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".     

Gas phase analogs of stable sodium-tin Zintl ions: anion photoelectron spectroscopy and electronic structure

Mass spectrometry and photoelectron spectroscopy together with first principles theoretical calculations have been used to study the electronic and geometric properties of the following sodium-tin, cluster anion/neutral cluster combinations, (Na(n)Sn(4))(-)/(Na(n)Sn(4)), n = 0-4 and (NaSn(m))(-)/(NaSn(m)), m = 4-7. These synergistic studies found that specific Zintl anions, which are known to occur in condensed Zintl phases, also exist as stable moieties within free clusters. In particular, the cluster anion, (Na(3)Sn(4))(-) is very stable and is characterized as (Na(+))(3)(Sn(4))(-4); its moiety, (Sn(4))(-4) is a classic example of a Zintl anion. In addition, the cluster anion, (NaSn(5))(-) was the most abundant species to be observed in our mass spectrum, and it is characterized as Na(+)(Sn(5))(2-). Its moiety, (Sn(5))(2-) is also known to be present as a Zintl anion in condensed phases.     

Bismuth-doped tin clusters: experimental and theoretical studies of neutral Zintl analogues

The electron count of gas-phase clusters is increased gradually by element substitution in order to mimic the total number of electrons of known stable closo-clusters. A combination of elements from the fourth and fifth group of the periodic table such as Sn and Bi is well-suited for this approach. Hence, these small Sn-Bi clusters are investigated by employing the electric field deflection method. For clusters in the series Sn(M-N)Bi(N) (M = 5-13, N = 1-2), the beam profiles obtained in cryogenic experiments are dominated by beam broadening, indicating the presence of a permanent electric dipole moment that is sensitive to the (rigid) cluster structure. An intensive search for the global minimum structure employing a density functional theory/genetic algorithm method is performed. Dielectric properties for the identified low-energy isomers are computed. The structural and dielectric properties are used in beam profile simulations in order to discuss the experimental data. Comparison of theoretical and experimental results enables identification of the growing pattern of these small bimetallic clusters. For multiply doped clusters, it is concluded that the dopant atoms do not form direct Bi-Bi bonds, but more interestingly, a rearrangement of the cluster skeleton becomes apparent. The structural motifs are different from pure tin clusters but rather are rationalized using the corresponding structures of tin anions or are based on the Wade-Mingos concept. Further evidence for this idea is deduced from nuclear independent chemical shift calculations, which show nearly identical behavior for negatively charged pure and neutral bimetallic clusters. All of these findings are consistent with the idea of neutral Zintl analogues in the gas phase.     

Synthesis, structure, and bonding of Eu3Bi(Sn,Bi)4. A rare inverse-Cr5B3-type structure with a new tin/bismuth network

The ternary phase Eu3Bi(Sn1-xBix)4 ( approximately 0 < x < approximately 0.15) has been synthesized by solid-state methods at high temperature. The crystal structure of the limiting Eu3Bi(Sn3.39Bi0.61(3)) has been determined by single-crystal X-ray analysis to be isopointal with an inverse-Cr5B3-type structure [space group I4/mcm, Z = 4, a = 8.826(1) A, c = 12.564(3) A, and V = 978.6(3) A3]. The structure contains slabs of three-bonded Sn/Bi atoms as puckered eight- and four-membered rings interlinked at all vertices, and these are separated by planar layers of individual Eu and Bi atoms. In the normal (stuffed) Cr5B3-type analogue Eu5Sn3Hx, these two units are replaced by a more highly puckered network of Eu cations around isolated Sn atoms and planar layers of isolated Eu atoms and Sn dimers, respectively. Band structures of limiting models of the phase calculated by TB-LMTO-ASA methods show a metallic character and indicate that the mixed Sn/Bi occupancy in the slabs in this structure for x > 0 probably originates with the electronic advantages of the pseudogap that would occur at the electron count of the ideal Zintl phase Eu3Bi(Sn3Bi). The stability of a competing phase reduces this limit to Eu3Bi(Sn3.4Bi0.6).     

