Unprecedented change of the Jahn-Teller axis in a centrosymmetric Cu-II complex induced by lattice water molecules - Crystal and molecular structures of bis[bis(3,5-dimethylpyrazol-1-yl)acetato]copper(II) and its dihydrate
Kozlevcar B, Gamez P, de Gelder R, Driessen WL, Reedijk J
EUROPEAN JOURNAL OF INORGANIC CHEMISTRY (1): 47-50 JAN 2003

Abstract:
Two copper coordination compounds with the tridentate (NON) ligand bis(3,5-dimethylpyrazol-1-yl)acetic acid (Hbdmpza) are reported. The central coordination sphere in both compounds is fulfilled by two ligands in [CuL2]. The ligands are centrosymmetrically oriented around the copper ion, thus forming a trans-CuN4O2 elongated octahedral chromophore. The atoms in both compounds are not positioned at the same places in the Jahn-Teller-distorted octahedral environment. For compound [CuL2] (1) two nitrogen atoms are located on the longer axis [Cu-N: 2.438(2) Angstrom], while the other two nitrogen atoms [Cu-N: 2.006(2) Angstrom] and the two oxygen atoms [Cu-O: 1.983(2) Angstrom] form the basal plane of the octahedron. The coordination sphere for [CuL2].2H(2)O (2) is composed of four nitrogen atoms [Cu-N: 2.013(3), 2.038(2) Angstrom] that form the basal plane, while the two oxygen atoms are at a longer distance [Cu-O: 2.293(2) Angstrom]. The water molecules in 2 are hydrogen bonded to the non-coordinated carboxylate oxygen atoms, forming bridges between two neighbouring monomeric units and leading to an infinite chain. Significant differences are observed for both compounds by spectroscopic investigations (EPR, IR, ligand field).