Vanadium Oxide Cluster Anion Calculations - Optimized Structures and Reactivity with Small Organic Molecules

               

Principal Investigator

Gary D. Willett

School of Chemistry

The University of New South Wales

Co-Investigators

Adriana Dinca

School of Chemistry

The University of New South Wales

Projects

h14 - VPP

With the recent developments in both software
quantum chemical packages and computer
power, molecular modelling has become an available tool to the experimental scientist. We are interested in mapping the reactivity of transition metal and metal oxide clusters toward organic molecules. Clusters form the transition 'state' between molecules and surface (or bulk) states. We are able with the help of Fourier transform ion cyclotron resonance mass spectrometry to study gas phase reactions of molecular and cluster ions in a solvent free environment, determine intermediate and final products, and kinetic properties. To understand some of the reaction pathways and products, determination of the structures of both parent and product ions is essential. Thus in this project we are interested in calculating ground state structures of cluster ions we have observed experimentally, as well as reaction channels (transition state) and structures of product ions. To this end we will use the Gaussian 98 suite of programs.
   
         
               

     
               

What are the results to date and the future of this work?

Laser ablation of vanadium pentoxide (V2O5) produces a series of cluster ions: VO+, VO3-, V2O5-, V3O7-, V3O8-, and V4O10-. So far we have undertaken preliminary calculations on these ions and their corresponding neutrals using density functional theory at B3LYP level of theory with 3-21G and 6-311G** basis sets. Results indicate large partial positive charges on the vanadium atoms which are consistent with the reactivity of the anions towards the molecules studied (alcohols, methacrylates). Optimized geometries and vibrational frequencies were calculated for the two smaller ions. However, for the VO3- ion the optimized geometry obtained does not correspond to the latest literature report (photoelectron spectroscopy, electron spin resonance measurements), so further investigation is necessary, involving the use of other ab initio methods.

It is worthwhile noting that simple models of structure are not easily applied to predicting the structure of even 'simple' ions such as VO3-. For example one might expect the VO3- ion to have a planar trigonal structure. Our calculations indicate a trigonal pyramidal structure.

               
- Appendix B

 
               

       

In order to understand the results from the FT/ICR MS experiments, it is thus necessary to have a good understanding of the chemical structures of the reagents, vanadium oxide ions in this case. Thus further work will involve the study of the remaining ions, as well as some product ions such as the methylene molecule adduct to the VO3- ion and methanol molecule adduct to the V2O5- ion in their respective reactions with methanol neutrals.

What computational techniques are used?

Molecular orbital calculations were carried out using Gaussian 94 and Gaussian 98 program packages in order to optimize geometries of parent and product anions. Calculations were carried out at the B3LYP (density functional) level, using the 3-21G, 6-311G** basis sets. Further work will involve use of frozen core potentials (e.g. Lan2DZ) and other (hybrid) functionals such as B3PW91.

Publications

A. Dinca, T.P. Davis, K.J. Fisher, D.R. Smith, G.D. Willett Vanadium Oxide Anion Cluster Reactions with Methyl Isobutyrate and Methyl Methacrylate Monomer and Dimer: A Study by FT/ICR Mass Spectrometry, to appear in Int. J. Mass Spectrom., 182-183, 1999.

       
Appendix B -