Exploratory synthesis in the area of polar intermetallics has yielded a rich variety of structures that offer clues into the transition in bonding between Zintl and Hume-Rothery phases. In this article, we present a bonding analysis of one such compound, Ca 10Pt 7Si 3, whose large Ca content offers the potential for negative formal oxidation states on the Pt. The structure can be divided into a sublattice of Ca cations and a Pt–Si polyanionic network built from Pt 7Si 3 trefoil units linked through Pt–Pt contacts of 3.14 ？. DFT-calibrated Hückel models reveal that the compound adheres well to a Zintl-like electron counting scheme, in which the Pt–Si and Pt–Pt contacts are equated with two-center two-electron bonds. The experimental electron count is in excess of that predicted by 2%, a discrepancy which is attributed to the electron transfer from the Ca to the Pt–Si network being incomplete. For the Pt–Pt contacts, the occupancy of the bonding orbitals is dependent on the participation of the surrounding Ca atoms in bridging interactions. This use of multi-center interactions isolobal to classical two-center two-electron bonds may illustrate one path by which the bonds delocalize as one moves from the Zintl phases toward the Hume-Rothery domain.
References
[1]
Sch？fer, H.; Eisenmann, B.; Müller, W. Zintl Phases: Transitions between Metallic and Ionic Bonding. Angew. Chem. Int. Ed. 1973, 12, 694–712, doi:10.1002/anie.197306941.
[2]
Kauzlarich, S.M. Chemistry, Structure, and Bonding of Zintl Phases and Ions; Wiley-VCH: New York, NY, USA, 1996.
[3]
Hume-Rothery, W.; Raynor, G.V. The Structure of Metals and Alloys; Institute of Metals: London, UK, 1962.
[4]
Belin, C.; Tillard-Charbonnel, M. Frameworks of clusters in alkali metal-gallium phases: Structure, bonding and properties. Prog. Solid State Chem. 1993, 22, 59–109, doi:10.1016/0079-6786(93)90001-8.
[5]
Xu, Z.; Guloy, A.M. Synthesis, Structure and Bonding of SrCa2In2Ge: A New Zintl Phase with an Unusual Inorganic π-System. J. Am. Chem. Soc. 1997, 119, 10541–10542, doi:10.1021/ja9721125.
[6]
F？ssler, T.F.; Kronseder, C. BaSn3: A Superconductor at the Border of Zintl Phases and Intermetallic Compounds. Real-Space Analysis of Band Structures. Angew. Chem. Int. Ed. 1997, 36, 2683–2686.
[7]
Xu, Z.; Guloy, A.M. Ca5In9Sn6: Interplay of Structural and Electronic Factors between Intermetallic and Zintl Phases. J. Am. Chem. Soc. 1998, 120, 7349–7350, doi:10.1021/ja980398n.
[8]
Goodey, J.; Mao, J.; Guloy, A.M. Ba2NiSi3: A One-Dimensional Solid-State Metallocene Analog. J. Am. Chem. Soc. 2000, 122, 10478–10479, doi:10.1021/ja0016102.
[9]
Amerioun, S.; H？ussermann, U. Structure and Bonding of Sr3In11: How Size and Electronic Effects Determine Structural Stability of Polar Intermetallic Compounds. Inorg. Chem. 2003, 42, 7782–7788, doi:10.1021/ic0301829.
[10]
Lee, C.S.; Miller, G.J. Ba14Zn5？xAl22+x: A new polar intermetallic compound with a novel 2D network. J. Solid State Chem. 2003, 170, 94–105, doi:10.1016/S0022-4596(02)00032-4.
[11]
Mao, J.G.; Goodey, J.; Guloy, A.M. Synthesis and Structure of Ca18Li5In25.07: A Novel Intergrowth of Li-Centered In12 Icosahedral Clusters and Electron-Precise Zintl Layers. Inorg. Chem. 2003, 43, 282–289.
[12]
Lupu, C.; Downie, C.; Guloy, A.M.; Albright, T.A.; Mao, J.G. Li17Ag3Sn6: A Polar Intermetallic π-System with Carbonate-like [AgSn3]11？ Anions and Trefoil Aromatic [Ag2Sn3]6？ Layers. J. Am. Chem. Soc. 2004, 126, 4386–4397.
[13]
Guttsche, K.; Rosin, A.; Wendorff, M.; R？hr, C. Ba5(Al/Ga)5(Sn/Pb): New compounds at the Zintl border. Z. Naturforsch. BJ. Chem. Sci. 2006, 61, 846–853.
[14]
Corbett, J.D. Exploratory Synthesis: The Fascinating and Diverse Chemistry of Polar Intermetallic Phases. Inorg. Chem. 2009, 49, 13–28, doi:10.1021/ic901305g.
[15]
You, T.S.; Tobash, P.H.; Bobev, S. Mixed Cations and Structural Complexity in (Eu1？xCax)4In3Ge4 and (Eu1？xCax)3In2Ge3—The First Two Members of the Homologous Series A2[n+m]In2n+mGe2[n+m] (n, m = 1, 2, ...∞; A = Ca, Sr, Ba, Eu, or Yb). Inorg. Chem. 2010, 49, 1773–1783, doi:10.1021/ic902144h.
[16]
Mills, A.M.; Lam, R.; Ferguson, M.J.; Deakin, L.; Mar, A. Chains, planes, and antimonides. Coord. Chem. Rev. 2002, 233–234, 207–222, doi:10.1016/S0010-8545(02)00097-8.
