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

Abstract

<p>Di-2-pyridyl ketone acetic acid hydrazone hydrate, dpkaah.0.5H₂O (<b>1</b>), 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 (<b>3</b>), Cd (<b>4</b>) or Hg(<b>5</b>)}. X-ray structural analysis on single crystals of dpkaah (<b>2</b>) and <b>3</b>–<b>5</b> 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 <b>3</b>–<b>5</b> vary, while <b>5</b> adopts a square pyramidal geometry, <b>4</b> has a structure halfway between square pyramidal and trigonal bipyramidal and <b>3</b> is less distorted from square pyramidal than <b>3</b>. The extended structures of <b>3</b>–<b>5</b> exposed extensive networks of non-covalent interactions, and in the case of <b>4</b> 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 <b>1</b> and <b>3</b>–<b>5</b>. Spectrophotometric titrations of protophilic solutions (dmf or dmso) of <b>1</b> with MCl₂ revealed facile coordination of MCl₂ to <b>1</b> and disclosed low concentrations of MCl₂ can be detected and determined using protophilic solutions of <b>1</b>. Electrochemical measurements on dmf solutions divulged electrochemical decomposition of uncoordinated <b>1</b>, the facile coordination of <b>1</b> to MCl₂, and the stability of <b>3</b>–<b>5</b> decreases as the size of the metal ion increases.</p