In recent years, our program has been focused on the synthesis and characterization of lanthanide molecules and clusters with extraordinary NIR emission properties. Chalcogen based anions (i.e. SC6F5-, SeSe2-, Te2-) are particularly useful for the preparation of highly NIR emissive materials, because the relatively long, weak Ln-E bond effectively decreases energy transfer and vibrational quenching processes. Our molecular efforts currently focus on the design and synthesis of new types of chalcogenolate ligands intended to produce lanthanide compounds with superior chemical/electronic properties. Our cluster program is devoted to the preparation of increasingly large/complex cluster compounds, using chalcogen based anions to encapsulate and ‘stabilize’ cluster cores with a surprising variety of ligand types. The utility of these molecules and clusters in emerging polymer based optical fiber technologies has been demonstrated in collaboration with Ajith Kumar and Richard Riman. Most recently, we started to explore the related chemistry of the actinides Th and U.
Lanthanide Oxide Clusters
The persistent request for ‘air stable’ emissive clusters led us to investigate the synthesis of oxide clusters with chalcogen encapsulants. Santanu Banerjee's first product in this area was from a reaction with SeO2 that gave (THF)8Ln8Se2O2(SePh)16. The Nd compound was particularly significant as it was the most efficient molecular source of 1.34 µm emission currently available (up until the fluoride cluster mentioned below), and this energy is important to the telecommunications industry.
The compound was also notable as the first molecular Nd compound to emit at 1.81 µm. Santanu's latest oxocluster result is a highly emissive Nd12O6 compound shown below. The structural characteristics of the oxo core of this material are distinctly similar to those of solid state Nd2O3, but the compound differs in that it emits NIR radiation at 1352 nm, while vibations of the Nd2O3 lattice quench this emission. Note that in the Nd12 cluster both phonon coupling and concentration quenching lead to elimination of the 1840 nm emission found in the previously described octanuclear cluster.
The apparent stability of these oxo materials with respect to disproportionation led Mike Romanelli to attempt the synthesis of even more stable cluster cores, and his first success in this area came with the isolation of the nanoscale product
(py)24Ln28F68(SePh)16 (Ln = Pr, Nd). The 44% quantum efficiency of the Nd cluster is more than twice that of our oxide clusters.
Our lanthanide work has led, indirectly, to the synthesis and characterization of novel main group and transition metal chalcogenolate complexes with extraordinary physical properties, i.e. the II-VI precursors of Yifeng Cheng. 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, as found in the homoleptic Ln(III) pyridinethiolates of Mike Berardini.
Virtually air stable thiolates can also be prepared with fluorinated thiolate ligands. Jonathan Melman has described the synthesis of Ln(SC6F5)n (n = 2, 3) and Kieran Norton has just completed a structural and spectroscopic investigation of the analogous fluorinated phenoxides. These fluorinated compounds are considerably more stable than their C6H5 counterparts and they are soluble in hydrocarbon solvents. Using these ligands Mark Fitzgerald prepared the first toluene soluble lanthanide sulfido and selenido clusters.
We’ve recently started investigating the related chemistry of the actinides. Using fluorinated chalcogenolates, we’ve prepared hydrocarbon soluble molecular Th compounds (i.e. the thiolate and selenolate pictured here) and are using these as entry points for the preparation of nanoscale actinide materials.
Initial results include a series of cubane clusters, where we have focused on the chemistry of diamagnetic thorium to allow an NMR investigation into solution behavior. While we were not surprised to find that these cubanes remain as intact tetrametallic species in strong donor solvents such as pyridine, we were surprised to note that the structures are static – using a combination of DFT (in collaboration with Peter Hrobárik) and 77Se NMR, we were able to show that there is no exchange between bridging and terminal SePh ligands.
- G. Gotthelf, M. A. Stuber, A. Y. Kornienko, T. J. Emge, J. G. Brennan, “Organosoluble Tetravalent Actinide Di- and Trifluorides”, Chem. Commun. 2018, xxxx.
- M. Ringgold, W. Wu, M. Stuber, A. Y. Kornienko, T. J. Emge, J. G. Brennan, “Monomeric Thorium Chalcogenolates with Pyridine and Terpyridine Ligands” Dalton Transactions 2018, xxxx.