Reactions of exo-substituted RSn9(3-) clusters with Pd: endohedral cluster formation and oxidative insertion

Pyridine/ethylenediamine solutions of [Sn(9)SnCy(3)](3-) (1) react with [Pd(PPh(3))(4)] to give new clusters [Pd@Sn(9)SnCy(3)](3-) (2) and [Pd@Sn(9)PdSnCy(3)](3-) (3), depending on stoichiometry. These compounds are formed sequentially and are the first transition metal derivates of exo-substituted Zintl clusters. Oxidative insertion of a Pd atom into the Pd@Sn(9)-SnCy(3) bond of 2 to form 3 represents a new reaction type for Zintl cluster compounds. The conversion Sn(9)(4-)→1→2→3 is a rare case in which charge and mass are conserved in a series of Zintl clusters. Complexes 1, 2, and 3 are all highly fluxional in solution. In all three clusters, the nine Sn vertices are in rapid exchange on the NMR timescale. In 1 and 2, the exo-SnCy(3) substituent also scrambles intramolecularly around the outside of the clusters. In 3, the SnCy(3) group remains attached to the vertex Pd atom. The disparate reactions with the other RSn(9)(3-) ions are discussed.     

Endohedral nickel and palladium atoms in metal clusters: analogy to endohedral noble gas atoms in fullerenes in polyhedra with five-fold symmetry

Nickel and palladium atoms with their closed-shell d(10) electronic configurations are encapsulated in the icosahedral clusters [Ni@Ni(10)E(2)(CO)(18)](4-)(E = Sb, Bi, Sb[rightward arrow]Ni(CO)(3), CH(3)Sn and n-C(4)H(9)Sn) and the geometrically related pentagonal antiprismatic cluster Pd@Bi(10)(4+) found in Bi(14)PdBr(16). Such endohedral d(10) atoms in pentagonal antiprismatic clusters are donors of zero skeletal electrons and interact only weakly with the atoms in the surrounding polyhedron so that they may be regarded as analogous to endohedral noble gases in fullerenes such as He@C(60). On the other hand, endohedral nickel and palladium atoms in 10- and 11-vertex flattened deltahedral bare metal clusters of group 13 metals without five-fold symmetry, such as Ni@E(10)(10-) found in Na(10)NiE(10)(E = Ga, In) and Pd@Tl(11)(7-) found in A(8)Tl(11)Pd (A = Cs, Rb, K), interact significantly with the cluster atoms, particularly those at the flattened vertices of the deltahedron. The role of endohedral d(10) atoms Ni and Pd in polyhedra with five-fold symmetry as "pseudo-noble-gases" can be related to their positions at the "composite divide" of the "Metallurgists' Periodic Table" proposed by H. E. N. Stone on the basis of alloy systematics as well as the equivalence of the five d orbitals in polyhedra with five-fold symmetry.     

An Unprecedented (1infinity)

A chain of vertex-linked "bare" nido-Ge(9)(2-) clusters (shown in the picture) is featured by the novel polymeric Zintl anion formed from the binary alloy "KGe(4)", ethylenediamine, and [18]crown-6. The polymerization of nido-Ge(9)(4-) clusters is counterintuitive to known two-electron oxidation behavior of nido clusters and the existence of the isolated closo-Ge(9)(2-) ion. The novel semiconducting cluster "wire" establishes direct structural and mechanistic links between molecular Zintl cluster ions with the extended structures of Zintl phases and elemental nanophase materials.     

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.     

Structures of medium sized tin cluster anions

The structures of medium sized tin cluster anions Sn(n)(-) (n = 16-29) were determined by a combination of density functional theory, trapped ion electron diffraction and collision induced dissociation (CID). Mostly prolate structures were found with a structural motif based on only three repeatedly appearing subunit clusters, the Sn(7) pentagonal bipyramid, the Sn(9) tricapped trigonal prism and the Sn(10) bicapped tetragonal antiprism. Sn(16)(-) and Sn(17)(-) are composed of two face connected subunits. In Sn(18)(-)-Sn(20)(-) the subunits form cluster dimers. For Sn(21)(-)-Sn(23)(-) additional tin atoms are inserted between the building blocks. Sn(24)(-) and Sn(25)(-) are composed of a Sn(9) or Sn(10) connected to a Sn(15) subunit, which closely resembles the ground state of Sn(15)(-). Finally, in the larger clusters Sn(26)(-)-Sn(29)(-) additional bridging atoms again connect the building blocks. The CID experiments reveal fission as the main fragmentation channel for all investigated cluster sizes. This rather unexpected "pearl-chain" cluster growth mode is rationalized by the extraordinary stability of the building blocks.     

