Crystal synthesis of 1,4-phenylenediamine salts and coordination networks

Para-Phenylenediamine (ppda) may be ground together with metal chloride salts MCl₂ to produce the coordination network compounds [{(ppda)MCl₂}_n] {M = Zn (2), Cd (4), Cu (6)}. Its dihydrochloride salt [H₂ppda]Cl₂ can be ground with MCl₂ to produce the layered salt structures [H₂ppda] [MCl₄] {M = Zn (1), Cd (3), Cu (5)}, which (when M = Zn or Cd) may then be converted into 2 or 4 respectively by grinding with solid KOH. Alternatively, [H₂ppda][MCl₄] will react directly with appropriate basic metal compounds (hydroxides and/or carbonates) to give 2 or 4, which can then be converted back to the salts by reaction with gaseous HCl. The interconversion of 5 and 6 is more complicated, with different combinations of starting material giving different products. The crystal structure of 2 has been solved ab initio from the powder-diffraction data, and is shown to consist of zigzag polymeric chains containing alternating ppda and MCl₂ units.