Potassium heptafluorotantalate
Encyclopedia
Potassium heptafluorotantalate is an inorganic compound
with the formula K2TaF7. This white, water-soluble solid is an intermediate in the purification of tantalum
from its ore
s and is the precursor to the metal.
, can be viewed as a trigonal prism defined by six fluoride
ions with the seventh fluoride ion positioned above the center of the one the three rectangular faces. The anion has C2v symmetry. The salt undergoes a series of phase transitions at lower temperatures. The Ta-F distances vary in the range of 1.976-1.919 Å. Two types of fluoride polyhedra surround the two potassium cations. The first polyhedron has K-F distance range of 2.905-2.646 Å, and the second one has 2.956-2.651 Å.
and wet methods. The anhydrous method involves the reaction of tantalum oxide with potassium bifluoride
or ammonium bifluoride according to the following equation:
The basic method was reported by Berzelius
.
K2TaF7 can also be precipitated from solutions in hydrofluoric acid provided that the concentration of HF is below about 42%. Solutions having higher concentrations of HF yield potassium hexafluorotantalate (KTaF6). The K-salt can be also precipitated from a solution in hydrofluoric acid
of tantalum pentachloride:
K2TaF7 is susceptible to hydrolysis. For example, a boiling aqueous solution of K2TaF7 yields potassium oxyfluorotantalate (K2Ta2O3F6), known as “Marignac’s
salt”. In order to prevent hydrolysis and co-precipitation of potassium oxyfluorotantalate, a small excess of HF is added to the solution.
Inorganic compound
Inorganic compounds have traditionally been considered to be of inanimate, non-biological origin. In contrast, organic compounds have an explicit biological origin. However, over the past century, the classification of inorganic vs organic compounds has become less important to scientists,...
with the formula K2TaF7. This white, water-soluble solid is an intermediate in the purification of tantalum
Tantalum
Tantalum is a chemical element with the symbol Ta and atomic number 73. Previously known as tantalium, the name comes from Tantalus, a character in Greek mythology. Tantalum is a rare, hard, blue-gray, lustrous transition metal that is highly corrosion resistant. It is part of the refractory...
from its ore
Ore
An ore is a type of rock that contains minerals with important elements including metals. The ores are extracted through mining; these are then refined to extract the valuable element....
s and is the precursor to the metal.
Structure
The structure of solid potassium heptafluorotantalate consists of potassium ions and the complex anion TaF72-. The seven-coordinate coordination sphere for Ta(V), established by X-ray crystallographyX-ray crystallography
X-ray crystallography is a method of determining the arrangement of atoms within a crystal, in which a beam of X-rays strikes a crystal and causes the beam of light to spread into many specific directions. From the angles and intensities of these diffracted beams, a crystallographer can produce a...
, can be viewed as a trigonal prism defined by six fluoride
Fluoride
Fluoride is the anion F−, the reduced form of fluorine when as an ion and when bonded to another element. Both organofluorine compounds and inorganic fluorine containing compounds are called fluorides. Fluoride, like other halides, is a monovalent ion . Its compounds often have properties that are...
ions with the seventh fluoride ion positioned above the center of the one the three rectangular faces. The anion has C2v symmetry. The salt undergoes a series of phase transitions at lower temperatures. The Ta-F distances vary in the range of 1.976-1.919 Å. Two types of fluoride polyhedra surround the two potassium cations. The first polyhedron has K-F distance range of 2.905-2.646 Å, and the second one has 2.956-2.651 Å.
Preparation
Potassium heptafulorotantalate can be produced by both anhydrousAnhydrous
As a general term, a substance is said to be anhydrous if it contains no water. The way of achieving the anhydrous form differs from one substance to another...
and wet methods. The anhydrous method involves the reaction of tantalum oxide with potassium bifluoride
Potassium bifluoride
Potassium bifluoride is the inorganic compound with the formula KHF2. This colourless salt consists of the potassium cation and the bifluoride anion. The salt is used in etchant for glass...
or ammonium bifluoride according to the following equation:
- Ta2O5 + 4 KHF2 6 HF → 2 K4TaF7 + 5 H2O
The basic method was reported by Berzelius
Berzelius
Berzelius is a secret society at Yale University named for the Swedish scientist Jöns Jakob Berzelius, considered one of the founding fathers of modern chemistry...
.
K2TaF7 can also be precipitated from solutions in hydrofluoric acid provided that the concentration of HF is below about 42%. Solutions having higher concentrations of HF yield potassium hexafluorotantalate (KTaF6). The K-salt can be also precipitated from a solution in hydrofluoric acid
Hydrofluoric acid
Hydrofluoric acid is a solution of hydrogen fluoride in water. It is a valued source of fluorine and is the precursor to numerous pharmaceuticals such as fluoxetine and diverse materials such as PTFE ....
of tantalum pentachloride:
- 5 HF + 2 KF + TaCl5 → K2TaF7 + 5 HCl
K2TaF7 is susceptible to hydrolysis. For example, a boiling aqueous solution of K2TaF7 yields potassium oxyfluorotantalate (K2Ta2O3F6), known as “Marignac’s
Jean Charles Galissard de Marignac
Jean Charles Galissard de Marignac was a Swiss chemist whose work with atomic weights suggested the possibility of isotopes and the packing fraction of nuclei and whose study of the rare earth elements led to his discovery of ytterbium in 1878 and codiscovery of gadolinium in 1880.- Life and work...
salt”. In order to prevent hydrolysis and co-precipitation of potassium oxyfluorotantalate, a small excess of HF is added to the solution.