Periodatonickelates
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]2Ni(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
- ^ 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.
- ^ a b c d 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.
- ^ 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.
- ^ 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.
- ^ a b 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.
- ^ 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
- ^ a b 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.