Cd(II) complexes with phthalic acids: solution study and crystal structure of cadmium(II) phthalate hydrate

摘要: The acid–base properties of phthalic acid (H2L) have been determined by simultaneous spectroscopic, potentiometric, and polarographic measurements. Stability constants of the complexes CdHL+, CdL, CdL22−, CdL34−, CdH−2L24− and their distribution versus pH were determined at 25 °C and ionic strength in 0.1 M NaNO3. The advantages of each method are pointed out in such a way as to describe more precisely the interactions between cadmium and phthalic acid over a wide range of ligand and metal concentrations. The crystal structure of the [CdL] complex has been established by single-crystal X-ray diffraction. Cd(C8H4O4)•H2O is orthorhombic, space group Pbca, a = 23.463(5), b = 9.293(2), c = 7.730(1) Å, Z = 8, and ρ = 2.323 g cm−3. The structure was refined to a final R value of 0.054 for 3231 unique reflections with I > 3σ(I). The crystal is a three-dimensional polymeric network in which the Cd atom is seven-coordinated. The first ligand coordinates in a bidentate carboxylate (O,O′) mode (Cd—O = 2.372(5) and 2.445(5) Å); a second ligand is part of a seven-membered ring formed with its two carboxylate groups (Cd—O = 2.317(5) and 2.341(5) Å); two other phthalic ligands make one coordination bond (Cd—O = 2.255(5) and 2.449(5) Å) while the seventh bond is a water molecule (Cd—O = 2.333(6) Å). Key words: crystal structure, cadmium complexes, phthalic acid complexes.