Structure-Property Relationships in Photoluminescent Bismuth Halide Organic Hybrid Materials.

Seven novel bismuth(III)-halide phases, Bi2Cl6(terpy)2·0.5(H2O) (1), Bi2Cl4(terpy)2(k2-TC)2(2) (TC = 2-thiophene monocarboxylate), BiCl(terpy)(k2-TC)2 (3A-Cl), BiBr(terpy)(k2-TC)2 (3A-Br), BiCl(terpy)(k2-TC)2 (3B-Cl), [BiCl(terpy)(k2-TC)2][Bi(terpy)(k2-TC)3]·0.55(TCA) (4), [BiBr3(terpy)(MeOH)] (5), and [BiBr2(terpy)(k2-TC)][BiBr1.16(terpy)(k2-TC)1.84] (6), were prepared under mild synthetic conditions from methanolic/aqueous solutions containing BiX3 (X = Cl, Br) and 2,2':6',2″-terpyridine (terpy) and/or 2-thiophene monocarboxylic acid (TCA). A heterometallic series, 3A-Bi1-xEuxCl, with the general formula Bi1-xEuxCl(terpy)(k2-TC)2 (x = 0.001, 0.005, 0.01, 0.05) was also prepared through trace Eu doping of the 3A-Cl phase. The structures were determined through single-crystal X-ray diffraction and are built from a range of molecular units including monomeric and dimeric complexes. The solid-state photoluminescent properties of the compounds were examined through steady-state and time-resolved methods. While the homometallic phases exhibited broad green to yellow emission, the heterometallic phases displayed yellow, orange, and red emission that can be attributed to the simultaneous ligand/Bi-halide and Eu centered emissions. Photoluminescent color tuning was achieved by controlling the relative intensities of these concurrent emissions through compositional modifications including the Eu doping percentage. Notably, all emissive homo- and heterometallic phases exhibited rare visible excitation pathways that based on theoretical quantum mechanical calculations are attributed to halide-metal to ligand charge transfer (XMLCT). Through a combined experimental and computational approach, fundamental insight into the structure-property relationships within these Bi halide organic hybrid materials is provided.

Synthesis and photoluminescence of three bismuth(III)-organic compounds bearing heterocyclic N-donor ligands.

Three bismuth(iii)-organic compounds, [Bi4Cl8(PDC)2(phen)4]·2MeCN (1), [BiCl3(phen)2] (2), and [Bi2Cl6(terpy)2] (3), were prepared from solvothermal reactions of bismuth chloride, 2,6-pyridinedicarboxylic acid (H2PDC), and 1,10-phenanthroline (phen) or 2,2';6',2''-terpyridine (terpy). The structures were determined through single crystal X-ray diffraction and the compounds were further characterized via powder X-ray diffraction, Raman and infrared spectroscopy, and thermogravimetric analysis. The photoluminescence properties of the solid-state materials were assessed using steady state and time-dependent techniques to obtain excitation and emission profiles as well as lifetimes. The compounds exhibit visible emission ranging from the yellow-green to orange region upon UV excitation. Theoretical quantum mechanical calculations aimed at elucidating the observed emissive behavior show that the transitions can be assigned as predominantly ligand-to-ligand and ligand-to-metal charge transfer transitions. The solid-state structural chemistry, spectroscopic properties, and luminescence behavior of the bismuth compounds are presented herein.

Excitation-Dependent Photoluminescence Color Tuning in Lanthanide-Organic Hybrid Materials.

A series of lanthanide organic hybrid materials was synthesized via hydrothermal methods and structurally characterized using single-crystal X-ray diffraction. Four phases were obtained from reactions of La, Eu, and Tb ions with 1,10-phenanthroline (phen) and 2-thiophenecarboxylate (TC): [La2(phen)2(k1-TC)2(µ2-TC)2(η3-TC)2(H2O)2] (La-1/La-2), [Eu2(phen)2(k2-TC)2(µ2-TC)2(η3-TC)2]·2(H2O) (Eu-3), and [Tb2(phen)2(k2-TC)2(µ2-TC)4]·2(H2O) (Tb-4). Although each of the structures consists of homometallic ligand bridged dimers, the four distinct phases arise from subtle differences in ligand binding modes and supramolecular interactions. Ln doping was explored and resulted in analogous heterometallic systems, [Eu2-xLax(phen)2(k2-TC)2(µ2-TC)2(η3-TC)2]·2(H2O) (Eu2-xLax-3; x = 0.47-1.51) and [Tb2-yLay(phen)2(k2-TC)2(µ2-TC)4]·2(H2O) (Tb2-yLay-4; y = 0.42, 0.67). The photoluminescent properties of the solid-state materials were assessed using steady-state and time-dependent techniques to obtain excitation and emission profiles, transition energies, and lifetimes. The La phase exhibited ligand-based emission, whereas both Eu and Tb phases produced characteristic red and green metal-centered emission, respectively. By comparison, the heterometallic compounds exhibited both Ln- and ligand-based emission and photoluminescent color tuning of emission chromaticity. Further examination revealed that the color tuning was dependent on the relative La/Eu or La/Tb ratios as well as the excitation wavelength. These compounds are a rare example of single-phase Ln hybrid materials built from molecular units that exhibit excitation-dependent photoluminescent color tuning in the solid state.

