Transition metals crystal structures

Coles SJ, Edwards PG, Fleming JS et al (1995) Triphosphorus macrocycle complexes of divalent group 6 transition metals. Crystal structure of bromotricarbonyl-[l,5,9-tris(isopropyl)-l,5,9-triphosphacyclododecane]-molybdenum(II) tetraphenylborate. J Chem Soc Dalton Trans 4091 097... 

In fact, iron exhibits all three common metallic crystal structures bcc, fee, and hep within its pressure-temperature phase diagram, as is shown by the inset of Fig. 8.14. The transition from the bcc a phase to the hep e phase... 

The nohle gases and most metals crystallize in either the hep or the ccp structure as would be expected for neutral atoms. The alkali metals, barium, and a few transition metals crystallize In the body-centered cubic system, though the reasons for this choice are unknown. 

Sulphur is less electronegative than oxygen, and in consequence no sulphide of composition AS2 crystallizes with any of the typically ionic structures commonly found among the oxides A02. A number of sulphides have the cadmium iodide layer structure, but many others, particularly those of the transition metals, have structures unrepresented among the compounds so far considered. A few of these are of sufficiently common occurrence to warrant discussion. 

AnX3 compounds, where X is a non-transition element from group III and IV or a late transition metal, crystallize in various structure types. Most of them crystallize in the cubic AuCu3 structure (space group Pm3m), where dAn An is equal to the lattice parameter a (see fig. 3.21). They constitute the second-largest group of... 

TABLE 5.1 Crystal Structures of Transition Metals, and Structure Progression in Nitrides and Carbides... 

The third class of hydrides is the metallic, or interstitial, hydrides, which are formed when transition metal crystals are treated with hydrogen gas. The hydrogen molecules dissociate at the metal s surface, and the small hydrogen atoms migrate into the crystal structure to occupy holes, or interstices. These metal-hydrogen mixtures are more like solid solutions than true compounds. Palladium can absorb about 900 times its own volume of hydrogen gas. In... 

As is usually the case with a displacive phase transition, the crystal structure of the high-temperature (/3) form (Jeitschko, 1973) comes close to the average of the (two) different orientation states of the low-temperature (jS ) form. In both forms the Gd atoms are seven-coordinated and the Mo atoms tetrahedrally coordinated by oxygen atoms. The oxygen atoms have either two or three near metal neighbors (fig. 30.12). The positional differences between the /3 and /3 ... 

A limited number of non-transition-metal derivatives of thiophene will be considered in this subsection. There are no short-range contacts between the lithium atoms originating from the (LiO)6 cores and the sulfur atoms in [Li—O—EMc2 (2-C4H3S)]6 (E = C, Si) (97OM5032), and evidence for Tr-interactions can be found in the X-ray crystal structures of these compounds. Theoretical computations show that a- (S ) Li" " interactions are weak, whereas Tr-Li" contributions are considerable, in accord with the general reasoning on the electronic characteristics of uncomplexed thiophene. 

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