Niobium chloride

Niobium silicide (NbSi3) is deposited by the silane reaction with niobium chloride. It has an A15 structure and is a superconductor. 

Table 6.1 Increase in the extent of metal-metal bonding in niobium chlorides as the number of valence electrons per niobium atom (n) increases.

Overview of the Chemistry of Niobium Chloride and Niobium Oxide Cluster Compounds 83... 

In contrast to chloride compounds, niobium oxides have a VEC of 14 electrons, due to an overall anti-bonding character of the a2u state, caused by a stronger Nb-O anti-bonding contribution. In some cases, the VEC cannot be determined unambiguously due to the uncertainty in the electron distribution between the clusters and additional niobium atoms present in the majority of the structures. The 14-electron compounds exhibit semiconducting properties and weak temperature-independent paramagnetism. Unlike niobium chlorides, the oxides do not exhibit a correlation between the electronic configuration and intra-cluster bond distances. 

Niobium was prepared in the metallic state for the first time by Blomstrand in 1866, later by Moissan, and still later, by Goldschmidt. While Blomstrand reduced niobium chloride with hydrogen to form niobium, Moissan and Goldschmidt reduced the oxide with carbon (in an electrical furnace) and aluminum powder, respectively. 

He never succeeded in isolating niobium, and in fact the element eluded chemists for more than six decades. In 1864, however, C. W. Blomstrand reduced niobium chloride by heating it strongly in an atmosphere of hydrogen (48), and saw the shining steel-gray metal. 

Porphyrin derivatives of Nbv and Tav were first reported in 1972 and have since aroused increasing interest. Fluoride complexes MF3L were obtained from MC1S and the oc-taethylporphyrin in the presence of HF (L = OEP),321,322 Niobium chloride and bromide... 

Since niobium pentachloride and tetrachloride decompose readily in the presence of oxygen or moisture, all solvents and vessels used in the reactions must be dried by accepted methods. The niobium chlorides should also be free of any oxy species. The potassium thiocyanate and 2,2 -bipyridine should be purified by recrystallization from water and ether, respectively, and then dried at a pressure of ca. 10" torr for 72 hrs. 

Niobium Chloride (NbClg) Enthalpy Reference Tempemtnrc ... 

Supports and Catalysts. The preparation of the supports used in this study was discussed in detail elsewhere. The two phosphate supports, A O AIPO and 4MgO lSA O 10A1P0 were co-precipi-tated using the necessary nitrate salts, phosphoric acid, and ammonium hydroxide at a fixed pH (.] ) Niobia was precipitated by adding ammonium hydroxide to a methanolic solution of niobium chloride (8). The niobia-silica support was prepared by impregnating SiO (Davison 952) to incipient wetness with a hexane solution of niobium ethoxide. The sample was then dried and calcined to obtain a homogeneous surface phase oxide (9). 

Niobium (Nb, at. mass 92.91) hydrolyses (in the absence of complexing anions) over the pH range 0-14. Polymerized forms of Nb(V) give pseudo-solutions or they separate as a white precipitate. When fused with NaOH, Nb20s forms the niobate, which is soluble in NaOH solutions. Niobium(V) forms stable fluoride, tartrate, oxalate, and peroxide complexes. The niobium complexes are more stable than the corresponding Ta complexes. A niobium chloride complex is formed in >5 M HCl solutions. Niobium(V) can be reduced to coloured species of Nb(III) and Nb(IV). In an acid medium, zinc metal reduces Nb(V), but not Ta(V). 

The common reaction pathway for the formation of Nb Sn films is hydrogen reduction of niobium chloride and tin chloride precursors (Eq. 2.1). There are several schemes... 

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