A pair of mer-octahedral lanthanide chalcogenolate coordination complexes [(THF)(3)Ln(EC(6)F(5))(3) (Ln = Er, E = Se; Ln = Yb, E = S)] have been isolated and structurally characterized. Both compounds show geometry-dependent bond lengths, with the Ln-E bonds trans to the neutral donor tetrahydrofuran (THF) significantly shorter than the Ln-E bonds that are trans to negatively charged EC(6)F(5) ligands. Density functional theory calculations indicate that the structural trans influence evidenced by the differences in these bond lengths results from a covalent Ln-E interaction involving ligand p and Ln 5d orbitals.

Reactions of Ln(SePh)3 with SeO2 in THF give octanuclear oxoselenido clusters with the general formula (THF)8Ln8O2Se2(SePh)16 (Ln = Ce, Pr, Nd, Sm). In this isomorphous series, the eight Ln(III) ions are connected in the center by a pair of mu3-O2- ligands and mu5-Se2- ligands, with 14 bridging and two terminal selenolate ligands capping the cluster surface. Thermal decomposition at 700 degrees C of the Nd compound in vacuo led to the formation of a phase mixture of NdSe2, Nd2Se3, and Nd2O3. Near-IR emission experiments on the (THF)8Nd8O2Se2(SePh)16 and the fluorinated thiolate compound (DME)2Nd(SC6F5)3 demonstrate that clusters with oxo ligands are not only highly emissive, but also they emit at wavelengths not found in conventional oxides.

Lanthanoid-doped fluoride glasses are intense near-IR (NIR) emission sources because of the low-energy phonon characteristics of fluoride lattices. [1][2][3][4][5] These materials are particularly useful in optical applications, [6][7][8][9][10][11][12] because fluorides are absolutely air-stable. Unfortunately, the extreme insolubility of lanthanoid ions in the presence of fluoride sources [13][14][15] has always presented a barrier to developing alternative synthetic approaches to LnF x materials, particularly in media that would preclude the incorporation of NIR-emission-quenching OH groups. Herein we demonstrate that by using unconventional chalcogen-based ligands we can dramatically alter the solubility characteristics of lanthanoid cations in the presence of fluoride anions. We describe the synthesis, structural characterization, and exceptional NIR emission properties of the largest known lanthanoid cluster.Exposure of in situ prepared Ln(SePh) 3 to fluoride sources does not result in the immediate precipitation of solid LnF 3 . Metathesis reactions of Ln(SePh) 3 with HgF 2 , CsF, or Me 4 NF have yet to deliver crystalline products, but reactions of Ln(SePh) 3 with NH 4 F in pyridine with subsequent filtration and saturation of the solution (either by layering with hexane or slow cooling) result in the crystallization, in 5-20 % yields, of nanoscale lanthanoid fluoride clusters that were shown, by low-temperature single crystal Xray diffraction, [16] molecular structure of 1 and 2 is shown in Figure 1, with significant bond distances for 1 and 2 given in the caption; complete structural information is given as Supporting Information. Clusters 1 and 2 contain a central set of four 12-coordinate Ln ions encapsulated by six triply bridging and six tetrahedral fluoride ions, which coordinate to the next layer of 24 lanthanoid ions that are then further connected through additional m 2 , m 3 , and m 4 fluorides, with the surface of the cluster capped by pyridine and selenolates. While the internal Ln coordination numbers are 12, the surface ions are either 8-or 9-coordinate. The surprising solubility of these LnF 3 -containing materials can be attributed to the relative instability of the selenolate starting materials. Chalcogenolate instability has been used to rationalize the apparent stability of SePhencapsulated lanthanoid oxo cluster compounds, [17] but in that system Ln 2 O 3 starting materials did not appear to react with Ln(SePh) 3 , and so thermodynamic stability of the clusters remained unproven. In the present system, suspended LnF 3 reacts with a solution of Ln(SePh) 3 , but a crystalline product of this reaction has not yet been obtained. Still, the observation of a reaction is additional evidence that selenolate-encapsulated fluoride clusters are thermodynamically stable with respect to precipitation of LnF 3 . Presumably the total energy of the system is lowered when the selenolate ligands are distributed over a number of Ln III ions. The potential utility of these clusters as signal amplificat...

The optical properties of the nanoscale neodymium ceramic cluster (THF)8Nd8O2Se2(SePh)16 (Nd8) and molecular (DME)2Nd(SC6F5)3 (Nd1) were studied by optical absorption, photoluminescence, and time-resolved spectroscopy. Both complexes exhibited emission characteristic of solid-state materials with bands centered at 927, 1078, 1360, and 1843 nm for Nd8 and 897, 1071, 1347, and 1824 nm for Nd1. The observed red-shift in the absorption and emission bands of Nd8 is attributed to the increased covalency and nephelauxetic effect. Using the calculated radiative decay time, the quantum efficiency of the 4F3/2 → 4I11/2 transition is calculated to be 16% in Nd8 and 9% in Nd1 with corresponding stimulated emission cross sections of 3.04 × 10-20 cm2 in Nd8 and 1.61 × 10-20 cm2 in Nd1 that are comparable to those of solid-state inorganic systems. This efficiency is the highest reported value for “molecular” neodymium compounds. This finding, along with the novel 1.8 μm emission, is attributed to the absence of direct Nd3+ coordination with fluorescence quenching vibrational groups such as hydrocarbon or hydroxide groups. The direct coordination of S, Se, and F accounts for the improved fluorescence spectral properties, because these heavy anions facilitate a low phonon energy host environment for neodymium. Monte Carlo simulation permitted analysis of energy transfer processes to show the primary source of fluorescence quenching. Cross relaxation is responsible for the quenching of the 4F3/2 → 4I15/2 emission whereas excitation migration quenches the 4F3/2 → 4I9/2 emission. These processes are mediated by a dipole−dipole interaction for Nd8 and a quadrupole−quadrupole interaction for Nd1.

Reductive cleavage of C(6)F(5)SeSeC(6)F(5) with elemental M (M = Zn, Cd, and Hg) in pyridine results in the formation of (py)(2)Zn(SeC(6)F(5))(2), (py)(2)Cd(SeC(6)F(5))(2), and Hg(SeC(6)F(5))(2). Structural characterization of the Zn and Cd compounds reveals tetrahedral coordination environments, while the Hg compound shows a complicated series of linear structures with two short, nearly linear Hg-Se bonds, up to two longer and perpendicular Hg...Se interactions, and no coordinated pyridine ligands. All three compounds exhibit well-defined intermolecular pi-pi-stacking interactions in the solid state. They are volatile and decompose at elevated temperatures to give MSe and either (SeC(6)F(5))(2) or Se(C(6)F(5))(2).

Fluoride clusters of lanthanoids can be prepared in organic solvents by metathetical reactions of Ln(SePh)3 with NH4F. The first products of these reactions, [(py)24Ln28F68(SePh)16] (Ln=Pr, Nd; py=pyridine; see structure), are currently the largest discrete lanthanoid clusters ever isolated. Emission experiments on the neodymium compound reveal a near‐IR quantum efficiency of 41 %.

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