Copper(II) nitrato and chloro complexes with sterically hindered tridentate ligands: Influence of ligand framework and charge on their structure and physicochemical properties

Copper(II) coordination complexes of the neutral ligand, tris(3-tert-butyl-5-methyl-1-pyrazolyl) methane (L2'), i.e. the copper(II) nitrato complexes [Cu(L2')(NO3)][Cu(NO3)4](1/2) (1) and [Cu(L2')(NO3)](ClO4) (2) and the copper(II) chloro complex [Cu(L2')(Cl)](ClO4) (3), and its anionic borate analogue, hydrotris(3-tert- butyl-5-methyl-1-pyrazolyl) borate (L2), i. e. the copper(II) nitrato complex [Cu(L2)(NO3)] (4) and the copper(II) chloro complex [Cu(L2)(Cl)] (5), were synthesized in order to investigate the influence of ligand framework and charge on their structure and physicochemical properties. While X-ray crystallography did not show any definitive trends in terms of copper(II) atom geometry in four-coordinate copper(II) chloro complexes 3 and 5, different structural trends were observed in five-coordinate copper(II) nitrato complexes 1, 2, and 4. These complexes were also characterized by spectroscopic techniques, namely, UV-Vis, ESR, IR/far-IR, and X-ray absorption spectroscopy. (C) 2009 Elsevier B. V. All rights reserved.