Hafnium is a chemical element; it has symbol Hf and atomic number 72. A lustrous, silvery gray, tetravalent transition metal, hafnium chemically resembles zirconium and is found in many zirconium minerals. Its existence was predicted by Dmitri Mendeleev in 1869, though it was not identified until 1923, by Dirk Coster and George de Hevesy, making it the penultimate stable element to be discovered. Hafnium is named after Hafnia, the Latin name for Copenhagen, where it was discovered.
Zirconium is a chemical element; it has symbol Zr and atomic number 40. The name zirconium is derived from the name of the mineral zircon, the most important source of zirconium. The word is related to Persian zargun. It is a lustrous, grey-white, strong transition metal that closely resembles hafnium and, to a lesser extent, titanium. Zirconium is mainly used as a refractory and opacifier, although small amounts are used as an alloying agent for its strong resistance to corrosion. Zirconium forms a variety of inorganic and organometallic compounds such as zirconium dioxide and zirconocene dichloride, respectively. Five isotopes occur naturally, four of which are stable. Zirconium compounds have no known biological role.
Zirconium dioxide is a white crystalline oxide of zirconium. Its most naturally occurring form, with a monoclinic crystalline structure, is the mineral baddeleyite. A dopant stabilized cubic structured zirconia, cubic zirconia, is synthesized in various colours for use as a gemstone and a diamond simulant.
Hafnium(IV) chloride is the inorganic compound with the formula HfCl4. This colourless solid is the precursor to most hafnium organometallic compounds. It has a variety of highly specialized applications, mainly in materials science and as a catalyst.
Zirconium(IV) bromide is the inorganic compound with the formula ZrBr4. This colourless solid is the principal precursor to other Zr–Br compounds.
Zirconium(IV) iodide is the chemical compound with the formula ZrI4. It is the most readily available iodide of zirconium. It is an orange-coloured solid that degrades in the presence of water. The compound was once prominent as an intermediate in the purification of zirconium metal.
Organozirconium chemistry is the science of exploring the properties, structure, and reactivity of organozirconium compounds, which are organometallic compounds containing chemical bonds between carbon and zirconium. Organozirconium compounds have been widely studied, in part because they are useful catalysts in Ziegler-Natta polymerization.
Hafnium tetrafluoride is the inorganic compound with the formula HfF4. It is a white solid. It adopts the same structure as zirconium tetrafluoride, with 8-coordinate Hf(IV) centers.
Langbeinites are a family of crystalline substances based on the structure of langbeinite with general formula M2M'2(SO4)3, where M is a large univalent cation, and M' is a small divalent cation. The sulfate group, SO2−4, can be substituted by other tetrahedral anions with a double negative charge such as tetrafluoroberyllate, selenate, chromate, molybdate, or tungstates. Although monofluorophosphates are predicted, they have not been described. By redistributing charges other anions with the same shape such as phosphate also form langbeinite structures. In these the M' atom must have a greater charge to balance the extra three negative charges.
Zirconium perchlorate is a molecular substance containing zirconium and perchlorate groups with formula Zr(ClO4)4. Zr(ClO4)4 is a volatile crystalline product. It can be formed by reacting zirconium tetrachloride with dry perchloric acid at liquid nitrogen temperatures. Zr(ClO4)4 sublimes slowly in a vacuum at 70°C showing that the molecule is covalently bound rather than being ionic. The reaction also forms some zirconyl perchlorate (or zirconium oxyperchlorate) ZrO(ClO4)2 as even apparently pure perchloric acid is in equilibrium with dichlorine heptoxide, hydronium ions and perchlorate ions. This side product can be minimised by adding more dichlorine heptoxide or doing the reaction as cold as possible.
Zirconium nitrate is a volatile anhydrous transition metal nitrate salt of zirconium with formula Zr(NO3)4. It has alternate names of zirconium tetranitrate, or zirconium(IV) nitrate.
A selenate selenite is a chemical compound or salt that contains selenite and selenate anions (SeO32- and SeO42-). These are mixed anion compounds. Some have third anions.
Neodymium perrhenate is an inorganic compound with the chemical formula Nd(ReO4)3, which exists in anhydrous and tetrahydrate. It can be obtained by reacting excess neodymium oxide with 240 g/L perrhenic acid solution. In its solution, NdReO42+ and Nd(ReO4)2+ can be observed with stability constants of 16.5 and 23.6, respectively.
Hafnium compounds are compounds containing the element hafnium (Hf). Due to the lanthanide contraction, the ionic radius of hafnium(IV) (0.78 ångström) is almost the same as that of zirconium(IV) (0.79 angstroms). Consequently, compounds of hafnium(IV) and zirconium(IV) have very similar chemical and physical properties. Hafnium and zirconium tend to occur together in nature and the similarity of their ionic radii makes their chemical separation rather difficult. Hafnium tends to form inorganic compounds in the oxidation state of +4. Halogens react with it to form hafnium tetrahalides. At higher temperatures, hafnium reacts with oxygen, nitrogen, carbon, boron, sulfur, and silicon. Some compounds of hafnium in lower oxidation states are known.
Praseodymium(III) selenate is an inorganic compound, the salt of praseodymium and selenic acid with the chemical formula Pr2(SeO4)3. It forms green crystals when hydrated.
Nickel(II) selenate is a selenate of nickel with the chemical formula NiSeO4.
Erbium(III) selenate is an inorganic compound, with the chemical formula Er2(SeO4)3. It exists as an anhydrate or an octahydrate.
Holmium(III) selenate is an inorganic compound with the chemical formula Ho2(SeO4)3. It exists in the anhydrous form and as an octahydrate. It can be obtained by dissolving holmium(III) oxide in selenic acid solution and evaporating and crystallizing it. It co-crystallizes with other selenates in solution to obtain complex salts such as K3Ho(SeO4)3·nH2O, NH4Ho(SeO4)2·3H2O and CH3NH3Ho(SeO4)2·5H2O.
Cerium(IV) selenate is an inorganic compound with the chemical formula Ce(SeO4)2.
Cerium(III) selenate is an inorganic compound with the chemical formula Ce2(SeO4)3. It can be obtained by reacting selenic acid and cerium(III) carbonate, and the solvent is evaporated to precipitate crystals. The double salt CsCe(SeO4)2·4H2O can be obtained from mixing cerium(III) selenate and cesium selenate in an aqueous solution, and then evaporating and crystallizing the solution.
