Faculty and Staff

View faculty members by
• Alphabetical Listing
• Research Interests
• Departmental Divisions

Research

Summary

We continue to focus our attention on understanding the chemistry of lanthanide ions coordinated to sulfur, selenium, and tellurium based anionic ligands. Our synthetic efforts are geared toward the synthesis of volatile compounds for CVD applications and the systematic preparation of increasingly large/complex cluster compounds with pre-ordained chemical and physical properties. We have shown that our lanthanide chalcogenolates react with elemental chalcogen (S, Se, Te) and are, as such, useful molecules for doping lanthanide ions into fiber optic and semiconductor devices. Lately, we have started developing the chemistry of these materials in organic polymers (Appl. Phys. Lett. 2006, 88, 91902; Diaz-Torres, Opt. Materials 2006, 29, 12).

Lanthanide Clusters

We have been able to control reactions of Ln(EPh)₃ with elemental S, Se, or Te to give crystalline lanthanide chalcogenido clusters; (Melman, Chem. Commum., 1997, 2269; Freedman, J. Amer. Chem. Soc. 1997, 119, 11112; Freedman, Inorg. Chem 1998, 37, 4162; Melman, Inorg. Chem. 1999, 38, 2117; Freedman, Inorg. Chem, 1999, 38, 4400); Freedman, J. Amer. Chem. Soc. 1999, 121,11713. We found that chalcogenolates can be replaced with halides to give chalcogen rich precursors to lanthanide chalcogenide solids. Our first product, (THF)₆Yb₄I₂(S)(SS)₄ (right), can be isolated from two different synthetic approaches, and decomposes to give Yb₃S₄ with no significant iodide incorporation (Melman, J. Amer. Chem. Soc. 1999, 121, 10247).






The analogous Selenium compounds are more complicated. Both Ln₄Se₉ and Ln₆Se₆I₆ clusters are synthetically possible (Kornienko, Inorg. Chem. 2002, 41, 121). With EPh ligands replacing the halogen, a variety of structurally complicated products are observed (Kornienko, J. Amer. Chem. Soc. 2001, 123, 11933). The first isolable clusters of Te have also been prepared (Kornienko et al., Inorg. Chem. 2002, 41, 492). More recently, we have described the first lanthanide cluster with internal Ln ions, (THF)₁₄Er₁₀S₆I₆(SeSe)₆. This nanoscale cluster is soluble in organic solvents, can be dispersed into polymeric matrices, and has emission properties that rival solid state materials (Kornienko, J. Am. Chem. Soc. 2005, 127, 3501), with a 3.8ms excited state lifetime. Related molecules and clusters are among the most emissive lanthanide materials known (Kumar, Chem. Mater. 2005, 17, 5130). This decanuclear structure self-disassembles in pyridine to give dimeric compounds with two coordinate S^2- (Huebner, Inorg. Chem. 2005, 44, 5118).


We have also extended this reactivity to the synthesis of oxocluster compounds, in reactions with SeO₂ that give (THF)₈Ln₈Se₂O₂(SePh)₁₆. The Nd compound (right) is particularly significant as it currently represents the most intense molecular source of 1.34µm emission currently available. This energy is important to the telecommuncations industry (Banerjee, J. Amer. Chem. Soc. 2005, 127, 15900; Kumar, Chem. Mater. 2007, in press).


Our latest oxocluster result is a highly emissive Nd₁₂O₆ cluster shown at right (Banerjee, J. Amer. Chem. Soc. 2007, in press). The oxo core of this material is distinctly similar to solid state Nd₂O₃, but the compound differs in that it emits NIR radiation at 1352 nm. Note that both phonon coupling and Nd-Nd interactions have effectively quenched the 1840 nm emission found in the previously described octanuclear cluster.

Heterometallic Compounds: Ionic Ln and Covalent M

The potential utility of heterometallic compounds in emission/upconversion/photon splitting processes continues to motivate our investigations into the chemistry of heterometallic chalogenolates. In Group IV studies, the phenylchalcogenolate ligand was replaced by the chelating pyridinethiolate ligand and the product crystallized as a heterometallic Eu-Sn coordination polymer (Lee, Inorg. Chem. 1997, 36, 5064). More recently, we've used heterometallic interactions to stabilize Sm(SePh)₂ in the form of polymeric (THF)₃Sm(SePh)₃Zn(SePh) (Freedman, Inorg. Chem. 2000, 39, 2168), and, using the fluorinated ligands noted below, we have described a series of LnHg compounds with fluorothiols (Banerjee, Inorg. Chem. 2004, 43, 6307).

The heterometallic cluster story continues to evolve. We've shown that the Sm/Zn polymer decomposes to give heterometallic cluster salts (Kornienko, Inorg. Chem. 2003, 42, 8476), in which there are no Ln-E-M linkages. With these results in mind, we were finally able to design and execute the first rational synthesis of Ln/M chalcogenido clusters with clearly defined Ln-E-M connectivities (Kornienko, J. Am. Chem. Soc. 2005, 127, 14008). These clusters decompose to give ternary solid state materials, and the Er derivatives are highly emissive.

Chalcogenolate complexes

Our lanthanide work has led, indirectly, to the synthesis and characterization of novel main group and transition metal chalcogenolate complexes with extraordinary physical properties (Brennan and Cheng, US Patents #5,527,909 and 5,681,975; Cheng, Inorg. Chem. 1996, 35, 342 & 7339). We are still pursuing a number of chemically interesting synthetic targets with significant CVD applications.

These chelating ligands are important in Ln chemistry because they form relatively air stable products, for example homoleptic Ln(III) thiolates (Berardini, Inorg. Chem. 1997, 36, 5772). These compounds are relatively electron rich, where, for example, the Yb(II) compound reduces organic ligands as efficiently as does SmI₂.

Virtually air stable thiolates can also be prepared with fluorinated thiolate ligands. We have recently described the synthesis of both Eu(SC₆F₅)₂ and Sm(SC₆F₅)₃. These compounds are considerably more stable than their SC₆H₅ counterparts and they are soluble in hydrocarbon solvents. Both compounds have significant pi-stacking interactions and well defined Ln-F bonds (Melman, Inorg. Chem. 2001, 40, 1078; Inorg. Chem., 2002, 41, 28). These ligands have also yielded the first organosoluble sulfido and selenido clusters (Fitzgerald, Inorg. Chem. 2002, 41, 3528).







Finally, we are still interested in the synthesis of heterometallic complexes that can be used to deliver two or more chemotherapeutically active metal based drugs in a controlled fashion (Inorg. Chem. 1993, 32, 2724).