Deltahedral Zintl Ions Research Articles

Doped deltahedral organo-Zintl superalkali cations

The doped deltahedral Zintl clusters are known for decades. Here, we report a functionalized doped organo-Zintl clusters [Ge7P2R3](R = CH3, C2H5 & C3H3) derived from the doped [Ge7P2]2− Zintl ion by replacing germanium atoms in deltahedral Ge94− cluster with Phosphorus (P). Using first principle calculation, we show that, it is also possible to design superalkali compounds by using doped deltahedral Zintl ions as a core with suitable organic aliphatic and cyclic ligands. The calculated vertical electron affinities (VEAs) of designed Zintl complexes are lower than alkali metals ionization energy (IE = 3.89–5.34 eV).

On the Affinity between Fullerenes and Deltahedral Zintl Ions: A UV/Vis Spectroscopic Investigation

The close relationship of C60 and deltahedral tetrel element cluster anions has been pointed out before. We report herein on UV/Vis spectra of the Zintl anions and compounds [Ge9]2–, [(CH2=CH)2Ge9]2–, [{(Me3Si)3Si}3Ge9]–, {(Me3Si)3Si}3Ge9CH2CH3, {(Me3Si)3Si}3Ge9(CH2)2CH3, {(Me3Si)3Si}3Ge9(CH2)3CH=CH2, and [{(Me3Si)3Si}3Ge9CH2CH3]Pt(PPh3). The spectra are compared to those of the C60 fullerene, which were recorded under the same conditions. The UV/Vis spectrum of pristine [Ge9]2– resembles that of C60 and at higher concentration hint at the known trimeric [(Ge9)3]6–. The influence of ligand substitution at the Ge9 cluster‐core is highlighted. For this, the synthesis of the specifically functionalized deltahedral Ge9 clusters {(Me3Si)3Si}3Ge9(CH2)2CH3, {(Me3Si)3Si}3Ge9(CH2)2CH=CH2, and {(Me3Si)3Si}3Ge9(CH2)3C6H5 are reported for the first time and is achieved by the reaction of K[{(Me3Si)3Si}3Ge9] with the respective alkyl halides in acetonitrile. The newly synthesized products were characterized by NMR spectroscopy.

Trimetallic deltahedral Zintl ions [Sn9−m−nGemBin](4−n)−for n = 1–4 and m = 0–(9 − n): a theoretical survey with prediction and rationalization of the possible structures

The recent discovery of trimetallic deltahedral Zintl ions based on Sn, Ge, and Bi revealed the possibility to obtain such clusters with a variety of different Sn/Ge/Bi ratios. Although only the dimer [(BiSn(6)Ge(2))-(Ge(2)Sn(6)Bi)](4-) was structurally characterized, a number of other nine-atom clusters with various stoichiometries were detected by electrospray mass spectrometry. The lack of structural data for the latter persuaded us to use relativistic density functional calculations in order to determine and rationalize theoretically the most stable structure conformation of each cluster and the positional preferences for the different atoms in the series [Sn(9-m-n)Ge(m)Bi(n)]((4-n)-) where n = 1-4 and m = 0-(9 - n). The analysis revealed strong dependence of the cluster geometry on the cluster stoichiometry and revealed sites with significantly different charge distribution. In addition, we introduce a parameter ϕ based on certain angles in order to rationalize the obtained structures as monocapped square antiprisms (C(4v)), tricapped trigonal prisms (D(3h)), or intermediates (C(2v)).

Developing organo-Zintl deltahedral clusters as ligands for coordination to transition-metals via their organic tethers

Deltahedral Zintl ions Ge94- are disubstituted with organic fragments that have various functional groups. Some of the latter are appropriate for coordination to transition-metals to eventually form coordination compounds where the organo-Zintl species act as ligands. Examples of [Ge9R2]2- include R = –CHCH-Im(Me), –CHCH–C6H4–OMe, –CHCH-Fc, –CHCH–(CH2)4–CCH, –CHCH–C6H4–CCH, CHCH–C6H4–NH2, CHCH-Py, –CHCH–(CH2)3–CN, –CHCHCH(OEt)2, –C(CH3)2CCH. Furthermore, the reported coexistence of [Fe(en)3]2+ and [Ge9-(CHCH-Fc)2]2- in the structure of [Fe(en)3][Ge9-(CHCH-Fc)2]•3.5en shows that some transition metals in 2 + oxidation state may not oxidize the disubstituted clusters and could potentially coordinate to them.

