Crystal structure of the co-crystal of 5-aminoisophthalic acid and 1,2-bis(pyridin-4-yl)ethene

The supramolecular structure of the title 1:1 co-crystal consists of (100) sheets linked by O—H⋯N and N—H⋯O hydrogen bonds.


Chemical context
5-Amino-isophthalic acid (5AIA) is an emerging secondary building unit for a wide variety of metal-organic frameworks (MOFs). (Zeng et al., 2009;Wang et al., 2011;Cox et al., 2015) This compound is also a convenient precursor for the synthesis of azo-derivatized framework ligands, a key component in the rapidly evolving field of photochromic MOFs. (Brown et al., 2013;Castellanos et al., 2016;Walton et al., 2013;Patel et al., 2014). Similarly, 1,2-bis(pyridin-4-yl)ethene (BE) is also commonly used in MOF synthesis; however, it is routinely used in co-crystal engineering as well (Kongshaug & Fjellvag, 2003;MacGillivray et al., 2008;Desiraju, 1995) The 5AIA-BE co-crystal presented herein was produced as part of an undergraduate physical chemistry laboratory experiment developed by Jason Benedict.

Structural commentary
The 5AIA-BE co-crystal crystallizes with one molecule of 5AIA and one molecule of BE in the asymmetric unit ( Fig. 1). Both molecules are effectively planar in the solid state (r.m.s. deviation for 5AIA = 0.155 Å ). The BE moiety shows whole molecule disorder over two sets of sites, consistent with a local C2 rotation about the long axis of the molecule. The occupancy of the major and minor components was refined to be 0.588 (3) and 0.412 (3), respectively.

Supramolecular features
In this structure, the 5AIA molecule forms hydrogen bonds to both itself and the BE moiety, forming extended sheets (Table 1 and Fig. 2). The 5AIA-5AIA interactions consist of N(amine)-HÁ Á ÁO=C hydrogen bonds where each 5AIA makes two hydrogen bonds with two neighboring 5AIA molecules. The 5AIA-BE interaction consists of an O-HÁ Á ÁN(pyridyl) hydrogen bond such that each 5AIA makes one hydrogen bond with two neighboring BE molecules. The sheets formed by these interactions stack along the the a axis to produce a layered structure (Fig. 3).

Figure 2
Diagram illustrating the hydrogen-bonding interactions present in the two-dimensional sheets found in the 5AIA-BE co-crystal.

Figure 1
The asymmetric unit of the title compound, showing the numbering scheme. Displacement ellipsoids are shown at the 50% probability level.

Figure 3
View down [001] showing the (100) sheets in the extended structure of the title compound.
5AIA forms hydrogen bonds with two 5AIA molecules and two BP molecules. The 5AIA-BP interactions and one of the 5AIA-5AIA interactions are similar to those found in 5AIA-BE. The remaining 5AIA-5AIA interaction in 5AIA-BP consists solely of an N(amine)-HÁ Á ÁOH hydrogen bond, as opposed to the N(amine)-HÁ Á ÁO=C interaction found in 5AIA-BP. Interestingly, this results in a total of five hydrogen bonds in the 5AIA-BP structure compared to the six hydrogen bonds observed in 5AIA-BE.

Synthesis and crystallization
Solid BE (0.0119 g, 6.53 Â 10 À5 mol) and 5AIA (0.0109 g, 6.02 Â 10 À5 mol) were added to a 25 ml scintillation vial. To this was added approximately 15 ml of ethyl acetate followed by gentle heating. An additional 2 ml of methanol was added and all remaining solids dissolved. The loosely capped vial was then placed into a dark cabinet. After two weeks, yellow block-shaped crystals of the title compound suitable for singlecrystal X-ray diffraction measurements were obtained.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. Heteroatom hydrogen atoms were located in difference electron-density maps and freely refined.

Figure 4
Diagram illustrating the hydrogen bonding interactions present in the previously reported 5AIA-BP co-crystal. program(s) used to solve structure: SHELXT (Sheldrick, 2015); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015b); molecular graphics: OLEX2 (Dolomanov et al., 2009). 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.