- M. Ringgold, David Rehe, Peter Hrobárik, A. Kornienko, T. J. Emge, and J. G. Brennan, “Thorium Cubanes – Synthesis, Solid-state and Solution Structure, Thermolysis, and Chalcogen Exchange Reactions”, Inorg. Chem. 2018, 57, 7129-7141.
- W. Wu, X. Zhang, A. Y. Kornienko, G.A. Kumar, D. Yu, J. Emge, R. E. Riman, and J. G. Brennan, “Efficient NIR Emission from Nd, Er, and Tm Complexes with Fluorinated Selenolate Ligands” Inorg. Chem. 2018, 57, 1912-1918.
- M. A. Stuber, A. Y. Kornienko, T. J. Emge and J. G. Brennan. “Tetrametallic Thorium Compounds with Th4E4 (E = S, Se) Cubane Cores” Inorg. Chem. 2017, 56, 10247-10256.
- D. Rehe, A. Kornienko, T. J. Emge, and J. G. Brennan. “Actinide Compounds with Bonds to Sulfur or Selenium: Synthesis, Structure, and Thermolysis” Inorg. Chem. 2016, 55, 6961-6967.
- K. Holligan, P. Roegler, D. Rehe, M. Pamula, Anna Kornienko, T. J. Emge, K. Krogh-Jespersen, and J. G. Brennan. “Copper, Indium, Tin and Lead Complexes with Fluorinated Selenolate Ligands: Precursors to MSex“ Inorg. Chem. 2015, 54, 8896-8904.
- A. Kumar, R. E. Riman, and J. G. Brennan, “NIR Emission from Molecules and Clusters with Lanthanide-Chalcogen Bonds”, Coord. Chem. Rev. 2014, 273-4, 111-124.
- B. F. Moore, T. J. Emge, and J. G. Brennan, “Lanthanide Clusters with Azide Capping Ligands”, Inorg. Chem. 2013, 52, 6021-6027.
- J. Brennan, Lanthanide Thiolates, Selenolates, and Tellurolates, “The Rare Earth Elements: Fundamentals and Applications”, J. Atwood, ed., pp 215-223 (2012)
- A. Kornienko, B. F. Moore, G. A. Kumar, M. C. Tan, R. E. Riman, M. G. Brik, T. J. Emge, J. G. Brennan “Highly NIR Emissive Lanthanide Polyselenides” Inorg. Chem. 2011, 50, 9184-90.
- B. F. Moore, G. A. Kumar, M. C. Tan, J. Kohl, R. E. Riman, M. G. Brik, T. J. Emge, J. G. Brennan, “Lanthanide Clusters with Chalcogen Encapsulated Ln: NIR Emission from Nanoscale NdSex” J. Amer. Chem. Soc. 2011, 132, 373-378.
- K. Norton, S. Banerjee, L. Huebner, S. Das, T. J. Emge and J. G. Brennan. “Lanthanide Oxochalcogenido Clusters“, JCS Dalton Transactions, 2010, 39, 6794-6800.
- T. J. Emge, M. D. Romanelli, B. Moore, and J. G. Brennan, ”Fluorinated Selenolates of the Group 12 Metals Zn, Cd, and Hg.” Inorg. Chem. 2010, 49, 7304-7312.
- S. Banerjee, J. Sheckelton, T. J. Emge and J. G. Brennan, “Heterometallic Ln/Hg Tellurido Clusters”, Inorg. Chem. 2010, 49, 3573-3580.
- K. Krogh-Jespersen, M. D. Romanelli, J. H. Melman, T. J. Emge, and J. G. Brennan. “Covalent Bonding and the Trans Influence in Lanthanide Compounds” Inorg. Chem. Inorg. Chem. 2010, 49, 552-560.
- T. J. Emge, A. Kornienko, and J. G. Brennan. “Trans Influence in a mer-Octahedral tris(iodo)-Lanthanide, YbI3THF3" Acta Cryst. C 2009, 65, m422-5.