Synthesis of Nine-atom Deltahedral Zintl Ions of Germanium and their Functionalization with Organic Groups

Although the first studies of Zintl ions date between the late 1890's and early 1930's they were not structurally characterized until many years later.1,2 Their redox chemistry is even younger, just about ten years old, but despite this short history these deltahedral clusters ions E9n- (E = Si, Ge, Sn, Pb; n = 2, 3, 4) have already shown interesting and diverse reactivity and have been at the forefront of rapidly developing and exciting new chemistry.3-6 Notable milestones are the oxidative coupling of Ge94- clusters to oligomers and infinite chains,7-19 their metallation,14-16,20-25 capping by transition-metal organometallic fragments,26-34 insertion of a transition-metal atom at the center of the cluster which is sometimes combined with capping and oligomerization,35-47 addition of main-group organometallic fragments as exo-bonded substituents,48-50 and functionalization with various organic residues by reactions with organic halides and alkynes.51-58 This latter development of attaching organic fragments directly to the clusters has opened up a new field, namely organo-Zintl chemistry, that is potentially fertile for further synthetic explorations, and it is the step-by-step procedure for the synthesis of germanium-divinyl clusters described herein. The initial steps outline the synthesis of an intermetallic precursor of K4Ge9 from which the Ge94- clusters are extracted later in solution. This involves fused-silica glass blowing, arc-welding of niobium containers, and handling of highly air-sensitive materials in a glove box. The air-sensitive K4Ge9 is then dissolved in ethylenediamine in the box and then alkenylated by a reaction with Me3SiC≡CSiMe3. The reaction is followed by electrospray mass spectrometry while the resulting solution is used for obtaining single crystals containing the functionalized clusters [H2C=CH-Ge9-CH=CH2]2-. For this purpose the solution is centrifuged, filtered, and carefully layered with a toluene solution of 18-crown-6. Left undisturbed for a few days, the so-layered solutions produced orange crystalline blocks of [K(18-crown-6)]2[Ge9(HCCH2)2]•en which were characterized by single-crystal X-ray diffraction. The process highlights standard reaction techniques, work-up, and analysis towards functionalized deltahedral Zintl clusters. It is hoped that it will help towards further development and understanding of these compounds in the community at large.

Synthesis of nine-atom deltahedral Zintl ions of germanium and their functionalization with organic groups.

Although the first studies of Zintl ions date between the late 1890's and early 1930's they were not structurally characterized until many years later. Their redox chemistry is even younger, just about ten years old, but despite this short history these deltahedral clusters ions E9(n-) (E = Si, Ge, Sn, Pb; n = 2, 3, 4) have already shown interesting and diverse reactivity and have been at the forefront of rapidly developing and exciting new chemistry. Notable milestones are the oxidative coupling of Ge9(4-) clusters to oligomers and infinite chains, their metallation, capping by transition-metal organometallic fragments, insertion of a transition-metal atom at the center of the cluster which is sometimes combined with capping and oligomerization, addition of main-group organometallic fragments as exo-bonded substituents, and functionalization with various organic residues by reactions with organic halides and alkynes. This latter development of attaching organic fragments directly to the clusters has opened up a new field, namely organo-Zintl chemistry, that is potentially fertile for further synthetic explorations, and it is the step-by-step procedure for the synthesis of germanium-divinyl clusters described herein. The initial steps outline the synthesis of an intermetallic precursor of K4Ge9 from which the Ge9(4-) clusters are extracted later in solution. This involves fused-silica glass blowing, arc-welding of niobium containers, and handling of highly air-sensitive materials in a glove box. The air-sensitive K4Ge9 is then dissolved in ethylenediamine in the box and then alkenylated by a reaction with Me3SiC≡CSiMe3. The reaction is followed by electrospray mass spectrometry while the resulting solution is used for obtaining single crystals containing the functionalized clusters [H2C=CH-Ge9-CH=CH2](2-). For this purpose the solution is centrifuged, filtered, and carefully layered with a toluene solution of 18-crown-6. Left undisturbed for a few days, the so-layered solutions produced orange crystalline blocks of [K(18-crown-6)]2[Ge9(HCCH2))2]•en which were characterized by single-crystal X-ray diffraction. The process highlights standard reaction techniques, work-up, and analysis towards functionalized deltahedral Zintl clusters. It is hoped that it will help towards further development and understanding of these compounds in the community at large.

