New Rare-Earth Metal Lithium Germanides Svilen Bobev , University of Delaware, DMR 0743916

As part of our ongoing systematic studies, we have synthesized and characterized six ternary compounds RELiGe2 (RE=La-Nd, Sm, Eu). The most prominent aspect of their structure is the one-dimensional chains, propagating parallel to the crystallo-graphic b-axis. They are linked together via chains of edge-shared LiGe4-tetrahedra, also running in the same direction. Emphasizing the covalency of the Li–Ge bonding, the structure can also be rationalized as a polyanionic [LiGe2] network, with rare-earth metal cations residing in the channels within it. The topological relation of the structure of the title compounds to that of the FeB-type REGe phases (RE = La-Pr) is particularly useful and is presented in a more detailed view in the enclosed figure. The illustration also shows that the RELiGe2 compounds can be considered as close relatives of the hypothetical RELiGe germanides with the TiNiSi (aka SrMgSi) structure type—a simple “insertion” of another germanium atom and an appropriate resizing of the unit cell accounts for the above-mentioned polyanionic [LiGe2] network. Notably, the three depicted structures share not only the same arrangement of rare-earth metal atoms, but the same symmetry as well (Pnma). The analogy with the FeB structure type can be used to rationalize the inability to extend the RELiGe2 series beyond Eu. It is known that the FeB structure type is common among the early rare-earth metals, whereas the late rare-earth metals form REGe with the CrB structure type, with polymorphic transitions between the two for the middle members of the 4f-block. This phenomenology has been attributed to the lanthanide contra-ction and the decreasing size of the rare-earth metals. Indeed, we observed that as the cation radius gradually decreases from La to Sm, the lattice parameters also monotonically decrease.

Bobev, S. et al. Inorg. Chem. 2012, 51, 620

New Rare-Earth Metal Lithium Germanides

Svilen Bobev , University of Delaware, DMR 0743916

Education and MentoringUndergraduate Participation:Chauntae Tyson (Delaware – BS’12)*Greg Darone (Delaware)

Graduate Participation:Nian-Tzu Suen – a 3rd year graduate student is working on the project since March 2010.

Post-doctoral Participation:Dr. Sheng-Ping Guo left after his 1st year and is employed at FJIRSMDr. Jiliang Zhang was recruited and started work on the project effective January 1, 2012.

Dissemination of the resultsFour seminars were presented by P.I. Bobev in the US (Reed College, Central Washington, Portland State, Purdue). Prof. Bobev has been invited as a keynote-speaker at the 8th International Conference of f-elements in Udine, Italy.

Six full papers have been published with results from our work - 3 in Journal of Solid State Chemistry; 2 in Inorganic Chemistry; and 1 in European Journal of Inorganic Chemistry.

Undergraduate students participated in a campus-wide Undergraduate research symposium. Mr. Darone presented and won 2nd place the the Intercollegiate student chemist conference (ISSC).

* Underrepresented minority student