Post-transition metals

Aim0 cmplxs. Sherman et al. (2000) have investigated the aqueous 

To understand how metals are transported in the Earth s crust, we need to predict the speciation of metal complexes in aqueous solutions as a function of pressure, temperature and composition. To do this using atomistic calculations, we must define an adequately large system (as a function of composition) and obtain a thermodynamic average of all the possible states of the system (as a function of pressure and temperature). 

Molecular dynamics and Monte Carlo simulations on aqueous solutions usually involve several fundamental approximations first, we are usually only interested in sampling the energy levels associated with the nuclear motions of the system. We will assume that all molecules and ions are in their ground electronic states. This will not 

For monatomic ions, it is usually easiest to use the formal charges in the coulombic term. For molecules, effective charges must be used. 

Pial mdkfowat A number of rigid models for water have been 

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Although there are several hundred biaary nitrides, only a relative few ternary bimetallic metal nitrides are known (6). A group of ternaries of the composition where M is an alkah, alkaline-earth, or a rare-earth metal and M is a transition or post-transition metal, have been synthesized (6). 

Attempts to classify carbides according to structure or bond type meet the same difficulties as were encountered with hydrides (p. 64) and borides (p. 145) and for the same reasons. The general trends in properties of the three groups of compounds are, however, broadly similar, being most polar (ionic) for the electropositive metals, most covalent (molecular) for the electronegative non-metals and somewhat complex (interstitial) for the elements in the centre of the d block. There are also several elements with poorly characterized, unstable, or non-existent carbides, namely the later transition elements (Groups 11 and 12), the platinum metals, and the post transition-metal elements in Group 13. 

The steady trend towards increasing stability of rather than M compounds in the sequence Ge, Sn, Pb is an example of the so-called inert-pair effect which is well established for the heavier post-transition metals. The discussion on p. 226 is relevant here. A notable exception is the organometallic chemistry of Sn and Pb which is almost entirely confined to the state... 

Several metals that are farther removed from the noble gases in the periodic table form positive ions. These include the transition metals in Groups 3 to 12 and the post-transition metals in Groups 13 to 15. The cations formed by these metals typically have charges of +1, +2, or +3 and ordinarily do not have noble-gas structures. We will postpone to Chapter 4 a general discussion of the specific charges of cations formed by these metals. 

Many of the transition and post-transition metals form more than one cation. Consider, for example, iron in Group 8. This metal forms two different series of compounds with non-metals. In one series, iron is present as a +2 cation... 

In naming the compounds of transition or post-transition metals, we ordinarily indicate the charge of the metal cation by a Roman numeral ... 

Positron emission tomography (PET), 516 Post-transition metal Lower members of periodic groups 13,14, and 15, such as PbandBi, 31,38-39... 

This supramolecular approach has been used as a way to facilitate the crystallization of cuboidal aqua ions and to capture single intermediates present in complex solution mixtures. For example, [M3Q4Clx(H20)9.x] (Q = S, Se) supramolecular adducts have been isolated for x =1-5 from aqueous HCl solutions by varying the acid concentrations where the aggregates contain in each case only one of all possible isomers [46]. In addition to the hydrogen bonds, other kinds of interactions, namely C1---H20, C1---C1 and Q---Q contacts, are also involved in the network propagation. This supramolecular approach has also been efficiently employed for the crystallization of a large number of aqua complexes within the [M3M Q4] cubane-type family, where M is a transition or post-transition metal [47]. 

But first the synthesis had to come John was interested in reduced metal halides, particularly for the post-transition metals cadmium, galHum, and bismuth (his Ph.D. dissertation was on anhydrous aluminum halides and mixed halide intermediates, a good start for what was to come ). However, he was not yet actively interested in rare-earth metals and their remarkable solubility in their halides. But these elements lured him one floor below where Adrian Daane headed the metallurgy section of Spedding s empire. He knew how to produce rare-earth metals with high purity and in sufficient quantity and also how to handle tantalum containers. What if one gave it a tr/ and reduced some rare-earth metal halides (John insists that this term is used correctly) from their respective metals at high temperatures under appropriate conditions. 

Slovokhotov, Yu.L. and Struchkov, Yu.T (1984) X-ray crystal structure of a distorted tetrahedral cluster in the salt [(Ph P)4Au4N] BF4 . Geometrical indication of stable electronic configurations in post-transition metal complexes and the magic number 18-e in centred gold clusters. Journal of Organometallic Chemistry, 177, 143-146. 

Some divalent transition and post-transition metal ions, Co", Nr, Cu", Zm, and Cd, have been studied in the same way, but these systems need a pH-control in order to avoid any precipitation. Although measurements have not been completed yet, a pair of waves has been observed only in the Cu system that is somewhat irreversible (—100 to —50 mV of the half-wave potential). In the other systems, any waves except ambiguous broad ones could not be obtained. While analyzing some waves, Cu seems to be facili-... 

