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Metal-Centered Deltahedral Zintl Ions: Synthesis of [Ni@Sn9]4– by Direct Extraction from Intermetallic Precursors and of the Vertex-Fused Dimer [{Ni@Sn8(μ-Ge)1/2}2]4–

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journal contribution
posted on 21.11.2011 by Miriam M. Gillett-Kunnath, Joseph I. Paik, Sara M. Jensen, Jacob D. Taylor, Slavi C. Sevov
Ni-centered deltahedral Sn9 clusters with a charge of 4–, i.e., [Ni@Sn9]4–, were extracted in ethylenediamine in high yield directly from intermetallic precursors with the nominal composition “K4Sn9Ni3”. The new endohedral clusters were crystallized and structurally characterized in K[K(18-crown-6)]3[Ni@Sn9]·3benzene (1a, triclinic, P1̅, a = 10.2754(5) Å, b = 19.5442(9) Å, and c = 20.5576(13) Å, α = 73.927(3)°, β = 79.838(4)°, and γ = 84.389(3)°, V = 3899.6(4) Å3, Z = 2) and K[K(2,2,2-crypt)]3[Ni@Sn9] (1b, triclinic, P1̅, a = 15.8028(8) Å, b = 16.21350(9) Å, and c = 20.1760(12) Å, α = 98.71040(10)°, β = 104.4690(10)°, and γ = 118.3890(10)°, V = 4181.5(4) Å3, Z = 2). The alternative method of a post-synthetic insertion of a Ni atom in empty Sn9 clusters by a reaction with Ni(cod)2 predominantly produces the more-oxidized clusters with a charge of 3–, i.e., the recently reported [Ni@Sn9]3–. Nonetheless, using substoichiometric amounts of 18-crown-6 as a cation sequestering agent, we also have been able to isolate the 4– clusters as a minor phase from such reactions. They were structurally characterized in K[K(en)][K(18-crown-6)]2[Ni@Sn9]·0.5en (2, monoclinic, P21/n, a = 10.4153(5) Å, b = 25.6788(11) Å, and c = 20.6630(9) Å, β = 102.530(2)°, V = 5394.7(4) Å3, Z = 2). The ability of the Ni-centered clusters to exist with both 3– and 4– charges parallels the same ability of the empty clusters and is very promising for similarly rich chemistry involving electron transfer and flexible “oxidation states”. We also report the synthesis and characterization of the endohedral heteroatomic dimer [{Ni@Sn8(μ-Ge)1/2}2]4– composed of two [Ni@(Sn8Ge)]-clusters fused at the Ge-vertex. The dimer was synthesized by reacting an ethylenediamine solution of a ternary precursor with the nominal composition “K4Ge4.5Sn4.5”, which is known to produce heteroatomic Ge9–xSnx clusters, with Ni(cod)2. It is isostructural with the reported [{Ni@Sn8(μ-Sn)1/2}2]4– and is structurally characterized in [K-(2,2,2-crypt)]4[{Ni@Sn8(μ-Ge)1/2}2]·2en (3, monoclinic, C2/c, a = 30.636(2) Å, b = 16.5548(12) Å, and c = 28.872(2) Å, β = 121.2140(10)°, V = 12523.5(15) Å3, Z = 4).