Platinides – Electronic Structure and Bonding

Ulrich Wedig, Gernot Stollhoff, Andrey Karpov, Jürgen Nuss, and Martin Jansen Max-Planck-Institut für Festkörperforschung

Heisenbergstraße 1, D-70569 Stuttgart, Germany

References[4] A. Karpov, J. Nuss, U. Wedig, M. Jansen, J. Am. Chem. Soc.. 2004,

accepted.[5] A. Karpov, U. Wedig, M. Jansen, Z. Naturforsch B 2004,

submitted.[6] A. Karpov, U. Wedig, R. E. Dinnebier, M. Jansen, Angew. Chem.

2004, submitted.

[1] T. Andersen, H. K. Haugen, H. Hotop, J. Phys. Chem. Ref. Data 1999, 28, 1511.

[2] P. Pyykkö, J.-P. Desclaux, Acc. Chem. Res. 1979, 12, 276.[3] A. Karpov, J. Nuss, U. Wedig, M. Jansen, Angew. Chem. 2003,

115, 4966; Angew. Chem. Int. Ed. 2003, 42, 4818.

 

  

Platinide ChemistryGold 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

Cs2Pt

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+)(1

∞[Pt]-).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 doesn‘t 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.

Cs2Pt

E(a,c) CRYSTAL98 DFT GC (B-LYP)

LA - charge analysis

The Cs2Pt molecule, calculated with GAUSSIAN98:

Method: CCSD(T)Basis set: Pt [6s5p4d2f]; Cs [5s4p2d1f]Pseudopot.: quasirelativistic; Pt 18 ve; Cs 9 ve

RCs-Pt: 2.96 ÅCs-Pt-Cs: 133°

Pt CsMulliken charge HF: -1.48 +0.74

CCD: -1.79 +0.89

•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.

 

Ba3Pt2

Ba2Pt

Table T1: Volumes (/Å3) of the basins of the total electron density and integrated valence electron density within these basins.

Ba2Pt Ba2Pt (mMT) Ba2N

vol. ne vol. ne vol. ne

Pt / N 43.3 11.9 44.8 11.8 3) 19.7 7.0 Ba 45.2 7.0 45.1 7.1 42.5 7.1 sum 1) 2) 401.1 77.9 405.0 78.2 314.1 63.0 sum (exp.) 398.5 78.0 398.5 78.0 313.8 63.0 1.3 formula units per hexagonal cell; Ba 5p included in the valence electron density. 2.Errors are up to 2 % for the volume due to the low density in the interlayer region. The impact on the

electron numbers however is negligible. 3.19.7 Å3 = 11.9 cm3/mole; c.f. the value reported by Bronger, Kniep and Kohout (ZAAC 630

(2004),117): 12.1 cm3/mole (Ba 5p in core).

BaPt

LMTO-TB-ASA LDA bandstructure in fatband representation

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, ne=10.6; red: Pt-Pt -bond, ne=0.5).The integrated value of the valence electron density within the Pt-basin of the total electron density amounts to 10.9.

Negative COHP values and their integral of the Pt-Pt bond in the chains parallel to the c-axis.

LMTO-TB-ASA LDA total and partial densities of states

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)

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 -1.2Ca3Pt2 -1.5Ca3Pd2 -1.4

LMTO-TB-ASA LDA total densities of statesnMT:Modified radii of the muffin tin spheres

Total and partial densities of states

Ba2Pt Ba2Pt (mMT) Ba2NELF-domains = 0.34

Ba2Pt Ba2Pt (mMT) Ba2NIsosurfaces of the electron density computed from the bands at the Fermi levelBa2Pt: = 0.003 e- / Bohr3 Ba2N: = 0.002 e- / Bohr3

Basis E R(Pt-Cs2) Δ R(Pt-Cs1) Δ a Δ c Δ Q(Pt) Q(Cs1) Q(Cs2) Bandgap

/ a.u. / Å / % / Å / % / Å / % / Å / % / eV

Exp. 3.270 4.043 5.676 9.471

HF Basis B -316.32755 3.57 9 4.20 4 6.19 9 8.85 -7 -1.92 0.94 0.97 7.11

Basis B2d -316.33798 3.60 10 4.23 5 6.23 10 8.91 -6 -1.76 0.87 0.89 6.57

GGA (BLYP) Basis B -319.33368 3.44 5 4.05 0 5.95 5 8.59 -9 -1.85 0.91 0.94 2.13

Basis B2d -319.35207 3.46 6 4.09 1 6.00 6 8.72 -8 -1.53 0.78 0.75 1.77

CR03 Basis B2d -319.34907 3.48 6 4.11 2 6.03 6 8.70 -8 -1.57 0.78 0.79 1.69

CR03 Basis B2d++ -319.35469 3.49 7 4.16 3 6.05 7 9.02 -5 -1.50 0.73 0.77 1.40

LDA (BH) Basis B -320.34347 3.19 -2 3.69 -9 5.53 -3 7.40 -22 -1.93 0.95 0.98 2.12

Basis B2d -320.35843 3.22 -2 3.72 -8 5.57 -2 7.49 -21 -1.43 0.74 0.69 1.93

LA Basis B 3.74 14 4.46 10 6.48 14 9.72 3 -2.26 1.07 1.22

Domains of the Electron Localization Function (ELF = 0.35)

LMTO-TB-ASA densities of states

The Cs2Pt molecule

CRYSTAL98 structure optimization

Pt HF LA(HF) LDA Cs2 HF LA(HF) LDA

6s 0.98 0.98 0.96 5s 0.97 0.98 0.97

6px,y 0.07 0.08 0.12 5px,y 0.96 0.96 0.94

6pz 0.02 0.02 0.04 5pz 0.99 1.00 0.99

5dz2 1.00 1.00 0.99 Cs1

5dxy,yz 1.00 1.00 0.99 5s 0.99 0.99 1.00

5dx2-y2,xy 0.99 0.99 0.98 5px,y 0.99 0.99 0.99

5pz 0.99 0.99 0.99