Application of factor analysis to the spectrophotometric determination of formation constants of complexes of nickel(II) with tridentate dyes

Abstract

Absorption curves of solutions containing a dye ligand and its 1:1 and 1:2 nickel(II) complexes have been analyzed by factor analysis to extract the (often) inaccessible absorption curve of the 1:2 complex and its formation constant, K2. The method was applied to an , '-dihydroxy phenylazo dye, Solochrome Violet (SV), and to two a-[(2-hydroxyphenyl)azo]-a-acetoacetonitrile dyes. Required inputs are a family of absorption curves containing various proportions of the dye and two complexes, reference curves for the dye and the 1:1 complex, the pKa's of the ligand'groups; and an independently determined value of the formation constant of the 1:1 complex, K¡. The derived value of K2 for SV agreed with the value determined earlier by potentiometric titration. The method was successful in cases where the absorption curves of the two complexes showed small differences in shape and/or Xmax but failed where the two curves differed only in amplitude. The values of Kj and K2 for the acetoacetonitrile dyes are smaller by several orders of magnitude than those of related dyes; the spectra and molecular models suggest that bohd angles and lengths are distorted in the chelates. The advantages and disadvantages of the approach are discussed.

Detailed Spectroscopic, Thermodynamic, and Kinetic Characterization of Nickel(II) Complexes with 2,2‘-Bipyridine and 1,10-Phenanthroline Attained via Equilibrium-Restricted Factor Analysis

“…11 Twenty-five years later, Reeves et al described its application to a system with nickel(II) complexes and tridentate dyes. 12 In such calculations, it is necessary to determine the true number of chemical species in the system. Including additional hypothetical species can obviously help to mathematically model the absorbance data more closely, but would not represent a chemically meaningful answer.…”

“…The problem is conveniently expressed using matrix algebra, which was first detailed by Wallace . Twenty-five years later, Reeves et al described its application to a system with nickel(II) complexes and tridentate dyes …”

Ultraviolet and light absorption spectrometry

“…A new differential method for determining association constants, illustrated with 3,3'diethylselenocarbocyanine in ethanol, is described in another paper (524). Stability constants of metal complexes have been determined by using a least-squares algorithm in which the constant is refined by a numerical search method (illustrated with the copper-imidazole complex) (47), a factor analysis of the absorption curve (illustrated with o,o -dihydroxyphenylazo dye, solochrome violet, and 2-a-[(2-hydroxyphenyl)azo]-aacetonitrile complexes of nickel) (392), and measurements at the isosbestic points (illustrated with the copper-2,2/-bipyridine-eriochrome cyanine R ternary complex) (581). In another paper, a mathematical modeling method was used to define the criteria for the limits of applicability of linear approximations for calculating stability constants from absorbance data obtained at a wavelength at which only the complex absorbs (208).…”