Formation of mixed-ligand complexes of cadmium(II) halide with tri-n-octylphosphine oxide and pyridine or substituted pyridines in 1,2-dichloroethane

Abstract

The formation of mixed-ligand complexes of cadmium(II) chloride and bromide with tri-n-octylphosphine oxide (topo) and pyridine or substituted pyridines (R-py)[R-py = pyridine (py), 4- methyl-(4Me-py), 3-methyl-(3Me-py), 2-methyl-(2Me-py), 2-ethyl(2Et-py), 4-acetyl-(4MeCO-py), or 4-cyano-pyridine (4CN-py)] in 1,2-dichloroethane has been investigated. The formation constants given by equations (i) and (ii) were determined by means of solvent extraction [CdX₂(topo)₂]+ R-py [graphic omitted] [CdX₂(topo)(R-py)]+ topo (i), [CdX₂(topo)(R-py)]+ R-py [graphic omitted] [CdX₂(R-py)₂]+ topo (ii) at 25.0 ± 0.1 °C. These constants linearly increase with increasing pK_a of the conjugate acid of the pyridine base except for the 2-methyl- and the 2-ethyl-pyridine complexes. The steric hindrance of the 2-substituents is not important in the monopyridine complexes of cadmium(II) chloride. The results for the topo systems are discussed by the comparison with those for the tetrahalogeno systems.