Tuning the coordination behavior of an unexplored asymmetric multidentate ligand for developing diverse heterometallic architectures with luminescent and magnetic properties

Recently, by tuning the coordination behavior of a new asymmetric multidentate ligand, H3L, containing two nitrogen and six oxygen donors by both metal centres and anions, H3L = 1-(2-hydroxy-3-methoxy-benzamido)-2-(2-hydroxy-3-methoxy-benzylideneamino)-2-hydroxy propane, three types of heterometallic compounds with the chemical composition of [Zn(8)Ln(2)L(2)(OH)(4)(OAc)(12)]center dot xCH(3)OH center dot yCH(3)CN center dot zH(2)O (Zn(8)Ln(2), where Ln = Nd, Tb, Dy and Er), [Ni3Tb2(HL)(2)(OH)(4)(OAc)(6)]center dot 3CH(3)CN center dot H2O (Ni3Tb2), and [Ni2Tb2(HL)(2)(OAc)(4)(NO3)(2)(H2O)(2)]center dot 4CH(3)CN center dot 3H(2)O (Ni2Tb2) were developed. Structural analysis revealed that four ellipsoidal decanuclear Zn-II-Ln(III) clusters resulted from the assembly of H3L with Zn(OAc)(2)center dot 2H(2)O and Ln(OAc)(3)center dot 6H(2)O. Replacement of Zn(OAc)(2)center dot 2H(2)O with Ni(OAc)(2)center dot 4H(2)O rendered a butterfly pentanuclear Ni-II-Ln(III) cluster, and upon further using Tb(NO3)(3)center dot 6H(2)O to replace Tb(OAc)(3)center dot 6H(2)O, a tetranuclear Ni-II-Ln(III) metallocycle was obtained. The luminescence studies on these compounds indicated that the Zn-II-containing chromophore is a good antenna for sensitizing the characteristic emission of Ln(3+) effectively from the visible to near-infrared region as a result of its energy match, perfect shielding and less concentration quenching compared to its Ni-II analogues, where the d -> d transitions characteristic of Ni2+ were observed in the excitation spectra when irradiated. Notably, weak emission bands characteristic of Tb3+ were observed in the spectrum of Ni2Tb2 but not in that of Ni3Tb2 when excited by the d -> d transition, which may be attributed to the difference in crystal field. Furthermore, the magnetic susceptibility studies indicate that the magnetic exchange for the Tb-III ions in Zn8Tb2, Ni3Tb2 and Ni2Tb2 is ferromagnetic, whereas that for the Dy-III ions in Zn8Dy2 is antiferromagnetic. Our results are of great significance for the rational design and synthesis of novel heterometallic supramolecular structures with interesting luminescence and magnetic properties.

Automated summary

By tuning the coordination behavior of a new asymmetric multidentate ligand, three types of heterometallic compounds were successfully developed and structurally analyzed. Luminescence studies indicated that the Zn-II-containing chromophore is an effective antenna and exhibits less concentration quenching compared to its Ni-II analogues.