3d transition-metal ions

Late transition metal or 3d-transition metal irons, such as cobalt, nickel, and copper, are important for catalysis, magnetism, and optics. Reduction of 3d-transition metal ions to zero-valent metals is quite difficult because of their lower redox potentials than those of noble metal ions. A production of bimetallic nanoparticles between 3d-transi-tion metal and noble metal, however, is not so difficult. In 1993, we successfully established a new preparation method of PVP-protected CuPd bimetallic nanoparticles [71-73]. In this method, bimetallic hydroxide colloid forms in the first step by adjusting the pH value with a sodium hydroxide solution before the reduction process, which is designed to overcome the problems caused by the difference in redox potentials. Then, the bimetallic species... 

The lanthanides have electrons in partly filled 4/orbitals. Many lanthanides show colors due to electron transitions involving the 4/orbitals. However, there is a considerable difference between the lanthanides and the 3d transition-metal ions. The 4/ electrons in the lanthanides are well shielded beneath an outer electron configuration, (5.v2 5p6 6s2) and are little influenced by the crystal surroundings. Hence the important optical and magnetic properties attributed to the 4/ electrons on any particular lanthanide ion are rather unvarying and do not depend significantly upon the host structure. Moreover, the energy levels are sharper than those of transition-metal ions and the spectra resemble those of free ions. 

These materials are normally colored by low concentrations of 3d transition-metal ions or more rarely by lanthanide ions. The pale green color of ordinary window glass is due to the presence of Fe2+ impurities and small amounts of doping of Cr3+ into AI2O3 (corundum) creates ruby. 

The colors are characteristic of the ions themselves and are due to transitions between the partly filled d orbitals of transition metals (d-d transitions) or the partly filled / orbitals of lanthanides (f-f transitions). In the 3d transition-metal ions, the 3d orbitals contain one or more electrons. When these ions are introduced into a solid, the orbital energies are split by interactions with the surrounding anions. The color observed is due to transitions between these split energy levels. The color observed varies considerably as the interactions are dependent upon the... 

Equation (S6.1) is applicable to the salts of lanthanide ions. These have a partly filled 4f shell, and the 4f orbitals are well shielded from any interaction with the surrounding atoms by filled 5.9, 5p, and 6.9 orbitals, so that, with the notable exceptions, Eu3+ and Sm3+, they behave like isolated ions. For the transition metals, especially those of the 3d series, interaction with the surroundings is considerable. Because of this, the 3d transition-metal ions often have magnetic dipole moments corresponding only to the electron spin contribution. The orbital moment is said to be quenched. In such materials Eq. (S6.1) can then be replaced by a spin-only formula ... 

The focus of this paper is on the role electronic structure plays in determining the site preference and mobility of 3d transition-metal ions in an oxide and how these factors in turn affect the resistance of metastable 3d transition-metal oxides against transformation. This is a relevant topic to the Li rechargeable battery field because 3d transition-metal oxides are often used as positive electrode materials. 

Given that the structural transformation of the a-NaFe02-type layered and orthorhombic structures to spinel only requires cation migration, the varying resistance of transition-metal compositions against the transformation (i.e., low resistance for Mn, high for Co) is most likely connected to the diffusion kinetics of the respective 3d transition-metal ions. 

A large volume of work64 has been published on the determination of stability constants for complexes of hydroxamic acids, e.g. acetohydroxamic acid.65 The stability of 3d transition metal ions (Mn2+ to Zn2+) with salicylhydroxamic and 5-methyl-, 5-chloro-, 5-bromo-, 5-nitro-, 4-chloro-, 4-bromo- and 3-chloro-salicylhydroxamic acids,66 as well as with methyltolylbenzohydroxamic acid,67 has been studied potentiometrically. Stability constants of iron(III) with a number of hydroxamic acids have been determined by redox potential studies.68... 

Co2+ 47 i (F) state. In fact, the absence of low-energy excited states is unique to Mn2+ among divalent tetrahedral 3d transition metal ions, and consequently Mn2+ is the only efficient 3d TM2+ activator for visible luminescence. 

Zeolites containing 3d transition-metal ions were considered in Beran et al. (109-112). The peculiarities of the donor-acceptor interactions of these cations located within six-membered rings with a zeolite lattice were discussed in terms of atomic charges, bond orders, and orbital energies. The redox properties of the cations, the acid-base properties of zeolites, and the dependence of these characteristics on the Si/Al ratio were discussed as well. The authors noted that the forms containing univalent copper and nickel ions should possess the highest electron-donor ability and consequently the... 

This differs from the familiar /Ueff = -Jntn + 2) formula, where n is the number of unpaired electrons, [or. 45(5 + 1), spin-only formula], often applicable to the 3d" transition metal ions, as in the latter case the orbital contribution to the moment is quenched by the interaction of the metal s 3d orbitals with the ligands. 

Apart from the data already discussed for salts of the 3d transition metal ions, significant bonding information has otherwise been obtained only for a few rare earth ions. The magnetic and crystallographic properties of many 4d and 5d... 

One-electron dioxygen reduction may also occur via an outer-sphere electron transfer, affording a noncoordinated superoxide and a one-electron oxidized metal complex. Essentially, all low-valent 3d transition metal ions and numerous 4d and 5d metal ions can react as one-electron reducing agents. 

Octahedral coordination is frequently adopted by the important 3d transition-metal ions. In this coordination polyhedron, each cation is surrounded by six anions, to form an octahedral [MOe] group, (Figure 7.14). The cubic structure of rhenium trioxide, ReC>3, a = 0.3750 nm, is... 

Complexes of Selected 3d Transition Metal Ions With Nucleic Acid Duplexes... 

These studies indicate that the sequence of duplexes and the accessibility of bases are the dominant factors that determine the binding pattern of the labile metal ions to DNA, and that the molecular electrostatic potential further affects the metal binding. Of importance for this chapter is that in all of the reported solution and solid-state structures, the 3d transition metal ions coordinate to the N7 of a G nucleobase and complete their octahedral coordination sphere with water molecules or with phosphate groups from adjacent nucleotides within the duplexes. Thus they do not form direct interstrand bridges. 

Due to these difficulties, only a limited number of stability constants could be determined and are listed in Table 20. For a given d-transition metal ion, the evolution of the data along the lanthanide series seems to parallel the tendency observed with the mononuclear precursors the Ns chelating unit in L35 induces less stable complexes with heavier lanthanides, contrary to the N2O donor site in L36. The difference, however, remains small and close to the experimental imcertainties. On the other hand, the 3d-transition metal ion has a much larger influence, compare for instance values for the LaM complexes with L36 the M = Zn"... 

Formation of RML3 helicates with kinetically inert trivalent 3d-transition metal ions Cr " and Co "... 

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