Static versus dynamic Jahn-Teller distortions in octahedral-like copper(II) complexes of 1,4,7-triazacyclononane and 1-oxa-4,7-diazacyclononane: implications for hydrolytic reactivity

The syntheses and characterizations by X-ray crystallography, EPR, and electronic absorption spectroscopy are reported for [Cu([9]aneN(3))(2)][CF3SO3](2).H2O (1) [Cu([9]aneN(2)O)(2)][BF4](2) (2) and [Cu([9]aneN(2)O)(2)][NO3](2) (3). The dynamic Jahn-Teller distortion present in the Cu([9]aneN(3))(2)(2+) cation is removed upon replacement of one nitrogen donor with oxygen. The pseudo-octahedral structures of 2 and 3, determined crystallographically, exhibit a strong tetragonal distortion with the two oxygen atoms in the elongated axial positions. In contrast, crystallographic characterizations of a number of Cu([9]aneN(3))(2)(2+) salts reveal that the octahedral-like coordination about the Cu(II) is dependent on crystal packing forces, and the degree of tetragonal distortion varies with the identity of the counter ion. A room temperature powder EPR spectrum of [Cu([9]aneN(2)O)(2)]Br-2 exhibits a static Jahn-Teller distortion while that of [Cu([9]aneN(3))(2)][CF3SO3](2) is dynamically averaged. Solution EPR and electronic absorption spectra of [Cu([9]aneN(2)O)(2)][CF3SO3](2) indicate a strong interaction between the equatorial nitrogen atoms and the Cu(II) as evidenced by the observation of nitrogen hyperfine splitting in g(x) and a shift of the ligand-field absorption to higher energy. The absence of a dynamic Jahn-Teller effect in the presence of the [9]aneN(2)O ligand correlates with a lowered reactivity for phosphodiester hydrolysis, suggesting that ligand fluxionality may be important in accessing the transition state in copper-promoted hydrolysis. (C) 2000 Elsevier Science S.A. All rights reserved.