The 1:1 adduct of 2,5-dihydroxy-1,4-benzoquinone with 4,4′-bipyridine

2,5-Di­hydroxy-1,4-benzo­quinone (DHBQ) and 4,4′-bi­pyridine (BPY) crystallize in a 1:1 ratio as a neutral molecular adduct, C₆H₄O₄·C₁₀H₈N₂, in space group C2/c, with half of each mol­ecule in the asymmetric unit. The mol­ecules are linked by a strong O—H...N hydrogen bond [O...N 2.6323 (15) Å] and a weak C—H...O hydrogen bond [C...O 3.2082 (17) Å] to form infinite stacks of parallel one-dimensional hydrogen-bonded ribbons. The two rings of the bi­pyridine are twisted at 28.3° with respect to each other, and the benzo­quinone ring is inclined at an angle of 18.3° with respect to the plane of the neighbouring pyridine ring. The 4,4′-bi­pyridine mol­ecule lies on a twofold axis and the benzo­quinone mol­ecule lies across an inversion centre.

S1. Comment

To investigate a variety of molecular interactions in the solid state, in particular N—H···O and O—H···N hydrogen bonds, we have produced co?crystals of 4,4'-bipyridine (BPY) and 2,5-dihydroxy-1,4-benzoquinone (DHBQ). Cocrystals of organic acids and bipyridines have been studied extensively and have been observed to form a wide variety of hydrogen bonds. They have the ability to form cocrystals with different stoichiometries of the constituents and a variety have been observed by ourselves and by other workers, namely 1:1, 1:2 and 2:1 cocrystals of 4,4'-bipyridine and pyromellitic acid (Lough et al., 2000; Williams et al., 2000), and also 1:1 (Reetz et al., 1994) and 2:3 ratios (MacLean et al., 1999) for cocrystals of 4,4'-bipyridine and squaric acid. Surprisingly, we have found only one stoichiometry for cocrystals of DHBQ and BPY and present here the crystal structure of the 1:1 adduct, (I). \sch

DHBQ is a weak organic acid with the possibility of single or double deprotonation, whereupon its shape and properties change significantly, as the charge becomes more delocalized. The neutral molecule was observed in the structure of the pure form by Semmingsen (1977), while the doubly deprotonated form was observed as the potassium salt by Kulpe (1974). In the neutral state, DHBQ can be a hydrogen-bond donor and/or an acceptor, making it an excellent and novel tool for studying weak interactions in `supramolecular' crystals.

BPY is a rather rigid weak bidentate base, popular in similar crystal-engineering studies because of its bridging ability (Zaman et al., 1999; Coupar et al., 1996; Sharma & Zaworotko, 1996; MacLean et al., 1999). The molecule can remain neutral or become singly or doubly protonated, its final state depending not only on the strength of the cocrystal acid, but also on its crystalline environment (Williams et al., 2000).

In the present structure, the molecular parameters of DHBQ compare closely with those of the neutral molecule (Semmingsen, 1977), and similarly for BPY, which in (I) is also typical of the neutral form. Both molecules are symmetrical, since the DHBQ lies across a crystallographic inversion centre and the BPY lies upon a twofold axis (Fig. 1). The angle subtended at the N atom of the bipyridine molecule [117.5 (1)°] compares well with the average of 116.5° taken from neutral bipyridine molecules in the Cambridge Structural Database (CSD; Allen & Kennard, 1993); the average CSD value for the recorded protonated form is 121.5°. This parameter also accords with H2 being bound to O2 and not to the bipyridine [O2—H2 0.96 (2) Å].

The dominant interaction for the packing is the strong O2—H2···N1 hydrogen bond [O···N 2.6323 (15) Å], which is assisted by the weaker C14—H14···O1 hydrogen bond [C···O 3.2082 (17) Å], thus linking the molecules together into one-dimensional chains. The chains lie in the ac plane and propagate in the [103] direction (Fig. 2).

The molecular synthon of (I) is similar to one of the two which were observed in the two structures of 4,4'-bipyridine and squaric acid reported by Reetz et al. (1994), in which the bipyridine and squarate molecules form similar hydrogen-bonded chains. The other synthon, which has the same shape, occurs when the bipyridine has become protonated and an N—H···O hydrogen bond is supported by a weak C—H···O hydrogen bond.

