Conformational characterization of square planar nickel(II) tetraaza macrocyclic complexes by proton NMR. Crystal structure of [Ni(13aneN4)]ZnCl4

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(13aneN 4 )] 2+ (13aneN 4 = 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(13aneN 4 )] 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(13aneN 4 )]ZnCl 4 . 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.