Transition metal ions nomenclature

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. 

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). 

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. 

In the first part of this section the elucidation of the mechanism will be presented, while the second part will be devoted to a discussion of the effect of cations on the viscoelastic properties. Both of these topics are grouped together because, as will be shown below, the relaxation mechanism of all the polymers discussed here is perfectly normal, i.e., simple molecular flow, [or the a mechanism according to the nomenclature of Ferry (27, 28, 29) and Hoff 37a), and the materials can thus be called chemically inactive. Finally, the work on viscoelasticity of bulk organic polyelectrol5des will be mentioned. The next section will be devoted to a discussion of the viscoelastic properties of materials in which, in addition to the a mechanism, bond interchange (the x mechanism) is also encoimtered, the chemical (hence x) activity being due to catalysis by transition metal ions. 

A description as a MMCT transition is not very obvious for this case. However, there is no essential difference between the physical origin of the colors of Pb(N02)2 and, for example, CU2WO4. Unfortunately the literature shows sometimes discussions on the nature of their excited states in terms of either MMCT or metal-ion-induced CT transitions. To us, such a discussion does not seem to be very fruitful. In the classification it is a matter of taste which nomenclature is used, in the (more difficult) characterization it is essential to determine the coefficients which indicate the amount of configuration interaction. The latter describe the nature of the excited state. 

Many metals (usually transition metals) may form cations of more than one charge. In this case, a Roman numeral in parenthesis after the name of the element is used to indicate the ion s charge in a particular compound. This Roman numeral method is known as the Stock system. An older nomenclature used the suffix -ous for the lower charge and -ic for the higher charge and is still used occasionally. 

If the cation and anion exist in only one common charged form, there is no ambiguity between formula and name. Sodium chloride must be NaCl, and lithium sulfide must be Li2S, so that the sum of positive and negative charges is zero. With many elements, such as the transition metals, several ions of different charge may exist. Fe ", Fe + and Cu+, Cu + are two common examples. Clearly, an ambiguity exists if we use the name iron for both Fe + and Fe + or copper for both Cu" and Cu +. Two systems have been developed to avoid this problem the Stock system and the common nomenclature system. 

In a seminal 1967 paper by Pedersen, the exceptional stability of macrocyclic crown ether complexes with alkali metal ions was reported." What followed was the birth of a new area of macrocyclic chemistry, one not involving transition metal complexes but focused more on organic chemistry. The field of supramolecular chemistry was just beginning to blossom. Perhaps the most studied of these macrocycles is the [18]crown-6. Nomenclature for the simple crown ethers derives from a simple notation that refers to the number of atoms in the ring enclosed in brackets,... 

Some metal atoms, especially those of transition and inner-transition elements, form more than one type of charged ion. Copper, for example, forms both Cu and Cu, and iron forms Fe and Fe. The names of ionic compounds containing such elements must indicate which ion is present in the compound. A nomenclature system that does this well indicates the ionic charge of the metal ion by a roman numeral in parentheses following the name of the metal. Thus, CuCl is copper(l) chloride and CUCI2 is copper(ll) chloride. These names are expressed verbally as copper one chloride and copper two chloride. ... 

In a more comprehensive treatment of nomenclature, compounds containing ions that exhibit more than one charge have the ionic charge indicated by the Roman numeral. For example, Sn and Pb are not transition metals, but their names require a Roman numeral because their charge can vary from one compound to another. 

In Chapters 2 and 3, we considered the history, nomenclature, and structures of coordination compounds. In these earlier discussions, we introduced the metal-ligand (M-L) coordinate-covalent bond in which the ligand shares a pair of electrons with the metal atom or ion. Now we are in a position to consider the nature of the M-L bond in greater detail. Is it primarily an ionic interaction between ligand electrons and a positively charged metal cation Or should the M-L bond be more properly described as predominantly covalent in character Whatever the character of the bond, the description of M-L interactions must account for (1) the stability of transition metal complexes, (2) their electronic and magnetic characteristics, and (3) the variety of striking colors displayed by these compounds. 

Luther s rule -> Luther studied the relation between the standard electrode -> potentials of metals that can exist in more than one oxidation state. For some electrochem-ically reversible systems (- reversibility) he showed theoretically and experimentally that for a metal Me and its ions Me+ and Me2+ the following relation holds (in contemporary nomenclature) for the -> Gibbs energies of the redox transitions ... 

The strong influence of Zintl on the description of chemical bonding in compounds at the border of salts and intermetallics led to the nomenclature Zintl ion f ° for soluble polyanions (as part of a polyanionic salt ) and Zintl phase f for compounds with anionic substructures obeying the (8 — N) rule. Further development and the perception that the salt-metal transition is not abrupt led to a continuous extension of these terms. Soluble polycations, discrete units, and low-dimensional substructures in Zintl phases are called Zintl ions. These ions commonly consist of metal- or semi metal-atoms, or of atoms of semiconducting elements. Clearly, they must be distinguished from classical ions as elucidated by a comparison of SnTe4 and the iso(valence)electronic ion S04 . 

Table 2.5 lists some common cations of the transition elements. Most of these elements have more than one ion, so require the Stock nomenclature system or the older suffix system. A few, such as zinc, have only a single ion that is normally encountered, and you usually name them by just the metal name. You would not be wrong, however, if, for example, you named Zn as zinc(II) ion. 

---