Crystal structures of 4-methoxybenzoic acid–1,3-bis(pyridin-4-yl)propane (2/1) and biphenyl-4,4′-dicarboxylic acid–4-methoxypyridine (1/2)

Crystal structures of the title hydrogen-bonded compounds have been determined at 98 K. In each crystal, the acid and base molecules are linked by short O—H⋯N/N—H⋯O hydrogen bonds, forming a linear hydrogen-bonded 2:1 or 1:2 unit of the acid and the base.


Figure 1
The molecular structure of compound (I), showing the atom-numbering scheme. Displacement ellipsoids of non-H atoms are drawn at the 50% probability level and H atoms are drawn as circles of arbitrary size.

Figure 2
The molecular structure of compound (II), showing the atom-numbering scheme. Displacement ellipsoids of non-H atoms are drawn at the 50% probability level and H atoms are drawn as circles of arbitrary size.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. All H atoms in compounds (I) and (II) were found in difference Fourier maps. The H atoms in both compounds which are involved in the O-HÁ Á ÁN/N-HÁ Á ÁO hydrogen bonds were found to be disordered over two positions in difference Fourier maps. The positional parameters and the occupancy factors were refined with bondlength restraints of O-H = 0.84 (2) Å and N-H = 0.88 (2) Å , and with U iso (H) = 1.5U eq (O,N). Other H atoms were positioned geometrically (C-H = 0.95-0.99 Å ) and were treated as riding, with U iso (H) = 1.2U eq (C) or 1.5U eq (methyl C). For compound (I), six reflections were omitted in the final refinement owing to poor agreement between the measured and calculated intensities. For both structures, data collection: RAPID-AUTO (Rigaku, 2006); cell refinement: RAPID-AUTO (Rigaku, 2006); data reduction: RAPID-AUTO (Rigaku, 2006); program(s) used to solve structure: Il Milione (Burla et al., 2007); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: CrystalStructure (Rigaku, 2010) and PLATON (Spek, 2009).

4-Methoxybenzoic acid-1,3-bis(pyridin-4-yl)propane (2/1) (I)
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 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. Reflections were merged by SHELXL according to the crystal class for the calculation of statistics and refinement. _reflns_Friedel_fraction is defined as the number of unique Friedel pairs measured divided by the number that would be possible theoretically, ignoring centric projections and systematic absences.     where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.35 e Å −3 Δρ min = −0.26 e Å −3 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 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. Reflections were merged by SHELXL according to the crystal class for the calculation of statistics and refinement. _reflns_Friedel_fraction is defined as the number of unique Friedel pairs measured divided by the number that would be possible theoretically, ignoring centric projections and systematic absences.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (