Spectroscopic and electrochemical properties of group 12 acetates of di-2-pyridylketone thiophene-2-carboxylic acid hydrazone (dpktch-H) complexes. The structure of [Cd(η3-N,N,O-dpktch-H)2]

•M(OAc)2·nH2O + [dpktch] + CH3CN + Δ → [M(η2-O,O-OAc)(η3-N,N,O-dpktch-H)]·nH2O (M = Zn → Hg).•The electronic spectra of [M(η2-O,O-OAc)(η3-N,N,O-dpktch-H)]·nH2O are solvent dependent.•The acetate group of [M(η2-O,O-OAc)(η3-N,N,O-dpktch-H)]·nH2O is labile.•M(η2-O,O-OAc)(η3-N,N,O-dpktch-H)·nH2O are electrochemically unstable.•X-ray structural analysis show 35% of the volume of [Cd(η3-N,N,O-dpktch-H)2] is empty.

The reaction between [dpktch] and [M(OAc)2] (M = group 12 metal atom) in refluxing CH3CN gave [M(η2-O,O-OAc)(η3-N,N,O-dpktch-H)]·nH2O (n = 0 or 1). The infrared and 1H NMR spectra are consistent with the coordination of [η2-O,O-OAc] and [η3-N,N,O-dpktch-H]− and the proposed formulations. The electronic absorption spectra of [M(η2-O,O-OAc)(η3-N,N,O-dpktch-H)]·nH2O measured in non-aqueous solvents revealed a highly intense intra-ligand-charge transfer (ILCT) transition due to π–π∗ of dpk followed by dpk → thiophene charge transfer. The electronic transitions of [M(η2-O,O-OAc)(η3-N,N,O-dpktch-H)]·nH2O are solvent and concentration dependent. Spectrophotometric titrations of dmso solutions of [M(η2-O,O-OAc)(η3-N,N,O-dpktch-H)]·nH2O with benzoic acid revealed irreversible inter-conversion between [M(η2-O,O-OAc)(η3-N,N,O-dpktch-H)]·nH2O and it conjugate acid [M(η2-O,O-OAc)(η3-N,N,O-dpktch)]·nH2O pointing to ligand exchange between the acetate and benzoate anions. When CH2Cl2 solutions of [M(η2-O,O-OAc)(η3-N,N,O-dpktch-H)]·nH2O were titrated with dmso, changes appeared pointing to solvolysis or ligand exchange reactions. Electrochemical measurements on dmso solutions of [M(η2-O,O-OAc)(η3-N,N,O-dpktch-H)]·nH2O divulged irreversible redox transformations consistent with electrochemical decomposition of [M(η2-O,O-OAc)(η3-N,N,O-dpktch-H)]·nH2O. The solid state structure of a single crystal of [Cd(η3-N,N,O-dpktch-H)2] obtained from a dmso solution of [Cd(η2-O,O-OAc)(η3-N,N,O-dpktch-H)]·nH2O confirmed the ligand scrambling of [M(η2-O,O-OAc)(η3-N,N,O-dpktch-H)]·nH2O. The extended structure of [Cd(η3-N,N,O-dpktch-H)2] revealed stacks of [Cd(η3-N,N,O-dpktch-H)2] locked via a network of hydrogen bonds. A significant amount of empty space (35.5%) was observed in the solid state structure of [Cd(η3-N,N,O-dpktch-H)2].

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