- K. Norton, A. Kumar, J. Dilks, R. E. Riman, T. J. Emge, and J. G. Brennan. “Fluorinated alkoxides of the Lanthanides: NIR Emission from Nd, Tm, and Er”, Inorg. Chem. 2009, 48, 3573-3580.
- M. Romanelli, T. J. Emge, and J. G. Brennan, “Tetrakis(1,2-dimethoxyethane)ytterbium(II) bis(2-phenylselenolato)bis[bis(phenylselenolato) mercurate(II)]. Acta Cryst. (E), 2008, E64, m987-m988.
- M. Romanelli, G. A. Kumar, R. E. Riman, T. J. Emge, and J. G. Brennan, "Highly Emissive Nanoscale Lanthanide Fluoride Clusters", Angew. Chemie. 2008, 47, 6049.
- S. Banerjee, A. Kumar, T. Emge, R. Riman, and J. G. Brennan, "Thiolate-Bound Thulium Molecules: Synthesis, Structure, and NIR Emission", Chem. Mater. 2008, 20, 4367.
- R. Riman, G. A. Kumar, V. Atakan, J. G. Brennan, J. Ballato, "Engineered solution synthesis of rare-earth nanomaterials and their optical properties.", Proc. SPIE 2007, 670707/1.
- K. Norton, T. Emge, and J. Brennan, "Lanthanide Compounds with Fluorinated OC6F5 Ligands: Homo- and Hetero-valent Complexes of Eu(II) and Eu(III)", Inorg. Chem. 2007, 46, 4060.
- S. Banerjee, G. A. Kumar, R. Riman, T. J. Emge, and J. Brennan, "Monodisperse Oxoclusters of the Lanthanides Begin to Resemble Solid State Materials at Very Small Cluster Sizes: Structure and Near-IR Emission from Nd(III)", J. Amer. Chem. Soc. 2007, 129, 5926.
- G. A. Kumar R. E. Riman, L.A. Diaz Torres, S. Banerjee, M. D. Romanelli, T. J. Emge, J. G. Brennan, "Near Infrared Optical characteristics of Chalcogenide-Bound Nd Organometallic Complexes", Chem. Mater. 2007, 19, 2937.
- L. A. Diaz-Torres, G. A, Kumar, R. E. Riman, S. Banerjee, A. Kornienko, J. G. Brennan, "Photoluminescence of bound rare earth nanoscale complexes.", Optical Materials 2006, 29, 12.
- R. Riman, G. A. Kumar, S. Bannerjee, J. G. Brennan, "Molecular Minerals: Lyophilic Colloids for Ceramicists", J. Am. Ceram. Soc. 2006, 89, 1809.
- G. A. Kumar, R. Riman, S. Chen, D. Smith and J. Ballato, S. Banerjee, A. Kornienko, J. G. Brennan, "Infrared Fluorescence and Optical Gain Characteristics of new Er Nanocluster Polymer Composites", Appl. Phys. Lett. 2006, 88, 91902.
- S. Banerjee, L. Huebner., M. D. Romanelli, G.A. Kumar, R.E. Riman, T. J. Emge, and J. G. Brennan, "Oxoselenido Clusters of the Lanthanides: Rational Introduction of Oxo Ligands and Near-IR Emission from Nd(III)", J. Am. Chem. Soc. 2005, 127, 15900.
- A. Kornienko, S. Banerjee, A. Kumar, R. Riman, T. Emge, and J. Brennan, "Heterometallic Lanthanide Main Group Metal Chalcogenido Clusters; Highly Emissive Precursors to Ternary Solid State Materials ", J. Am. Chem. Soc. 2005, 127, 14008.
- G. A. Kumar, R. Riman, S. Banerjee, A. Kornienko, J. G. Brennan, "Chalcogenide-Bound Erbium Complexes: Paradigm Molecules for Infrared Fluorescence Emission", Chem. Mater. 2005, 17, 5130.
- L. Huebner, A. Kornienko, T. J. Emge, and J. G. Brennan, "Lanthanide Clusters with Internal Ln: Fragmentation and the Formation of Dimers with bridging Se2- and SeSe2- Ligands", Inorg. Chem. 2005, 44, 5118.