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Platinides Electronic Structure and Bonding Ulrich Wedig, Gernot Stollhoff, Andrey Karpov, Jrgen Nuss, and Martin Jansen Max-Planck-Institut fr Festkrperforschung Heisenbergstrae 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. Pyykk, 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 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 Cs 2 Pt is an ionic insulator crystallizing in the Ni 2 In structure. From structure- chemical considerations, Cs 2 Pt can be affiliated to the alkali-metal mono- chalcogenides [3]. BaPt can be formulated, in terms of the Zintl-Klemm concept, as (Ba 2+ )( 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]. Ba 3 Pt 2, cystallizing in the Er 3 Ni 2 structure, is isotypic to Ca 3 Pd 2, Ca 3 Pt 2 and Sr 3 Pt 2. It is remarkable that the structure type of the platinum compounds doesnt change when varying the size of the cation [5]. Ba 2 Pt [6] is the first intermetallic phase adopting the CdCl 2 structure. The compound which can be formulated as (Ba 2+ ) 2 (Pt 2- ). 2e - shows surprising similarities to the nitride Ba 2 N. Cs 2 Pt E(a,c) CRYSTAL98 DFT GC (B-LYP) LA - charge analysis The Cs 2 Pt molecule, calculated with GAUSSIAN98: Method:CCSD(T) Basis set:Pt [6s5p4d2f]; Cs [5s4p2d1f] Pseudopot.:quasirelativistic; Pt 18 ve; Cs 9 ve R Cs-Pt :2.96 Cs-Pt-Cs :133 PtCs Mulliken chargeHF:-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. Ba 3 Pt 2 Ba 2 Pt 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, n e =10.6; red: Pt-Pt -bond, n e =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 - / Bohr 3 covalent region (left) = 0.05 e - / Bohr 3 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. Ba 3 Pt 2 -1.2 Ca 3 Pt 2 -1.5 Ca 3 Pd 2 -1.4 LMTO-TB-ASA LDA total densities of states nMT:Modified radii of the muffin tin spheres Total and partial densities of states Ba 2 Pt Ba 2 Pt (mMT) Ba 2 N ELF-domains = 0.34 Ba 2 Pt Ba 2 Pt (mMT) Ba 2 N Isosurfaces of the electron density computed from the bands at the Fermi level Ba 2 Pt: = 0.003 e - / Bohr 3 Ba 2 N: = 0.002 e - / Bohr 3 Domains of the Electron Localization Function (ELF = 0.35) LMTO-TB-ASA densities of states The Cs2Pt molecule CRYSTAL98 structure optimization