Oxidation of Zintl phases

Jürgen Nuss, Sabine Prill-Diemer, Fei Wang, Ulrich Wedig

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Motivation

Using NaTl as an example, Zintl developed the concept that was later named after him, and which was subsequently generalized by Klemm. The Zintl-Klemm concept belongs to one of the most successful concepts in solid state chemistry. Assuming that all valence electrons of a donor (metal) were transmitted to an acceptor (nonmetal or semimetal), one can understand and predict essential elements of the topologies of the resulting anionic partial structures, in boundary of metallic and ionic bonding. The most frequently used tool to control the connectivity of the anionic partial structure is the variation of the ratio metal / nonmetal in the compound, and therefore the direct tuning of the valence electron concentration at the anions. Another possibility is the oxidation or reduction of an already existing Zintl phase (Barium phosphides), or the use of oxygen as a third component to generate a further degree of freedom (Thallides).

Ba₃P₃I₂ and Ba₅P₅I₃: stepwise oxidation of barium phosphide with iodine

The Zintl phases Ba₃P₂ with isolated P^3– ions or Ba₄P₃ which contains P^3– ions and P₂^4– dumbbells, react with iodine in a direct way to Ba₃P₃I₂ and BaI₂ (eq. (1) and (2)). A characteristic detail of the new compound are P₃ chains; therefore an oxidation of the anionic partial structure results. The consequence is a P—P bonding formation and an enlargement of the phosphorus chains. The reaction was carried out at 1050 K, which is obviously below the melting points of the binary phosphides. Thus, the planned oxidation of a Zintl anion in the solid phase could be successfully realized.
     To avoid the formation of BaI₂ as a byproduct, a mixture with the composition 'BaP', containing Ba₃P₂, Ba₄P₃ and Ba₃P₄ can be used, too (eq. (3)). The use of P₂I₄ as an oxidation reagent is also possible (eq. (4)).

(1)   3 Ba₃P₂ + 5 I₂ ---> 2 Ba₃P₃I₂ + 3 BaI₂

(2)   Ba₄P₃ + 2 I₂ ---> Ba₃P₃I₂ + BaI₂

(3)   3 BaP + I₂ ---> Ba₃P₃I₂

(4)   2 Ba₃P₂ + P₂I₄ ---> 2 Ba₃P₃I₂

Reducing the amount of iodine has a direct influence on the anionic partial structure. Therefore one obtains, when using the composition Ba₃P ₃I_1.8 the new compound Ba₅P₅I₃, which contains additional P₄ chains besides P₃.
     The new compounds Ba₃P₃I₂ and Ba₅P₅I₃ are sensitive to air and moisture. They crystallize in new structure types: Ba₃P₃I₂ (oP32; Pnma; a = 1719.5(5) pm; b = 462.4(2) pm; c = 1427.2(4) pm; Z = 4, Ba₅P₅I₃ (mC52; C2/m; a = 4266.4(13) pm; b = 456.3(2) pm; c = 943.1(3) pm; β = 92.20(3)°; Z = 4. Both can be described as double salts of hypothetic Zintl phases ('Ba₂P₃' or 'Ba₇P₁₀') and a halide (BaI₂). Characteristic structural features are  P₃ and P₄ chains, corresponding to Ba₃[P₃]I₂ and Ba₁₀[P₃]₂[P₄]I₆, respectively.

This example of the oxidation of barium phosphide with iodine shows, that this concept works with solid Zintl phases, too. The electron configuration of, e. g., P^2– or P^3– corresponds to that of a halogen or a halide, respectively. During the oxidation one moves to the left in the periodic table, and the connectivity increases.

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Alkali metal thallide oxides

Cs8Tl8O Cs8Tl8O crystallizes in a novel structure type. The oxygen atoms are surrounded by an octahedral arrangement of six cesium atoms. Two further Cs atoms are located above and below each oxygen atom. The resemblance of the Cs—O separation in Cs8Tl8O (290 pm) to those in Cs2O (287 pm) is indicative for a full ionization of the Cs atoms with a charge transfer to oxygen atoms and formation of cationic [OCs6+2]6+ groups. The electrons released are accommodated by the, previously unknown, isolated [Tl8]6– oligoanion. Topologically, the {Tl8} cluster can be regarded as being generated by condensation of an octahedron with two tetrahedra (bicapped octahedron). The clusters are arranged analogous to a cubic-closed packing, with the octahedral holes completely occupied by {OCs6+2} groups. The structure can therefore be understood as an NaCl derivative, with one of the threefold axes of the originally cubic system being elongated.