Tri-metallic deltahedral Zintl ions: experimental and theoretical studies of the novel dimer [(Sn6Ge2Bi)2]4−

We report the synthesis, characterization, and computational rationalization of the first trimetallic deltahedral Zintl ions. The novel nine-atom clusters were structurally characterized as dimers of [(Sn(6)Ge(2)Bi)(2)](4-) with Ge-Ge intercluster bonds. They are synthesized either by reacting bimetallic clusters (Sn(9-x)Ge(x))(4-) with BiPh(3) or by direct extraction from precursors with nominal composition "K(4)Ge(4)Sn(4)Bi".

ChemInform Abstract: Addition of a Thallium Vertex to Empty and Centered Nine‐Atom Deltahedral Zintl Ions of Germanium and Tin.

AbstractThe empty and Ni‐centered Ge9 and Sn9 clusters react with TlCp and add a tenth Tl‐vertex to form bicapped square antiprismatic closo‐clusters [M9Tl]3‐ (M: Ge, Sn) and [Ni@M9Tl]3‐.

“n-Doping” of Deltahedral Zintl Ions

We report a simple and efficient method for replacing germanium atoms in deltahedral Ge(9)(4-) clusters with Sb or Bi. While reactions of Ge(9)(4-) with EPh(3) (E = Sb, Bi) at room temperature are known to produce mono- and disubstituted clusters [Ph(2)E-Ge(9)-Ge(9)-EPh(2)](4-) and [Ph(2)E-Ge(9)-EPh(2)](2-), respectively, at elevated temperatures or with sonication they result in exchange of Ge cluster atoms with Sb or Bi. Structurally characterized from such reactions are the novel "n-doped" deltahedral Zintl ions [(EGe(8))-(Ge(8)E)](4-), (Sb(2)Ge(7))(2-), and [(SbGe(8))-SbPh(2)](2-).

Addition of a Thallium Vertex to Empty and Centered Nine-Atom Deltahedral Zintl Ions of Germanium and Tin

Nickel atoms were inserted into nine-atom deltahedral Zintl ions of E(9)(4-) (E = Ge, Sn) via reactions with Ni(cod)(2) (cod = cyclooctadiene), and [Ni@Sn(9)](3-) was structurally characterized. Both the empty and the Ni-centered clusters react with TlCp (Cp = cyclopentadienyl anion) and add a thallium vertex to form the deltahedral ten-atom closo-species [E(9)Tl](3-) and [Ni@E(9)Tl](3-), respectively. The structures of [Ge(9)Tl](3-) and [Ni@Sn(9)Tl](3-) showed that, as expected, the geometry of the ten-atom clusters is that of a bicapped square antiprism where the Tl-atom occupies one of the two capping vertices. This illustrates that centering a nine-atom cluster with a nickel atom does not change its reactivity toward TlCp. All compounds were characterized by electrospray mass spectrometry.

Structural, Vibrational, and Optical Characterization of Anodically Electroplated Germanium Thin Films

Germanium thin films were anodically electrodeposited from ethylenediamine solutions of which contain the well known deltahedral Zintl ions. The anodes were -doped Si(100) wafers or ITO-covered glass slides. The films were studied for their optical and structural properties by Raman spectroscopy, TEM, and luminescence measurements. The Raman spectra of the films show peaks shifted to lower frequencies compared to the same peaks in bulk germanium and indicate nanocrystalline structure for the films. This is further corroborated by the TEM observations. Laser-induced crystallization at selected areas of the films results in significant growth of the nanocrystals. The films exhibit photoluminescence in the visible light range. This has been attributed to a combination of nanocrystallinity and surface defects. Overall, the optical and structural properties of the anodically electrodeposited thin germanium films can be effectively adjusted by tuning the electrodeposition parameters.

