Studies of the β-type binuclear chelates of the lanthanides with p-lodochlorophosphonazo

Abstract

This paper describes work carried out on the colour-forming reaction between p-iodochlorophosphonazo (p-ICP) and the lanthanides. In the pH range 3.0–4.0 (λ= 700–800 nm)β-type mononuclear chelates are formed between Eu³⁺, Gd³⁺, Tb³⁺, Dy³⁺, Ho³⁺, Er³⁺, Tm³⁺ or Yb³⁺ and p–ICP. A synergistic colour effect is clearly observed when equimolar amounts of other lanthanide ions are added to chelate solutions of Er³⁺, Tm³⁺ or Yb³⁺, i.e., a β-type binuclear complex is formed. Maximum molar absorptivities were obtained with gadolinium. The calibration graph is linear in the 0–8 × 10^–6M range for Ce³⁺, Pr³⁺, Ho³⁺, Tb³⁺, Dy³⁺, Tm³⁺ and Lu³⁺, and the 0–1.0 × 10^–5M range for Nd³⁺ and Sm³⁺ when Yb³⁺= 8.0 × 10^–6M.