Effect of a halogen bond on the crystal structure of terphenyldicarboxylic acid derivatives

The syntheses and structures of dimethyl [1¹,2¹:2⁴,3¹-terphenyl]-1⁴,3⁴-dicarboxylate (1), dimethyl 2²,2⁵-diiodo[1¹,2¹:2⁴,3¹-terphenyl]-1⁴,3⁴-dicarboxylate (2), potassium [1¹,2¹:2⁴,3¹-terphenyl]-1⁴,3⁴-dicarboxylate (3) and dimethyl [1,1'-biphenyl]-4,4'-dicarboxylate (4) are reported. Neighboring phenyl rings in compounds 1, 3 and 4 have a planar structure (torsion angles are 0.6-4.1°) and the molecules are packed into regular layers. In the structure of the iodinated derivative of terphenyldicarboxylic acid (2), the middle benzene ring of the terphenyl fragment is rotated relative to the other rings by 64° due to the repulsion between the protons and the iodine atoms of neighboring rings. The formation of halogen bonds between iodine and oxygen atoms of the carbonyl group leads to the movement of molecules of one layer into another layer and the loss of layered structure. Potassium [1¹,2¹:2⁴,3¹-terphenyl]-1⁴,3⁴-dicarboxylate (3) forms crystals with an ionic structure. The coordination number of the potassium cation is eight and the resulting coordination polyhedron is a distorted square antiprism. Dianions in the potassium salt crystal are packed in layers similar to the layers in the dimethyl ethers 1 and 4. Salt 3 has high thermal stability to 500°C.