 

A10Tl6O2 (A = K, Rb) The new alkali metal thallide oxides, A10Tl6O2 (A = K, Rb), crystallize in a unique structure consisting of hypoelectronic [Tl6]6– clusters in the shape of compressed octahedra, together with oxygen-centred alkali metal octahedra that have been identified as constitutive of alkali metal sub-oxides.

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J. Nuss, M. Jansen: On the Rare Earth Metal Bismuthide Oxides RE₂BiO₂ (RE = Nd, Tb, Dy, Ho)
Z. Anorg. Allg. Chem. 638 (2012) 611-613. doi:10.1002/zaac.201100529

V. Saltykov, J. Nuss, U. Wedig, D. L. V. K. Prasad, M. Jansen: First isolated “hypoelectronic” [In₆]^6– cluster in insulating Cs₂₂In₆(SiO₄)₄
Z. Anorg. Allg. Chem. 637 (2011) 834-839. doi:10.1002/zaac.201100074

V. Saltykov, J. Nuss, U. Wedig, M. Jansen: Regular [Tl₆]^6– Cluster in Cs₄Tl₂O, Exhibiting Close Shell Configuration and Energetic Stabilization due to Relativistic Spin-Orbit Coupling
Z. Anorg. Allg. Chem. 637 (2011) 357-361. doi:10.1002/zaac.201000405

V. Saltykov, J. Nuss, M. Jansen: Cs₁₀Tl₆SiO₄, Cs₁₀Tl₆GeO₄ and Cs₁₀Tl₆SnO₃ — First Oxotetrelate Thallides Containing "Hypoelectronic" [Tl₆]^6– Clusters
Z. Anorg. Allg. Chem. 637 (2011) 1163-1168. doi:10.1002/zaac.201000358

V. Saltykov, J. Nuss, U. Wedig, M. Jansen: Impact of Spin-Orbit Coupling on the Structure of Thallium Clusters
Z. Anorg. Allg. Chem. 636 (2010) 2040. doi:10.1002/zaac.201008005

U. Wedig, V. Saltykov, J. Nuss, M. Jansen: Homoatomic stella quadrangula [Tl₈]^6– in Cs₁₈Tl₈O₆, Interplay of Spin-Orbit Coupling and Jahn-Teller Distortion
J. Am. Chem. Soc. 132 (2010) 12458-12463. doi:10.1021/ja1051022

J. Nuss, M. Jansen: BaAuP and BaAuAs, Synthesis via Disproportionation of Gold upon Interaction with Pnictides as Bases
Z. Anorg. Allg. Chem. 635 (2009) 1514-1516. doi:10.1002/zaac.200900070

J. Nuss, M. Jansen: Crystal structure of terbium antimonide oxide, Tb₉Sb₅O₅
Z. Kristallogr. NCS 224 (2009) 11-12. doi:10.1524/ncrs.2009.0007

J. Nuss, M. Jansen: Syntheses, structures and properties of the pnictide oxides R₂PnO₂ (R = Ce, Pr; Pn = Sb, Bi)
J. Alloys. Comp. 480 (2009) 57-59. doi:10.1016/j.jallcom.2008.09.181

J. Nuss, M. Jansen: Reticular merohedral twinning within the La₉Sb₅O₅ structure family: structure of Pr₉Sb₅O₅, Sm₉Sb₅O₅ and Dy₉Sb₅O₅
Acta Crystallogr., Sect. B: Struct. Sci. 63 (2007) 843-849. doi:10.1107/S0108768107051282

A. Karpov, M. Jansen: A₁₀Tl₆O₂ (A = K, Rb) cluster compounds combining structural features of thallium cluster anions and of alkali metal sub-oxides.
Chem. Commun.(2006) 1706-1708. doi: 10.1039/b601802e

A. Karpov, M. Jansen: [Tl₈]^6- in Cs₈Tl₈O: A Naked Eight-Vertex closo-Deltaeder as a Cluster Anion.
Angew. Chem. 117 (2005) 7813-6. doi: 10.1002/ange.200502283; Angew. Chem. Int. Ed. Engl. 44 (2005) 7639-43. doi: 10.1002/anie.200502283

J. Nuss, M. Jansen: Ba₃P₃I₂ and Ba₅P₅I₃: Stepwise Oxidation of Barium Phosphide with Iodine.
Z. Anorg. Allg. Chem. 629 (2003) 387-393. doi:10.1002/zaac.200390064