Tetramethyl anthracene-2,3,6,7-tetracarboxylate–tetramethyl 9,10-dihydro-9,10-dioxoanthracene-2,3,6,7-tetracarboxylate (1/1)CAS 116896-77-6 and 113431-17-7.

Abstract

In the title co-crystal, C22H16O10·C22H18O8, the independent tetramethyl 9,10-dihydro-9,10-dioxoanthracene-2,3,6,7-tetracarboxylate, (I), and tetramethyl anthracene-2,3,6,7-tetracarboxylate, (II), components occupy separate crystallographic inversion centers. In (II), the dihedral angles between the mean aromatic plane and the two independent carboxylate planes are 41.32 (10) and −38.35 (10)°. The methylcarboxylate groups of (I) are disordered, with each resolvable into two groups. In the least disordered carboxylate, the apparent angles between the mean aromatic plane and the two partial carboxylate planes [site occupations = 0.510 (3) and 0.490 (3)] are 16.8 (3) and 23.3 (3)°. In the highly disordered group, the apparent angles between the mean aromatic plane and the two partial carboxylate planes [site occupations = 0.510 (3) and 0.490 (3)] are 78.3 (3) and −74.1 (3)°. In addition, this extreme disorder leads to an artificially elongated C(aromatic)—C(carboxyl) bond.