Syntheses, characterization, X-ray crystal structures and emission properties of copper(II), zinc(II) and cadmium(II) complexes of pyridyl-pyrazole derived Schiff base ligand - Metal selective ligand binding modes

The varying coordination modes of the title ligand, L [5-methyl-1-(pyridin-2-yl)-N'[pyridin-2-ylmethy-lidene]pyrazole-3-carbohydrazide] towards the different metal centers is reported by preparation and characterization of Cu(II), Zn(II) and Cd(II) complexes, [Cu(L)NO3 center dot H2O](NO3) (1) [Zn(L)(2)](ClO4)(2)center dot 2DMF (2) and [Cd(L)(I)(2)] (3) respectively. In 1, the neutral ligand serves as tetradentate 4 N donor where both pyridine and pyrazole nitrogen atoms of pyridyl-pyrazole part are coordinatively active, leaving the carbonyl oxygen of the carbohydrazide part inactive. The same pyridine and pyrazole N atoms remain abstained from the coordination process towards the Zn(II) and Cd(II) metal centers. For 2 and 3 the ligand behaves as a tridentate NNO donor where the two nitrogen atoms come from azomethine, pyridine of pyridine-2-carbaldehyde parts and O from carbonyl oxygen atoms (carbohydrazide part). The complex 1 and 2 are distorted octahedral while complex 3 adopts distorted square pyramidal geometry. All the complexes are X-ray crystallographically characterized. (C) 2010 Elsevier Ltd. All rights reserved.