Tetravalent Compounds

The +4 state is important not only for uranium but for the three elements directly following it. Because of the persistence of the tetravalent state in this series of elements, they are sometimes referred to as members of a uranide series, or occasionally, in view of their resemblance to tetravalent thorium, as the ihoride series. (Note that such language refers specifically to the oxidation state the +3 states of the same group of elements are considered members of the much longer actinide series.) 

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Rhenium Halides and Halide Complexes. Rhenium reacts with chlorine at ca 600°C to produce rheniumpentachloride [39368-69-9], Re2Cl2Q, a volatile species that is dimeric via bridging hahde groups. Rhenium reacts with elemental bromine in a similar fashion, but the metal is unreactive toward iodine. The compounds ReCl, ReBr [36753-03-4], and Rel [59301-47-2] can be prepared by careful evaporation of a solution of HReO and HX. Substantiation in a modem laboratory would be desirable. Lower oxidation state hahdes (Re X ) are also prepared from the pentavalent or tetravalent compounds by thermal decomposition or chemical reduction. 

Binding affinities of the new flexible synthetic glycocluster toward type-1-piliated E. coli were evaluated by HAI and bladder-binding assay (BBA). The results indicated that, with an inhibition of bacterial bladder-cell binding at 12 nM ( 6000- and 64-fold lower than mannose and 59, respectively), the tetravalent compound 60 is currently one of the most promising antiadhesive drugs under development for the treatment of urinary tract infections. 

Most usual coordination numbers for its tetravalent compounds are 4,5 and 6, although examples of 7 and 8 coordination are known. While bivalent organotin compounds such as (CsHs Sn and [(MesSi CIThSn are 2-coordinate, coordination numbers of 6 and 7 have been observed for arene-tin(II) compounds30. 

Tin is comparable in its toxicological behavior to lead and mercury. Bivalent tin compounds generally are more toxic than the tetravalent compounds. Furthermore, organic tin compounds are more toxic than inorganic ones and the trialkyl analogs (triethyltin, trimethyltin, tributyltin) are the most toxic. As the number of carbon atoms attached to tin increases, the toxicity of the organic tin compounds rapidly declines9,77. 

The fourth spectrum on Fig. 22, that of TiO, has lost the 5 ev. peak which characterized the tetravalent compounds. The amplitude of this spectrum is reduced compared to that of Ti02. 

In solution Am4+ ion is not so stable, slowly reducing to trivalent Am3+. However, simple and also complex tetravalent compounds of americium are known. Some examples are Am(OH)4, AmF4, LiAmFs, andK2AmF4. Am(OEf)4 is stable in basic solution and results from the oxidation of Am(OH)3 by hypochlorite ion. 

The chemical properties of germanium fall between those of silicon and tin. It forms both the divalent and tetravalent compounds, the oxidation state +4 being more stable than the +2 oxidation state. The metal is stable in air and water at ambient temperatures. However, it reacts with oxygen at elevated temperatures forming divalent and tetravalent oxides, GeO and Ge02. 

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. 

Elemental silicon is relatively stable in most substances at ordinary temperatures. Silicon shows similarity with other elements of its group, especially with germanium in many chemical properties. It forms tetravalent compounds with tetrahedral geometry almost exclusively. However, only in silicon monoxide, SiO, is its valence +2. Also, unlike carbon, silicon does not form unsaturated double or triple bond compounds. Silicon dissolves in germanium... 

Unlike carbon, which forms only stable tetravalent compounds, phosphorus forms stable trivalent, tetravalent, and pentavalent compounds. A phosphoryl transfer reaction such as... 

In keeping with its 4d%5s electron configuration, molybdenum forms many compounds in which its oxidation state is 6+. to an even greater extent than chromium. Also, like chromium, it forms compounds in which II is divalent and those in which it is trivalenl unlike chromium, il forms a number of pentavalenl compounds, and a few more tetravalent compounds, especially complexes. 

In addition to the dioxide MoO and the disulfide. MoS . example of leLravalem molybdenum compounds include the tetrachloride. MoClj. and teurabromide. MoBr. both of which are hydrolyzed in hot l-l-O. Other tetravalent compounds include a few of the complexes. 

In keeping witii its 5d 6s2 electron configuration, tungsten forms many compounds in which its oxidation state is 6+, just as molybdenum does. It forms divalent and tetravalent compounds to about the same extent as molybdenum but its bivalent and pentavalent compounds are somewhat fewer. Its anion chemistry is closely akin to that of molybdenum. 

Xenon also forms compounds, possibly clatlirates. with certain substances in nonstoichiometric proportions. Crystalline compounds with benzene or hydroquinone, formed under 40 aim osp lie res pressure, contain about 26% xenon by weight. Alkaline hydrolysis of XeF6 produces salts of octavalent xenon. No persistent divalent or tetravalent compounds are found in aqueous solution, but the former is intermediate in hydrolysis of the fluondes, and the latter in reactions of XeC>3 with XeF2, Hi02, and various organics... 

Most platinum compounds exist as coordination complexes the tetravalent compounds typically are more toxic than the hexavalent ones [10]. Certain neutral platinum complexes exhibit antitumor activity and therefore are used in chemotherapy drugs such as cisplatin. Speeiation is required to distinguish platinum chemotherapy drugs from their metabolites in patients blood and serum samples. 

Estimates of formation enthalpies of MX2 and MX4 (X = F, Cl, Br, I, S042", C032, N03 and P043 ) for Po and element 116 [150] made on the basis of the MCDF atomic calculations confirmed the instability of the 4+ state of element 116. The chemistry of element 116 is expected to be mainly cationic an ease of formation of the divalent compounds should approach that of Be or Mn, and tetravalent compounds should be formed with the most electronegative atoms, e.g., 116F4. 

Other convenient reagents for the imidation of sulfides and selenides are imidoiodanes such as A-(/>-tolylsulfonyl)-imino(phenyl)iodane (PhI=NTs).304 Unfortunately, these reagents are sometimes difficult to prepare due to their thermal sensitivity and some have even been claimed to be explosive.305 Selenimides are tricoordinate tetravalent compounds and can be isolated in optically active forms. They can be prepared from optically active selenoxides, a reaction which was shown to occur with an overall retention of stereochemistry.306 They can also be obtained by optical resolution of a diastereomeric selenimide and stereochemical issues including kinetics of epimerization by pyramidal inversion were studied in detail.307 Also the enantioselective imidation of prochiral selenides of type 179 is possible by using a combination of A-(/>-tolylsulfonyl)imino(phenyl)iodane (PhI=NTs) and a catalytic amount of... 

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