[17]
Slabon, A.; Cuervo-Reyes, E.; Kubata, C.; Mensing, C.; Nesper, R. Exploring the Borders of the Zintl-Klemm Concept: On the Isopunctual Phases Eu5+xMg18–xGe13(x = 0.1) and Eu8Mg16Ge12. Z. Anorg. Allg. Chem. 2012, 638, 2020–2028, doi:10.1002/zaac.201200058.
Karpov, A.; Nuss, J.; Wedig, U.; Jansen, M. Covalently Bonded [Pt]？ Chains in BaPt:Extension of the Zintl-Klemm Concept to Anionic Transition Metals? J. Am. Chem. Soc. 2004, 126, 14123–14128, doi:10.1021/ja0401186.
[21]
Karpov, A.; Wedig, U.; Dinnebier, R.E.; Jansen, M. Dibariumplatinide: (Ba2+)2Pt2？ 2e？ and Its Relation to the Alkaline-Earth-Metal Subnitrides. Angew. Chem. Int. Ed. 2005, 44, 770–773, doi:10.1002/anie.200462055.
[22]
Karpov, A.; Jansen, M. A New Family of Binary Layered Compounds of Platinum with Alkali Metals (A = K, Rb, Cs). Z. Anorg. Allg. Chem. 2006, 632, 84–90.
[23]
K？hler, J.; Chang, J.H.; Whangbo, M.H. Bonding and Oxidation State of a Transition Metal Atom Encapsulated in an Isolated Octahedral Cluster Cation of Main Group Elements: Synthesis, Crystal Structure, and Electronic Structure of Pt2In14Ga3O8F15 Containing Highly Positive 18-Electron Complex [PtIn6]10+ and Low-Valent In+ Ions. J. Am. Chem. Soc. 2005, 127, 2277–2284.
[24]
Whangbo, M.H.; Lee, C.; K？hler, J. Transition-Metal Anions in Solids and Their Implications on Bonding. Angew. Chem. Int. Ed. 2006, 45, 7465–7469, doi:10.1002/anie.200602712.
[25]
Chizhov, P.S.; Prots, Y.; Antipov, E.V.; Grin, Y. Ce2Pt8P: A Phosphido-platinide with Covalently Bonded Framework Polyanion. Z. Anorg. Allg. Chem. 2009, 635, 1863–1868, doi:10.1002/zaac.200900252.
[26]
Whangbo, M.H.; Lee, C.; K？hler, J. Metal Anions in Metal-Rich Compounds and Polar Intermetallics. Eur. J. Inorg. Chem. 2011, 2011, 3841–3847, doi:10.1002/ejic.201100378.
[27]
Hoffmann, R. Building Bridges Between Inorganic and Organic Chemistry (Nobel Lecture). Angew. Chem. Int. Ed. 1982, 21, 711–724.
[28]
Kresse, G.; Furthmüller, J. Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set. Phys. Rev. B 1996, 54, 11169–11186, doi:10.1103/PhysRevB.54.11169.
[29]
Kresse, G.; Furthmüller, J. Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis set. Comput. Mater. Sci. 1996, 6, 15–50, doi:10.1016/0927-0256(96)00008-0.
Kresse, G.; Joubert, D. From ultrasoft pseudopotentials to the projector augmented-wave method. Phys. Rev. B 1999, 59, 1758–1775, doi:10.1103/PhysRevB.59.1758.
[32]
Momma, K.; Izumi, F. VESTA 3 for three-dimensional visualization of crystal, volumetic and morphology data. J. Appl. Cryst. 2011, 44, 1272–1276, doi:10.1107/S0021889811038970.
[33]
Stacey, T.E.; Fredrickson, D.C. Perceiving molecular themes in the structures and bonding of intermetallic phases: The role of Hückel theory in an ab initio era. Dalton Trans. 2012, 41, 7801–7813, doi:10.1039/c2dt30298e.
[34]
Landrum, G.A.; Glassey, W.V. YAeHMOP: Yet Another extended Hückel Molecular Orbital Package. Available online: http://sourceforge.net/projects/yaehmop/ (accessed on 23 August 2013).
[35]
Fredrickson, R.T.; Fredrickson, D.C. Fragmentation of the Fluorite Type in Fe8Al17.4Si7.6: Structural Complexity in Intermetallics Dictated by the 18 Electron Rule. Inorg. Chem. 2012, 51, 10341–10349, doi:10.1021/ic3015089.
[36]
Fredrickson, R.T.; Fredrickson, D.C. The Modulated Structure of Co3Al4Si2: Incommensurability and Co–Co Interactions in Search of Filled Octadecets. Inorg. Chem. 2013, 52, 3178–3189, doi:10.1021/ic302650r.
[37]
Cotton, F.A. Chemical Applications of Group Theory; Wiley: New York, NY, USA, 1990.
[38]
K？hler, J.; Whangbo, M.H. Electronic Structure Study of the [Ag–Ag]4？, [Au–Au]4？, and [Hg–Hg]2？ Zintl Anions in the Intermetallic Compounds Yb3Ag2, Ca5Au4, and Ca3Hg2: Transition Metal Anions As p-Metal Elements. Chem. Mater. 2008, 20, 2751–2756, doi:10.1021/cm703590d.
