Research in the Maverick group

We are studying two different groups of transition-metal complexes: polynuclear “host” molecules with well defined three-dimensional cavities, and volatile metal-organic compounds that can be used to prepare electronic materials.

Molecular Recognition and Porous Inorganic Molecules

Here we use organic bridging ligands to join two or more metal atoms into hollow “hosts” into which “guest” molecules can fit. Our goal is to use the hosts as catalysts for reactions of the guests (similar to the way metalloenzymes work), or as sensors for small guest molecules.

We are studying two types of hosts. In one of these, a 1,8-disubstituted anthracene bridging unit keeps the two metal atoms in a cofacial orientation. We have prepared hosts such as [ABI](Rh(CO)2)2, shown below, and are now exploring their ability to react with small guest molecules such as O2 and C2H4.

[Note: The right-hand panels in many of the sketches below will show you rotatable 3-D images of the molecules, if you have the free Chime plug-in installed. For information about Chime, see http://www.mdli.com.]

The other family of hosts is based on the bis(b-diketone) NBAH2. The sketch below shows the adduct of the host Zn2(NBA)2 with the organic guest piperazine. We are now studying hosts with functional groups on the inside of the naphthalene bridges, for attack on the bound guest molecules.

We are also adapting these hosts to the synthesis of larger polynuclear complexes and new types of porous inorganic-organic solids. For example, the bis(b-diketone) C1baH2, with a 1-carbon bridge, should produce a much larger hexanuclear host:
Cu6(C1ba)6 (H atoms not shown)

 
New approaches to porous molecules and solids

We will extend this chemistry to three-dimensional structures by using multidentate "nodes" to join the metal-containing "rods" (see sketch at left).  For example, a tris(b-diketone) should react with metal ions to produce a dodecahedral molecule nearly 5 nm in diameter, comprising 20 ligands (nodes) and 30 metal atoms:

Schematic drawing of proposed dodecahedral host
This product would be similar to complexes recently prepared by Stang and co-workers, but with the advantage that the metal atoms would be coordinatively unsaturated and therefore likely to react with substrate molecules.
 

Electronic Materials

We are developing new ways of making thin films of copper and other highly conductive materials for use in the next generations of integrated circuits. These rely on chemical vapor deposition (CVD), in which a volatile "precursor" passes over a hot silicon wafer and reacts to form a thin film of the desired material. This is a collaborative project with chemical engineers at LSU.

One precursor commonly used as a source for Cu metal is the b-diketone complex Cu(hfac)2, which produces Cu when heated with H2. We have found that its adduct with isopropyl alcohol, Cu(hfac)2(i-PrOH), produces Cu films without the need for H2 by using the alcohol as the reducing agent:

Cu(hfac)2(i-PrOH) ¾® Cu + 2hfacH + (CH3)2C=O

This reaction occurs both faster and at a lower substrate temperature than the H2 reaction.

The copper(I) cluster amides [CuNR2]4 shown below (e.g. R = SiMe3, i-Pr) can be used for Cu CVD, and they are also photosensitive. We are trying to find out how the photochemical activity and volatility of these Cu(I) clusters depends on the choice of R group.
[CuN(SiMe3)2]4 (H atoms not shown)

A new direction for our electronic materials research is the deposition of thin films of diffusion barriers, refractory materials that are also needed for integrated circuit applications. We have shown that TaCl5 is reduced by reaction with gaseous reductants, and we are adapting this reaction to the production of films of the diffusion barrier materials Ta, TaN, and TaxSiyN.

Selected Publications:

"New Routes Toward Chemical and Photochemical Vapor Deposition of Copper Metal"; Maverick, A. W.; James, A. M.; Fan, H.; Isovitsch, R. A.; Stewart, M. P.; Azene, E.; Cygan, Z. T. In: Inorganic Materials Synthesis: New Directions for Advanced Materials; ACS Symp. Ser. 727; Winter, C. H.; Hoffman, D. M., Eds.; American Chemical Society:Washington, DC, 1999; pp. 100-112.

"Phosphorescence and Structure of a Tetrameric Copper(I)–Amide Cluster"; James, A. M.; Laxman, R. K.; Fronczek, F. R.; Maverick, A. W. Inorg. Chem. 1998, 37, 3785-3791.

"Electronic Absorption Spectra and Phosphorescence of Oxygen-Containing Molybdenum(IV) Complexes"; Isovitsch, R. A.; Beadle, A. S.; Fronczek, F. R.; Maverick, A. W. Inorg. Chem. 1998, 37, 4258-4264.

"A New Binucleating Ligand Based on Anthracene and Its Cofacial Diiridium(I) and Dirhodium(I) Complexes"; Benites, M. R.; Fronczek, F. R.; Hammer, R. P.; Maverick, A. W. Inorg. Chem. 1997, 36, 5826-5831.

"Endo and Exo Coordination to Cofacial Binuclear Copper(II) Complexes"; Maverick, A. W.; Billodeaux, D. R.; Ivie, M. L.; Fronczek, F. R.; Maverick, E. F. J. Inclusion Phenom. Macrocyclic Chem., 2001, 39, 19-26.

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This document was last updated: 31 August 2001

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