Friday, July 31, 2009

Metal-organic networks on metal surfaces

Metal-organic networks formed by coordination bonding between metallic centers and organic ligands can be efficiently engineered to exhibit specific magnetic, electronic, or catalytic properties. This project focuses on 2D metal-organic networks resulting from benzoic acids self-assembled on Cu metal surfaces. Our numerical simulations based on Density Functional Theory (DFT), pseudopotentials, and plane-waves, are used to unveil the detailed atomistic and electronic structures of the nanostructures, as well as their energetics of formation. Moreover, the theoretical results provides new fundamental insight for understanding the novel magnetic and catalytic properties of these metal-organic networks.

Molecular necklaces
Structure and self-assembly of benzoic acids on Cu(110).

The adsorption structure and network formation mechanisms of trimesic acid (TMA) on Cu(110) is studied by combining STM measurements and DFT calculations. At low coverages, STM images shows the formation of linear chains. The calculations reveals that the organic ligands are linked together by dimers of Cu adatoms. A new phase appears at higher coverages, formed by interlocked TMA-Cu chains having lower periodicity than those observed at low coverages. We predict that in this case the organic ligands coordinate only one Cu adatom, whose presence, despite being essential for the cohesion of the nanostructure, cannot be imaged by STM due to an electronic effect. The TMA-Cu chains are the intrinsic nanostructures on Cu(110), but functional MOCCs require different elements than Cu as metallic centers. TMA-Fe chains are formed by codepositing Fe and TMA on Cu(110). Besides determining their structure, spin-polarized calculations suggests that the Fe centers within the 1D chains have magnetic properties similar to those of isolated Fe adatoms, a necessary (although not sufficient) condition for the emergence of intriguing magnetic properties induced by the low dimensionality.

Chemical reactivity of metal-organic networks

We focus on systems formed by Fe metal centers coordinated by terephthalic acid (TPA) and supported by Cu(001). The metal centers form characteristic carboxylate-bridged di-iron units having chemical and structural environments compatible to that one present into several metalloproteins. We have discovered a new mechanism of O2 activation and dissociation, which was identified by means of numerical simulation, involving a high degree of correlation between reactions occurring on neighboring metal centers.

Hierarchical self-assembly

Hierarchical self-assembly, i.e. “the formation of an ordered structure through a set of interactions that decreases in strength” is an extremely efficient way of constructing complex functional architectures often encountered in biological systems. We show that by opportunely designing planar benzene-carboxylic acids the dimensionality of metal-organic structures formed on a Cu(110) substrate can be continuously and predictably tuned from 1D to 2D. This demonstrates that molecular design is indeed possible but also that it is dependent upon very subtle origins whose understanding is at the basis of controlled and programmed bottom-up nanostructure design.

In collaboration with:

  • University of Warwick (G. Costantini)
  • Max Planck Institut fuer Festkoerperforschung (Th. Classen, G. Costantini, and K. Kern)
  • Hong Kong University (N. Lian)
  • University of Liverpool (S. Haq and R. Raval)
  • Universita` di Genova (M. Ferrando)

T. Classen, G. Fratesi, G. Costantini, S. Fabris, F. L. Stadler, C. Kim, S. de Gironcoli, S. Baroni, and K. Kern
Templated growth of metal-organic coordination chains at surfaces
Angew. Chem. Int. Ed. 44, 6142 (2005)

S. Clair, S. Pons, S. Fabris, S. Baroni, H. Brune, K. Kern, and J. V. Barth
Monitoring two-dimensional coordination reactions: directed assembly of Co-terephthalate nanosystems on Au(111)
J. Phys. Chem B 110, 5627 (2006)

T. Classen, M. Lingenfelder, Y. Wang, R. Chopra, G. Costantini, K. Kern, G. Fratesi, S. Fabris, S. Baroni, S. Haq, and R. Raval
Hydrogen and Coordination Bonding Supramolecular Structures of Trimesic Acid on Cu(110)
J. Phys. Chem. A 111, 12589 (2007)

G. Costantini, Y. Wang, S. Fabris, R. Ferrando, Th. Classen, and K. Kern
Programming Hierarchical Supramolecular Nanostructures by Molecular Design
in preparation

Metal-organic networks formed by coordination bonding between metallic centers and organic ligands can be efficiently engineered to exhibit specific magnetic, electronic, or catalytic properties. This project focuses on 2D metal-organic networks resulting from benzoic acids self-assembled on Cu metal surfaces. Our numerical simulations based on Density Functional Theory (DFT), pseudopotentials, and plane-waves, are used to unveil the detailed atomistic and electronic structures of the nanostructures, as well as their energetics of formation. Moreover, the theoretical results provides new fundamental insight for understanding the novel magnetic and catalytic properties of these metal-organic networks.

