Divalent oxidation state

Reduction lowers the charge to radius ratio of transition metal ions, promoting higher rates of ligand substitution. Reduced, divalent oxidation states of manganese, iron, cobalt, and nickel are also quite soluble (Table II). 

The earlier literature on patterns of reactivity in the formation of platinum hydrides by protonation reactions of platinum in zerovalent and divalent oxidation states has been briefly... 

The chemistry of carbene complexes is a field which has developed in the past 20 years. The current interest is primarily centered on the chemistry of the early transition elements, but much of the early work was carried out at low valent, metal centers. The major complexes formed by platinum are those with the metal in a divalent oxidation state. 

Binuclear platinum complexes with the o -pyridinato ligand can be formed with the metals in a divalent oxidation state. Two such complexes are the head-to-tail dimer [Pt(QH4NO)(NH3)2]2+ and the head-to-head tetramer [Pt2(CsH4NO)2(NH3)4]2+. This tetrame-ric platinum(II)-(II) compound is prepared under experimental conditions where the pH is kept around neutrality to avoid the formation of the partially oxidized complex.1120 Platinum-195 NMR spectroscopy can be used to show that the head-to-head to head-to-tail isomerization of these complexes involves dissociation of one ligand arm followed by an intramolecular linkage isomerization. Finally bond formation occurs between the divalent platinum with the vacant coordination site and the uncoordinated end of the ligand.1121... 

In our case a similar explanation can be advanced. Preliminary IR data (15) indicate that CO can be chemisorbed on catalyst C (RhSnfC g)2/Si02) in a linear and bridged manner, suggesting that the dialkyl tin fragment and CO could be adsorbed on rhodium in a close vicinity. It is also reasonnable to assume that tin is in the divalent oxidation state. In this case, the mechanism of the citral hydrogenation could be the following ... 

In 1956 it was found that europium and ytterbium dissolve in liquid ammonia with the characteristic deep blue color known for the alkali and alkaline earth metals [36-40]. This behavior arises from the low density and high volatility of those metals compared to the other lanthanide elements [41]. Samarium, which normally also occurs in the divalent oxidation state, does not dissolve under... 

Consistent with the stability of the divalent oxidation states see Formal Oxidation State) of ytterbium and europium, the triflates of Yb(III) and Eu(III) are reduced by the bis(trimethylsilyl)allyl anion, leading to Ln(II) species (equation A) The same compounds can be made in higher yield by starting with Yb(II) and Eu(II) triflates directly. 

Our results show that as expected Am is the actinide element which forms the divalent oxidation state most easily. In our attempts to form divalent Pu and Cm we found instead sharp line spectra caused by the tetravalent state. Our experiments do not exclude the possibility that divalent ions of these elements are formed because we do not have an unambiguous method of detection. In our attempts to make divalent ions we have found interesting solid-state chemical effects attributed to the high level of radiation in the crystals. 

Judging from UV-Vis spectroscopy, Eu2+ has a remarkably high stability in [C4mim][PF6] and the complexation of Eu2+ with 15-crown-5 has been studied in this solvent [21]. Indeed, ionic liquids are useful to stabilize the divalent oxidation state of lanthanides which has been shown by the synthesis and structural characterization of [C4mpyr]2[Eu(Tf2N)5] [22],... 

Ngj, N(. .) and Ngr denote the numbers of silicon atoms, sulfur atoms in the lowest (divalent) oxidation state, and bromine atoms, respectively. The contribution of silicon atoms to Vw was estimated by using an "internal consistency" condition between the key correlations, namely by requiring that the value of Vw calculated by using equations 3.10 and 3.11, when inserted into the equations for the molar volume, should provide reasonable agreement with the observed densities [17] of silicon-containing polymers. 

NBr and Np are the numbers of sulfur atoms in the lowest (divalent) oxidation state, bromine atoms, and fluorine atoms, respectively, in the repeat unit. 

The divalent oxidation state of the lanthanide elements is commonly found for europium and ytterbium, though some simple salts have been prepared for most of the 4f-series (12). Only a few molecular compounds have been described and these have been mainly with cyclopentadienyl and cyclooctateraene ligands (18b). None have been characterized by X-ray methods since the compounds are generally insoluble and nonvolatile an observation that is consistent with a polymeric constitution. 

The divalent oxidation state was the first found for any member of the actinide series (20,21) and, therefore, stirred a strong theoretical and experimental effort to establish the reasons for the unexpected stability of this state in Md, and subsequently, in the adjacent actinides. We shall summarize the interpretations for divalency in the heaviest actinides in a later section of this review, but in this section, only the known properties of Md + will be presented. 

A central feature in the chemistry of No is the dominance of the divalent oxidation state (26). In this respect, No is unique within the lanthanide and actinide series, since none of the other twenty-seven members possess a highly-stable divalent ion. The electronic configuration of the neutral atom obtained from relativistic Hartree-Fock calculations is 5f 7s 2 (j>). Clearly, the special stability of No + must arise from the difficulty in ionizing an f valence electron from the completed 5f shell. Thus, pairing of the last electron, to close the shell, results in the f electron levels taking a rather abrupt drop in energy below the Fermi surface. 

---