In the closely related system combining 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone (chloranilic acid) and BPY to form 1:1 crystals (Zaman et al., 1999), the molecules also link together to form chains, but with a distinctly different synthon. The 4,4'-bipyridine in this adduct is the doubly protonated [BPY-2H]²⁺, and the molecules are linked by bifurcated hydrogen bonds at each N atom, resulting in the planes of the quinone and the bipyridine lying mutually perpendicular and alternating their orientation along the molecular chain.

The differences observed in the four structures discussed above can be attributed primarily to the relative strengths of the three acids, squaric acid, 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone and 2,5-dihydroxy-1,4-benzoquinone.

Related literature

For related literature, see: Allen & Kennard (1993); Coupar et al. (1996); Kulpe (1974); Lough et al. (2000); MacLean et al. (1999); Reetz et al. (1994); Semmingsen (1977); Sharma & Zaworotko (1996); Williams et al. (2000); Zaman et al. (1999).

S2. Experimental

Equimolar portions of BPY and DHBQ were dissolved in methanol/water, producing an orange solution. Crystals of (I) suitable for X-ray structure determination were prepared by slow evaporation of the solvent at room temperature.

S3. Refinement

All H atoms were found in difference Fourier maps and were refined with isotropic displacement parameters. The C—H and O—H distances all refined to within standard ranges and there were no anomalous values of U_iso.

Computing details

Data collection: SMART (Bruker, 1997); cell refinement: SMART; data reduction: SAINT (Bruker, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997).

Figures

	Fig. 1. The molecules of (I) shown with 50% probability displacement ellipsoids. The dashed lines indicate hydrogen bonds and H atoms are drawn as small spheres of arbitrary radii [symmetry codes: (i) 1/2 - x, 1/2 - y, 2 - z; (ii) -x, y, 1/2 - z].
	Fig. 2. The packing diagram for (I) viewed along the c axis. H atoms have been omitted for clarity.

2,5-Dihydroxy-1,4-benzoquinone–4,4'-bipyridine (1/1)

Crystal data

C6H4O4·C10H8N2	F(000) = 616
Mr = 296.28	Dx = 1.478 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 932 reflections
a = 20.8676 (17) Å	θ = 13.7–29.5°
b = 7.0151 (7) Å	µ = 0.11 mm^−1
c = 9.1087 (8) Å	T = 150 K
β = 92.843 (5)°	Needle, orange
V = 1331.8 (2) Å^3	0.54 × 0.20 × 0.12 mm
Z = 4

Data collection

Bruker SMART CCD diffractometer	1286 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.060
Graphite monochromator	θmax = 27.5°, θmin = 2.0°
ω scans	h = −26→27
6874 measured reflections	k = −9→9
1520 independent reflections	l = −11→11

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.041	Hydrogen site location: difference Fourier map
wR(F^2) = 0.113	All H-atom parameters refined
S = 1.06	w = 1/[σ^2(Fo^2) + (0.0652P)^2 + 0.6747P] where P = (Fo^2 + 2Fc^2)/3
1520 reflections	(Δ/σ)max < 0.001
124 parameters	Δρmax = 0.29 e Å^−3
0 restraints	Δρmin = −0.22 e Å^−3

