g.v. gibbs 1 , david f. cox 2 , kevin m. rosso 3 , nancy l. ross 1 and robert t. downs 4
DESCRIPTION
Bonded interactions in Fe and Cu Sulfides; Do electroneutrality requirements hold in the classical sense for sulfides?. G.V. Gibbs 1 , David F. Cox 2 , Kevin M. Rosso 3 , Nancy L. Ross 1 and Robert T. Downs 4 1 Department of Geosciences, Virginia Tech, Blacksburg, VA 24061 - PowerPoint PPT PresentationTRANSCRIPT
Chemical E ngineeri ng UHV Sur face Scie nce Laborat ory
Bonded interactions in Fe and Cu Sulfides;
Do electroneutrality requirements hold in the classical sense for
sulfides?G.V. Gibbs1, David F. Cox2, Kevin M. Rosso3, Nancy L. Ross1
and Robert T. Downs4
1Department of Geosciences, Virginia Tech, Blacksburg, VA 240612Department of Chemical Engineering, Virginia Tech, Blacksburg, VA
24061
3William R. Wiley Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratories, Richland, Washington 99352
4Department of Geosciences, University of Arizona, Tucson, AZ, 85721.
Chemical E ngineeri ng UHV Sur face Scie nce Laborat ory
Chemical Formula Ni3S2
A representative block of the heazlerwoodite structure: Three NiS4 tetrahedra sharing a common
edge
Ni
S
Ni-Ni bond path
2.498Å
Bulk Ni metalR(Ni-Ni) 2.492Å
Gibbs, Cox, Ross, Rosso, Downs and Prewitt (2005) J. Phys. Chem.,
What are the oxidation states of Ni and S?
Chemical E ngineeri ng UHV Sur face Scie nce Laborat ory
Chemical E ngineeri ng UHV Sur face Scie nce Laborat ory
0.0 0.1 0.2 0.3 0.4 0.5 0.60.0
0.1
0.2
0.3
0.4
0.5
0.6
(r c)
e/Å
3 (cal
cula
ted)
(rc) e/Å3 (experimental)
Ni-Ni
Ni-S
S-S
Comparison of experimental and theoretical bond critical points properties for the Ni-S, Ni-Ni and S-S bonded interactions for heazlewoodite, Ni3S2
Gibbs, Cox, Ross, Rosso and Downs, J. Phys. Chem. (2007)
Spackman, Gibbs and Downs (Experimental, In prep.)
Chemical E ngineeri ng UHV Sur face Scie nce Laborat ory
pyrite, FeS2 marcasite, FeS2
troilite, FeSgreigite, Fe3+Fe2+Fe3+S4
Fe2+, Fe3+
Fe3+
Fe2+ Fe2+
Fe2+
hs
lsls
S
S2 dimer connected by bond path with a bond critical point
Chemical E ngineeri ng UHV Sur face Scie nce Laborat ory
Smythite Fe3S4
Chemical E ngineeri ng UHV Sur face Scie nce Laborat ory
cubanite, CuFe2S3chalcopyrite, CuFeS2
CuFeCuFe
Chemical E ngineeri ng UHV Sur face Scie nce Laborat ory
Gibbs, Cox, Ross, Rosso and Downs, J. Phys. Chem. (accepted)
VIFehs2+- S
IVFehs2+?- S
IVFehs3+- S
VIFels2+- S
Chemical E ngineeri ng UHV Sur face Scie nce Laborat ory
Gibbs, Cox, Ross, Rosso and Downs, J. Phys. Chem. (accepted)
VIFehs2+- S
IVFehs2+?- S
IVFehs3+- S
VIFels2+- S
Chemical E ngineeri ng UHV Sur face Scie nce Laborat ory
Gibbs, Cox, Ross, Rosso and Downs, J. Phys. Chem. (accepted)
VIFehs2+- S
IVFehs2+?- S
IVFehs3+- S
VIFels2- - S
Chemical E ngineeri ng UHV Sur face Scie nce Laborat ory
X-ray photoemission and L2,3 - edge X-ray
absorption spectra recently determined by Pearse et al.
(2006) show that the Fe atom in chalcopyrite is
unequivocally Fe3+‘Given that Fe is trivalent in
chalcopyrite, ‘What are the oxidation states of
the Fe atomscomprising greigite and cubanite?’
Chemical E ngineeri ng UHV Sur face Scie nce Laborat ory
Hoggins and Steinfink (1976) predicted the oxidation state for
the Fe atom in greigite to be Fe3.92+ and that for chalcopyrite
and cubanite to be Fe2.79+ and Fe2.77+, respectively.
Chemical E ngineeri ng UHV Sur face Scie nce Laborat ory
Bob Shannon (1981) observed that a Fe-S bond valence-bond length
connection predicts a IVFe4+-S bond length of 2.144 Å compared
with that observed 2.147Å for greigite.
He concluded that the oxidation state of Fe atom in greigite is Fe4+
Chemical E ngineeri ng UHV Sur face Scie nce Laborat ory
Fe4+ is known but it is rare and an unlikely state!
But there exist materials like FeS2 and Ba3FeS5 which must contain
Fe4+ if electrical neutrality requirements hold and (2) only S-2 anions
are only present.
Chemical E ngineeri ng UHV Sur face Scie nce Laborat ory
Neutron diffraction and Mössbauer studies show that the two
edge sharing tetrahedra in cubanite are inversion center
equivalent.
