Multimetal Lanthanide Phosphonocarboxylate Frameworks: Structures, Colour Tuning And Near-Infrared Emission

A series of isostructural lanthanide phosphonocarboxylate frameworks {(H3O)(3)[Ln(7)(pbpdc)(6)(DMF)(4)(H2O)(3)]center dot 4H(2)O}(n) (named LnPCF, Ln = Tb, Eu and Gd, H(4)pbpdc = 4 '-phosphono-[1,1 '-biphenyl]-3,5-dicarboxylic acid) were solvothermally synthesized and characterized by the single crystal X-ray diffraction technique. By combining lanthanide cations with a phosphonocarboxylate ligand, a heptametallic lanthanide phosphonate [Ln(7)(PO3)(6)(COO)(12)] core was obtained. This core exhibited as a rare highly 18-connected node and was linked by the 3-connected pbpdc(4-) ligand, forming a (3,18)-connected framework with a novel topology of {4(3)}(6){4(38)center dot 6(76)center dot 8(39)}. This LnPCF structure is an ideal platform for accommodating various lanthanide ions. The TbPCF and EuPCF show efficient luminescence emission due to the "antenna effect" and incorporating Gd3+ into the TbPCF results in a drastic luminescence enhancement. Fine colour tuning between green and red can be easily achieved in bimetallic Tb(x)Gd(1-x)PCFs. More significantly, upon combining a few percent of Nd3+ and Gd3+ with Tb3+, the resulting trimetallic Tb0.4Gd0.5Nd0.1PCF shows dual emissions of both visible and near-infrared light.