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 = H(2)CA) with organic and metal complex partners, [Hmel][CA](0.5).H2O (1), [Htptz][HCA].H2O (2), [Fe(terpy)(2)][CA].6H(2)O (3), and [TTF][CA](0.5)[(red)H(4)CA](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 (CA(2-)). 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: (red)H(4)CA).