1. Unique Magnetic Signature of Transition Metal Atoms on Organic Template
Anil K. Kandalam*
Department of Physics
Michigan Technological University
In collaboration with: Prof. Ravi Pandey, Prof. B. K. Rao*, Prof. P. Jena*
*Physics Department, Virginia Commonwealth University, Richmond, VA

2. Overview of this Presentation
Introduction
Background
Previous Studies by our research group
Computational Method
Results
Present Work
Computational Procedure
Results from Present work
Summary

3. Interaction of clusters with metallic/organic supports is important
Introduction
Stable nano-clusters can act as building blocks for novel materials
Problem
Bare clusters interact with each other and finally coalesce at short distances and hence are not stable in proximity of each other
Solution
Weakly interacting clusters
Isolating the clusters from each other
Inserting them in zeolites
Depositing on substrates
Coating with organic materials
Interaction of clusters with metallic/organic supports is important

4. Background
What happens when transition metal atoms are supported on organic molecular surfaces ??

5. Questions to be Answered
Effect of organic substrates on the magnetic moments of transition metal atoms
Equilibrium geometries of transition metal organic complexes in gas phase
Energetics like Electron Affinity, Ionization Potential and Dissociation Energies
Solutions
Experimental Studies (Laser Vaporization techniques)
Theoretical Calculations

6. Previous Studies Experimental Studies: Theoretical Studies:
K. Judai, M. Hirano, H. Kawamata, S. Yabushita, A. Nakajima, K. Kaya, Chem. Phys. Lett. 270 (1997) 23
P. Weis, P. R. Kemper, M. T. Bowers, J. Phys. Chem. A. 101 (1997) 8207 (Expt and theory)
T. Kurikawa, H. Takeda, M. Hirano, K. Judai, T. Arita, S. Nagao, A. Nakajima, K. Kaya, Organometallics 18 (1999) 1430
D. van Heijnsbergen, G. von Helden, G. Meijer, P. Maitre, M. A. Duncan, J. Am. Chem. Soc. 124 (2002) 1562
Theoretical Studies:
S. M. Mattar, W. Hamilton, J. Phys. Chem. 93 (1989) 2997
C. W. Bauschlicher, H. Partridge, S. R. Langhoff, J. Phys. Chem. 96 (1992) 3273

7. Previous Theoretical Studies by our group
M – (Benzene) systems
Chem. Phys. Lett. 321 (2000)
Mn – (Benzene)m (n = 1; m = 1, 2) systems
J. Am. Chem. Soc. 123 (2001)
M = 3d Transition metal atoms

8. Computational Method
DMol program : “Density functional theory calculations for Molecules”
Density Functional Theory (DFT) based calculations
Exchange-Correlation functional form: BPW91
Basis set : Double Numeric supplemented with polarization functions (DNP)
Geometry Optimization: C6v symmetry constraint for M-(Benzene) complexes
D6h symmetry constraint for M-(Benzene)2 complexes

9. M-(Benzene) Complex M Neutral Anion Sc 2.00 2.08 Ti 1.97 1.59 V 1.61Cr
1.85 Mn
1.52
1.68 Fe
1.50
1.63 Co
1.46
1.34 Ni
1.45
Distances are given in Angstroms

10. Distances are given in Angstroms
M-(Benzene)2 Complex M
Neutral
Anion Sc
1.97
1.95 Ti
1.78
1.75 V
1.67
1.68 Cr
1.60
1.62 Mn
1.69 Fe
1.72 Co
1.83
1.76 Ni
1.91
1.86
Distances are given in Angstroms

11. Variations in Spin Multiplicity

12. De[M(Bz)2] = -{E[M(Bz)2] – E[MBz] – E[Bz]}
Dissociation Energy
De(MBz) (eV)
De[M(Bz)2] (eV) M
Theo.
Expt. Sc
1.78
2.04 Ti
1.71
0.96
3.32
3.20 V
0.81
0.79
3.57
3.19 Cr
0.09
0.12
2.78
2.70 Mn
0.37
1.18 Fe
> 0.7
1.09 Co
1.83
0.34
0.42 Ni
1.70
0.02
De[M(Bz)2] = -{E[M(Bz)2] – E[MBz] – E[Bz]}

13. Brief Summary The structure of M(Benzene) complexes have C6v symmetry
M-(Benzene)2 complexes prefer sandwich structures
M-(Benzene) complexes: Magnetic moments of
Sc, Ti, and V atoms are increased
Mn, Fe, Co and Ni are decreased from their free – atom values
M-(Benzene)2 complexes: Magnetic moments are quenched to their lowest possible values
Addition of extra benzene significantly increases the binding energy of M-(Benzene)2 complexes (Sc to Mn)

