1,4-Anthraquinone ( Fig. 1) is an important molecule as a dienophile for the Diels-Alder reaction and as a kind of redox system. To the best of our knowledge, two polymorphic crystal structures of 1,4-anthraquinone have already been reported in RefCode COBBIE, 1 COBBIE02, 2 COBBIE03, 1 and COBBIE04 3 from CCDC, in which COBBIE and COBBIE02 are isomorphic and a pair of COBBIE03 and COBBIE04 is another isomorph. The atomic coordinates were elucidated in only COBBIE04. Recently, we performed an

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... ay analysis of needle-shaped 1,4-anthraquinone, and found that the crystal structure is different from that for COBBIE04, namely, another polymorph. We now refer to our crystal structure as the β-form (COBBIE04 as α-form). We report here on the crystal structure of another polymorph of 1,4-anthraquinone in detail. 1,4-Anthraquinone was prepared in 88% yield (764 mg) by the reduction of 1,4-dihydroxy-9,10-anthraquinone (1.0 g, 4.19 mmol) with NaBH4 (1.0 g, 26.5 mmol) in methanol (60 mL), followed by a treatment with 50% AcOH (60 mL). Single crystals in the β-form for X-ray crystallography were grown from a toluene-ethanol solution. The selection of toluene and ethanol solvents afforded the β-form exclusively. The X-ray data were collected using a Rigaku/MSC Mercury CCD diffractometer with graphite monochromated Mo-Kα (λ = 0.71070 Å) radiation at 223 K. The structure was solved by a x293 ANALYTICAL SCIENCES 2006, VOL. 22 X-ray Structure Analysis Online The crystal structure of another polymorph of 1,4-anthraquinone was determined. The compound crystallizes in monoclinic, space group P21/n with a = 7.301(1), b = 9.674(2), c = 13.831(2)Å, β = 93.175(8)Å, V = 975.5(3)Å 3 , Z = 4. There is antiparallel π-π stacking between aromatic rings. The packing arrangement is different from another crystal structure for 1,4-anthraquinone (space group P21/b with a = 8.430(1), b = 19.846(2), c = 5.927(1)Å, γ = 100.21(2)˚, CCDC code: COBBIE04).