Analysis of Surface Adsorption for Iron Porphyrin-like Molecules on a Pt(111) surface David Shaker and Daniel P. Miller Figure 1, Table of bond lengths across the studied porphyrin-like molecules
Introduction:
Molecule
In this study the molecular surface absorptions of various iron porphyrins in the high spin state onto a platinum surface. This was done particularly to compare this with the results of a prior study in which the spin state of iron within porphyrin was modified by changing the distance of iron to the platinum surface.
Fe-Porphyrin (a) Fe-Porphyrazine (b) Fe-Chlorin (d) Fe-Bacteriochlorin (e) Fe-Isobacteriochlorin (f) Fe-Phthalocyanine (c) Fe-Tetrabenzoporphyrin (g)
Computational Details: • • • • •
Average C-Pt bond length (Å) 2.27 2.20 2.29 2.28 2.86 2.26 2.42
Average Fe-Pt bond length (Å) 2.72 2.64 2.64 2.62 2.67 2.70 2.73
Average Outer Aromatic C-Pt bond length (Å) 2.21 2.20
VASP software package Results vdW-DF-optPBE density functional with a plane-wave energy cutoff of 500 eV Performed geometry optimizations on the entire system, but keeping the bottom two layers of the four layer Pt(111) surface fixed in place. Iron porphyrin and porphyrazine were very similar in most aspects except that iron The Hubbard U correction at 3 eV was used to properly treat the ‘Fe’ electrons. porphyrazine has stronger bonding with the Pt(111) surface. Spin unrestricted (polarized) calculations were performed so that unpaired electrons could be explicitly treated.
The iron chlorin-like structures were very similar in terms of their adsorption Characteristics save for iron isobacteriochlorin, which has one side adsorbed to the platinum sheet in a similar fashion to the other chlorins but has its opposite side at a much larger distance from the platinum sheet.
Figure 2, top views of Iron porphyrin (a), porphyrazine (b), phthalocyanine (c), chlorin (d), bacteriochlorin (e), isobacteriochlorin (f), and tetrabenzoporphyrin (g) on PT(111) surface (a)
Average Fe-N bond length (Å) 2.15 2.10 2.16 2.17 2.17 2.09 2.16
Iron phthalocyanine and iron tetrabenzoporphyrin are very similar to each other in terms of adsorption except for iron tetrabenzoporphyrin’s increased carbon-platinum bond length.
(d) (g)
Thus, we conclude that replacing the methine bridge in a porphyrin type ligand with a nitrogen induces stronger adsorption to the Pt(111) surface
Future work (b)
(e)
Figure 3 side views of Iron porphyrin (a), porphyrazine (b), phthalocyanine (c), chlorin (d), bacteriochlorin (e), isobacteriochlorin (f), and tetrabenzoporphyrin (g) on PT(111) surface (e) (a)
(c)
Reference (f)
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(f)
(b)
In the future we intend to pursue research on the S = 1 (Intermediate) spin states of these molecules that were studied herein are in the S = 2 (High) spin state.
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(g)
Electronic Structure of Iron Porphyrin Adsorbed to the Pt(111) Surface Daniel P. Miller, James Hooper, Scott Simpson, Paulo S. Costa, Nina Tymińska, Shannon M. McDonnell, Jason A. Bennett, Axel Enders, and Eva Zurek The Journal of Physical Chemistry C 2016 120 (51), 29173-29181 DOI: 10.1021/acs.jpcc.6b09408