14. Extension and re-examination Process
M – (Benzene)2 geometries: Restricted to sandwich structures (D6h symmetry)
Co – (Benzene)2 and Ni – (Benzene)2: Not in agreement with experimental results
No experimental or theoretical works on negatively charged Mn – (Benzene)m (n >1; m > 2) complexes
Anionic complexes are useful in studying the photo-detachment spectroscopy

15. Present Work
System under Study: Neutral and Anionic Vn – (Benzene)m (m = n +1, n = 1-3) complexes
Aim:
To identify the equilibrium geometries and ground state spin multiplicities
Calculate the Electron Affinity (EA) Ionization Potential (IP) Dissociation Energies (De)

16. Computational Procedure
Gaussian98 program suite
More flexibility in the basis sets
Density Functional Theory (DFT) based calculations
Gradient Corrected Density Functional: BPW91
Exchange functional: Becke88
Correlation functional: Perdew-Wang91
Two different basis sets are used
Lanl2dz (frozen core)
6-311G** (all electron basis)

17. Geometry and Spin Optimization
A two-step Optimization Approach
BPW91/Lanl2dz: Geometry optimization for all the possible spin states
BPW91/6-311G**: For the lowest energy spin state, geometry re-optimization
Geometry optimization was done without any symmetry constraints

18. VBz Complex

19. V(Benzene)2 Complexes

20. Rice Ball to Sandwich

21. Results for V(Benzene)2
Neutral
Anion
Lanl2dz
6-311G** A
1.44
1.43 B
1.09 C
1.69
1.67
1.68
1.66
All the distances are in Angstroms
Staggered sandwich is 0.05 eV higher in energy
Anionic V(Benzene)2 is unstable against auto-detachment

22. V2(Benzene)3 Complexes

23. Results for V2(Benzene)3
Distances are given in Angstroms
Neutral
Anion
Lanl2dz
6-311G** A
1.45
1.43 B
1.46
1.47 C
1.09 D
1.67
1.65
1.68
1.64 E
1.75
1.73
1.71
1.70
Staggered Sandwich: 0.09 eV and Rice-ball: 0.68 eV higher in energy

24. V3(Benzene)4 Complexes Rice-ball structure is not considered
Only Lanl2dz basis set is used for the calculations

25. Results for V3(Benzene)4
Distance (Å)
Neutral
Anion A
1.45 B
1.47 C
1.09 D
1.66
1.65 E
1.76
1.78 F
1.72
1.68

26. Variation of bond distances in Benzene

27. Variation in Spin Multiplicities
Lanl2dz based results

28. Vertical Ionization Potential

29. Vertical Ionization Potential (eV)
System
Lanl2dz
6-311G**
Expt.
VBz
5.53
5.71
5.11 ± 0.04
VBz2
5.87
5.96
5.75 ± 0.03
V2(Bz)3
4.73
4.82
4.70 ± 0.04
V3(Bz)4
4.07
----
4.14 ± 0.05

30. Electron Affinity (eV)
System
Vertical
Adiabatic
Expt. (Adiabatic)
VBz
0.52
0.44
0.62 ± 0.07
VBz2
-0.48
-0.50
Negative
V2(Bz)3
0.16
0.13
----
V3(Bz)4
0.56
Calculations are performed using Lanl2dz basis set

31. Dissociation Energy System BPW91/Lanl2dz (eV) Expt. (eV) VBz 0.67 0.79
De (VBz) = - [E (VBz) – E (V) – E (Bz)]
De [V(Bz)2] = - [E (VBz2) – E (VBz) – E (Bz)]
De [V2(Bz)3] = - [E (V2Bz3) – E (VBz2) – E (VBz)]
De [V3(Bz)4] = - [E (V3Bz4) – E (V2Bz3) – E (VBz)]
System
BPW91/Lanl2dz (eV)
Expt. (eV)
VBz
0.67
0.79
VBz2
3.13
3.19
V2(Bz)3
2.32
----
V3(Bz)4
2.29

32. Summary
Vn – (Benzene)m systems prefer sandwich structures to rice-ball structures
C – C and C – H distances are independent of the size of the system
Magnetic moment of Vn – (Benzene)n+1 complexes increases linearly with the size of the system (i.e., n)
Negligible geometrical changes upon addition of an electron
V – (Benzene)2 anion is unstable against auto-detachment of extra electron
Ionization Potential decreased with an increase in the size of the system