Synthesis and Characterization of Heteronuclear Copper(II)-Lanthanide(III) Complexes of N,N′-1,3-Propylenebis(Salicylaldiminato) Where Lanthanide(III) = Gd or Eu
Three complexes, namely, [Cu(salbn)] (1), [Cu(salbn)Gd(NO3)3·H2O] (2), and [Cu(salbn)Eu(NO3)3·H2O] (3) where salbn = N,N′-1,3-propylenebis (salicylaldiminato) have been synthesized and characterized by elemental analyses, ICP-AES, IR, UV, NMR, MS, EDX, powder XRD, and EPR spectroscopies. The EDX results suggest the presence of two different metal ions in heteronuclear complexes (2) and (3). The ligand(salbn), complex (1), and complex (3) crystallize in triclinic system while complex (2) crystallizes in monoclinic system. The EPR studies suggest that [Cu(salbn)] complex is tetragonally coordinated monomeric copper(II) complex with unpaired electron in the orbital and spectral features that are the characteristics of axial symmetry while complex (2) in DMF solution at liquid nitrogen temperature exhibits an anisotropic broad signal around g？~？2.03 which may suggest a weak magnetic spin-exchange interaction between Gd(III) and Cu(II) ions. The fluorescence intensity of Eu(III) decreased markedly in the complex (3). 1. Introduction The spectroscopic and unique properties of copper(II)-lanthanide(III) complexes have become a subject of intense research interest with coordination chemists because of their wide arrays of applications in electroluminescent devices, biomedicine, MRI, magneto magnets, and many more [1–5]. The coordination chemistry of lanthanide(III) ions is also increasing day by day, owing to the relevance of these compounds in basic and applied research in various fields to chemistry, material science, life science, and so forth [6–8]. Lanthanide complexes possessing higher stability are especially important in two different fields of research where inert complexes are potentially useful, namely, for the design of Gd(III) contrast agents for NMR imaging and for the separation of the lanthanides as a set of metals [9]. Most of the heteronuclear copper(II)-lanthanide(III) complexes have been synthesized with heterodonor ligands of N and O which are coordinated to copper and lanthanide atoms. The structural chemistry of the lanthanides is interesting as they have a strong tendency to form complexes with higher coordination numbers up to twelve. Because of their large size and their tendency to form ionic bonds rather than covalent bonds, lanthanide(III) ions may form complexes having higher coordination numbers with monodentate, simple bidentate or polydentate ligands possessing small chains [10]. The structural versatility arises from the lack of strong crystal efforts for the 4f electronic configurations as well as from the large ionic radii of
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