Synthesis, structures and luminescent properties of new heterobimetallic Zn-4f Schiff base complexes

New stable heterobimetallic Zn-Ln (Ln = La, Gd, Nd, Yb, Er) Schiff base complexes have been synthesized and characterized. The photophysical properties of these Schiff base complexes can be tuned by changing the electronic properties of the substituents. By extending the conjugation, both the absorption and emission bands of the complexes show bathochromic shifts. Energy transfer is observed from the triplet state of the Zn-Ln complex to the excited state of lanthanide metal (Ln = Nd, Er, Yb) which then emits in the NIR region. A series of new 3d-4f heterobimetallic Schiff base complexes of the general formula [Zn(μ-L2)Ln(NO3)3(H2O)n] (Ln = La 1, Nd 2, Gd 3, Er 4 and Yb 5; n = 1 or 2; H2L2= N,N′-bis(3-methoxy-5-p-tolylsalicylidene) ethylene-1,2-diamine) are synthesized and characterized. Complexes 1, 2, 4 and 5 are structurally characterized by X-ray crystallography. The photophysical properties of these complexes are also investigated. At room temperature, complexes 1-5 exhibit similar solution absorption and emission spectra in the UV-Vis region. Furthermore, compounds 2, 4 and 5 exhibit solution emission corresponding to the lanthanide(III) ion in the near-infrared region at room temperature. The triplet state emission of the 3d-4f bimetallic complexes without energy transfer is also determined through the photophysical study of complex 3.