First transition series divalent state

The high affinity shown by carboxylic acids for copper (II) compared with the remaining divalent metals of the first transition series appears to be due in part to the stabilization of the extracted complexes by the formation of the well-known dimeric structure (1) in which copper(II) carbox-ylates exist in the solid state and in non-donor solvents.54 The axial ligands, L, consist of undissociated carboxylic acid molecules55 or, in the absence of an excess amount of extractant, they may consist of water or other solvent molecules.56 Copper was successfully removed from nickel sulfate solutions on the base-metal plant at Matthey Rustenburg Refiners in South Africa by being extracted into Versatic 10 acid at a controlled pH value. The process is believed to have been discontinued only because improvements in the selective leaching of copper and nickel rendered it unnecessary. 

Cations of the first transition series do not conform to the smooth pattern for the lanthanide elements shown in fig. 6.1. This is illustrated in fig. 6.2a by the radii of divalent cations in oxides containing transition metal ions in high-spin states. There is an overall decrease of octahedral ionic radius from Ca2+to Zn2+, but values first decrease to V2+, then rise to Mn2+, decrease to Ni2+, and rise again to Zn2+. The characteristic double-humped curve shown in fig. 6.2a has... 

The most stable and important state is Cr111, d3, which in an octahedral complex has each t2g level singly occupied, giving a sort of half-filled shell stability. The lower oxidation states are strongly reducing in aqueous solution only the divalent state, Cr2+, is known. Since for Cr and also for the following elements of the first transition series the more important oxidation states are the lower ones, we discuss them first. 

The methoxide of manganese (II) was described by Kandelaki [874] and first obtained and described in the individual state by the group of Martin in the late 1960s along with a series of methoxide derivatives ofthe divalent 3d-transition metals [6],... 

The transition element cations, which comprise Schwarzenbach s class C, have 0 to 10 subshell electrons in the M shell (first series) or N shell (second series), etc. Examination of Table 3.5 shows that the class C cations are generally considered either hard or borderline hard-soft acids. These cations have partially filled 3d subshells either in the ground state or when ionized (Table 3.6). Moving across the periodic chart from Sc to Cu, protons are added to the nucleus and electrons to the unfilled inner 3d subshell. Attraction of these inner electrons to the nucleus leads to an overall decrease in cation radii (Table 3.7). The divalent ions are generally sixfold, coordinated in complexes. is an exception and, because of its small size and unique electronic configuration, tends... 

If it is assumed that californium metal does exhibit two metallic valences, then two phases for each valence form can be selected from the crystallographic data in Table 11.3. For the trivalent form, metallic radii of 1.69 and 1.75 A would be obtained, which is in accord with the radii obtained for the first three transplutonium metals, when allowing for a small systematic decrease in radius in going across the series. The divalent form would yield a radius of 2.0 A, which is similar to the radii of divalent europium or ytterbium metals. The trivalent form of californium metal is well-established if a divalent form does exist, it is favored in small quantities (thin films) obtained from higher temperatures (quendted from the vapor or molten states). Only a limited effort has been made to establish transition temperatures for californium metal [72]. 

Manganese can exist in multiple oxidation states from manganese(II) to man-ganese(VII). Of these states, only the lowest three exist in cationic form. Man-ganese(II) hydrolyses at the highest pH of the divalent first series transition metals and, conversely, manganese(III) at the lowest pH of the corresponding trivalent metals. 

The sulfate ion (S04 ), though a simple dianionic ligand, exhibits a rather flexible symmetry and variable mode of binding with metal ions in the crystalline state. Interest in metal sulfate interactions with the hydra-zinium cation arises from the fact that these compounds exhibit one- and three-dimensional magnetic interactions of a linear-chain antiferromag-net. Dihydrazinium sulfate forms a series of double sulfates with divalent and trivalent cation that are well crystallized and, in a few instances, are even less soluble than hydrazinium sulfate itself. The most easily prepared double sulfates are those of Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd, Li, Mg, Al, La, Ce, Pr, Nd, and Sm. These salts are similar to the ammonium alums obtained with some metal sulfates. In contrast to the ammonium double salts, the hydrazinium metal sulfates of first row transition elements and lithium crystallize without water, whereas the lighter lanthanides and aluminum form hydrated salts. 

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