5,5′-(Ethyne-1,2-diyl)diisophthalic acid dimethyl sulfoxide tetrasolvate

In the title compound, C18H10O8·4C2H6OS, the mid-point of the triple bond of the main molecule is located on a special position, i.e. about an inversion center. The carboxyl groups are twisted slightly out of the planes of the aromatic rings to which they are attached, making dihedral angles of 24.89 (1) and 7.40 (2)°. The cystal packing features strong O—H⋯O hydrogen bonds, weaker C—H⋯O interactions and O⋯S contacts [3.0981 (11) Å] and displays channel-like voids extending along the a-axis direction which contain the dimethyl sulfoxide solvent molecules.

Financial support by the Deutsche Forschungsgemeinschaft (Priority Program 1362 "Porous Metal-Organic Frameworks") is gratefully acknowledged by AÁM. FÁK. thanks the European Union (European regional development fund) and the Ministry of Science and Art of Saxony (Cluster of Excellence "Structure Design of Novel High-Performance Materials via Atomic Design and Defect Engineering [ADDE]").

Comment
During the last years tetracarboxylic acid linker molecules of which 3,3′,5,5′-biphenyltetracarboxylic acid is the prototype have proven highly effective both in the construction of porous metal-organic (MOF) (Chen et al., 2005;Münch et al., 2011) and hydrogen bond supported frameworks (Coles et al., 2002) as well as in the formation of hydrogen bond assembled layer structures (Zhou et al., 2007). Insertion of an ethynylene unit into the molecular backbone such as in the title compound, 5,5′-(ethynylene)diisophthalic acid, was undertaken in order to expand lattice porosity and also to introduce an additional interaction site for improved solid-gas adsorption behaviour (Hausdorf et al., 2009;Zheng et al., 2013). This has been confirmed showing high acetylene uptake of a corresponding MOF-framework (Hu et al., 2009).
But as a rigid tetrafunctional carboxylic acid, the title compound should also capable of forming complex hydrogen bonded aggregate structures in the solid state (Hauptvogel et al., 2011) of which the present solvate with dimethyl sulfoxide finishes another evident proof. The title compound crystallizes in the monoclinic space group P2 1 /n with half a molecule of 5,5′-(ethynylene)diisophthalic acid and two dimethyl sulfoxide molecules in the asymmetric part of the unit cell. The tolane fragment devites from ideal linear geometry (C2-C1≡C1 i = 178.29 (18)°) and the carboxyl groups are slightly twisted out of the aromatic ring plane -dihedral angles 24.89 (1)° (O4═C9-O3) and 7.40 (2)° (O2═C8-O1)].

Experimental
The titled compound was synthesized via a Sonogashira-Hagihara cross coupling reaction of dimethyl 5ethynylisophthalate and dimethyl 5-iodoisophthalate. For the synthetic procedure, see: Hausdorf et al. (2009), Zhou et al. (2007. Colourless single crystals suitable for X-ray diffraction were grown by slow evaporation from a dimethyl sulfoxide/mesitylene (2:1) solution.

Refinement
The H atoms were positioned geometrically and allowed to ride on their parent atoms, with O-H = 0.84Å and U iso (H) = 1.5U eq (O) for hydroxyl H atoms, C-H = 0.95Å and U iso (H) = 1.2U eq (C) for aryl H atoms, and C-H = 0.98Å and U iso (H) = 1.5U eq (C) for methyl H atoms.

Computing details
Data collection: APEX2 (Bruker, 2007); cell refinement: SAINT (Bruker, 2007); data reduction: SAINT (Bruker, 2007); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).    Solvent channels along the crystallographic a-axis in the packing structure. -1,2- where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.32 e Å −3 Δρ min = −0.28 e Å −3 Extinction correction: SHELXL97 (Sheldrick, 2008), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.0065 (7) Special details Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'s 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 > 2σ(F 2 ) is used only for calculating R-factors(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.