Role of Anions on the Crystal Structures of Copper(II) and Zinc(II) Complexes of a Tunable Butterfly Cyclophane Macrocycle

Three crystal structures of a ditopic cyclophane ligand (L) in which two 1,5,8,12-tetraamine molecules have been attached through methylene spacers to the ortho positions of a benzene ring are reported. The first one (1) corresponds to the tetraprotonated free macrocycle (H₄L⁴⁺) having two tetrachlorozincate(II) counteranions (C₂₄H₅₄O₂N₈Cl₈Zn₂, a = 9.1890(2) Å, b = 14.0120(3) Å, c = 15.3180(3) Å, α = 89.2320(7)°, β = 82.0740(6)°, γ = 83.017(1)°, Z = 2.00, triclinic, P1̄); the second one (2) is of a binuclear Cu²⁺ complex having coordinated chloride anions and perchlorate counteranions (C₂₄H₅₈O₁₄N₈Cl₄Cu₂ a = 9.9380(2) Å, b = 30.2470(6) Å, c = 53.143(1) Å, orthorhombic, F2dd, Z = 18), and the third one (3) corresponds to an analogous Zn²⁺ complex that has been crystallized using triflate as counteranion (C₂₆H_51.2O_6.6N₈Cl₂F₆S₂Zn₂ a = 8.472(5) Å, b = 9.310(5), c = 13.745(5) Å, α = 84.262(5)°, β = 77.490(5)°, γ = 73.557(5)°, triclinic, P1̄, Z = 2). The analysis of the crystallographic data clearly shows that the conformation of the macrocycle and, in consequence, the overall architecture of the crystals are controlled by the anions present in the moiety, π−π-stacking associations, and hydrogen bonding interactions. The protonation and stability constants for the formation of the Cu²⁺ and Zn²⁺ complexes in aqueous solution have been determined potentiometrically in 0.15 mol dm^-3 NaClO₄ at 298.1 K. Intramolecular hydrogen bonding defines the protonation behavior of the compound. Positive cooperativity is observed in the formation of the Cu²⁺ complexes.