Superparamagnetic Luminescent MOF@Fe₃O₄/SiO₂ Composite Particles for Signal Augmentation by Magnetic Harvesting as Potential Water Detectors

Herein, we present the generation of a novel complex particle system consisting of superparamagnetic Fe₃O₄/SiO₂ composite microparticle cores, coated with luminescent metal–organic frameworks (MOFs) of the constitution _∞²[Ln₂Cl₆(bipy)₃]·2bipy (bipy = 4,4′-bipyridine) that was achieved by intriguing reaction conditions including mechanochemistry. The novel composites combine the properties of both constituents: superparamagnetism and luminescence. The magnetic properties can be exploited to magnetically collect the particles from dispersions in fluids and, by gathering them at one spot, to augment the luminescence originating from the MOF modification on the particles. The luminescence can be influenced by chemical compounds, e.g., by quenching observed for low concentrations of water. Thus, the new composite systems present an innovative concept of property combination that can be potentially used for the detection of water traces in organic solvents as a magnetically augmentable, luminescent water detector

²_∞[Bi₂Cl₆(pyz)₄]: A 2D-Pyrazine Coordination Polymer As Soft Host Lattice for the Luminescence of the Lanthanide Ions Sm³⁺, Eu³⁺, Tb³⁺, and Dy³⁺

The 2D-coordination polymer ²_∞[Bi₂Cl₆(pyz)₄] was synthesized from BiCl₃ and a self-consuming melt of pyrazine (pyz). It proves to be a suitable soft host lattice for <i>in situ</i> co-doping of the lanthanide ions Sm³⁺, Eu³⁺, Tb³⁺, and Dy³⁺ during network formation. The series of luminescent networks ²_∞[Bi_{(2–<i>x</i>)}Ln_<i>x</i>Cl₆(pyz)₄] obtained exhibits an efficient antenna effect on the lanthanide ions. Emission is almost exclusively observed from the lanthanide centers at room temperature, whereas cooling to 77 K reveals a bismuth–pyrazine metal-to-ligand charge transfer related phosphorescence, which is also present without lanthanide participation. All parts of the coordination polymer can function for light uptake. Partial substitution is achieved by statistic replacement of bismuth with lanthanides and can range up to 25 at. % for trivalent europium