The per­iodato­nickelates are a series of anions and salts of nickel complexed to the periodate anion. The most important of these salts are the di­periodato­nickelates, in which nickel exhibits the +4 oxidation state: these are powerful oxidising agents, capable of oxidising bromate to perbromate.

The first per­iodato­nickalates discovered were sodium nickel periodate (NaNiIO6·​0.5H2O) and potassium nickel periodate (KNiIO6·​0.5H2O). P. Ray and B. Sarma obtained these dark purple double salts in 1949, mixing nickel sulfate with potassium or sodium periodate and (as oxidant) a boiling aqueous solution of an alkali persulfate salt.[1] It is now known that ozone can replace the persulfate salt, and that similar solids exist for other alkali (RbNiIO6·​0.5H2O, CsNiIO6·​0.5H2O, and NH4NiIO6·​0.5H2O), as well as certain other tetravalent metals (including manganese, germanium, tin and lead).[2]

The crystalline salts are insoluble in water, acid, or base.[2] The colour is due to absorbance of visible light shorter than 800 nm, with a peak at 540 nm.[2] The crystal structure of each has space group P312. The structure is built from hexagonal oxygen layers; in every other layer, alkali atoms fill one-third of the hexagon centers and iodine and nickel fill the remainder; in the other layers, the centers are vacant.[2]

The di­periodato­nickelates, also known as dihydroxy­diperiodato­nickelates,[3] contain nickel in the +4 oxidation state along with two periodate anions. A solid mono­periodato­nickelate salt KNiIO6·​0.5H2O will dissolve in a solution of potassium hydroxide and potassium periodate to yield a di­periodato­nickelate solution.[4]

The [Ni(OH)2[IO5OH]2]6− ion can form a brown salt with sodium (Na4H2​[Ni(OH)2[IO5OH]2]·​6H2O), another acidic sodium salt (Na5​[Ni(OH)2[IO5OH]2]·​H2O) and an orange salt with cobalt ([Co(en)3]2​Ni(OH)2[IO5OH]2).[5][6] Di­periodato­metalates with the same formula also exist for palladium and nickel, and similar di­periodato­metalates can be made for Cu, Ag, Au, Ru and Os.[5]

A di­periodato­nickelate will dissolve in alkaline water. Depending on pH and concentration, the resulting solution is an equilibrium between [Ni(OH)2[IO3(OH)3]2]2− and [Ni(OH)2[IO3(OH)3][IO4(OH)2]]3−.[7] It is also a strong oxidiser: like very few reagents, it oxidises bromate to perbromate. In the reaction, NiIV reduces to NiIII with the release of a hydroxyl radical. The radical then oxidises bromate to a BrO42− radical, which NiIII then converts to perbromate BrO4−.[7]

References

  1. ↑ Ray, P.; Sarma, B. (11 May 1946). "Tetrapositive Nickel as Alkali Nickel Periodates". Nature. 157 (3993): 627. Bibcode:1946Natur.157..627R. doi:10.1038/157627a0.
  2. 1 2 3 4 Currie, David B.; Levason, William; Oldroyd, Richard D.; Weller, Mark T. (1994). "Synthesis, spectroscopic and structural studies of alkali metal–nickel periodates MNilO6(M = Na, K, Rb, Cs or NH4)". J. Chem. Soc., Dalton Trans. (9): 1483–1487. doi:10.1039/DT9940001483.
  3. ↑ Li, Zhi-Ting; Chang, Qing; Li, Bao-Wen; Yang, Li-Ting; Wang, An-Zhou (May 2000). "Kinetics and Mechanism of Oxidation of Ethylenediamine by Dihydroxydiperidatonickelate(IV) Complex Ion in Alkaline Medium". Retrieved 3 June 2016.
  4. ↑ Hiremath, Chanabasayya V.; Hiremath, Deepak C.; Nandibewoor, Sharanappa T. (May 2007). "Ruthenium(III) catalysed oxidation of gabapentin (neurontin) by diperiodatonickelate(IV) in aqueous alkaline medium: A kinetic and mechanistic study". Journal of Molecular Catalysis A: Chemical. 269 (1–2): 246–253. doi:10.1016/j.molcata.2007.01.024.
  5. 1 2 Dengel, Andrew C.; El-Hendawy, Ahmed M.; Griffith, William P.; Mostafa, Sahar I.; Williams, David J. (1992). "Transition-metal periodato complexes. Their preparations and properties as catalytic oxidants, and X-ray crystal structure of Na4 K[Au{IO5(OH)}2]·KOH·15H2O". J. Chem. Soc., Dalton Trans. (24): 3489–3495. doi:10.1039/DT9920003489.
  6. ↑ Mukherjee, H. G.; Mandal, Bhansidhar; De, Shyamali (9 October 1984). "Preparation and studies of the complex periodatoferrate (III) hexahydrate and periodatonickelate (IV) monohydrate". Chemischer Informationsdienst. 15 (41). doi:10.1002/chin.198441038. not consulted
  7. 1 2 Bilehal, Dinesh C.; Kulkarni, Raviraj M.; Nandibewoor, Sharanappa T. (January 2002). "Kinetics and Mechanism of Oxidation of Bromate by Diperiodatonickelate(IV) in Aqueous Alkaline Medium--A Simple Method for Formation of Perbromate". Inorganic Reaction Mechanisms. 4 (1–2): 103–109. doi:10.1080/1028662021000020244.
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