Vanadium, Niobium, Tantalum

When a violent reaction stops, heat the metal again. After evaporation of all the halogen from test tube 2, seal ofi constriction 3 very carefully. Repeatedly pass the halogen over the heated metal. When the halogen vapour disappears in the apparatus, distil the product into section 4 or 7 and seal it ofi. 

The Preparation of Ammonium HeptafluozirconateflV). In a platinum bowl, dissolve 20 g of zirconium(IV) oxide in a hot 40% hydrogen fluoride solution taken in an excess of 20% relative to the calculated amount needed to convert the zirconium(IV) oxide to the tetrafluoride. Cool the solution in a bath with ice to 5 °C and filter it through a paper filter (preliminarily cover the funnel with a thin layer of paraffin). 

Calculate the amount of ammonium fluoride needed to convert the zirconium tetrafluoride to ammonium heptafluozirconate, and weigh a three-fold excess of the substance (why should the excess ammonium fluoride be taken ). Dissolve the ammonium fluoride in a minimum amount of water (see Appendix 1, Table 1), filter the solution, and add it to the zirconium tetrafluoride solution. If no ammonium heptafluozirconate precipitate appears, add 10-20 ml of ethanol. Filter ofi the precipitate with the aid of a Buchner funnel, rinse it several times on the filter with ethanol, and dry it in the air. 

It is good to perform all the operations in platinum ware. Transfer the product into a weighed weighing bottle and weigh it. Calculate the yield in per cent. Ammonium heptafluohafnate can be prepared in a similar way. 

Indicate the position of vanadium, niobium, and tantalum in Mendeleev s periodic table of the elements, the electron configurations and size of their atoms, and their oxidation states. 

A plethora of stoichiometries and structural types are found for the chalcogen compounds of the Group 5 metals. Phases approximating to the composition MX have the NiAs-type structure, whereas the MX2 compounds have layer structures related to M0S2, Cdl2, or CdCl2 types. Sometimes complex layer sequences occur in which the 6-coordinate metal atom is alternatively octahedral and trigonal prismatic. 

Several ternary phases occur, others exhibiting 3D structures (like BaVS3, BaTaS3) and others containing discrete tetrahedral anions, such as the [VS4] unit in M3VS4 (M = Na, K, Tl, NH4). 

Vanadium(III) sulfide, V2S3 niobium(IV) sulfide, NbS2 niobium(IV) selenide, NbSe2 niobium(IV) telluride, NbTe2 tantalum(IV) sulfide, TaS2 tantalum(IV) selenide, TaSe2 tantalum(IV) telluride, TaTe2. 

Let us note in addition that the layered sulfides M0S2 and WS2 have been found to form nanotubes and other fullerene-type structures, on account of their highly folded and distorted nature that favors the formation of rag and tubular structures. Such materials have been synthesized by a variety of methods [78] and exhibit morphologies, which were described as inorganic fiillerenes (IF), single sheets, folded sheets, nanocrystals, and nested IFs (also known as onion crystals or Russian dolls ). 

Most commonly available Group 6-16 binary chalcogenides  

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Borides are inert toward nonoxidizing acids however, a few, such as Be2B and MgB2, react with aqueous acids to form boron hydrides. Most borides dissolve in oxidizing acids such as nitric or hot sulfuric acid and they ate also readily attacked by hot alkaline salt melts or fused alkaU peroxides, forming the mote stable borates. In dry air, where a protective oxide film can be preserved, borides ate relatively resistant to oxidation. For example, the borides of vanadium, niobium, tantalum, molybdenum, and tungsten do not oxidize appreciably in air up to temperatures of 1000—1200°C. Zirconium and titanium borides ate fairly resistant up to 1400°C. Engineering and other properties of refractory metal borides have been summarized (1). 

The corrosion behaviour of amorphous alloys has received particular attention since the extraordinarily high corrosion resistance of amorphous iron-chromium-metalloid alloys was reported. The majority of amorphous ferrous alloys contain large amounts of metalloids. The corrosion rate of amorphous iron-metalloid alloys decreases with the addition of most second metallic elements such as titanium, zirconium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, nickel, copper, ruthenium, rhodium, palladium, iridium and platinum . The addition of chromium is particularly effective. For instance amorphous Fe-8Cr-13P-7C alloy passivates spontaneously even in 2 N HCl at ambient temperature ". (The number denoting the concentration of an alloy element in the amorphous alloy formulae is the atomic percent unless otherwise stated.)... 

DAMPS) combined with oxysalts of vanadium, niobium, tantalum or titanium, zirconium, hafnium ... 

Gmelin Handbuch der Anorganische Chemie , Vanadium — Niobium—Tantalum, Springer Verlag, Berlin, 1973. 

However, explanations for growth limitation based on repulsion of metal ions may be somewhat oversimplified. Elements other than vanadium, niobium, tantalum, molybdenum, and tungsten do not form isopoly anions. Other ions which have appropriate radii (e.g., Al,+, 67 pm Oa5+, 76 pm I7"1. 67 pm) for discrete isopoly anion formation instead form chains, sheets, or three-dimensional frameworks. Why does polymerization stop for isopoly anions An oxygen atom in a terminal position in an isopoly anion is strongly n bonded to a transition metal such as Mo(V ) or W (VI). These terminal oxygen atoms are never found trans to one another because they avoid... 

The elements vanadium, niobium, tantalum and protoactinium constitute Subdivision A of the Fifth Group of the Periodic Classification. The general properties of Subdivision B are considered elsewhere in... 

P oly 0 xome tall ate s, derived from both isopoly adds and heteropoly adds, are important homogeneous oxidation catalysts. The metals involved are vanadium, niobium, tantalum, molybdenum, and tungsten. The reactions involved are the oxidation of a wide range of organic compounds by hydrogen peroxide or organic hydroperoxide. 

COMPLEXES OF THE TRANSITION METALS 13.6.3.1 Titanium, Zirconium, Vanadium, Niobium, Tantalum... 

In this paper we review the results of our systematic work on the catalytic and adsorptive properties of transition metal carbides (titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, and iron). We focus our attention on the oxidation of hydrogen, carbon monoxide, ammonia, and the oxidative coupling of methane. The first two reactions are examples of complete (non-selective) oxidation, while the oxidation of ammonia simulates a selective oxidation process. The reaction of oxidative coupling of methane is being intensively explored at present as a means to produce higher hydrocarbons.5 10... 

The group 5-7 supported transition metal oxides (of vanadium, niobium, tantalum, chromium, molybdenum, tungsten, and rhenium) are characterized by terminal oxo bonds (M =0) and bridging oxygen atoms binding the supported oxide to the cation of the support (M -0-MSUpport). The TOF values for ODH of butane or ethane on supported vanadia were found to depend strongly on the specific oxide support, varying by a factor of ca. 50 (titania > ceria > zirconia > niobia > alumina > silica). 

Vanadium Niobium Tantalum Chromium Molybdenum Tungsten... 

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