Complexes, transition metal, periodic trends

Analytical Chemistry of the Transition Elements Coordination Numbers Geometries Coordination Organometallic Chemistry Principles Hydride Complexes of the Transition Metals Oxide Catalysts in Sohd-state Chemistry Periodic Table Trends in the Properties of the Elements Sol Gel Synthesis of Solids Structure Property Maps for Inorganic Solids Titanium Inorganic Coordination Chemistry Zirconium Hafnium Organometallic Chemistry. 

Many other metals have been shown to be active in HDS catalysis, and a number of papers have been published on the study of periodic trends in activities for transition metal sulfides [15, 37-43]. Both pure metal sulfides and supported metal sulfides have been considered and experimental studies indicate that the HDS activities for the desulfurization of dibenzothiophene [37] or of thiophene [38, 39] are related to the position of the metal in the periodic table, as exemplified in Fig. 1.2 (a), 1.2 (b), and 1.2 (c). Although minor differences can be observed from one study to another, all of them agree in that second and third row metals display a characteristic volcano-type dependence of the activity on the periodic position, and they are considerably more active than their first row counterparts. Maximum activities were invariably found around Ru, Os, Rh, Ir, and this will be important when considering organometallic chemistry related to HDS, since a good proportion of that work has been concerned with Ru, Rh, and Ir complexes, which are therefore reasonable models in this sense however, Pt and Ni complexes have also been recently shown to promote the very mild stoichiometric activation and desulfurization of substituted dibenzothiophenes (See Chapter 4). 

There is experimental evidence that supports this trend. For example, hydration energies for M(II) ions of the first row transition metals exhibit a W-shaped pattern, as a result of crystal field stabilization superimposed on the expected periodic increase (Figure 7.6), consistent with this model. Likewise, the measured lattice energies of transition metal fluorides (MF2) display a very similar pattern. The predominance of low spin d6 complexes is also consistent with the model, as there is a significant difference in LFSE between spin states in favour of low spin in the model. However, there are concerns with the model that have attracted criticism for example, one might anticipate low spin d5 more often than is observed. However, it is a simple and sufficient model to use at a basic level. 

Periodic Trends in the Bond Energies of Transition Metal Complexes... 

Accurate Density Functional calculations make possible today the systematic investigation of periodic trends in the bond energies of transition metal complexes. Computational results are presented for metal-metal bonds in dimers of the group 6 transition metals, metal-ligand bonds in early and late transition metal complexes, and metal-carbonyl bonds in hexa- penta- and tetra-carbonyl complexes. 

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