Structural and Quantum Chemical Study of Bi(5)(3+) and Isoelectronic Main-Group Metal Clusters. The Crystal Structure of Pentabismuth(3+) Tetrachlorogallate(III) Refined from X-ray Powder Diffraction Data and Synthetic Attempts on Its Antimony Analogue

Pentabismuth(3+) tetrachlorogallate(III), (Bi(5)(3+))(GaCl(4)(-))(3), has been synthesized by reducing a BiCl(3)-GaCl(3) melt with bismuth metal and the crystal structure refined from X-ray (Cu Kalpha(1)) powder diffraction data. The structure was found to belong to space group R-3c, with the lattice parameters a = 11.871(2) ? and c = 30.101(3) ? (Z = 6). It is isostructural with the previously characterized Bi(5)(AlCl(4))(3). An attempt to synthesise the antimony analogue Sb(5)(GaCl(4))(3) by reducing a SbCl(3)-GaCl(3) mixture with gallium metal produced a black solid phase. The gallium content of this phase is consistent with the stoichiometry Sb(5)(GaCl(4))(3), and the Raman spectrum of the phase dissolved in SbCl(3)-GaCl(3) comprises strong, low-frequency bands attributable to Sb-Sb stretch vibrations in Sb(5)(3+) or another reduced antimony species. Quantum chemical analyses have been performed for the isoelectronic, trigonal pyramidal closo-clusters Sn(5)(2-), Sb(5)(3+), Tl(5)(7-), Pb(5)(2-), and Bi(5)(3+), both with extended Hückel (eH) and Hartree-Fock (HF) methods. The HF calculations were performed with and without corrections for the local electron-electron correlation using second-order M?ller-Plesset perturbation theory (MP2). All theoretical results are compared and evaluted with respect to experimental cluster structures and vibrational frequencies. The results from the calculations agree well with available experimental data for the solid-state structures and vibrational spectra of these cluster ions, except for the Tl(5)(7-) ion. Isolated Tl(5)(7-) is suggested to be electronically unstable because of the high charge density. The Sb(5)(3+) cluster ion is indicated to be stable. According to the calculations, Sn(5)(2-) and Pb(5)(2-) may be described in terms of edge-localized bonds without substantial electron density between the equatorial atoms, whereas Sb(5)(3+) and Bi(5)(3+) have electron density evenly distributed over all M-M vectors. Furthermore, the theoretical results give no support for a D(3h) --> C(4v) fluxionality of these clusters.     

Experimental and theoretical investigation on binary semiconductor clusters of Bi/Si, Bi/Ge, and Bi/Sn

Bi(m)M(n)- (M = Si, Ge, Sn) binary cluster anions are generated by using laser ablation on mixtures of Bi and M (M = Si, Ge, Sn) samples and studied by reflectron time-of-flight mass spectrometer (RTOF-MS) in the gas phase. Some magic number clusters are present in the mass spectra which indicate that they are in stable structures. For small anions (m + n < or = 6), their structures are investigated with the DFT method and the energetically lowest lying structures are obtained. For the binary anionic clusters with the same composition containing Si, Ge, and Sn, they share similar geometric and electronic structure in the small size except that BiSi3-, BiSi5-, Bi2Si2-, Bi2Si3-, and Bi4Sn2- are different for the lowest energetic structures, and the ground states for all the anions are in their lowest spin states. The calculated VDE (vertical detachment energy) and binding energy confirm the obviously magic number cluster of BiM4- (M = Si, Ge, Sn), which agrees with the experimental results.     

