Nomenclature transition metals

Although the lUPAC has recommended the names tetrahydroborate, tetrahydroaluminate, etc, this nomenclature is not yet ia general use. Borohydrides. The alkaU metal borohydrides are the most important complex hydrides. They are ionic, white, crystalline, high melting soHds that are sensitive to moisture but not to oxygen. Group 13 (IIIA) and transition-metal borohydrides, on the other hand, are covalendy bonded and are either Hquids or sublimable soHds. The alkaline-earth borohydrides are iatermediate between these two extremes, and display some covalent character. 

Calculations [104] show that for L7 > A (the heavier transition metal ions) the gap is of the charge-transfer type, whereas for 1/ < A (the lighter transition metal ions) the gap is of the d-d type. In our nomenclature this may be translated as MMCT LMCT. In the charge-transfer semiconductors the holes are light (anion valence band) and the electrons are heavy (d bands). Examples are CuClj, CuBrj, CuO, NiClj, NiBrj and Nil2. 

This overview covers some of the rules for naming simple inorganic compounds. There are additional rules, and some exceptions to these rules. The first part of this overview discusses the rules for deriving a name from a chemical formula. In many cases, the formula may be determined from the name by reversing this process. The second part examines situations in which additional information is needed to generate a formula from the name of a compound. The transition metals present some additional problems therefore, there is a section covering transition metal nomenclature and coordination compounds. 

Many transition metals and the group of six elements centered around lead on the periodic table commonly have more than one valence. The valence of these metals in a compound must be known before the compound can be named. Modern nomenclature rules indicate the valence of one of these metals with a Roman numeral suffix (Stock notation). Older nomenclature rules used different suffixes to indicate the charge. Examples ... 

An area of current development is the nomenclature of organometallic compounds. Organometallic compounds of Main Group elements can, to a first approximation, be considered to be derivatives of hydrides, and the methods of substitutive nomenclature can be applied. Even then, the accessibility of different oxidation states, as with phosphorus(iii) and phosphorus(v), introduces complications. Transition metal organometallic compounds are even more difficult to treat, and the development of a unified, self-consistent and accepted and applied nomenclature is not easy. Witness the different ways (k, t and italicised symbols) for denoting donor atoms in ligands. 

FIGURE 1. Nomenclature for O atoms in constitutionally asymmetric peroxides (R = alkyl, aryl R = H, metal, transition metal, group 13-17 elements)... 

We shall note, that the difficulties arise precisely when modelling is to be applied to molecules involving transition metal atoms mainly of the second half of the first transition row. Moreover, even among the TMCs formed by these atoms the problems are not uniformly distributed the normal chemical nomenclature does not provide here an adequate classification. 

Although the physical basis of the crystal field model is seen to be unsound, the fact remains that, in summarizing the importance of the symmetry of the ligand environment, it qualitatively reproduces many of the features of the magnetic and spectral properties of transition metal complexes. This early qualitative success established its nomenclature in the fields of these properties. While we shall have little more to say about crystal field theory as such, much of the rest of this article will be couched in the language of the crystal field model, and for that reason some little trouble has been taken to outline its development. 

Calix[ ]arenes are a family of macrocycles prepared by condensation reactions between n /v/ra-substituted phenols and n formaldehyde molecules under either base or acid catalysis. Different sizes of the macrocycles can be obtained (n = 4-20) (Stewart and Gutsche, 1999) depending on the exact experimental conditions, which were mastered in the 1960 s (Gutsche, 1998), but the most common receptors are those with n =4,6,8 (macrocycles with an odd number of phenol units are more difficult to synthesize). We use here the simplified nomenclature in which the number of phenolic units is indicated between square brackets and para substituents are listed first.4 Calixarenes, which can be easily derivatized both on the para positions of the phenolic units and on the hydroxyl groups, have been primarily developed for catalytic processes and as biomimics, but it was soon realized that they can also easily encapsulate metal ions and the first complexes with d-transition metal ions were isolated in the mid-1980 s (Olmstead et al., 1985). Jack Harrowfield characterized the first lanthanide complex with a calixarene in 1987, a bimetallic europium complex with p-terf-butylcalix[8]arene (Furphy etal., 1987). 

It is perhaps inopportune to elaborate on the nomenclature, but some of the data reported for the tantalum ylide indicate that there may be a fundamental difference between this transition metal compound and the formally related ylides of the Group Yb elements. The most significant discrepancy is found with the 13C NMR shift of the carbene/ylide carbon atoms, which typically is downfield for the Va element, but upheld for the Vb element derivatives. Ylidic carbon atoms may, therefore, possibly bear a much higher negative charge. 

Complex ions combine with cations or anions to form coordination complexes. These complex ions usually consist of a transition metal ion attached to ligands. You should be familiar with the basic nomenclature for coordination complexes. 

Finally, I wish to thank those members of Inorganic Syntheses, Inc., who read the original manuscripts and gave me much valuable advice and help. I am especially indebted to Professors Eugene C. Ashby and Herbert D. Kaesz who contacted prospective authors for the syntheses of main group hydrides and transition metal hydrides, respectively. I also wish to thank Warren H. Powell and Mr. Thomas E. Sloan for their invaluable assistance in nomenclature matters and in the copy-editing of the manuscripts as well as Professor W. Conard Fernelius for his meticulous reading of proof for the entire volume. 

For an excellent review of transition metal nanocluster formation and nomenclature, as well as the difference between colloids and nanoclusters, see Finke, R. G. Transition Metal Nanoclusters in Metal Nanoparticles Synthesis, Characterization, and Applications, Dekker New York, 2002. 

Decades of heterogeneous catalysis research have found empirically that combinations of transition metals are often better catalysts than the pure metal components by themselves. It remains challenging in many cases, however, to understand why these multi-metallic materials are better catalysts than the pure components. We focus in this review on combinations of transition metals where mixing of the components has occurred on atomic length-scales (as opposed to the conceptually simpler situation where the two components co-exist in pure but separated forms). We will refer to these combinations genetically as alloys, although below we define a more precise nomenclature for the range of possible materials that exist. 

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