Tripositive structure

Reference has been made already to the existence of a set of inner transition elements, following lanthanum, in which the quantum level being filled is neither the outer quantum level nor the penultimate level, but the next inner. These elements, together with yttrium (a transition metal), were called the rare earths , since they occurred in uncommon mixtures of what were believed to be earths or oxides. With the recognition of their special structure, the elements from lanthanum to lutetium were re-named the lanthanons or lanthanides. They resemble one another very closely, so much so that their separation presented a major problem, since all their compounds are very much alike. They exhibit oxidation state + 3 and show in this slate predominantly ionic characteristics—the ions. LJ+ (L = lanthanide), are indeed similar to the ions of the alkaline earth metals, except that they are tripositive, not dipositive. 

The magnetic method cannot be applied to tripositive chromium, the structures of the two extreme types having the same number of unpaired electrons and entering into resonance with each other. The chemical properties of the chromium complexes indicate that chromium, like the other iron-group elements, forms hyperligating bonds... 

Neutral N-derivatized octadentate ligands based on cyclen (1,4,7,10-tetraazacy-clododecane) form tripositive cationic complexes with the trivalent lanthanides [116-124]. The N-substituted tetraamide derivatives have proven useful in understanding the relationship between the solution structure of the Ln3+ complex and its water exchange rate, a critical issue in attaining optimal relaxation efficiency of CA s [125-131]. 

B. von Ahsen, M. Berkei, G. Henkel, H. Willner, and F. Aubke, The Synthesis, Vibrational Spectra, and Molecular Structure of [Ir(CO)6][SbF6]3-4HF - The First Structurally Characterized Salt with a Tripositive, Homoleptic Metal Carbonyl Cation and the First Example of a Tetrahedral Hydrogen-Bonded (HF)4 Cluster, J. Am. Chem. Soc. 124, 8371-8379 (2002). 

Some compounds with formulas corresponding to [CuCl5]3" do, in fact, contain such discrete tbp anions if the cations are large and tripositive, for example, [M(NH3)6]3+. However, with smaller cations (e.g., M CuC15 of the alkalis) there are discrete [CuCLJ2" ions of D2< structure together with isolated Cl" ions. 

The metallobiochemistry of staphylococcal nuclease has been extensively investigated. It was shown early that the tripositive lanthanide ions, Ln, are potent competitive inhibitors of the enzyme, binding to it with K s of about 9/uM and acting with inhibitory constants of l-2 iM. The binding of Ln + ions enhances the binding of pdTp. Ln " ions, but not Ca, stabilize the enzyme toward tryptic proteolysis. The paramagnetism of Gd " was exploited in H and P resonance relaxation studies on pdTp bound in the ternary complex to determine that the structure in solution was consistent with the observed x-ray structure. Some differences were observed but these were of uncertain significance. 

Energy-level structure of the tripositive lanthanide ions in LaCl<... 

The highest oxidation states for Ir are VI and V, stabilized by ligands such as F. IrFg (a yellow crystalline solid, /Xgff = 2.9 /xb at 300 K) is formed by the direct fluorination of Ir metal. Molecules of IrFg are octahedral, and the structure has been studied in the gas phase by electron diffraction and in the solid phase by EXAFS. IrFg is hydrolyzed by water, and reactions (1 - 4) illustrate its general reactivity. Reaction four represents the formation of the first binary, tripositive metal carbonyl complex. 

Because the tripositive ions are the most stable for all the rare earth elements in almost all compounds, the thermochemistry of the solid (crystalline) rare earth sesquioxides dominates this chapter. Some rare earths have divalent or tetravalent states, so the chemistry of solid monoxides and dioxides are included. There are also many nonstoichiometric binary oxides of cerium, praseodymium, and terbium. As much as possible, the thermochemistry of these nonstoichiometric binary oxides is included. The stability, phase diagrams, and structures of ternary and polynary... 

---