Strong photoluminescence and sensing performance of nanosized Ca0.8Ln0.1Na0.1WO4 (Ln = Sm,Eu) compounds obtained by the dry "top-down" grinding method.

Two lanthanide doped nanosystems Ca0.8Ln0.1Na0.1WO4 (Ln = Eu, Sm), denoted as Eu@CWO and Sm@CWO, were prepared by a "top-down" approach in three simple steps: activation, miniaturization by high-energy milling, and further calcination. The solids were thoroughly characterized by X-ray powder diffraction (XRPD) and Scanning-electron microscopy (SEM). Also, analyses of the structure of the compounds and the impact of milling on the crystallite shape and size were carried out through Rietveld refinements. Solid-state photoluminescence was studied in terms of excitation, emission, lifetimes (τobs) and europium-quantum yields. Finally, the Eu@CWO sample was employed as a potential water-stable chemical sensor towards toxic cations, showing a quenching effect in the presence of iron ions.

Monomeric and Trimeric Thorium Chlorides Isolated from Acidic Aqueous Solution.

Two thorium(IV) compounds, [Th(H2O)4Cl4]·2(HPy·Cl) (1) and (HPy)3[Th3(H2O)2Cl10(OH)5]·4(HPy·Cl) (2) (HPy = pyridinium), were isolated from acidic aqueous solution. The compounds were synthesized at room temperature and subsequently characterized using single crystal X-ray diffraction along with Raman and IR spectroscopies. Whereas compound 1 is built from discrete mononuclear Th(H2O)4Cl4 units, compound 2 consists of a novel hydroxo-bridged trimeric [Th3(OH)5]7+ core. Such species are largely absent from discussions of Th solution and solid-state chemistry and their isolation may be attributed to outer coordination sphere interactions that help stabilize the structural units; extensive hydrogen bonding and π-π stacking interactions are present in 1 and 2. Density functional theory calculations were performed to predict the respective vibrational frequencies of the structural units, and their relative stability was predicted at the correlated molecular theory level. Small-angle X-ray scattering analysis of [Th3(OH)5]7+ in water indicates that the trimeric structural unit remains intact and that it is indeed an important species that necessitates consideration in geochemical models and for design of Th materials from water.

Photoluminescence of Visible and NIR-Emitting Lanthanide-Doped Bismuth-Organic Materials.

A bismuth-organic compound containing 2,2':6'2"-terpyridine (terpy) and 2-thiophenecarboxylate (TC), of the general formula (terpy)Bi(κ2 -TC)3 ⋅0.47 H2 O (BiOM-1), has been synthesized under hydrothermal conditions. Addition of a lanthanide nitrate solution to the reaction mixture led to statistical replacement of the bismuth centers, and yielded isomorphous lanthanide containing compounds Bi1-x Lnx OM-1 (Ln=Nd, Sm, Eu, Tb, Dy, Er, and Yb) that showed bismuth and/or ligand sensitized lanthanide-centered emission, and the first example of NIR emission from a lanthanide doped BiOM. The structure was determined by single-crystal X-ray diffraction, and the level and uniformity of lanthanide ion incorporation into the bismuth host was determined by ICP-OES and electron microprobe analysis. For the visible emitters, lifetime data and quantum yields are presented. A high efficiency of sensitization was calculated for the europium analog (50.1 %), showing significant improvement over previously reported europium thiophenecarboxylates. These novel materials may provide strategies to address concerns over the long-term sustainability of the rare earth elements, especially relating to optical devices.