Metals catenation

The investigation of mixed metal catenates represents an interesting challenge, particularly in view of difficulties with their syntheses3. However, the photochemistry of... 

Germanium forms a wide range of compounds with hydrogen, silicon, the heavier group 14 elements, some main group metals, and transition metals. Catenated hydrides, Ge H2 +2, have already been discussed. The majority have carbon bonded to Ge and are included in the next article (see Germanium Organometallic Chemistry). 

The first report on the photophysical properties of metal catenates dates back to 1989 [54h], when a comparison between a 27- (Cu.4 Figure 2) and 30-membered (Cu.5 Figure 14) ring catenates was reported. 

For the [2]catenand 5, two clearly distinct protonation reactions are found, and it was demonstrated unambiguously that both protonated forms have a catenate structure [60, 67], i.e., the two dap fragments are arranged in an entwined structure identical to that involved for metal catenates. The driving force for this unexpected behavior is likely to be the nn electronic donor-acceptor interactions between phenathroline and anisyl fragments that can be established only in the catenate-type arrangement, and not in a open form. The luminescence properties of 5 and its protonated forms H-S" " and (H2).5 are reported in Table 9. 

The direct linking of like atoms, such an essential feature of carbon chemistry, occurs to only a limited extent with other elements. Metal-metal bonds are not uncommon but they are always weak examples are found in the polynuclear carbonyls (p. 306) and compounds such as SugRg and PbgRfi (R = alkyl). Among the other non-metals catenation is displayed by boron, silicon, germanium, phosphorus and sulphur none of the substances... 

The two ends of the bipyridyl-bis-crown ether ligand LI 154 can be clipped together by K+. Reaction of [Cu(MeCN)4]+ with two equivalents of LI 154 gave the precursor [Cu(Ll 154)2]+, which with an excess of KPFe gave the novel alkali-metallated catenate [Cu(KL1154)2](PF6)3. The potassium binds the benzo-15-crown-5 units sufficiently tightly for demetallation, with potassium or tetramethy-lammonium cyanide, to be feasible, giving the [2]-catenane (KL 1154)2 as its hexafluorophosphate salt [299] (Scheme 4-32),... 

All Group IV elements form tetrachlorides, MX4, which are predominantly tetrahedral and covalent. Germanium, tin and lead also form dichlorides, these becoming increasingly ionic in character as the atomic weight of the Group IV element increases and the element becomes more metallic. Carbon and silicon form catenated halides which have properties similar to their tetrahalides. 

The structures of metal-rich borides can be systematized by the schematic arrangements shown in Fig. 6.6, which illustrates the increasing tendency of B atoms to catenate as their concentration in the boride phase increases the B atoms are often at the centres of trigonal prisms of metal atoms (Fig. 6.7) and the various stoichiometries are accommodated as follows ... 

Figure 6.6 Idealized patterns of boron catenation in metal-rich borides. Examples of the structures (a)-(f) are given in the text. Boron atoms are often surrounded by trigonal prisms of M atoms as shown in Fig. 6.7.

The extent to which B3O3 rings catenate into more complex structures or hydrolyse into smaller units such as [B(OH)4] clearly depends sensitively on the activity (concentration) of water in the system, on the stoichiometric ratio of metal ions to boron and on the temperature (7-A5). 

Some of the alkali metal-group 15 element systems give compounds of stoichiometry ME. Of these, LiBi and NaBi have typical alloy stmc-tures and are superconductors below 2.47 K and 2.22 K respectively. Others, like LiAs, NaSb and KSb, have parallel infinite spirals of As or Sb atoms, and it is tempting to formulate them as M+ (E )" in which the (E )" spirals are iso-electronic with those of covalently catenated Se and Te (p. 752) however, their metallic lustre and electrical conductivity indicate at least some metallic bonding. Within the spiral chains As-As is 246 pm (cf. 252 pm in the element) and Sb-Sb is 285 pm (cf. 291 pm in the element). 

