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