Synthesis, structure, and dynamic properties of [Ni2Sn17]4-

The ligand-free [Ni2Sn17]4- ion comprises two [Ni@Sn9]2- clusters that share a common vertex. The cluster sequentially loses Sn atoms in the gas phase and shows global exchange of all Sn atoms on the NMR time scale in solution at 60 degrees C. At lower temperatures, the fluxionality is localized to the ends of the cluster and does not involve the central 8-coordinate Sn5 atom.     

The [Sn(9)Pt(2)(PPh(3))](2)(-) and [Sn(9)Ni(2)(CO)](3)(-) complexes: two markedly different Sn(9)M(2)L transition metal zintl ion clusters and their dynamic behavior

[Sn(9)Pt(2)(PPh(3))](2)(-) (2) was prepared from Pt(PPh(3))(4), K(4)Sn(9), and 2,2,2-cryptand in en/toluene solvent mixtures. The [K(2,2,2-cryptand)](+) salt is very air and moisture sensitive and has been characterized by ESI-MS, variable-temperature (119)Sn, (31)P, and (195)Pt NMR and single-crystal X-ray diffraction studies. The structure of 2 comprises an elongated tricapped Sn(9) trigonal prism with a capping PtPPh(3), an interstitial Pt atom, a hypercloso electron count (10 vertex, 20 electron) and C(3)(v)() point symmetry. Hydrogenation trapping experiments and deuterium labeling studies showed that the formation of 2 involves a double C-H activation of solvent molecules (en or DMSO) with the elimination of H(2) gas. The ESI-MS analysis of 2 showed the K[Sn(9)Pt(2)(PPh(3))](1)(-) parent ion, an oxidized [Sn(9)Pt(2)(PPh(3))](1)(-) ion, and the protonated binary cluster anion [HSn(9)Pt(2)](1)(-). 2 is highly fluxional in solution giving rise to a single time-averaged (119)Sn NMR signal for all nine Sn atoms but the Pt atoms remain distinct. The exchange is intramolecular and is consistent with a rigid, linear Pt-Pt-PPh(3) rod embedded in a liquidlike Sn(9) matrix. [Sn(9)Ni(2)(CO)](3)(-) (3) was prepared from Ni(CO)(2)(PPh(3))(2), K(4)Sn(9), and 2,2,2-cryptand in en/toluene solvent mixtures. The [K(2,2,2-cryptand)](+) salt is very air and moisture sensitive, is paramagnetic, and has been characterized by ESI-MS, EPR, and single-crystal X-ray diffraction. Complex 3 is a 10-vertex 21-electron polyhedron, a slightly distorted closo-Sn(9)Ni cluster with an additional interstitial Ni atom and overall C(4)(v)() point symmetry. The EPR spectrum showed a five-line pattern due to 4.8-G hyperfine interactions involving all nine tin atoms. The ESI-MS analysis showed weak signals for the potassium complex [K(2)Sn(9)Ni(2)(CO)](1-) and the ligand-free binary ions [K(2)Sn(9)Ni(2)](1)(-), [KSn(9)Ni(2)](1)(-), and [HSn(9)Ni(2)](1)(-).     

Electronic structure similarities in Pb(x)Sb(y)(-) and Sn(x)Bi(y)(-) clusters

The geometric and electronic structure of Pb(x)Sb(y)(-) and Sn(x)Bi(y)(-) clusters are investigated by photoelectron spectroscopy and theoretical methods. It is found that PbSb(2)(-) and SnBi(2)(-) have similar spectroscopic patterns, reflecting correlations in electronic nature that are a result of their isoelectronic character and common geometries. Analogous findings are presented for Pb(2)Sb(2)(-) and Sn(2)Bi(2)(-). Further, we investigate the effect of altering the total valence count, and separately the geometry, on spectroscopic patterns. We conclude that these heavy p-block elements are interchangeable and that the electronic structure correspondence can be preserved regardless of elemental composition. This represents an extension of the traditional concepts of periodicity, where elements of similar valence configuration are grouped into columns. Instead, elements from different columns may be combined to yield similarities in chemistry, given the overall valence count is preserved.     

"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-).     

