Investigating the crystal structures of alkali and alkaline-earth metal salts of 2,5-(dianilino)terephthalic acid

Abstract

From the reactions between 2,5-(dianilino)terephthalic acid and Li₂CO₃ or Mg(OH)₂ in water, three new layered compounds were prepared. The corresponding structures were determined by single crystal X-ray diffraction studies. Depending on the experimental conditions, two polymorphs can be obtained when using Li₂CO₃ as base namely [(Li(OH₂)₃)₂(C₂₀H₁₄N₂O₄)]·2H₂O (Ia) and [(Li(OH₂)₄)₂(C₂₀H₁₄N₂O₄)] (Ib). Compound Ia (form α) crystallizes in the P space group with lattice parameters a = 7.4372(6) Å, b = 8.2866(5) Å, c = 10.6200(13) Å, α = 98.674(7)°, β = 107.377(14)°, and γ = 90.655(6)°, whereas compound Ib (form β) adopts the P2₁/c space group with cell parameters a = 11.955(2) Å, b = 6.2885(4) Å, c = 16.030(2) Å, and β = 91.726(12)°. The neutralization reaction with Mg(OH)₂ leads to the formation of [Mg(OH₂)₆(C₂₀H₁₄N₂O₄)]·2.8H₂O (II), which crystallizes in the P space group with lattice parameters a = 13.6558(19) Å, b = 15.903(3) Å, c = 16.6894(10) Å, α = 94.295(11)°, β = 113.23(1)°, and γ = 110.377(11)°. All these structures can be systematically described by the stacking of alternating bi-layers as previously reported with the sodiated counterpart. One layer consists of 2,5-(dianilino)terephthalate dianions (C₂₀H₁₄N₂O₄²⁻) while the other is composed of the corresponding cations (Li⁺ or Mg²⁺) coordinated by water molecules. The distance between the two layers depends on the nature of the cation and its coordination as well as the conformation of the organic anion. Such original 2-D host lattices appear quite interesting as anion-inserting electrode materials for promoting the emerging field of p-type rechargeable organic batteries.