Mössbauer spectrum indicates that the Fe atom in cubanite has an oxidation state of
Fe2.5+ with a chemical formula CuFe2.5+Fe2.5+S3. (McCammon,
1995)
Chemical E ngineeri ng UHV Sur face Scie nce Laborat ory
Gibbs, Cox, Ross, Rosso and Downs, J. Phys. Chem. (accepted)
VIFehs2+- S
IVFehs3+- S
IVFehs4+?- S
Fels2+ - S
IVFehs2.5?- S
Chemical E ngineeri ng UHV Sur face Scie nce Laborat ory
Structure of the molecule (S4 point group) geometry optimized at the
B3LYP/6-311++G(2d,p) level.
R(Fe-S) (opt) = 2.130 Å
R(H-S) = 1.349 Å<S –Fe –S = 108.30o 2x<S –Fe –S = 110.06o 4x<Fe –S –H = 99.70o
R(Fe-S) (greigite) = 2.147Å
S
Fe4+
H
H4Fe4+S4
Chemical E ngineeri ng UHV Sur face Scie nce Laborat ory
Gibbs, Cox, Ross, Rosso and Downs, J. Phys. Chem. (accepted)
VIFehs2+- S
IVFehs3+- S
IVFehs4+?- S
IVFehs2.5+?- S
VIFels2+- S
Chemical E ngineeri ng UHV Sur face Scie nce Laborat ory
Gibbs, Cox, Ross, Rosso and Downs, J. Phys. Chem. (accepted)
VIFehs2+- S
IVFehs4+?- S
IVFehs2.5+?- S
VIFels2+- S
IVFehs3+ - S
Chemical E ngineeri ng UHV Sur face Scie nce Laborat ory
Gibbs, Cox, Ross, Rosso and Downs, J. Phys. Chem. (accepted)
VIFehs2+- S
IVFehs3+- S
IVFehs4+?- S
IVFehs2.5+?- S
VIFels2+- S
Chemical E ngineeri ng UHV Sur face Scie nce Laborat ory
The properties of low spin VIFe-S bonded interactions are
distinct from those of high spin VIFe-S bonded interactions.
For the low spin VIFe-S bonded interactions, (1) Fe-S bond lengths are shorter,
(2) ρ(rc ) is larger,
(3) the bonded radii are smaller, (4) the Fe and S atomic charges are smaller.
Comments
Chemical E ngineeri ng UHV Sur face Scie nce Laborat ory
The presence of Fe4+ in greigite is consistent with (1) the metastability of greigite, (2) the difficulty of its synthesis,
(3) the predicted oxidation state of 3.92+, (4) its short observed IVFe-S bond length and (5) the properties calculated for the H4Fe4+S4.
Chemical E ngineeri ng UHV Sur face Scie nce Laborat ory
What is the status of the Fe atom in cubanite?
CuFe2.5+Fe2.5+S3?
CuFe2+Fe3+S3 with Fe2+,Fe3+ disorder?
None of the above?
Chemical E ngineeri ng UHV Sur face Scie nce Laborat ory
The evidence suggests that a simple connectionbetween stoichiometry and oxidation state is notalways a virtue of sulfides in the classical sense!
Chemical E ngineeri ng UHV Sur face Scie nce Laborat ory
Congratulations Alex for the many elegant
contributions that you have made to our science.
Chemical E ngineeri ng UHV Sur face Scie nce Laborat ory
Shared bonded interaction
Intermediate bonded interaction
Closed-shell bonded interaction
Gibbs, Cox, Ross, Rosso (2006) J. Chemical Physics
ViFe2+-SIVFe3+?-S
IVFe4+?-S
Chemical E ngineeri ng UHV Sur face Scie nce Laborat ory
0.0 0.2 0.4 0.6 0.8 1.0
2.0
2.5
3.0
3.5
4.0 native sulfur sulfide crystals
R(S
-S) Å
(rc) e/Å3
Chemical E ngineeri ng UHV Sur face Scie nce Laborat ory
G(rc)
H(rc)
Na-OMg-O
Al-O
S-O
Si-O
P-O
V(rc)
Gibbs, Cox, Ross, Rosso (2006) J. Chemical Physics
Chemical E ngineeri ng UHV Sur face Scie nce Laborat ory
Gibbs, Cox, Ross, Rosso (2006) J. Chemical Physics
VIFe2+-SIVFe3+-SIVFe4+-S
Chemical E ngineeri ng UHV Sur face Scie nce Laborat ory
Chemical E ngineeri ng UHV Sur face Scie nce Laborat ory
Chemical E ngineeri ng UHV Sur face Scie nce Laborat ory
Given that a bonded interaction is shared when
¼2(rc) = 2G(rc) + V(rc) 0 and that a bonded interaction is closed when
H(rc) = G(rc) + V(rc) ≥ 0.then
2G(rc) + V(rc) = 0 |V(rc)| /G(rc) ≥ 2 and
G(rc) + V(rc) = 0, |V(rc)| /G(rc) 1. A bonded interaction is classified as
shared when |V(rc)| /G(rc) ≥ 2,
closed-shell when |V(rc)| /G(rc) 1 and intermediate when 1 < |V(rc)| /G(rc)< 2.
Chemical E ngineeri ng UHV Sur face Scie nce Laborat ory
S
Fe-S bcp
Fe2+
S-S bcp
Chemical E ngineeri ng UHV Sur face Scie nce Laborat ory
Gibbs, Jayatililaka, Spackman, Cox and Rosso (2006) J. Phys. Chem.