3d-metal cations

Structural and energetic values for 3d metal cations (Me) in trigonal zeolite sites... 

Like H2LI7IO considered above, the ligand H2LI7I8 is able to form binuclear species not only with 3d metal cations, but also with the much larger U02 ion. The 1 -f 1 open-chain condensation product in the form of the complex U02(0H)(HL1723) (Eq. 8.33) has been isolated from reaction of the ligsons on a uranyl matrix in the presence of LiOH [82]. A similar species is likely to be the first intermediate on the way to construction of the final macrocyclic compound H2LI7I8. 

In transition metal cations, 3d is lower in energy than 4s. 

Chiral-at-metal cations can themselves serve as chirality inducers. For example, optically pure Ru[(bipy)3] proved to be an excellent chiral auxihary for the stereoselective preparation of optically active 3D anionic networks [M(II)Cr(III)(oxalate)3]- n (with M = Mn, Ni), which display interesting magnetic properties. In these networks all of the metalhc centers have the same configuration, z or yl, as the template cation, as shown by CD spectroscopy and X-ray crystallography [43]. 

Table 9-8. Excitation Energies [eV] of 3d-Transition Metal Cations. ...

The discovery of 1 (1), in 1970, opened a new and fascinating chapter of organometallic chemistry. This cation was the first compound derived from the hypothetical borabenzene 2 and the first complex of a classical boron-carbon ligand. Since then approximately 100 borabenzene derivatives, mainly complexes of 3d metals, have been characterized. Other unsaturated boron-carbon systems have been shown to act as ligands to metals (2). This development has also strongly stimulated the challenging quest for the simple species 2-5. 

Most PET fluorescent sensors for cations are based on the principle displayed in Figure 10.7, but other photoinduced electron transfer mechanisms can take place with transition metal ions (Fabbrizzi et al., 1996 Bergonzi et al., 1998). In fact, 3d metals exhibit redox activity and electron transfer can occur from the fluorophore... 

Stepwise stability constants decrease regularly in the normal manner 178), log > log K2 > log K, as may be exemplified by the values for the Ni -maltolate system, viz. 5.5, 4.3, and 2.7, respectively 179). Stability constants (log Kf) for a selection of 3-hydroxy-4-pyranonate and 3-hydroxy-4-pyridinonate complexes of some first-row transition metal 2+ cations are listed in Table IV 10,128,180—184). The values for the 3d transition metal cations conform to the long-established Irving-Williams order... 

Using ionic valences found through a large series of calculations on substituted Mn oxides, a qualitative ionization scale between Mn and other 3d metals has been constructed. This scale allows one to predict the valences for Mn (in octahedral and/or tetrahedral coordination) coexisting with another 3d TM cation (in octahedral coordination) in a ccp oxide. This could be useful for designing TM oxide materials with improved kinetic stability over the range of Li concentrations covered by electrochemical cycling. 

With the oxide semiconductors, anionic chemisorption would take place over the metal cations, and the interaction problem would be between the orbitals on the foreign atom and the cation band (the 3d band in CU2O, for example). The discussion in this section is relevant if this is the highest filled band. 

In any cubic field, or in the case of octahedral coordination by eight anions, the 3d-state of a transitional-metal cation splits into six states of t2g symmetry with orbital wave functions of the form... 

The situation is a bit different for the formation of ions from the transition metal elements than it is for the main-group elements. Transition metals form cations by first losing their valence-shell s electrons and then losing d electrons. As a result, all the remaining valence electrons in transition metal cations occupy d orbitals. Iron, for instance, forms the Fe2+ ion by losing its two 4s electrons and forms the Fe3+ ion by losing two 4s electrons and one 3d electron ... 

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