Syntheses, Crystal Structures and Characterization of Two New Lanthanide Mercury Halide Compounds

Two new lanthanide mercury halide compounds with isonicotinic acid as a ligand, namely, [Gd(μ2-HIA)2(μ3-IA) (H2O)2(HgCl2)]n(nHgCl4)·3nH2O (1) (HIA = isonicotinic acid) and {[Nd(μ2-HIA)3(DMF)(H2O)]n}[(Hg4Br11)n] (2HgBr2)(nBr)·nH3O (2), were synthesized with solvothermal reactions and characterized by single-crystal X-ray diffraction. Compound 1 is characterized by a two-dimensional (2-D) layer-like structure, while compound 2 features a one-dimensional (1-D) chain-like structure. The lanthanide ions in both compounds are eight coordinated and show a square antiprism geometry. The mercury ions exhibit various coordination motifs. Compound 1 exhibits ultraviolet upconversion photoluminescence emission, whereas compound 2 displays red photoluminescence. The photoluminescence emissions arise from the characteristic 4f electron intrashell transitions of the 6P7/2 → 8S7/2 of the Gd3+ ions in compound 1 and the 4F9/2 → 4I9/2, 4F7/2 + 4S3/2→ 4I9/2, 4F5/2 + 2H9/2→ 4I9/2, 4F3/2 → 4I9/2 of the Nd3+ ions in compound 2. Compound 2 has CIE (Commission Internationale de l’Éclairage) chromaticity coordinates of (0.7142, 0.2857) and its CCT (correlated color temperature) is 138,224 K. Solid-state UV/Vis diffuse reflectance spectra revealed that the semiconductor band gaps of the compounds are 3.12 eV and 3.23 eV, respectively. Elemental analyses and FT-IR spectroscopy were carried out to confirm the purity of the compounds.