Influence of thermally induced structural transformations on the magnetic and luminescence properties of tartrate-based chiral lanthanide organic-frameworks

This work reports on the synthesis and characterization of five enantiomeric pairs of isostructural 3D metal-organic frameworks (MOFs) with the general formula {[Ln(2)(mu(4)-tar)(2)(mu-tar)(H2O)(2)]center dot xH(2)O}(n)[where Ln(iii) = Tb (Tb-LandTb-D), Dy (Dy-LandDy-D), Ho (Ho-LandHo-D), Er (Er-LandEr-D) and Tm (Tm-LandTm-D); tar = tartrate (d- orl-) andx= 3 or 4 depending on the counterpart], which possess interesting luminescence and magnetic properties. These MOFs undergo progressive and reversible dehydration processes upon controlled heating yielding three crystalline phases (Ln-L ',Ln-L '' andLn-L '''). Alternating current magnetic measurements on Tb, Dy and Er-based compounds exhibit field induced single-molecule magnet behavior dominated by QTM, which is partially suppressed when diluted on a Y-based matrix. Tartrate ligands show poor room temperature sensitization of Tb and Dy centers that is enhanced at low temperature (10 K), even enabling weak Tm-based emission. More interestingly, the dehydration modulates both magnetic and photoluminescence properties on the basis of both the distortions occurring in the coordination shells and a decrease of water molecules acting as quenchers, respectively, endowing these materials with potential humidity sensing capacity. Remarkably, the Tb-based MOF shows circularly polarized luminescence (CPL), being one of the examples of this very scarce family of CPL emitters reported so far.