Heteroatomic Deltahedral Zintl Ions of Group 14 and their Alkenylation

Reported is the synthesis of Ge(9-x)Sn(x) heteroatomic deltahedral Zintl ions and their alkenylation by reactions with alkynes. The nine-atom clusters are made either by extraction from mixed Ge/Sn precursors with nominal composition K(4)Ge(9-x)Sn(x) or by dissolution of mixtures of the corresponding binary precursors K(4)Ge(9) and K(4)Sn(9) in solvents with high dielectric constants such as DMF, DMSO, and acetonitrile. Reactions of the heteroatomic clusters with alkynes such as Me(3)SiC[triple bond]CSiMe(3), HC[triple bond]CCpr (Cpr = cyclopropyl), and HC[triple bond]CPh in ethylenediamine resulted in the following structurally characterized compounds with alkenylated heteroatomic clusters: [K-(2,2,2-crypt)](3)[GeSn(8)-CH=CH(2)].en.tol (1), triclinic, P1, a = 13.9220(3) A, b = 14.9788(3) A, and c = 21.5892(5) A, alpha = 94.2580(10) degrees , beta = 98.5210(10) degrees , and gamma = 98.4890(10) degrees , V = 4382.31(16) A(3), Z = 2; [K-(2,2,2-crypt)](4)[Ge(2)Sn(7)(CH=CH(2))(2)](2).en (2), monoclinic, P2(1)/c, a = 48.1883(15) A, b = 12.1551(4) A, and c = 21.4824(7) A, beta = 90.052(2) degrees , V = 12583.0(7) A(3), Z = 4; [K-(2,2,2-crypt)](3)[GeSn(8)-CH=CHCpr].en (3), monoclinic, P2(1)/c, a = 17.9132(9) A, b = 22.7967(11) A, and c = 21.6922(12) A, beta = 98.409(2) degrees , V = 8763.0(8) A(3), Z = 4; [K-(2,2,2-crypt)](3)[Ge(2)Sn(7)-CH=CHPh].2en (4), monoclinic, P2(1)/n, a = 13.2583(5) A, b = 47.0565(17) A, and c = 15.9978(6) A, beta = 111.536(2) degrees , V = 9284.1(6) A(3), Z = 4. The potassium countercations of the divinyl-substituted cluster in 2 were exchanged for tetrapropylammonium cations, and the resulting compound was also crystallized and structurally characterized: [Pr(4)N](4)[Ge(2)Sn(7)(CH=CH(2))(2)](2) (5), triclinic, P1, a = 11.6757(8) A, b = 18.8150(16) A, and c = 21.0608(17) A, alpha = 112.327(3) degrees , beta = 91.550(3) degrees , and gamma = 91.892(3) degrees , V = 4273.5(6) A(3), Z = 2. All clusters were also characterized in solution by electrospray mass spectrometry.

Functionalization of Nine-Atom Deltahedral Zintl Ions with Organic Substituents: Detailed Studies of the Reactions

Presented are the results of a systematic investigation of the reactions of nine-atom deltahedral clusters of germanium (Zintl ions, Ge(9)(n-)) with alkynes and alkyl halides that result in alkenylation and alkylation of the clusters, respectively. The reaction pathways have been probed in depth using various, appropriately substituted alkynes and organic halides, including some typical mechanistic probes and radical clocks. The regioselectivity and stereoselectivity of the reaction with alkynes was examined by systematically varying the steric and electronic nature of the substituents. The studies showed that the Zintl clusters act as strong, anionic nucleophiles toward the alkynes and primary and secondary alkyl halides but, most likely, as electron donors in reactions with tertiary alkyl halides and halogenated olefins. The pentenyl and methylcyclopropyl functionalized clusters, [Ge(9)(C(5)H(9))](3-) and [Ge(9)(CH(2)CH(CH(2))(2))](2-), respectively, were crystallographically characterized in compounds with [K-crypt](+) countercations. All compounds were also analyzed by NMR and electrospray mass spectrometry.

Chemistry of Deltahedral Zintl Ions

This review focuses on the reactivity of nine-atom deltahedral clusters of group 14, also known as deltahedral Zintl ions, toward various main-group and transition-metal compounds. The redox chemistry of these species and their ability to form oligomers, polymers, and functionalized clusters are discussed, and the cluster geometries, their bonding, and electronic structures are described.

Organozinc Derivatives of Deltahedral Zintl Ions: Synthesis and Characterization of closo-[E9Zn(C6H5)]3- (E = Si, Ge, Sn, Pb)

Reactions of group 14 deltahedral Zintl ions E94- (E = Si, Ge, Sn, Pb) with diphenylzinc yielded the organically functionalized heteroatomic closo-clusters [E9Zn-Ph]3- (E = Si (1), Ge (2), Sn (3), Pb (4)). All four clusters exhibit the same bicapped square antiprismatic geometry in which one of the capping positions is occupied by the ZnPh organometallic fragment. Three filled molecular orbitals of the cluster overlap with three empty orbitals at the ZnPh fragment, and the cluster acts as a six-electron ligand analogous to cyclopentadienyl and benzene ligands. The species were characterized by single-crystal X-ray diffraction in [K(2,2,2-crypt)]3[Si9Zn(C6H5)]·2py, [K(2,2,2-crypt)]3[Ge9Zn(C6H5)]·2en·tol, [K(2,2,2-crypt)]3[Sn9Zn(C6H5)]·tol, and [K(2,2,2-crypt)]6[Pb9Zn(C6H5)]2·2en·tol. The presence of these clusters in solution was confirmed by electrospray mass spectrometry and 13C{1H} NMR experiments.

