X-ray crystallographic, spectroscopic, and electrochemical properties of Group 12 metal-chlorides of di-2-pyridyl ketone acetic acid hydrazone (dpkaah)

Abstract

Di-2-pyridyl ketone acetic acid hydrazone hydrate, dpkaah.0.5H₂O (1), prepared from the acid catalyzed condensation of di-2-pyridyl ketone (dpk) with acetic acid hydrazide in refluxing ethanol, undergoes facile coordination to Group 12 metal-chlorides in CH₃CN to form [MCl₂(κ³-N,N,O-dpkaah)] {M=Zn (3), Cd (4) or Hg(5)}. X-ray structural analysis on single crystals of dpkaah (2) and 3–5 confirmed their identities and revealed pseudo-coordination of the carbonyl group (C=O). Infrared measurements confirmed the pseudo-coordination of the carbonyl group to MCl₂. The geometries of 3–5 vary, while 5 adopts a square pyramidal geometry, 4 has a structure halfway between square pyramidal and trigonal bipyramidal and 3 is less distorted from square pyramidal than 3. The extended structures of 3–5 exposed extensive networks of non-covalent interactions, and in the case of 4 chloride bridges of the type Cd(μ-Cl)₂Cd were observed. Spectroscopic measurements in different solvents and variable temperature studies confirmed the stability of the keto form of 1 and 3–5. Spectrophotometric titrations of protophilic solutions (dmf or dmso) of 1 with MCl₂ revealed facile coordination of MCl₂ to 1 and disclosed low concentrations of MCl₂ can be detected and determined using protophilic solutions of 1. Electrochemical measurements on dmf solutions divulged electrochemical decomposition of uncoordinated 1, the facile coordination of 1 to MCl₂, and the stability of 3–5 decreases as the size of the metal ion increases.

Keywords:

• Di-2-pyridyl ketone acetic acid hydrazone
• spectroscopy
• synthesis
• electrochemistry
• X-ray

Acknowledgements

The authors acknowledge the University of the West Indies for financial support and the United States National Science Foundation and Colby College for support of the X-ray diffraction facility at Colby College and would like to express their gratitude to Dr Ordel Brown, Ms Toni Johnson, and Mr Raymond Lawrence for various contributions.