Lee, S. S. Yoon, I. Park, K.-M. Jung, J. H. Lindoy, L. F. Nezhadali, A. Rounaghi, G. Competitive bulk membrane transport and solvent extraction of transition and post transition metal ions using mixed-donor acyclic ligands as ionophores. J. Chem. Soc.-Dalton Trans. 2002, 2180-2184. 

Metallaborane cluster complexes of the post-transition metals 167... 

Studies on borohydride complexes of post-transition metals are as follows. Theoretical calculations on M(BH4) (M = Cu, Ag, Au) at the ab initio level indicate that Cu(i) and Ag(i) congeners have tetrahydridoborate structures, while the gold complex adopts a hydridoborane structure HAu(BH3).37 MeZn 2 /-BH4) 30 is prepared by addition of B2H6 to ZnMe2 or MeZnCl and Li[BH4]. The X-ray structure shows a polymeric helical arrangement of ZnMe + and [BH4]- fragments—similar to Be(BH4) or H2Ga(BH4) 50.38... 

Some examples of complexes of metallaboranes of post-transition metals are given in Table 14. 

The main group duster chemistry discussed in this book can be considered to originate from two important, but apparently unrelated developments in inorganic chemistry in the 1930s. The first was the identification of the neutral boron hydrides by Stock [1]. The second was the observation by Zintl and co-workers [2-5] of anionic clusters formed from potentiometric titrations of post-transition metals (i.e., heavy main group elements) with sodium in liquid ammonia. 

Bare Ionic Post-transition Metal Clusters The Zintl Phases... 

The polyhedral boranes and carboranes discussed above may be regarded as boron clusters in which the single external orbital of each vertex atom helps to bind an external hydrogen or other monovalent atom or group. Post-transition main group elements are known to form clusters without external ligands bound to the vertex atoms. Such species are called bare metal clusters for convenience. Anionic bare metal clusters were first observed by Zintl and co-workers in the 1930s [2-5], The first evidence for anionic clusters of post-transition metals such as tin, lead, antimony, and bismuth was obtained by potentiometric titrations with alkali metals in liquid ammonia. Consequently, such anionic post-transition metal clusters are often called Zintl phases. 

Rules for counting the number of skeletal electrons provided by each vertex atom need to be established in order to determine the number of skeletal electrons in polygonal and polyhedral clusters of the post-transition elements. The rules discussed above for polyhedral boranes can be adapted to bare post-transition metal vertices as follows ... 

The post-transition metals utilize a four-orbital sp3 valence orbital manifold. 

Application of this procedure to post-transition metal clusters indicates that bare Ga, In, and Tl vertices contribute one skeletal electron bare Ge, Sn, and Pb vertices contribute two skeletal electrons bare As, Sb, and Bi vertices contribute three skeletal electrons and bare Se and Te vertices contribute four skeletal electrons in two- and three-dimensional aromatic systems (see Chapter 1.1.3). Thus, Ge, Sn, and Pb vertices are isoelectronic with BH vertices and As, Sb, and Bi vertices are isoelectronic with CH vertices. 

Fig. 1-7. Examples of the shapes of bare post-transition metal clusters.

Some examples of bare ionic post-transition metal clusters are depicted in Figure... 

GaUium is truly an exotic element in that it has so many unusual characteristics. It can form fflonovalent and divalent as weU as trivalent compounds. It is considered a post-transitional metal that is more hke aluminum than the other elements in group 13. It has few similar characteristics to the two elements just below it in group 13 (In and Ti). 

Stability constants represent primary data when considering a ligand type for use in a medical application. Stability constant determinations have been undertaken for the N4 donor macrocyclic ligand derivatives (180) and (18H with a range of divalent first-row transition and post-transition metal ions (including Mn )." In all cases the natural (Irving-Williams) stability order was observed to obtain for the 1 1 (M L) complexes. 

Application of the Wade-Mingos Rules to Bare Post-Transition Metal Clusters 10... 

The efforts to rationalize the formulas and structures of Zintl ions and related species predated extensive definitive structural information on anionic post-transition metal clusters obtained by Corbett and his group in the 1970s [8, 9]. After enough such structural information on the bare post-transition metal clusters became available, the resemblance of their polyhedra to the known polyhedral boranes became apparent. For this reason, the simple Zintl-Klemm concept has been largely superseded by newer, more advanced descriptions of chemical bonding in such clusters, initially those applied to the polyhedral boranes. 

Removal of two vertices from a deltahedron leads to arachno polyhedra having 2n + 6 skeletal electrons according to the Wade-Mingos rules [13-16]. Among the many theoretical possibilities for arachno polyhedra, the pentagonal antiprism, generated by removal of a pair of antipodal vertices from an icosahedron, is the most significant in bare post-transition metal cluster chemistry. 

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