Equilibrium studies on the protonation and Cu(II) complexation by an hexaaza macrocycle containing p -xylyl spacers. The crystal structure of the hexaprotonated ligand and the kinetics of decomposition of the Cu(II) complexes
Abstract The protonation constants of the ligand 3,6,9,16,19,22-hexaazatricyclo[22.2.2.211,14]triaconta-1(26),11(12),13,24,27, 29-hexaene (L, BPXD) have been determined in water at 25°C by potentiometric procedures and indicate a lower basicity than that corresponding to the analogue ligand with m-xylyl spacers between the diethylenetriamine subunits (BMXD). The crystal structure of a salt of H6L6+ containing Br− and NO3 − as anions has been solved by X-ray diffraction procedures and reveals that the macrocycle adopts an almost planar configuration. The protonated amine groups are involved in a complex network of hydrogen bonds with the anions and water molecules, with two anions being placed close to the cavity of the macrocycle. Despite the lower basicity of BPXD, the stability of the mononuclear CuL2+ and HCuL3+ complexes is several log units higher than that corresponding to the analogous BMXD complexes, which suggests the possibility of a different coordination mode for both closely related ligands. Actually, the whole set of stability constants for the mono and binuclear Cu(II)–L complexes can be rationalised by considering that the macrocycle acts as tetradentate in the mononuclear species. In contrast, the kinetic parameters for decomposition of the mono and binuclear Cu(II)–L complexes in acid solutions are only slightly different from those previously determined for the BMXD complexes.
Molecular structure and characterization of a pair of hydrate isomers for dinuclear copper(II) complexes with a 26-membered hexaazamacrocycle
Abstract A pair of seldom seen hydrate isomers with a formula of LCu 2 (CH 3 COO) 2 (H 2 O) 2 (ClO 4 ) 2 , where L is the dinucleating macrocyclic ligand bis- p -xytylBISDIEN, have been prepared and characterized by X-ray crystallography, UV⧹Vis spectra and magnetic measurements. The blue isomer, [LCu 2 (CH 3 COO) 2 (H 2 O) 2 ] (ClO 4 ) 2 , crystallizes in the triclinic system and the violet isomer, [LCu 2 (CH 3 COO) 2 ](ClO 4 ) 2 · 2H 2 O, crystallizes in the orthorhombic system. The blue complex consists of one cation [LCu 2 (CH 3 COO) 2 (H 2 O) 2 ] 2 and two ClO 4 − anions. The two copper atoms are independent to each other with a separation of 6.781(9) A. Each has a square pyramidal geometry and is five-coordinated by three N atoms from the macrocycle and two O atoms from the monodentate acetate anion and the coordinated water molecule, respectively. In violet isomer, both central copper atoms are located in an approximately square planar environment and are not coordinated by the water molecules. The isomers have different reflectance spectra due to the different coordination geometry but can rapidly interchange in solution at ambient temperature. Both compounds exhibit quite weak antiferromagnetic couplings verified by the small but negative Weiss constant ( θ = −5.72 K for the blue and −25.6 K for the violet isomer).
Hydrogen bonding between free fluoride ions and water molecules: two X-ray structures
Abstract The structures of two copper complexes, [Cu(cyclam) (H2O)2]F2·4H2O (cyclam = 1,4,8,11-tetraazacyclotetradecane) and [Cu(en)2(H2O)2]F2·4H2O (en=ethylenediamine), are reported, in which the fluoride ions within their lattices are solvated by four water molecules attached by strong hydrogen bonds. The configurations of these and other “free” [F(H2O)n]− groupings are compared, and the strength of the hydrogen bonds discussed.