Coordination chemistry with pyrazole-based chelating ligands: molecular structural aspects

Pyrazole-based chelating ligands form a variety of coordination complexes with a number of metal ions, providing varying coordination geometry and nuclearity. Recent years have seen considerable interest in the designing of various pyrazole-based ligands and to study their structural properties to serve specific stereochemical requirement of a particular metal-binding site. Using over 120 pyrazole-based chelating ligands, the stereochemical properties of over 110 discrete coordination complexes, studied by single-crystal X-ray crystallography were analysed. Various bonding modes for a given chelating ligand are involved, and are reviewed with reference to ligand structure and the resulting coordination complexes. It is shown that the metal coordination number of the resulting complexes varies from two to eight. The ligands are introduced systematically as a function of their denticity, making easy access to information on specific type of ligands and coordination complexes thereof. X-ray crystallographically-determined bond lengths of various donor atoms/groups are collected in a table, thus providing an accessible source for reference purposes. Source material for the review amounts to about 130 references. (C) 2000 Elsevier Science S.A. All rights reserved.