Sodium periodate
chemical compound
Sodium periodate is an inorganic salt, composed of a sodium cation and the periodate anion. It may also be regarded as the sodium salt of periodic acid. Like many periodates, it can exist in two different forms: sodium metaperiodate (formula NaIO4) and sodium orthoperiodate (normally Na2H3IO6, but sometimes the fully reacted salt Na5IO6). Both salts are useful oxidising agents.
Preparation
Classically, periodate was produced in the form of sodium hydrogen periodate (Na3H2IO6). This commercially available, but can also be produced by the oxidation of iodates with chlorine and sodium hydroxide. Or, similarly, from iodides by oxidation with bromine and sodium hydroxide:
NaIO3 + Cl2 + 4 NaOH → Na3H2IO6 + 2NaCl + H2O
NaI + 4 Br2 + 10 NaOH → Na3H2IO6 + 8 NaBr + 4 H2O
Modern industrial scale production involves the electrochemical oxidation of iodates, on a lead dioxide (PbO2) anode, with the following standard electrode potential:
H5IO6 + H+ + 2e− → IO−3 + 3 H2O E° = 1.6 V
Sodium metaperiodate can be prepared by the dehydration of sodium hydrogen periodate with a strong mineral acid, such as nitric acid:
Na3H2IO6 + 2 HNO3 → NaIO4 + 2 NaNO3 + 2 H2O
Structure
Sodium metaperiodate (NaIO4) forms tetragonal crystals (space group I41/a) consisting of slightly distorted IO−4 ions with average I–O bond distances of 1.775 Å; the Na+ ions are surrounded by 8 oxygen atoms at distances of 2.54 and 2.60 Å.
Sodium hydrogen periodate (Na2H3IO6) forms orthorhombic crystals (space group Pnnm). Iodine and sodium atoms are both surrounded by an octahedral arrangement of 6 oxygen atoms; however the NaO6 octahedron is strongly distorted. IO6 and NaO6 groups are linked via common vertices and edges.
Powder diffraction indicates that Na5IO6 crystallises in the monoclinic system (space group C2/m).
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