Structural Diversity of Lanthanide 3-Nitrotrispyrazolylborates: Tunable Nuclearity and Intra-Ligand Charge Transfer Sensitization of Visible and NIR Ln3+ Emission



Reported are the synthesis, crystal structures and photophysical properties of twenty-eight, novel lanthanide compounds across five structural types, [Ln(3-NO2Tp)2(NO3)] (1-Ln, Ln = La – Tm, except Pm), [Bu4N][Ln(3-NO2Tp)(NO3)3] (2-Ln, Ln = Yb, Lu), [Eu(3-NO2Tp)2Cl(H2O)]·2iPrOH (3-Eu), [{Ln(3-NO2Tp)2}2(μ2-CO3)] (4-Ln, Ln = La – Gd, except Pm) and [{Ln(3-NO2Tp)}4(μ2-OMe)6(μ4-O)] (5-Ln, Ln = Pr – Tb, except Pm) with the 3-nitrotrispyrazolylborate (3-NO2Tp–) ligand. Reaction of methanol or isopropanol solutions of LnX3 (X = Cl, NO3) with the tetrabutyl ammonium salt of the flexidentate 3-NO2Tp–, ([Bu4N][3-NO2Tp]) yields Ln(3-NO2Tp)x complexes of various nuclearities as either monomers (1-Ln, 2-Ln, 3-Eu), dimers (4-Ln) or tetramers (5-Ln) owing to the efficient conversion of atmospheric CO2 to CO32– (dimers) or ligand controlled solvolysis of lanthanide ions (tetramers). 3-NO2Tp– is an efficient sensitizer for both the visible and near-IR (NIR) emissions of most of the lanthanide series, except thulium. Optical measurements, supported by density functional theory calculations, indicate that the dual visible and NIR Ln3+ emission arises from two intra-ligand charge transfer (ILCT) transitions of 3-NO2Tp–. This is the first report of lanthanide complexes with a nitro-functionalized pyrazolylborate ligand. The derivatization of the known Tp– ligand results in new coordination chemistry governed by the increased denticity of 3-NO2Tp–, imparting remarkable structural diversity and charge transfer properties to resultant lanthanide complexes.


Supplementary material

Supplementary materials
PXRD patterns, reflectance spectra and luminescence excitation and emission spectra not included in the main article.