Structure and thermal reactivity of Zn(II) salts of isocinchomeronic acid (2,5-pyridinedicarboxylic acid)

The synthesis, an improved refined crystal and molecular structure re-determination, and the thermal decomposition behavior of two Zn(II) derivatives of isocinchomeronic acid (2,5-pyridinedicarboxylic acid or H₂2,5-pydc) are presented. Zn(2,5-pydc)(H₂O)₃Zn(2,5-pydc)(H₂O)₂]₂ (1) crystallizes in the triclinic P-1 space group with a = 7.106(2), b = 11.450(2), c = 11.869(1) Å, α = 107.29(1), β = 104.08(1), γ = 90.32(2)°, and Z = 2. Zn(2,5-pydc)(H₂O)₂] · H₂O (2) is orthorhombic (P2₁2₁2₁ space group), with a = 7.342(1), b = 9.430(1), c = 13.834(2) Å, and Z = 4. The structures were refined to agreement R ₁-factors of 0.0315 (1) and 0.0336 (2). Complex (1) is arranged as molecular Zn₄(2,5-pydc)₄(H₂O)₁₀ tetramers, the cages of which define channels that remain unblocked by anions. Compound (2) is polymeric with Zn(2,5-pydc)(H₂O)₂ and Zn(2,5-pydc)(H₂O)₃ units linked through bridging ligands. Both compounds were synthesized under mild conditions in aqueous media, without need to resort to hydrothermal media. Changing the pH from 4.51 to 5.75 suffices to direct the chemical processes toward the orthorhombic compound rather than to the triclinic one.