Niobium pentaiodide

Niobium pentaiodide is the inorganic compound with the formula Nb₂I₁₀. Its name comes from the compound's empirical formula, NbI₅.^[1] It is a diamagnetic, yellow solid that hydrolyses readily. The compound adopts an edge-shared bioctahedral structure, which means that two NbI₅ units are joined by a pair of iodide bridges. There is no bond between the Nb centres.^[2] Niobium(V) chloride, niobium(V) bromide, tantalum(V) chloride, tantalum(V) bromide, and tantalum(V) iodide, all share this structural motif.

Niobium pentaiodide

Names
Other names Niobium(V) iodide
Identifiers
CAS Number	13779-92-5 Y
3D model (JSmol)	Interactive image
ChemSpider	75550
ECHA InfoCard	100.034.006
EC Number	237-422-1
PubChem CID	83728
UNII	6YYE4L5XPW Y
CompTox Dashboard (EPA)	DTXSID1065633
InChI InChI=1S/5HI.Nb/h5*1H;/q;;;;;+5/p-5 Key: FWIYBTVHGYLSAZ-UHFFFAOYSA-I
SMILES [Nb](I)(I)(I)(I)I
Properties
Chemical formula	Nb2I10
Molar mass	1475
Appearance	yellow solid
Density	5.30 g/cm3
Melting point	543 °C (1,009 °F; 816 K) sublimes
Hazards
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H314
Precautionary statements	P260, P264, P280, P301+P330+P331, P303+P361+P353, P304+P340, P305+P351+P338, P310, P321, P363, P405, P501
Related compounds
Related compounds	Tantalum pentaiodide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Preparation

Niobium pentaiodide forms from the reaction of niobium with iodine:

2 Nb + 5 I₂ → 2 NbI₅

The method used for the preparation of tantalum(V) iodide using aluminium triiodide fails to produce pure pentaiodide.^[3]

Properties

Niobium(V) iodide forms of dark, brassy, extremely moisture-sensitive needles or flakes. Its crystallises in the monoclinic crystal system with space group P2₁/c (space group no. 14), a = 1058 pm, b = 658 pm, c = 1388 pm, β = 109.14°. The crystal structure consists of zigzag chains of corner-sharing NbI₆ octahedra. Since so far only twinned crystals of this phase have been obtained, and the structure determination is uncertain.^[4] If the reaction of the elements is carried out with an excess of iodine, a triclinic modification is created with the space group P1 (No. 2), a = 759.1 pm, b = 1032.2 pm, c = 697.7 pm, α = 90 .93°, β = 116.17°, γ = 109.07°, which consists of isolated molecules Nb₂I₁₀.^[3][5] This structure is isotypic with that of triclinic niobium(V) bromide.