstract: | Conformations in solution of several diamagnetic nickel(II) complexes of macrocyclic tetraaza ligands are elucidated using proton NMR. There are six possible configurational isomers of planar [Ni(13aneN4)]2+ (13aneN4 = 1,4,7,10-tetraazacyclotridecane due to the orientation of the N---H protons above or below the plane of the macrocyle. Using NMR it is shown that in aqueous solution the [Ni(13aneN4)]2+ complex has the R,S,R,S or trans-II configuration. A single-crystal X-ray study demonstrates the same configuration of the nitrogen atoms in the complex [Ni(13aneN4)]ZnCl4. In the case of the 14-membered ring macrocyle cyclam (cyclam = 1,4,8,11-tetraazacyclotetradecane), previous NMR studies revealed the presence, in aqueous solution, of the previously unobserved trans-I or R,S,R,S isomer, whose spectrum is examined in greater detail here. Solution structures of nickel(II) complexes of bicyclam (1,5,8,12-tetraazabicyclo[10.2.2]hexadecane) and dachden (N, N′-bis(2-aminoethyl)-1,4-diazacycloheptane) are also reported. |
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Keywords: | Macrocyclic complexes Proton NMR spectroscopy Crystal structures Nickel complexes |
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