Current Research in the Girolami Group

Girolami Research Interests We are primarily interested in the synthesis, properties, and reactivity of new inorganic, organometallic, and solid state species. Much of our research relates to one of three areas: mechanistic studies of organometallic reactions such as the activation of alkanes, the synthesis of new "molecule-based" magnetic materials, and the chemical vapor deposition of thin films from "designed" molecular precursors.

Organometallic Chemistry - Can Alkane Complexes be Isolated?

We are investigating whether it is possible to prepare kinetically stable coordination complexes in which one of the ligands is an alkane. Although such species have been observed spectroscopically at 10 K and have been surmised to be present as intermediates in certain reactions, none has ever been isolated at or near room temperature. We are investigating the protonation of certain osmium alkyl complexes, whose electronic and steric properties have been chosen so as to favor the formation of an alkane complex. We have found that, in complexes of the type [(C5Me5)L2OsH(CH2R)]+, the hydrogen atoms of the Os-H and Os-CH2R groups are rapidly exchanging even at -100 C, evidently by means of an alkane intermediate Os(CH3R): Such species offer exciting opportunities to explore the mechanism by which alkane C-H bonds are cleaved by certain organotransition metal species. We are also carrying out related studies of the activation of dihydrogen and organosilanes by transition metals, because the structures of these complexes are closely related to the structures thought to be important in the activation of alkanes.

Leading references:

Spencer, M. D.; Shelby, Q. D.; Girolami, G. S. "Titanium-Catalyzed Dehydrocoupling of Silanes: Direct Conversion of Primary Monosilanes to Titanium(0) Oligosilane Complexes with Agostic α-Si-H•••Ti interactions," J. Am. Chem. Soc. 2007, 129, 1860.

Gross, C. L.; Girolami, G. S. "Synthesis and NMR Studies of [(C5Me5)Os(L)H2(H2) +] Complexes. Evidence of the Adoption of Different Structures by a Dihydrogen Complex in Solution and the Solid State," Organometallics 2007, 26, 1658.

High-TC Molecule-Based Magnetic Materials.

We are investigating a building block approach to the synthesis of new magnetic solids. By connecting paramagnetic transition metal coordination complexes into three-dimensional arrays, we are able to make solids that behave as bulk ferro- or ferrimagnets. Our most interesting approach involves preparing metal-substituted analogues of the long-known solid Prussian blue. Prussian blue, which is a cyanoferrate with a cubic unit cell (Fig. 1), becomes magnetic at 5 K. By substituting metal atoms other than iron (particularly vanadium and chromium) into the structure, we can control the magnetic ordering temperature, coercive field, and optical response of the magnetic solid. Whereas molecule-based magnets with magnetic ordering temperatures above -170 C were unknown when we began our work, we now can prepare crystalline molecule-based magnets with ordering temperatures above +100 C. The optical properties are of particular interest; for example, it should prove possible to prepare a solid that switches from a diamagnet to a ferromagnet simply by irradiation with light. Such solids may be crucial to the development of computers in the 21st century that use light instead of electrons to carry out computations.

Leading references:

Holmes, S. M.; Whelpley, A. S.; Girolami, G. S. "Nanocomposite of a Chromium Prussian Blue with TiO2. Redox Reactions and the Synthesis of Prussian Blue Molecule-Based Magnets," Polyhedron 2007, 26, 2291.

Verdaguer, M.; Girolami, G. S. "Magnetic Prussian Blue Analogs," in Magnetism Molecules to Materials V, 2005, pp 283-346.

New Directions in Chemical Vapor Deposition.

Chemical vapor deposition (CVD) is an increasingly important technique in industry for the manufacture of integrated circuits and other solid state devices. In CVD, a gas is passed over a hot surface, initiating a chemical reaction in which one of the products is a thin film of a solid such as a metal, semiconductor, or insulator. Most CVD reactions require rather high temperatures (often over 1000 C), but we are developing new metal organic chemical vapor deposition (MOCVD) precursors and new methods that allow films to be grown at much lower temperatures (below 400 C). For thin films of refractory materials such as transition metal nitrides, carbides, and borides, however, low-temperature CVD processes suffer from severe drawbacks, one of which is that the films are often easily oxidized. This undesirable property arises because the refractory nature of these materials prevents annealing during film growth, so that the films are porous and contain residual amounts of hydrogen. We are investigating the use of a new approach to deposit thin films of refractory materials from metal-organic CVD precursors: remote plasma MOCVD, in which plasma-generated hydrogen atoms are directed at the growth surface to promote annealing while keeping the surface temperature low. This new approach, which combines the best features of chemical vapor deposition and physical vapor deposition methods, has the potential to revolutionize how refractory thin films are deposited. Leading references:

Lazarz, T. S.; Yang, Y.; Kumar, N.; Kim, D. Y.; Noh, W.; Girolami, G. S.; Abelson, J. R. "Low Temperature CVD of Ru from C6H8Ru(CO)3," Mater. Res. Soc. Symp. Proc. 2007, 990, 103.

Noh, W.; Girolami, G. S. "Synthesis and Characterization of the Cycloheptatrienyl Tantalum Mixed Sandwich Compounds (C5R5)Ta(C7H7)," Inorg. Chem. 2008, 47, 535.