Structural and Dynamic Studies of Zinc, Gallium, and Cadmium Complexes of a Dicarboxylate Pendant‐Armed Cross‐Bridged Cyclen

Abstract Zn II , Ga III , and Cd II complexes of a dicarboxylate pendant‐armed derivative of an important new cross‐bridged cyclen ligand were prepared and characterized spectrally. Crystal structures of the Zn II and Ga III complexes both feature pseudo‐octahedral metal centers, fully enveloped by the ligand’s cis ‐N 4 O 2 donor set with the zinc coordination sphere less distorted. All Ga−N and Ga−O bonds are significantly shorter than the corresponding values in the zinc structure. Solution NMR spectral studies revealed dynamic enantiomerization for the Zn II complex with Δ G ≠ = 12.3(1) kcal/mol (24 °C). By contrast, the Ga III complex gave only slow‐exchange limit spectra up to the highest temperature measured [87(2) °C; Δ G ≠ > 21.1(2) kcal/mol]. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)