Valence states, multiple

Figure 8.23A shows a simplified Eh-pH diagram for the Mn-O-H system. Within the stability field of water, manganese occurs in three valence states (2+, 3 +, and 4+). Figure 8.23A shows the condensed phases relative to the three valence states as the hydroxide pyrochroite Mn(OH)2 (2+), multiple oxide haus-mannite Mu304 (2+, 3 + ), sesquioxide Mu203 (3 + ), and oxide pyrolusite Mn02 (4+). 

H Many elements have multiple valence states. Additional ionic radii are listed 2 He... 

In decomposition reactions of dimethyl-metal complexes of palladium(II) and nickel (II) one finds the formation of only traces of methane [49] which may also attributed to an a-elimination process. In regard to the valence state, note that, formally, the alkylidene ligand is considered as a neutral ligand and therefore, in the tantalum-alkylidene complex in Fig. 4.29, tantalum is trivalent. The electronic structure of the alkylidene is of course reminiscent of the corresponding oxide CpTa(Cl)20, which we would definitely call pentavalent. All that matters is that there should be a sufficient number of electrons for the multiple bonds which we draw. 

The notion of the Valence State of an atom is based on that of Pauling [35] and Van Vleck [36] called atom in molecule . When considering only integral chemistry , where the multiplicity of bonds is represented by positive integers, and moreover, postulating that the highest multiplicity of the chemical bond considered is three1, the valence state of the atom can be described as a four-dimensional vector VVS [27, 37, 28, 38] ... 

Formally, a synthon S(A) is described by the 5-matrix. Off-diagonal entry atJ of the 5-matrix is defined as the multiplicity of the bond between the i-th and j-th atom (non-bonded atoms are bonded by zero-multiplicity bond). Diagonal entry au is defined as the four-dimensional vector of valence state of the i-th atom in 5 (A). 

The empirical valence bond model has shown good predicting power if one defines the bond multiplicity to be two for compounds such as CePd or BaPd and three for compounds such as LaRh, Ylr, or RhTh. The limitations of the model could also be shown (40) when applied to assumed quadruple bond formation, as in RuV or ThRu or to double bond formation as in CePt or ThPt. The case of ThRu (41) shows that quadruple bonding is approached where suitable valence states are available, but not fully achieved, apparently because of the directional requirements of the bonding in a diatomic molecule. The examples of CePt and ThPt (40) show the calculated values that have been based on an assumed double bond to be too low. Platinum has no suitable valence state for triple bond formation, but apparently forms triple bonds with other... 

Disproportionation can be used to deposit metals that are stable in multiple valence states depending on the temperature in the reactor. The precursor is typically a halide as for germanium deposition ... 

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