Thiosemicarbazones as co-ordinating agents. Part 3. Synthesis, spectroscopic characterization, and X-ray structure of methyl piruvate thiosemicarbazone hemihydrate, chloro(ethyl pyruvate thiosemicarbazonato)copper(II) (green form), and chloro(pyruvic acid thiosemicarbazonato)copper(II) dihydrate (blue form)