3d metals

Structural chemistry of pyridonate complexes of late 3d metals 97ACR89. 

Fig. 8.7 Superposition of density-of-states for B-N bonding BN>. states with corresponding metal states, reflected by their valence states from alkaline-earth (as Ca), lanthanide (as La), and 3d-metal (as Ni), and corresponding block schemes...

The number of metal wheels and, more generally, polynuclear cage complexes of the 3d metals has increased considerably in the last decade because of their magnetic properties, especially their behavior... 

Aroml G, Brechin EK (2006) Synthesis of 3d Metallic Single-Molecule Magnets. 122 1-67 Atanasov M, Daul CA, Rauzy C (2003) A DFT Based Ligand Field Theory 106 97-125 Atanasov M, see Reinen D (2004) 107 159-178 Atwood DA, see Conley B (2003) 104 181-193... 

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. 

Koopman s theorem is found to be valid only in the case of the vanadium (dA) complex 9. The amount of orbital reorganization is increasing considerably in the series 9-14-15-16. It is also found that strong metal-ligand interaction combined with low symmetry leads to extensive delocalization of the outer valence MO s especially in the cylobutadiene complex 16, only two orbitals with >80% metal character are found for which the convenient term essential 3d metal orbital would be justified. 

It is known that some spinel-structured 3d-metal oxides are good catalysts for many processes involving electron transfer [12]. However, their low conductivity does not allow for the direct use in the electrode of the battery, and grafting them onto the carbon matrix is also very difficult technical problem. It was found recently that this problem could be solved indirectly, creating the spinel catalytic centers on the surface of carbon by means of adsorption of some 3d-metal complexes on the graphite surface followed by subsequent pyrolysis at certain temperatures [13,14],... 

In this work we have studied the preparation of electrocatalysts on the graphite matrix using tri-nuclear complexes of 3d-metals with aminoalcohol ligands. Tri-nuclear complexes, 2[Co(Etm)3] Me(N03)2, where Etm = ethanolamine, Me = Zn2+, Cu2+, Ni2+, Co2+, were investigated. 

As it was shown in [15-18], such compounds, with bridging atoms of deprotonated amino alcohol, are formed when aminoalcoholate complexes of metal (III) react with bivalent 3d-metal ions. Many representatives of these compounds were synthesized in crystalline state the polynuclear compounds were also found to form in aqueous and methanol solutions. The structure of 2Co(III) - Ni(II) tri-nuclear complex, according to [17,18], is shown below in Figure 2. 

Modification of carbon materials by tri-nuclear complexes of 3d-metals with ethanolamine ligands increases the catalytic activity with regard to the electrochemical reaction of oxygen reduction. The Co-Ni complex is most active in this reaction if pyrolyzed at 600°C. 

On the basis of obtained data of cyclic voltammograms for 3d metals oxides electrodeposition the optimal conditions (current density, potential, process time, electrolyte composition, temperature) for dense oxide films (Ni, Cr and Co) deposition on steel foil have been elaborated. Data relating to several best films are summarized in Table 1. 

We managed to obtain dense and solid thin films of 3d-metal oxides using the techniques of electrochemical deposition from aqueous fluorine-containing electrolytes. The films have been studied as a possible cathode material for secondary cells. The best samples show good cycle retention and acceptable specific capacity in the range of 180 mAh/g. They also feature a plateau of electrochemical potential at approximately 3,5 V, which is acceptable for present industrially produced electrochemical devices. 

Such modification of the anisotropy would be hard to achieve, though, with Gd(III) ions, as their anisotropy would be minimal even with engineered ligand changes so this approach would be better suited to 3d chemistry, where the metal ion orbitals can interact more strongly with those of the ligands. Figure 9.9 tells us that isotropic 3d-metals are better for lower temperature work than anisotropic ones. 

For the Gd(III) compound -ASf is 21.4Jkg 1 K 1 (AH = 0 — 7T, 3K), whereas for Dy(III) this is only 11.6 J kg-11<-1. This is accounted for by the lower spin of Dy(III), but what is interesting is the fact that - ASM has already passed through a maximum at 4I<, compared to the Gd(III) plot, which is still rising at 3K, which is qualitatively in line with the work of Evangelisti and Brechin [13] for 3d metals. From this, we can say that the best lanthanide(III) for low-temperature MCE is gadolinium(III) indeed, there are only a handful of compounds using Dy(III) reported for this application. 

High-Nuclearity Paramagnetic 3d- Metal Complexes with Oxygen- and Nitrogen-Donor Ligands Richard E. P. Winpenny... 

Transition Metal Complexes with Bis(Hydrazone) Ligands of 2, 6-Diacetylpyridine. Hepta-Coordination of 3d Metals... 

Figure 7.11 Enthalpy of formation of binary oxides of the 3d transition metals (a) and (c), Frost diagram for the same 3d metals (b) Enthalpy of formation of binary oxides of the group 6 transition metals.

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... 

The above value of k4 1 s for bpy loss from Rh(bpy)3 + may be compared with k4 - 3 s for bpy loss from the formally related Co(bpy)32+ (13,14) Recently obtained results indicate that the rate constant for addition of bpy to Rh(bpy)2(H2O)2 (k 4 s 0.2 x lO Ms"1) is greater than that for the comparable cobalt(II) reaction (13,14) The more-or-less comparable labilities of Rh(bpy)3 T and Co(bpy)3 + are not unexpected in light of data for rates of ammonia loss from the two metal centers which are also available ammonia loss from rhodium(II) is quite rapid (10 s 1 to 10 s l with loss from Rh(NH3)5 H20 + being much faster than from Rh(NH3)4 +, etc ) W t>ut somewhat slower than the comparable process for cobalt(II) (15) Of course, here the relative affinities of the two metals for NH3 are not known and so cannot be taken into account A further reason these comparisons lack great validity is that, although these Co(II) complexes contain 3d metal centers, Co(bpy)3 + and Co(NH3)n + are high-spin complexes i.e. the ground states are (t2g) (eg) whereas 4d species are expected to be low spin, (t2g) (eg)1. Furthermore, as will be seen shortly it is not clear that even "low spin 4d " is an adequate description of the... 

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