Cerium tetrafluoride

Cerium phthalocyanine, 7 64 Cerium tetrafluoride, 20 63-67 lattice parameters, 20 64 Cerium trifluoroacetates, 17 5, 26 Cermets, nitrides in, 9 81-82 Cerous ion, reaction with hydroxyl ions, 3 187 Ceruloplasmin, 40 123, see also Blue copper oxidases... 

Many of the fluoride complexes are anhydrous, being prepared from melts, and even hydrates are not numerous among those prepared from aqueous solution. In the case of hydrates, the refractivity of water must be allowed for. An example of a hydrate, (NH4)3CeF7 H2O obtained in the NH4F-CeF4-H20 system (81, 86), is shown in Fig. 12. When the refractivity of H2O is subtracted, the point for the yet unknown anhydrous (NH4)sCeF7 compound falls on the line established by the known anhydrous ammonium fluoride-cerium tetrafluoride complexes. 

Hydrated phases are known for both the tetrahalides and the dihalides, but neither has been extensively characterized. Cerium tetrafluoride monohydrate, CeF4 H20, has been prepared by several procedures (Asker and Wylie, 1964). The product of digesting Ce02 in concentrated aqueous HF solution at 100-130° is CeF4.o-l.OH2O, while that obtained by reaction of the dioxide with anhydrous HF is CeF4.o-O.8H2O. Powder X-ray diffraction data are reported the structure is unknown and different from that of the anhydrous tetrafluoride. 

Cerium tetrafluoride is the only lanthanide halide which contains a metal atom in the highest oxidation state and which is significantly volatile. An earlier study of its structure had ruled out a tetrahedral model on the basis of the amplitudes of vibration, and it was thought that it must be distorted to Czv or C3V symmetry. Now that the vibrational frequencies have been observed for the molecule isolated in rare gas matrices, it has been possible to reinterpret the electron diffraction data, using the observed frequencies in the analysis." It has been shown that the data do indeed correspond to a tetrahedral structure for the Cep4 molecule. Using four observed vibrational frequencies and the diffraction data it was possible to refine five force constants and the Ce-F distance. The value is 200.9(5) pm, corresponding to 203.6(5) pm for the distance. This is substantially shorter than the distance rf) of 218 pm in cerium trifluoride. 

Ifl -Heptafluoro-, l/ir,2//-hexafluoro-, ltf,4 -hexafluoro-, 2//,3/f-hexa-fluoro-, and heptafluoro-2-methyl-cyclohexa-l,3-diene and Iff-heptaduoro-, l/f,2ff-hexafluoro-, and l f,4/f-hexafluoro-cyclohexa-l,4-diene have been transformed similarly into polyfluorobenzenes. 1, 4 -Hexafluoro- and 1/f-heptafluoro-cyclohexa-l,4-diene, together with l,4-bis(trifluoromethyl)-hexafluoro-, l/f-4-(trifluoromethyl)hexafluoro-, and 2ff,4tf-l-(trifluoro-methyl)pentafluoro-cyclohexa-l,4-diene, and decafluoro-, l f-nonafluoro-, l-(trifluoromethyl)nonafluoro-, and lJ7-2-(trifluoromethyl)octafluoro-cyclo-hexene have been found amongst the products of the fluorination of benzotri-fluoride with cerium tetrafluoride at 480—510 C. ... 

Sir Humphry Davy attempted to isolate this unidentified element through electrolysis—but failed. It was not until 1824 that Jons Jakob Berzehus (1779—1848), who had earlier discovered cerium, osmium, and iridium, became the first person to separate the element silicon from its compound molecule and then identify it as a new element. Berzehus did this by a two-step process that basically involved heating potassium metal chips with a form of silica (SiF = silicon tetrafluoride) and then separating the resulting mixture of potassium fluoride and silica (SiF + 4K —> 4KF + Si). Today, commercial production of sihcon features a chemical reaction (reduction) between sand (SiO ) and carbon at temperatures over 2,200°C (SiO + 2C + heat— 2CO + Si). 

The square antiprismatic or distorted square antiprismatic geometries are found in various inorganic and chelated complexes of the lanthanides and antinides. It has been suggested that the tetrafluorides of cerium (98) praseodymium (99),... 

The lanthanides, unlike the transition metals and the actinides, tend not to form compounds over a range of oxidation states. The +3 oxidation state is characteristic of all of the lanthanides, and the oxide fluorides of formula LnOF (Ln = lanthanide metal) are well known. The less stable oxidation states of + 2 and + 4 are known, but the latter is represented only by the dioxides and tetrafluorides of cerium, praseodymium, and terbium, and no tetravalent oxide fluorides have been reported. 

Among the fluorides, lanthanum forms only LaFs, whilst cerium forms CeFs and CeF4. (Tetrafluorides are also known for Pr and Tb, see Section 3.4). Why do neighbouring metals behave so differently First, examine the energetics of formation of LaFs using a Bom-Haber cycle. 

Cerium and terbium tetrafluoride can be prepared by the action of fluorine, xenon difluoride, and chlorine trifluoride on Ce02 or CeFs, and Tb407 or TbFs, respectively. These reactions are carried out at temperatures of 300-400 C in nickel or monel containers with exclusion of moisture and oxygen, For further details see the Gmelin Handbook (1976) and the literature cited therein. The preparation of... 

The tetrafluorides are white solids which are only slightly soluble in water, but decompose slowly to form trifluorides. The cerium compound which is appreciably more stable than those of praseodymium and terbium, reacts with moist air above 500°C to form Ce02 and HP. Additional properties of the tetrafluorides are described by B atsanova (1971). 

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