(1R*,2S*,4S*,5R*)-Cyclohexane-1,2:4,5-tetracarboxylic dianhydride

The title compound, C10H8O6, a promising raw material to obtain colorless polyimides which are applied to microelectronic and optoelectronic devices, adopts a folded conformation in which the dihedral angle between the two anhydro rings is 55.15 (8)°. The central six-membered ring assumes a conformation intermediate between boat and twist-boat. In the crystal, molecules are linked by weak C—H⋯O interactions, forming a layer parallel to the bc plane.

The title compound, C 10 H 8 O 6 , a promising raw material to obtain colorless polyimides which are applied to microelectronic and optoelectronic devices, adopts a folded conformation in which the dihedral angle between the two anhydro rings is 55.15 (8) . The central six-membered ring assumes a conformation intermediate between boat and twist-boat. In the crystal, molecules are linked by weak C-HÁ Á ÁO interactions, forming a layer parallel to the bc plane.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: IS5043). Aromatic polyimides (PI) have been widely applied to microelectronic and optoelectronic devices for their reliable combined properties: considerably high glass transition temperatures (T g ), non-flammability, and good dielectric and mechanical properties (Ando et al., 2010). Conventional aromatic PI films are intensively colored on the basis of chargetransfer (CT) interactions (Hasegawa & Horie, 2001). However, the coloration often disturbs optical applications of PIs.
Recently, there is a strong demand that further lightens the total weights of flat panel displays by replacing fragile inorganic glass substrates (~400 µm thick) by plastic substrates (~100 µm thick). However, it is not easy to develop the practically useful plastic substrates simultaneously possessing excellent optical transparency and sufficient heat resistance (T g 's > 250 °C) for the device fabrication processes such as inorganic transparent electrode deposition. The most effective strategy for completely erasing the significant PI film coloration is to use non-aromatic (cycloaliphatic) monomers either in tetracarboxylic dianhydride or diamine, thereby the CT interactions are inhibited. Our previous work illustrated that the equimolar polyaddition of cis, cis, cis-1,2,4,5-cyclohexanetetracarboxylic dianhydride (H-PMDA), synthesized by hydrogenation of pyromellitic dianhydride (PMDA), and some diamines indeed led to colorless PIs with very high T g 's (Hasegawa et al., 2007). However, the obtained PI films were very brittle in some cases owing to poor chain entanglement caused by insufficient molecular weights of the resultant PIs, which come from the insufficient reactivity of H-PMDA with diamines. The low reactivity of H-PMDA can be explained in terms of its steric structure (Uchida et al., 2003). In order to solve this crucial problem, we developed another H-PMDA isomer, i.e., 1R*, 2S*, 4S*, 5R*-cyclohexanetetracarboxylic dianhydride (H"-PMDA) (Hasegawa et al., 2008). The present work reports the crystal structure of this compound.
The pyromellitic acid tetrasodium salt formed was hydrogenated in a high-pressure hydrogen atmosphere in the presence of a ruthenium catalyst, and neutralized with conc. HCl. The tetracarboxylic acid obtained was isomerized by dehydrating with acetic anhydride at a precisely controlled temperature. Crystals of the title compound suitable for X-ray analysis were obtained from an acetic anhydride solution.

Refinement
All H atoms were placed in geometrical positions (C-H = 0.98 and 0.97 Å for CH and CH 2 , respectively) and constrained to ride on their parent atoms with U iso (H) = 1.2U eq (C).

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 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 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.