Rationally functionalized deltahedral zintl ions: synthesis and characterization of [Ge9-ER3]3-, [R3E-Ge9-ER3]2-, and [R3E-Ge9-Ge9-ER3]4- (E=Ge, Sn; R=Me, Ph).

Six new derivatized deltahedral Zintl ions have been synthesized by reactions between the known Zintl ions Ge(9) (n-) with the halides R(3)EX and/or the corresponding anions R(3)E(-) for E=Ge or Sn. This rational approach is based on our previous discovery that these derivatization reactions are based on nucleophilic addition to the clusters. All species were structurally characterized as their salts with potassium countercations sequestered in 2,2,2-crypt or [18]crown-6 ether. The tin-containing anions were characterized also in solutions by (119)Sn NMR spectroscopy. The reaction types for such substitutions and the structures of the new anions are discussed.

Naked deltahedral silicon clusters in solution: synthesis and characterization of Si9(3-) and Si5(2-).

Elusive for over 100 years, deltahedral Zintl ions of silicon are finally synthesized and structurally characterized. The two clusters reported here, Si93- and Si52-, are analogous to known clusters of the heavier members of this group: Ge, Sn, and Pb.

Derivatization of deltahedral Zintl ions by nucleophilic addition: [Ph-Ge9-SbPh2]2- and [Ph2Sb-Ge9-Ge9-SbPh2]4-.

The type of the reactions of addition of exo-bonded groups to deltahedral Zintl ions such as Ge9(n-) has been established as addition of anionic nucleophiles. Various nucleophiles such as Ph2Bi-, Ph2Sb-, Ph- interact with the relatively low-lying LUMO of Ge9(2-) and/or the half filled HOMO of Ge9(3-) and bond to the clusters. The title anions, characterized in their (K-crypt) salts where crypt = 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo-[8.8.8]-hexacosane, and the previously characterized [Ph2Sb-Ge9-SbPh2](2-) are made by a reaction of K4Ge9 with SbPh3 in ethylenediamine. [Ph-Ge9-SbPh2](2-) is the first ogranically functionalized deltahedral Zintl ion, i.e., a deltahedral ion with a direct carbon-cluster covalent bond, that can exists without the substituents as well. The Ge(9) clusters resemble tricapped trigonal prisms with one elongated edge (one of the three edges parallel to the pseudo 3-fold axis). The two substituents are always bonded to the vertexes of such an elongated edge. The same is true for the intercluster bond in [Ph2Sb-Ge9-Ge9-SbPh2)](4-).

Heteroatomic deltahedral clusters of main-group elements: synthesis and structure of the Zintl ions [In4Bi5]3-, [InBi3]2-, and [GaBi3]2-.

Reported are the first heteroatomic deltahedral Zintl ions made of elements differing by more than one group, indium or gallium and bismuth. Nine-atom clusters [In4Bi5]3- are characterized in two different compounds, (Na-crypt)3[In4Bi5] (4, P2(1)/n, a = 23.572(6) A, b = 15.042(4) A, c = 24.071(4) A, beta = 106.00(3) degrees, Z = 4) and (K-crypt)6[In4Bi5][In4Bi5].1.5en.0.5tol (5, P2(1)/c, a = 28.532(2) A, b = 23.707(2) A, c = 28.021(2) A, beta = 93.274(4) degrees, Z = 4). Tetrahedra of [InBi3]2- or [GaBi3]2- are found in (K-crypt)2[InBi3].en (1, P2(1), a = 12.347(4) A, b = 20.884(4) A, c = 12.619(7) A, beta = 119.02(4) degrees, Z = 2) and in the isostructural (Rb-crypt)2[InBi3].en (2, a = 12.403(8) A, b = 20.99(1) A, c = 12.617(9) A, beta = 118.83(4) degrees) and (K-crypt)2[GaBi3].en (3, a = 12.324(5) A, b = 20.890(8) A, c = 12.629(5) A, beta = 118.91(3) degrees). All compounds are crystallized from ethylenediamine/crypt solutions of precursors with nominal composition "A5E2Bi4" where A = Na, K, or Rb and E = Ga or In. The cluster in 4 is a well-ordered monocapped square antiprism with the four indium atoms occupying the five-bonded positions. Compound 5 contains two independent [In4Bi5]3- clusters; one is the same as the cluster in 4, while the other is a tricapped trigonal prism with two elongated prismatic edges. All compounds are EPR-silent and therefore diamagnetic.