Crystal Engineering Using the Versatility of 2,5-Dichloro-3,6-dihydroxy-1,4-benzoquinone with Organic and Metal Complex Partners

Four compounds of 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone (chloranilic acid = H2CA) with organic
and metal complex partners, [Hmel][CA]0.5·H2O (1), [Htptz][HCA]·H2O (2), [Fe(terpy)2][CA]·6H2O (3), and
[TTF][CA]0.5[redH4CA]0.5 (4) (mel = melamine, tptz = 2,4,6-tris(2-pyridyl)-1,3,5-triazine, terpy = 2,2‘,6‘,2‘ ‘-terpyridine,
TTF = tetrathiafulvalene) are synthesized and characterized by single-crystal X-ray diffraction. For the obtained
compounds, chloranilic acid shows various oxidation states and hydrogen bonding modes with multistage
deprotonation processes. For compounds 1 and 3, chloranilic acid shows its complete deprotonated form (CA2-). For
compound 2, the monodeprotonated form of chloranilic acid (HCA-) is observed. Interestingly, compound 4 shows
a reduced form of protonated chloranilic acid (1,4-dichloro-2,3,5,6-tetrahydroxybenzene:  redH4CA).