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 ·H 2 O ( 1 ), [Htptz][HCA]·H 2 O ( 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).