Tantalum structural data

Tantalum coordination compounds classification and analysis of crystallographic and structural data. C. E. Holloway and M. Melnik, Rev. Inorg. Chem., 1985,7,1 (161). 

The last decade has seen enormous developments in SS NMR, and techniques that were used only in soluhon have become available also for solid samples. Nowadays, even conformers can be identified by solid-state NMR [22]. Therefore, this section outlines these improvements as well as their application to the characterization of selected surface organometallic species. An application of EXAFS to the characterization of surface organometallic tantalum species is also shown. Structural data obtained through EXAFS (such as that in Table 11.1) are often essential for comparisons with data obtained by DFT calculations. 

Table 44 Structural Data for Various Niobium and Tantalum Ousters of Type (M6X12)4+...

The crystal structures of both (PPN)[M(CO)6] derivatives have been determined.717 The coordination polyhedron is octahedral (Nb—C 2.098(5) A CNbC 89.2(2)°). The PPN moiety is constrained to be centrosymmetric, and thus linear. These compounds correspond to the lowest oxidation state of niobium and tantalum for which structural data are available. A single v(CO) is found in the IR (1854 and 1852 cm-1 for Nb and Ta respectively). Comparable spectra are observed for Na[M(CO)6] in pyridine, but in solvents of lower dielectric constants such as tetrahydrofuran, additional bands attributed to distortion of the anion by the countercation are observed. [Nb(CO)6] appears to be the most labile carbonyl of the group VA analogs. 

Nevertheless, the precipitation process can be specified based on data available on the complex structure of the strip solutions. In the case of tantalum strip solutions, the interaction can be written as follows ... 

Calculate the atomic radius of each of the following elements from the data given (a) platinum, fee structure, density 21.450 g-cm 3 (b) tantalum, bcc structure, density 16.654 g-cm-3. 

The major difference in the dithiocarhamato chemistry of tantalum and niobium is the existence of the Ta(V) species Ta(R2C tc)5, whereas the comparable niobium compound is unknown. The preparative methods for Ta(R2C tc)5 involve either a CS2 insertion in Ta(NR2)j (R = Me )) or a reaction between TaClj and sodium or ammonium dithiocarbamate (R = Et (7), R2 = ( 112)4 ( ))- The structure of this interesting diamagnetic compound is not elucidated, but from infrared data the presence of one or more unidentate ligands is suggested 11,15). 

La-Pt-Sb. LaPtSb crystallizes with the Cahi2-type structure, a = 0.4560, c = 0.8263 (Rossi et al., 1981 powder X-ray diffraction data). The starting elements (La 3N, Pt 4N, Sb 4N) were melted under argon in tantalum crucible, and annealed at 773 K for one week. 

Chemical shift data have been obtained by photoelectron spectroscopy501" for the core electrons of niobium and tantalum compounds. The similarity in chemical shifts between structurally similar compounds of these two elements is in accord with the similarity in their ionic radii. 

Literature presents numerous data on the syntheses by ML method of oxide layers of titanium, aluminum, chromium, phosphorus, tantalum and series of other elements on silica and alumina surfaces, when appropriate chloride and vapour of water are used as initial reagents [13,35,18,42]. The synthesis thus proceeds without the change of oxidation state of elements. But the stability of Si-O-M bonds in the process of gaseous treatment of element-chloride surface structures is of significant importance. Our researches have shown [44,68], that the strength of Si-O-M bonds is influenced by the thermal stability of element-oxide chloride groups, quantity of their bonds with surfaces (factor m) and series other ones. The reason for the destruction is the hydrogen chloride which educes in the process of vapour hydrolysis [68]. 

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