Zintl clusters

The Sn6[M(CO)5]6 clusters (M = Cr, Mo, W) [51] are not prepared from Zintl anions, but the Siig octahedral cores can be viewed as a closo 2n+2 member of the deltahedral Zintl anion series and are similar to the cZoso-trigonal bipyramidal Sns ion. The Sn chemical shifts of the Sn6[M(CO)5]6 complexes are in the range 198-561 ppm and are somewhat downfield of the anionic Zintl clusters. Large one-bond Sn-Sn couplings of 1,800 Hz are suggestive of nonfluxional compounds. 

Sun D, Riley AE, Cadby AT et al (2006) Hexagonal nanoporous germanium through surfactant-driven self-assembly of Zintl clusters. Nature 441 1126-1130... 

Hull MW, Sevov SC (2007) Addition of alkenes to deltahedral zintl clusters by reaction with alkynes synthesis and stmcture of [Fc-CH=CH-Ge9CH-Fc] an organo-zinti-organometal-lic anion. Angew Chem Int Ed 46 6695-6698... 

Abstract This review highlights how molecular Zintl compounds can be used to create new materials with a variety of novel opto-electronic and gas absorption properties. The generality of the synthetic approach described in this chapter on coupling various group-IV Zintl clusters provides an important tool for the design of new kinds of periodically ordered mesoporous semiconductors with tunable chemical and physical properties. We illustrate the potential of Zintl compounds to produce highly porous non-oxidic semiconductors, and we also cover the recent advances in the development of mesoporous elemental-based, metal-chalcogenide, and binary intermetallic alloy materials. The principles behind this approach and some perspectives for application of the derived materials are discussed. 

Recently, we and others demonstrated that appropriate germanide Zintl clusters in non-aqueous liquid-crystalline phases of cationic surfactants can assemble well-ordered mesostructured and mesoporous germanium-based semiconductors. These include mesostructured cubic gyroidal and hexagonal mesoporous Ge as well as ordered mesoporous binary intermetallic alloys and Ge-rich chalcogenide semiconductors. 

Scheme 1 Typical Zintl clusters (a) [Gcg], (b) [Nl3 (Ge9)2], (c) [Pt Pbi2], (d)[GegZn]° and (e) [Sn9Pt2] as building block candidates for the construction of porous semiconductors...

The early attempts to produce mesostructured metal chalcogenide involved surfactant-templated cross-linking polymerization of Zintl clusters (MQ4, M4Q10 and Sn2Qe M = Ge, Sn Q = S, Se, Te) with various metal ions (Hg, Cd, Pt, ... 

Recently, we demonstrated that the Zintl clusters [Geg]" react with chalcogen atoms (S, Se, and Te) in the presence of surfactant templates to form ordered mesoporous Ge-rich chalcogenides [74]. The mesostructured frameworks grow through a coupling reaction of (Ge9)-clusters with chalcogens in formamide/ethy-lenediamine mixture solution in an unusual reaction that seems to be a redox process (5). 

Group 14 alkali metal bonded complexes Group 1-Group 14, 2, 55 Zintl clusters, 2, 24... 

Considerable evidence exits of the survival of Zintl ions in the liquid alloy. Neutron diffraction measurements [5], as well as molecular dynamics simulations [6, 7], give structure factors and radial distribution functions in agreement with the existence of a superstructure which has many features in common with a disordered network of tetrahedra. Resistivity plots against Pb concentration [8] show sharp maxima at 50% Pb in K-Pb, Rb-Pb and Cs-Pb. However, for Li-Pb and Na-Pb the maximum occurs at 20% Pb, and an additional shoulder appears at 50% Pb for Na-Pb. This means that Zintl ion formation is a well-established process in the K, Rb and Cs cases, whereas in the Li-Pb liquid alloy only Li4Pb units (octet complex) seem to be formed. The Na-Pb alloy is then a transition case, showing coexistence of Na4Pb clusters and (Pb4)4- ions and the predominance of each one of them near the appropiate stoichiometric composition. Measurements of other physical properties like density, specific heat, and thermodynamic stability show similar features (peaks) as a function of composition, and support also the change of stoichiometry from the octet complex to the Zintl clusters between Li-Pb and K-Pb [8]. 

The conceptual connection between cluster and solid-state chemistries is the unifying theme of the first seven chapters. Complementary empirical connections between cluster and solid-state chemistries are emphasized in this final chapter. That is, the synthesis of solid-state materials from molecular precursors including clusters permits the strengths of molecular synthesis to be used in the development of new materials. On the other hand, the utilization of Zintl clusters as novel reagents in solution permits the advantages of thermodynamically driven solid-state synthesis to be transferred to the production of clusters in solution. Most of the examples discussed could have been included in earlier chapters, but are gathered here to serve as a review as well as a stimulus to creative thought for future research in cluster and materials chemistries. 

Extraction of Zintl clusters from transition-metal cluster solids... 

Indium and thallium form a number of binary compounds with alkali metals in which the group 13 elements form well-defined anionic clusters (Zintl ions, see Section 1-9). Examples are K8Inu (Fig. 6-3) which has considerably fewer (2n-4) electrons than the minimum described by Wade s rules (2n + 2), KgIn10Zn and K10In10M (M = Ni, Pd, Pt).6 Closo-In16 and nido-Inu clusters have also been found. Thallium, too, forms Zintl clusters Na2H contains Tlf tetrahedra, while K8T1ii is similar to In, and KT1 contains Tl octahedra.7... 

In the meantime, homoatomic ligand-free Zintl clusters of tetrel atoms are known for compositions [ 4 , [ 5] , and [ g] with = Si, Ge, Sn, Pb and n = 2-4. A unique example of a cluster with ten vertices is [Pbio] with a bicapped quadratic anti-prismatic structure (Figure 3.1). The smallest clusters [ 4]" were first prepared in solid-state reactions of alkali metals (A = Na, K, Rb, Cs) with elemental tetrels ( = Si, Ge, Sn, Pb) in a 1 1 ratio [8]. 

Figure 17.2. A. Proposed structure of the Pt2[Ge4Sio] chalcogenide aerogel based on pair distribution function (PDF) analysis of X-ray data. Relevant inter-atomic distances are indicated. B. Different types of Zintl clusters (teal balls = Ge, Sn red balls = S, Se) employed in chalcogel formation with Pt ". Reproduced with permission from Science, 317 490-493 (2007). Copyright 2007, American Association for the Advancement of Science.

Table 1. HOMO-LUMO gap, binding energy Ej, and energy to remove one alltali atom for octet clusters, AePb clusters and Zintl clusters in gas phase. All quantities in eV.

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