Molecular necklaces
Structure and self-assembly of benzoic acids on Cu(110).

The adsorption structure and network formation mechanisms of trimesic acid (TMA) on Cu(110) is studied by combining STM measurements and DFT calculations. At low coverages, STM images shows the formation of linear chains. The calculations reveals that the organic ligands are linked together by dimers of Cu adatoms. A new phase appears at higher coverages, formed by interlocked TMA-Cu chains having lower periodicity than those observed at low coverages. We predict that in this case the organic ligands coordinate only one Cu adatom, whose presence, despite being essential for the cohesion of the nanostructure, cannot be imaged by STM due to an electronic effect. The TMA-Cu chains are the intrinsic nanostructures on Cu(110), but functional MOCCs require different elements than Cu as metallic centers. TMA-Fe chains are formed by codepositing Fe and TMA on Cu(110). Besides determining their structure, spin-polarized calculations suggests that the Fe centers within the 1D chains have magnetic properties similar to those of isolated Fe adatoms, a necessary (although not sufficient) condition for the emergence of intriguing magnetic properties induced by the low dimensionality.

Chemical reactivity of metal-organic networks

We focus on systems formed by Fe metal centers coordinated by terephthalic acid (TPA) and supported by Cu(001). The metal centers form characteristic carboxylate-bridged di-iron units having chemical and structural environments compatible to that one present into several metalloproteins. We have discovered a new mechanism of O2 activation and dissociation, which was identified by means of numerical simulation, involving a high degree of correlation between reactions occurring on neighboring metal centers.

Hierarchical self-assembly

Hierarchical self-assembly, i.e. “the formation of an ordered structure through a set of interactions that decreases in strength” is an extremely efficient way of constructing complex functional architectures often encountered in biological systems. We show that by opportunely designing planar benzene-carboxylic acids the dimensionality of metal-organic structures formed on a Cu(110) substrate can be continuously and predictably tuned from 1D to 2D. This demonstrates that molecular design is indeed possible but also that it is dependent upon very subtle origins whose understanding is at the basis of controlled and programmed bottom-up nanostructure design.

In collaboration with:

  • University of Warwick (G. Costantini)
  • Max Planck Institut fuer Festkoerperforschung (Th. Classen, G. Costantini, and K. Kern)
  • Hong Kong University (N. Lian)
  • University of Liverpool (S. Haq and R. Raval)
  • Universita` di Genova (M. Ferrando)

T. Classen, G. Fratesi, G. Costantini, S. Fabris, F. L. Stadler, C. Kim, S. de Gironcoli, S. Baroni, and K. Kern
Templated growth of metal-organic coordination chains at surfaces
Angew. Chem. Int. Ed. 44, 6142 (2005)

S. Clair, S. Pons, S. Fabris, S. Baroni, H. Brune, K. Kern, and J. V. Barth
Monitoring two-dimensional coordination reactions: directed assembly of Co-terephthalate nanosystems on Au(111)
J. Phys. Chem B 110, 5627 (2006)

T. Classen, M. Lingenfelder, Y. Wang, R. Chopra, G. Costantini, K. Kern, G. Fratesi, S. Fabris, S. Baroni, S. Haq, and R. Raval
Hydrogen and Coordination Bonding Supramolecular Structures of Trimesic Acid on Cu(110)
J. Phys. Chem. A 111, 12589 (2007)

G. Costantini, Y. Wang, S. Fabris, R. Ferrando, Th. Classen, and K. Kern
Programming Hierarchical Supramolecular Nanostructures by Molecular Design
in preparation

0 comments :

Post a Comment

you give times, i give you world,
if you have a website or something, please at the contents. thanks..

best regards,