![]() For example, this complex reacts with sodium cyclopentadienide to give the sandwich compound nickelocene. The dme ligands in this complex are labile. In the presence of water scavengers, hydrated nickel(II) chloride reacts with dimethoxyethane (dme) to form the molecular complex NiCl 2(dme) 2. NiCl 2 is the precursor to acetylacetonate complexes Ni(acac) 2(H 2O) 2 and the benzene-soluble (Ni(acac) 2) 3, which is a precursor to Ni(1,5-cyclooctadiene) 2, an important reagent in organonickel chemistry. Square planar complexes of nickel can often form five-coordinate adducts. For example, NiCl 2(PPh 3) 2, containing four-coordinate Ni(II), exists in solution as a mixture of both the diamagnetic square planar and the paramagnetic tetrahedral isomers. Some nickel chloride complexes exist as an equilibrium mixture of two geometries these examples are some of the most dramatic illustrations of structural isomerism for a given coordination number. Nickel(II) chloride solutions are acidic, with a pH of around 4 due to the hydrolysis of the Ni 2+ ion. A tetrahydrate NiCl 2♴H 2O is also known. The trans sites on the octahedral centers occupied by aquo ligands. It consists of infinite chains of NiCl 2, wherein both chloride centers are bridging ligands. The dihydrate NiCl 2♲H 2O adopts a structure intermediate between the hexahydrate and the anhydrous forms. The hexahydrate occurs in nature as the very rare mineral nickelbischofite. Cobalt(II) chloride hexahydrate has a similar structure. Only four of the six water molecules in the formula is bound to the nickel, and the remaining two are water of crystallization. In contrast, NiCl 2♶H 2O consists of separated trans- molecules linked more weakly to adjacent water molecules. Yellow NiBr 2 and black NiI 2 adopt similar structures, but with a different packing of the halides, adopting the CdI 2 motif. In NiCl 2 the Ni-Cl bonds have "ionic character". In this motif, each Ni 2+ center is coordinated to six Cl − centers, and each chloride is bonded to three Ni(II) centers. NiCl 2 ⋅ 6 H 2 O + 6 SOCl 2 ⟶ NiCl 2 + 6 SO 2 + 12 HCl Structure of NiCl 2 and its hydrates Simply heating the hydrates does not afford the anhydrous dichloride. The hydrates convert to the anhydrous form upon heating in thionyl chloride or by heating under a stream of HCl gas. ![]() ![]() The yellowish dihydrate, NiCl 2♲H 2O, is produced by heating the hexahydrate between 66 and 133 ☌. Nickel chloride is not usually prepared in the laboratory because it is inexpensive and has a long shelf-life. ![]() The largest scale production of nickel chloride involves the extraction with hydrochloric acid of nickel matte and residues obtained from roasting refining nickel-containing ores. Nickel salts have been shown to be carcinogenic to the lungs and nasal passages in cases of long-term inhalation exposure. The nickel chlorides are deliquescent, absorbing moisture from the air to form a solution. Nickel(II) chloride, in various forms, is the most important source of nickel for chemical synthesis. The anhydrous salt is yellow, but the more familiar hydrate NiCl 2♶H 2O is green. Nickel(II) chloride (or just nickel chloride) is the chemical compound NiCl 2. ![]()
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