2-(4-Hydroxyphenyl)acetic acid–4,4′-bipyridine (1/1)

In the acid molecule of the title complex, C10H8N2·C8H8O3, the acetyl C—C—C—O torsion angle is −32.1 (3)°, and in the molecule of the base, the dihedral angle between the two pyridine rings is 23.41 (10)°. In the crystal structure, intermolecular O—H⋯N hydrogen bonds link the acid and the base molecules into a one-dimensional triple-helix framework extended along the b axis.

In the acid molecule of the title complex, C 10 H 8 N 2 ÁC 8 H 8 O 3 , the acetyl C-C-C-O torsion angle is À32.1 (3) , and in the molecule of the base, the dihedral angle between the two pyridine rings is 23.41 (10) . In the crystal structure, intermolecular O-HÁ Á ÁN hydrogen bonds link the acid and the base molecules into a one-dimensional triple-helix framework extended along the b axis.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: PV2281).

Comment
The design and synthesis of coordination complexes have absorbed considerable attention due to their diverse structures with 4,4'-bipyridine linker (Han et al., 2009). Moreover, hydrogen bond can also play a role in forming motif structures (Tomura & Yamashita, 2001). We have designed the title complex in an attempt to prepare crystaline magnetic materials and report its crystal structure in this paper.
The end to end hydrogen-bonding interactions lead to the formation of a one-dimensional triple-helix structure framework along the b-axis, Fig 2. Between adjacent triple-helix chains there exist weak π-π interactions.
Experimental 2-(4-hydroxyphenyl)acetic acid (0.152 g, 1 mmol) and 4,4'-bipyridine (0.156 g, 1 mmol) were added to a mixed solution of ethanol (20 ml) and water (10 ml) with Cu(SO 4 ) 2 (0.127 g, 0.5 mmol) under stirred conditions at room temperature. A few minutes later a lot of blue deposit appeared. After the deposit was filtered out, a light blue solution was kept for evaporating.
Colorless single crystals of the title complex were obtained about 19 days later.

Refinement
The H atoms bonded to C atoms were positioned geometrically and refined using a riding model with C-H = 0.93 and 0.97 Å for methylene and aryl H-atoms, respectively and U iso (H) = 1.2U eq (C). The H atoms bonded to O atoms were located in a difference Fourier map and refined without restraints. Fig. 1. The molecular structure of the title complex. Displacement ellipsoids are drawn at the 30% probability level.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds supplementary materials sup-3 in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.