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

The acid-base properties of phthalic acid (H(2)L) have been determined by simultaneous spectroscopic, potentiometric, and polarographic measurements. Stability constants of the complexes CdHL(+), CdL, CdL(2)(2-), CdL(3)(4-) CdH(-2)L(2)(4-) and their distribution versus pH were determined at 25 degrees 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) Angstrom, Z = 8, and rho = 2.323 g cm(-3). The structure was refined to a final R value of 0.054 for 3231 unique reflections with I> 3 sigma(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) Angstrom), 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) Angstrom); two other phthalic ligands make one coordination bond (Cd-O = 2.255(5) and 2.449(5) Angstrom) while the seventh bond is a water molecule (Cd-O = 2.333(6) Angstrom).