Divalent compounds

Germanium forms divalent compounds with all the halogens. Germaniunil 1) chloride can be prepared by passing the vapour of germanium(IV) chloride (see below) over heated germanium. The reaction is reversible and disproportionation of germanium(II) chloride is complete at about 720 K at atmospheric pressure ... 

Mercury and its inorganic divalent compounds criteria document for an OEL... 

Despite the above similarities, many differences between the members of this triad are also to be noted. Reduction of a trivalent compound, which yields a divalent compound in the case of cobalt, rarely does so for the heavier elements where the metal, univalent compounds, or hydrido complexes are the more usual products. Rhodium forms the quite stable, yellow [Rh(H20)6] " ion when hydrous Rh203 is dissolved in mineral acid, and it occurs in the solid state in salts such as the perchlorate, sulfate and alums. [Ir(H20)6] + is less readily obtained but has been shown to occur in solutions of in cone HCIO4. 

Scheme 1 Synthesis of group 14 elements polysulfido complexes from divalent compounds bearing bulky substituents...

This interpretation of the experimental results was corroborated by ab initio calculations on the relative stabilities of a series of double bond compounds, [H2Pb=X] and their plumbylene type isomers, [frans-H-Pb-X-H] and [ciT-H-Pb-X-H] (X = O, S, Se, and Te) (vide supra) 6 The results of the theoretical calculations and experiments for lead-chalcogen double bond species are in sharp contrast to those of the other Group 14 element analogues which do not isomerize to the divalent compounds.14b... 

Reaction of Divalent Compounds of Group 14 Metals with Chalcogen Sources... 

Divalent compounds of group 14 metals, i.e., heavier analogs of carbenes, are highly reactive and readily insert into various bonds. Therefore, these species are useful for the formation of M-E (M = Si, Ge, Sn E = S, Se, Te) bonds. 

Forms only divalent compounds that are stable and have high heats of formation... 

Interest in divalent compounds of germanium has increased steadily over the past several years, and many new species have been prepared. In particular, unsymmetrical heteroleptic species GeLL have become much more prevalent. Several reviews covering the synthesis and chemistry of germylenes have appeared, and the... 

It is convenient to discuss the derivatives of the remaining heavier group 14 terphenyl elements together, since they have many features in common. This is particularly true for the divalent compounds. 

Europium has been characterized by several workers (3, 13) as divalent in the metallic state. This is again borne out by the isomer shift of the metal, which is clearly much closer to that of the covalent divalent compounds than that of the covalent trivalent compounds. (The comparison should be made with covalent compounds because in the metallic state the atoms are bonded together by sharing the valence electrons.)... 

Sulfoxidation reactions are characterized by enzymatic conversion of a divalent compound to sulfoxide (Fig. 15.7) or, in some cases, to sulfone (S SO O ). The degradation also may be catalyzed by minerals, converting organic sulfides (thioesters) and sulfites to the corresponding sulfoxides and sulfates. Because it is difficult to determine if the reaction is chemically or biologically induced, microbially mediated sulfoxidation in the subsurface environment can be established only when a biocatalyst is found. 

Several lanthanide cyclooctatetraene complexes have been synthesized, including both the divalent metal complexes Eu(CgHg) and Yb(CgH8) 44), and the trivalent complexes [M(CgH8)2] (M =Ce, Pr, Nd, SmorTb) 35). The former were preprired by direct reaction of the metal with cyclooctatetraene in liquid ammonia. No structural data exist for these divalent compounds, but they probably involve some kind of bridging interaction since, even with coordinated solvent, one COT... 

Lead forms amphoteric compounds in +2 and +4 valence states, forming plumbous and plumbic salts, such as PbCL and PbCL, as well as plumbites and plumbates, such as Na4Pb03 and Ca2Pb04,. Over a thousand compounds of lead are known which include divalent and tetravalent salts, complexes, and organometaUics. Divalent compounds of lead are far more numerous than the tetravalent compounds. Most compounds, however, result from the reactions involving other lead compounds, rather than elemental lead. Only the reactions involving elemental lead are outlined briefly below. 

The divalent compounds of samarium primarily are halides, the reddish-brown crystalline dichloride, SmCb [13874-75-4] the dark-brown diiodide, Sml2 [32248-43-4] and the dark brown dibromide, SmBr2 [50801-97-3]. Samarium also forms a difluoride, SmF2 [15192-17-3]. The trivalent salts of these halogens are more stable than their divalent counterparts. 

The present coverage is divided according to the class of intermediate carbocations, anions, carbenes (and related divalent compounds) and radicals. Within each class, the usual set of models is assessed, the exception being that molecular mechanics models have been excluded. These have not been explicitly parameterized for charged species or molecules with unpaired electrons, and cannot be expected to perform favorably. Note that in some, but not all cases, the quality of the experimental structural data is not up to the same standard as for other small molecules. This is particularly true for carbocations and anions, where differences among counterions may lead to large differences in structure. 

The few cases reported for CD sulphides and selenides of T1 all reported the monosulphide (selenide)—TIS or TlSe. T1 can be monovalent or trivalent, and these apparently divalent compounds are believed to be mixed-valence compounds, with both T1(I) and Tl(III) present. 

We turn now to the front end of each half-series, and the divalent ) compounds of Ce and Tb. Fig. la makes clear that the configurational choice offered here is not... 

Many other organochromium compounds have since been synthesized and found to be active, including those with chromium exhibiting every valence up to Cr (IV). Chromocene is a well-studied example of an active divalent compound (52-55). Pentadiene-Cr(II) (56) is another, along with allyl-Cr(II) (52, 57). Allyl-Cr(III) is also active (52, 57-61). -Stabilized alkyls of Cr(II) and Cr(IV) such as trimethylsilylmethyl-Cr(IV), which also polymerizes ethylene when supported on an oxide carrier, have been synthesized and tested in this laboratory (57,62). All these organochromium catalysts are comparable in activity to the Cr(VI)/silica standard. 

The apparent anomaly between mercury and the lighter elements of transition group 2. in that mercury regularly forms both univalent and divalent compounds, while zinc and cadmium do so very rarely, is partly under mm id from the observation that mercury III salts ionize even in the gaseous late to Hg.. rather than Hg Evidence for this double ion is provided by its Hainan spectral line, by the lineal CI-Hg-Hg-CI units in crystals or mercury It chloride, and by the cml of incrciirytll nitrate concentration cells The anomaly is fuitlicr removed by the obsetv.ttioii that cadmium also forms a (much less stable) diatomic ton Cdj T eg., ill Cd.-lAICL) . 

Among the divalent compounds of molybdenum are the dihromidc. MoBr-, and the dichloride. MoCI . There is also a complex ion of divalent molybdenum MosClJ. (flat is of particular interest because it does not yield Mo21 ions. The chloride sail of the ion. Mo CLi- has been shown, by precipitation with Ag+, to have two-thirds of its chlorine content present in a complex, so ils structure is established as [Mt CIsJCU, It is obtained by higher temperature disntutation of MoClj, while the corresponding dibromide ean be produced by direct reaction of the elements,... 

Due to its 4s24p4 electron configuration, selenium, like sulfur, forms many divalent compounds with two covalent bonds and two lone pairs, and d hybridization is quite common, to form compounds with Se oxidation states of 4+ and 6+. 

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