Lanthanide complexes of compartmental ligands

Abstract

Abstract Schiff base ligands having available adjacent, dissimilar coordination sets have been termed collectively compartmental ligands [1]. Such ligands may be prepared from the reaction of an α, ω-diamine with one terminal keto-function of a β-triketone or β-ketophenol (Fig. 1). The ligands are capable of forming mononuclear positional isomers, homobinuclear and heterobinuclear metal complexes (Fig. 2). The application of such ligands to the area of ‘d’ block transition metal chemistry has been recently reviewed [1]. We here describe some lanthanide complexes of compartmental ligands derived from the β-ketophenol, 2-proprionoacetylphenol. The reaction of 2-proprionoacetylphenol, (H 2 -pap), with α, ω-diamines leads to the Schiff bases I and II in Fig. 3. The ligands are readily characterised by i.r., m.s. and 1 H n.m.r. spectroscopy. Metal complexation reactions have been carried out using both the Schiff base ligands and the β-ketophenol precursor. Complexes of the β-Ketophenol The reaction of H 2 - pap with LN(NO 3 ) 3 ·xH 2 O (Ln = La, Pr, Eu) in methanol in the presence of LiOH gave fine powdery products. The products analysed as Ln 2 (pap) 2 (NO 3 )OH), nH 2 O (n = 2 for La, 3 for Eu and 6 for PR), and are assigned the cis binuclear structure, III, by analogy with transition metal analogues [2]. Mononuclear Complexes of the Schiff Bases The reaction of a chloroform solution of the Schiff base with a methanolic solution of Ln(NO 3 ) 3 · nH 2 O gave fine, powdery products. For I complexes were available for Ln = La→ Eu, and for II complexes were of the form Ln(H 2 −L)NO 3 ·xH 2 O and are assigned structure IV. Outer compartment occupancy is indicated by the absence, in the i.r., of v OH for the phenol and the presence of v NH . 1 H n.m.r. spectra of the La derivatives also support this proposition. The preference of lanthanide ions for oxygen donor environments would also suggest such an occupancy. Binuclear Complexes of the Schiff Bases Attempts to obtain homobinuclear lanthanide complexes have so far been unsuccessful as have been attempts to prepare heterobinuclear complexes by the reaction of the mononuclear lanthanum complexes with metal salts such as VO(IV), Th(IV), UO 2 (VI) - all metals with strong -O 2 o 2 preferences. The reaction of copper(II) ethanoate with IV gave the homobinuclear copper(II) derivative. The reaction of the mononuclear copper(II) complex of I having -N 2 O 2 occupancy with Ln(NO 3 ) 3 , nH 2 O gave no heterobinuclear product but reaction of the corresponding nickel(II) complex with Ln(NO 3 , nH 2 O did give heterobinuclear complexes of I (Ln = La, Pr, Eu).