Valence relationships

Tributsch H (1982) Photoelectrochemical Energy Conversion Involving Transition Metal d-States and Intercalation of Layer Compounds. 49 127-175 Truter MR (1973) Structures of Organic Complexes with Alkali Metal Ions. 16 71-111 Tytko KH, Mehmke J, Kurad D (1999) Bond Length-Bond Valence Relationships, With Particular Reference to Polyoxometalate Chemistry. 93 1-64 Tytko KH (1999) A Bond Model for Polyoxometalate Ions Composed of M06 Octahedra (MOk Polyhedra with k > 4). 93 65-124... 

Evidently the valency relationship is by no means rigid, and in addition the various observations do not agree amongst themselves. It has already been noted that the process of coagulation is the result of a series of independent operations primarily dependent on an adsorptive process due to diffusion the manner in which the... 

Hurtley and Smiles4 had isolated fused-ring derivatives of 2 as early as 1926, but were understandably unable to find a satisfactory explanation for the valence relationships on the basis of the views held at that time. Wizinger and Soder,6 in 1958, were the first to suggest that these aryl-l,3-benzodithiol-l-sulfonium salts were derivatives of the resonance-stabilized benzo-l,3-dithiolium cation. 

What is the physical origin of the transition-state valency relationship An analysis of the electronic structures of the initial, transition, and final states reveals that an answer to this question lies in the p orbitals of the adsorbates (except chemisorbed H). We find... 

Bond-Length - Bond-Valence Relationships in Inorganic Solids... 

A general consensus is that hardness increases (or softness decreases) with increasing positive oxidation state. For example, Ni(0) is soft, Ni(II) is borderline, but Ni(IV) is hard the sulfur atom in RS is soft, medium soft in RSO , and it is hard in RSOf is softer than SO 3 . There are a few exceptions to the rule, however. For instance, Tl(III), Sn(IV), and Pb(IV) are softer than their respective lower valent ions. Because T1(I), Sn(II), and Pb(II) ions have electrons in their outermost shells, the shielding of the d electrons decreases the so/tness of the lower valent species (12). One factual demonstration of this reverse hardness/valence relationship is that inorganic thallium compounds are generally more stable in the -1-1 valence state, while covalent organothallium derivatives are stable only in the -i-3 state. 

As Russell has noted [15], Thus out of a study of the periodic dependence of general chemical behaviour on atomic weights there emerged a new set of valency relationships that for the first two periods at least, revealed an underlying simplicity that was to prompt still more fundamental questions . 

The main reason for separating these elements must also be the valency relationships among them as well as more specific chemical similarities. 

The perovskite structure is a close-packed lattice with the general formula ABX3. Almost all the known rare earth perovskites are oxides with the rare earth ion occupying the A sites and the present discussion will hence be restricted to ABO3 type compounds. Since most of the rare earth ions are stable only in the trivalent state the valence relationship is A B " 03. It is much easier to obtain the compounds in polycrystalline than in single crystal form however in some instances crystals have been prepared for special applications. 

The failure of the related metal carbonyls and nitrosyls to obey the rule of eight was recognized very early. So it is not surprising that our present concepts of their valence relationships already are so close to the ideas presented here that no further discussion of them is necessary. 

---