Heteroatomic deltahedral clusters: synthesis and structures of closo-[Bi3Ni(4)(CO)6]3-, closo-[Bi4Ni4(CO)6]2-, the open cluster [Bi3Ni6(CO)9]3-, and the intermetalloid closo-[Nix@[Bi6Ni6(CO)8)]4-

Reactions of ethylenediamine solutions of K4Bi5 with Ni(PPh3)2(CO)2 yielded four novel hetero-atomic Bi/Ni deltahedral clusters. Three of them, the 7-atom pentagonal bipyramidal [Bi3Ni4(CO)6]3-, the 8-atom dodecahedral [Bi4Ni4(CO)6]2-, and the Ni-centered or empty 12-atom icosahedral [Nix@[Bi6Ni6(CO)8]4-, are closo-species according to both electron count and shape. The centered icosahedral cluster resembles packing in intermetallic compounds and belongs to the emerging class of intermetalloid clusters. The shape of the fourth cluster, [Bi3Ni6(CO)9]3-, can be derived from the icosahedral Ni-centered [Ni@[Bi6Ni6(CO)8]4- by removal of three Bi- and one Ni-atoms of two neighboring triangular faces. The clusters were structurally characterized by single-crystal X-ray diffraction in compounds with potassium cations sequestered by 2,2,2-crypt or 18-crown-6 ether. They were also characterized in solution by electrospray mass spectrometry.     

Pd3Sn8Bi6]4-: a 14-vertex Sn/Bi cluster embedding a Pd3 triangle

The endohedral cluster anion [Pd(3)Sn(8)Bi(6)](4-) crystallizes as its K([2.2.2]crypt)(+) salt 1 upon reaction of [K([2.2.2]crypt)](2)[Sn(2)Bi(2)]·en and Pd(dppe)(2) in 1,2-diaminoethane (en)/toluene and incorporates a complete Pd(3) triangular cluster within a medium-size 14-vertex cage of Sn and Bi atoms. 1 was characterized by a combination of single crystal diffraction, ESI mass spectrometry, elemental analysis, and magnetic measurements. According to quantum chemical investigations, the Pd(3) triangle interacts only weakly with the Sn/Bi cluster shell despite the relatively small cavity inside the cage.     

Synthesis and Structure of Ba(2)Sn(3)Sb(6), a Zintl Phase Containing Channels and Chains

The new Zintl phase dibarium tritin hexaantimonide, Ba(2)Sn(3)Sb(6) has been synthesized, and its structure has been determined by single-crystal X-ray diffraction methods. It crystallizes in the orthorhombic space group -Pnma with a = 13.351(1) ?, b = 4.4100(5) ?, c = 24.449(3) ?, and Z = 4 (T = -50 degrees C). The structure of Ba(2)Sn(3)Sb(6) comprises large channels [010] defined by 30-membered rings constructed from an anionic framework. This framework is built up from Sn-centered trigonal pyramids and tetrahedra, as well as zigzag chains of Sb atoms. Within the channels reside the Ba(2+) cations and additional isolated zigzag Sb-Sb chains. The simultaneous presence of Sn trigonal pyramids and tetrahedra implies that Ba(2)Sn(3)Sb(6) is a mixed-valence compound whose oxidation state notation can be best represented as (Ba(2+))(2)[(Sn(II))(2)(Sn(IV))(Sb(-)(III))(3)(Sb(-)(I))](2)(-)[(Sb(-)(I))(2)](2)(-).     

Nonclassical bonding in the novel structure of Ba2Bi3 and unexpected site preference in the coloring variant Ba2BiSb2

The new phase Ba(2)Bi(3) crystallizes in the W(2)CoB(2) structure type. Its structure contains rigorously planar anionic layers of (4.6.4.6)(4.6(2))(2) nets with three- and four-bonded Bi, that are separated by Ba atoms. An unexpected site preference is observed in the coloring variant Ba(2)BiSb(2) with Sb occupying only the three-bonded sites. The nonclassical bonding in the anionic network can be rationalized from a reformulation of the Zintl concept as (Ba(2+))(2)[Bi(3)](3)(-)(e(-)). Bonding distances suggest that the extra electron fills Bi-Bi antibonding states. The densities of states obtained from TB-LMTO-ASA calculations show metallic character for both compounds.