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
C1	0.18925 (6)	0.30700 (18)	0.93241 (14)	0.0216 (3)
O1	0.13723 (5)	0.34454 (16)	0.86910 (11)	0.0297 (3)
C2	0.23774 (6)	0.19269 (19)	0.85043 (14)	0.0226 (3)
O2	0.22213 (5)	0.14586 (16)	0.71195 (10)	0.0282 (3)
H2	0.1813 (11)	0.193 (3)	0.676 (3)	0.061 (7)*
C3	0.29392 (6)	0.1371 (2)	0.91739 (14)	0.0233 (3)
H3	0.3248 (8)	0.062 (2)	0.8663 (18)	0.027 (4)*
N1	0.11795 (6)	0.21530 (17)	0.54574 (13)	0.0258 (3)
C10	0.13339 (7)	0.1763 (2)	0.40779 (16)	0.0258 (3)
H10	0.1769 (8)	0.151 (2)	0.3935 (18)	0.026 (4)*
C11	0.08876 (7)	0.1733 (2)	0.28926 (15)	0.0248 (3)
H11	0.1015 (8)	0.136 (2)	0.192 (2)	0.035 (5)*
C12	0.02457 (6)	0.21488 (18)	0.31218 (14)	0.0215 (3)
C13	0.00852 (7)	0.2576 (2)	0.45608 (15)	0.0262 (3)
H13	−0.0336 (9)	0.288 (3)	0.481 (2)	0.038 (5)*
C14	0.05649 (7)	0.2554 (2)	0.56801 (15)	0.0288 (3)
H14	0.0478 (9)	0.285 (3)	0.670 (2)	0.042 (5)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0194 (6)	0.0255 (6)	0.0197 (6)	−0.0009 (5)	−0.0017 (5)	0.0015 (5)
O1	0.0230 (5)	0.0405 (6)	0.0251 (5)	0.0047 (4)	−0.0050 (4)	−0.0032 (4)
C2	0.0230 (7)	0.0266 (7)	0.0182 (6)	−0.0018 (5)	−0.0003 (5)	0.0002 (5)
O2	0.0260 (5)	0.0398 (6)	0.0184 (5)	0.0047 (4)	−0.0045 (4)	−0.0045 (4)
C3	0.0225 (7)	0.0274 (7)	0.0200 (6)	0.0026 (5)	0.0004 (5)	−0.0021 (5)
N1	0.0248 (6)	0.0296 (6)	0.0224 (6)	0.0002 (5)	−0.0043 (4)	0.0007 (4)
C10	0.0208 (7)	0.0306 (7)	0.0257 (7)	0.0025 (5)	−0.0024 (5)	−0.0021 (5)
C11	0.0225 (7)	0.0309 (7)	0.0208 (6)	0.0013 (5)	−0.0012 (5)	−0.0024 (5)
C12	0.0212 (6)	0.0225 (6)	0.0205 (6)	−0.0008 (5)	−0.0024 (5)	0.0007 (5)
C13	0.0213 (6)	0.0347 (7)	0.0225 (7)	0.0019 (5)	0.0004 (5)	−0.0018 (6)
C14	0.0264 (7)	0.0398 (8)	0.0198 (6)	0.0005 (6)	−0.0011 (5)	−0.0014 (6)

Geometric parameters (Å, º)

C1—O1	1.2321 (17)	C10—C11	1.3907 (19)
C1—C3^i	1.4495 (18)	C10—H10	0.941 (17)
C1—C2	1.5164 (19)	C11—C12	1.3966 (19)
C2—O2	1.3283 (16)	C11—H11	0.977 (19)
C2—C3	1.3519 (19)	C12—C13	1.4013 (18)
O2—H2	0.96 (2)	C12—C12^ii	1.490 (2)
C3—C1^i	1.4495 (18)	C13—C14	1.3931 (19)
C3—H3	0.967 (16)	C13—H13	0.945 (18)
N1—C14	1.3382 (19)	C14—H14	0.975 (19)
N1—C10	1.3408 (18)
O1—C1—C3^i	123.40 (12)	C11—C10—H10	120.2 (10)
O1—C1—C2	118.45 (12)	C10—C11—C12	119.42 (13)
C3^i—C1—C2	118.13 (12)	C10—C11—H11	120.6 (11)
O2—C2—C3	121.56 (13)	C12—C11—H11	119.9 (11)
O2—C2—C1	117.40 (12)	C11—C12—C13	117.38 (12)
C3—C2—C1	121.02 (12)	C11—C12—C12^ii	121.03 (14)
C2—O2—H2	114.3 (14)	C13—C12—C12^ii	121.59 (14)
C2—C3—C1^i	120.79 (12)	C14—C13—C12	119.07 (13)
C2—C3—H3	121.5 (10)	C14—C13—H13	117.9 (12)
C1^i—C3—H3	117.7 (10)	C12—C13—H13	123.1 (12)
C14—N1—C10	117.49 (12)	N1—C14—C13	123.42 (13)
N1—C10—C11	123.22 (13)	N1—C14—H14	114.4 (11)
N1—C10—H10	116.5 (10)	C13—C14—H14	122.2 (11)

Symmetry codes: (i) −x+1/2, −y+1/2, −z+2; (ii) −x, y, −z+1/2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O2—H2···N1	0.96 (2)	1.74 (3)	2.6323 (15)	154 (2)
C14—H14···O1	0.975 (19)	2.572 (19)	3.2082 (17)	122.9 (13)