Metal polysulfido complexes have attracted much interest not only from the viewpoint of fundamental chemistry but also because of their potential for applications. Various types of metal polysulfido complexes have been reported as shown in Fig. 1. The diversity of the structures results from the nature of sulfur atoms which can adopt a variety of coordination environments (mainly two- and three-coordination) and form catenated structures with various chain lengths. On the other hand, transition metal polysulfides have attracted interest as catalysts and intermediates in enzymatic processes and in catalytic reactions of industrial importance such as the desulfurization of oil and coal. In addition, there has been much interest in the use of metal polysulfido complexes as precursors for metal-sulfur clusters. The chemistry of metal polysulfido complexes has been studied extensively, and many reviews have been published [1-10]. 

Catenated Organic Compounds of the Group IV Elements, 4,1 Conjugate Addition of Grignard Reagents to Aromatic Systems, 1, 221 Cyclobutadiene Metal Complexes, 4, 95 Cyclopentadienyl Metal Compounds, 2, 365 Diene-Iron Carbonyl Complexes, 1, 1... 

The chalcogens have a rich metal chemistry both in molecular compounds and in the solid state, on account of their ability to catenate and to bind to multiple metal centers. 

Other supramolecular structures such as catenanes and rotaxanes can be formed using zinc as a template ion for example, a benzylic imine catenate formed by Leigh et a/.288 The reversible five-component assembly of a [2]catenane from a chiral metallomacrocycle and a dinaphtho-crown ether has been achieved. Zinc is used as the metal component and drives assembly via the coordination to a bipyridyl unit 7r interactions between the aromatic components are also... 

Because of the tendency of sulfur toward catenation, solutions containing sulfides react with sulfur to give polysulfides, which can be represented as SnJ (see Chapter 15). Sulfides of the group IA and IIA metals can also be produced by reducing the sulfates with carbon at high temperature. 

In these mixtures the catena-tvistibines are by far the most abundant chain species and even under favorable conditions [excess of cyc/6>-(RSb) ] the caten -tetrastibines form only as minor components. Nevertheless, recently the selective extraction and stabilization of these tetrastibines in the coordination sphere of a transition metal carbonyl complex was achieved by reacting mixtures of distibines and cyclostibines with... 

Laser flash photolysis of phenylated Group 14 catenates followed by trapping of the radical intermediates indicates that homolytic cleavage of the metal-metal bond is the... 

Metallocyclopentenes are frequently formed in photochemical reactions of the Group 14 metal alkyls or catenates in the presence of dimethylbutadiene. This class of compound also has an extensive photochemistry82. For example, photolysis of 51 (R = H or Me) produced the allylic alcohols 52 and 53 and, for R = H, 54. These alcohols could be dehydrated over AI2O3 to give the germole 55 along with other diene compounds. 

The polyether-diimine macrocycle (108) forms a catenate [Fe(cat)] which proved impossible to oxidize to [Fe(cat)] " but which is readily reducible, electrochemically in dichloromethane solution on a Pt or Hg surface, to [Fe(cat)]+ and to [Fe(cat)]°. " [Fe(bmpphen)2] (bmpphen = (109) can be electroreduced to [Fe(bmpphen)2] and to [Fe(bmpphen)2]. The relatively high stabilities of all three bmpphen complexes may be due to their entwined character. Here and below one should bear in mind the possibility, outlined in Section 5.4.1.3 above, that it is the ligand rather than the metal which is being reduced. 

Contents Formal Oxidation Numbers. Configurations in Atomic Spectroscopy. Characteristics of Transition Group Ions. Internal Transitions in Partly Filled Shells. Inter-Shell Transitions. Electron Transfer Spectra and Collectively Oxidized Ligands. Oxidation States in Metals and Black Semi-Conductors. Closed-Shell Systems, Hydrides and Back-Bonding. Homopolar Bonds and Catenation. Quanticule Oxidation States. Taxological Quantum Chemistry. 

Polysilanes are polymers in which there is catenation of silicon, that is, where silicon atoms are bonded to each other in a continuous manner. Synthesis of polysilanes involves the Wurtz coupling of diorganodichlorosilanes with sodium metal (Eq. 2-239) [Baldus and Jansen, 1997 Corriu, 2000 Manners, 1996 Miller and Michl, 1989 West, 1986 West and Maxka,... 

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