Pseudo-metals

J. L. Dye, Electrides From LD Heisenberg chains to 2D pseudo-metals. Inorg. Chem. 36, 3816-26 (1997). 

It has already been mentioned that black phosphorus has a greater electrical conductivity than other forms, and is therefore to be considered as the most metallic variety.2 The conductivity, however, like that of graphite, increases with rise of temperature, and this form is therefore only pseudo-metallic. 

On the basis of electrode kinetic data obtained in 1M NaOH for oxides in the range 0.1 < x < 0.5, van Buren et al. [77] concluded that the solid state electronic properties of these mixed oxies have no observable effect on the electron transfer kinetics and the oxides can be considered as pseudo-metallic from an electrochemical point of view. There are, however, several observations that make this conclusion questionable (a) Characterization data for the oxide electrode surfaces were not presented. In particular, the electrochemical real surface area (capacity, or BET) of the electrodes, and therefore comparison of apparent rate coefficients, are uncertain, (b) The... 

First, simple inductive effects cannot be used to explain the order of stability of the dialkylthallium(III) derivatives. An increase in the chain length of the alkyl group should reduce the effective charge on the pseudometal ion, and the values of Ki should decrease. Possibly increasing the chain length of R decreases the hydrophobic character of the pseudo-metal ion, and a solvation effect is really reflected by the stability order. A similar effect has been reported previously (20). 

Secondly, any effects which might be ascribed to B-strain seem to be absent. It might be expected that B-strain would be significant because R2TI+ is a linear ion, but R2TlCh would be a tetrahedral molecule. It is possible that the critical pseudo-metal ion would be diisopropylthal-lium(III) ion. 

The work of Irving and da Silva (16) shows how extensive a series of univalent pseudo-metal ions is available. These workers measured formation constants of complexes of ethylmercury(I), dimethylthallium(III), and uramil-7,7 -diacetic acid (R = R = H) and the 1-methyl- and 1,3-dimethylhomologs. 

Of course, the problems of hydrolysis can be obviated by using non-aqueous solvents, and pseudo-metal ions have the necessary solubilities. For example, spectrophotometric studies (18) of complex formation equilibria between 2,2 -bipyridine (bipy) and dialkyltin dichloride have been reported. The log K values for complexes R2SnCl2-bipy are 3.19 (R, n-C4H9), 3.36 (R, CH3), and 6.7 (R, Cl) in acetonitrile. There is surprisingly little difference between the constants for dimethyl- and the dibutyltin dichloride complexes. The equilibrium constant for the dibutyl-tin dichloride complex increases with increasing dielectric constant of an alcohol solvent. 

Type ni. Reactions of the Organo Moiety, Few, if any, studies have been made of reactions of the organo moiety of pseudo-metal ions. Presumably the course of these reactions would be affected by the presence of coordinated ligands. 

One elegant example of the use of a pseudo-metal ion as a central metal ion, and as a probe, is the study (42) of the electron distribution in the series of tetrahedral complexes of the type R2B(R COCHCOR"). A study of the B resonance indicated the pseudo-metal atom demanded electron donation from the chelate ring in a fixed amount which was found to be a function of R but not of R and R". Because an alteration of the structure of the chelate moiety (either ring size or donor atom) caused changes on the i B and HiNMR of the R2B unit, it was possible to evaluate the electronegativity of the ring system composed of the chelate moiety and the boron atom. 

This preparation illustrates a general method for making an oxyacid of a nonmetal or pseudo metal, that is, the oxidation of the element or its lower oxide by concentrated nitric acid. The element arsenic could be used to make arsenic acid, but arsenious oxide is more readily available and will be used instead. 

Porphyrins are known to coordinate with most of the metallic or pseudo-metallic elements. However, in spite of the large number of isolated metalloporphyrin derivatives, metal-carbon o-bonded complexes are limited only to the following series Fe, Ru, Co, Rh, Ir, Ti, Al, Ga, In, TI, Si, Ge, Sn, and Zn. 

Dye. J.L. Electrides From ID Heisenberg chains to 2D pseudo-metals. Inorg. Chem. 1997, 36. 3816-3826. Corbett. J.D. Exploratory synthesis in the solid state. Endless wonders. Inorg. Chein. 2000. 39. 5178-5191. Corbett, J.D. Diverse naked clusters of the heavy main-group elements. Electronic regularities and analogies. Stmct. Bond. 1997, 87. 157- 193. 

There have been reports of rod-like inorganic structures such as (SiS ) which is usually depicted as an extended chain polymer [I]. Also, polythiazyl, (SN), has been observed to display highly anisotropic character exhibiting pseudo-metallic behavior [2]. However, these materials do not melt, and the close proximity of the rods suggests that they are better classified as three-dimensional inorganic structures than as polymers. 

A case in point which does not involve a metal complex (excluding for purposes of discussion the proton as a pseudo metal ion) is the Kuhn effect. The late R. Kuhn and Albrecht showed that the quinine salt of 4,4 -dinitro-diphenic acid is dextro rotatory in chloroform. The quinine salts of two... 

The synthesis, chemical properties, and electrochemistry of metallo-porphyrins with metal-metal and metal-carbon bonds have recently been described in two extensive reviews Porphyrins are known to coordinate with most metallic and pseudo-metallic elements and, in theory, synthesis of numerous organometallic porphyrins is possible. However, to date, the synthesis of metal-carbon a-bonded complexes has been limited to metallo-porphyrins with the following central metals Fe, Ru, Co, Rh, Ir, Ti, Al, Ga, In, Tl, Si, Ge, Sn and Zn. These organometallic complexes are of importance as model compounds for understanding the functions and relationships of several biologically important macromolecules, as well as for their chemical reactivity. The insertion of small molecules between the metal ion and the carbon atom of a metalloporphyrin may result in activation of the inserted molecule or may generate new monomeric or polymeric materials. In addition, metal-carbon o-bonded porphyrins can act as precursors in the synthesis of metal-metal bonded derivatives. 

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