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Kein Folientitel

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Title: Kein Folientitel


1
Platinides Electronic Structure and Bonding
Ulrich Wedig, Gernot Stollhoff, Andrey Karpov,
Jürgen Nuss, and Martin Jansen Max-Planck-Institu
t für Festkörperforschung Heisenbergstraße 1,
D-70569 Stuttgart, Germany
Platinide Chemistry
Gold and platinum are the elements with the
highest electron affinity among all metals, 2.31
eV and 2.13 eV respectively 1, a property that
is related to the exceptional relativistic
contraction of the 6s orbital 2. These values
exceed the electron affinities of any chalcogen
atom that readily form anions. As a consequence
many compounds are known that contain gold in a
negative oxidation state. In constrast to this
rich auride chemistry we only recently managed to
synthesize and characterize several platinides
where the negative charge can be assigned
unambiguously to the platinum atoms. In these
compounds, platinum shows some surprising
parallels to main group elements.
Cs1
Cs2
Pt
Cs2Pt is an ionic insulator crystallizing in the
Ni2In structure. From structure-chemical
considerations, Cs2Pt can be affiliated to the
alkali-metal mono-chalcogenides 3.
BaPt can be formulated, in terms of the
Zintl-Klemm concept, as (Ba2)(18Pt-).e-. It
crystallizes in the NiAs structure type with an
extreme low c/a ratio (1.07). The band structure
reveals 2D metallic conductivity 4.
Ba3Pt2, cystallizing in the Er3Ni2 structure, is
isotypic to Ca3Pd2, Ca3Pt2 and Sr3Pt2. It is
remarkable that the structure type of the
platinum compounds doesnt change when varying
the size of the cation 5.
Ba2Pt 6 is the first intermetallic phase
adopting the CdCl2 structure. The compound which
can be formulated as (Ba2)2(Pt2-).2e- shows
surprising similarities to the nitride Ba2N.
BaPt
Cs2Pt
LMTO-TB-ASA densities of states
Reducible ELF-domain of the Pt 5d shell and
irreducible ELF-domain of the Pt-Pt ?-bond (both
in light-blue, ? 0.32). The corresponding basin
sets are shown on the left side (yellow Pt 5d
shell, ne10.6 red Pt-Pt ?-bond, ne0.5).The
integrated value of the valence electron density
within the Pt-basin of the total electron density
amounts to 10.9.
LA - charge analysis
LMTO-TB-ASA LDA bandstructure in fatband
representation
Negative COHP values and their integral of the
Pt-Pt bond in the chains parallel to the c-axis.
Ba3Pt2
Isosurfaces of the electron density computed
bands within certain energy regions ? 0.01 e-
/ Bohr3 covalent region (left) ? 0.05 e- /
Bohr3 atomic region (right)
CRYSTAL98 structure optimization
     
 
Negative COHP values and their integral of the
Pt-Pt bond in the dumbbells
Partial charges of Pt / Pd obtained from the
topological analysis of total electron
density. Ba3Pt2 -1.2 Ca3Pt2 -1.5 Ca3Pd2 -
1.4
LMTO-TB-ASA LDA total and partial densities of
states
The Cs2Pt molecule
Ba2Pt
  • Polarisation effects Tight d-function on Cs 1
    ve pseudopotential gives no bonding
  • correlation of the 5s/5p semi-core shell
    contributes dominantly.
  • HF underestimates, LDA overestimates bonding
    significantly.
  • Gradient corrected functionals give reasonable
    results, compared to CCSD(T).
  • The basis set optimized for CRYSTAL98 is not
    suitable for molecular calculations due to large
    BSSE.
  • Vibrational frequencies are at about 20 cm-1 and
    2 x 100 cm-1.

Ba2Pt Ba2Pt (mMT) Ba2N ELF-domains ? 0.34
Ba2Pt Ba2Pt (mMT) Ba2N Isosurfaces of the
electron density computed from the bands at the
Fermi level Ba2Pt ? 0.003 e- / Bohr3 Ba2N
? 0.002 e- / Bohr3
LMTO-TB-ASA LDA total densities of
states nMTModified radii of the muffin tin
spheres
Total and partial densities of states
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