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

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posted on 17.10.2005, 00:00 by Martin Chadim, Pilar Díaz, Enrique García-España, Jana Hodačová, Julio Latorre, Malva Liu-González, Santiago V. Luis, José M. Llinares, Jiří Závada
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 (C26H51.2O6.6N8Cl2F6S2Zn2 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.