Niobium monoxide

Niobium monoxide is the inorganic compound with the formula NbO. It is a grey solid with metallic conductivity.^[1]

Niobium monoxide

Names
Other names niobium(II) oxide
Identifiers
CAS Number	12034-57-0 Y
3D model (JSmol)	Interactive image
ChemSpider	74751 Y
ECHA InfoCard	100.031.631
PubChem CID	82838
CompTox Dashboard (EPA)	DTXSID101014241
InChI InChI=1S/Nb.O Y Key: BFRGSJVXBIWTCF-UHFFFAOYSA-N Y
SMILES O=[Nb]
Properties
Chemical formula	NbO
Molar mass	108.905 g/mol[1]
Appearance	grey solid[1]
Odor	odorless
Density	7.30 g/cm3[1]
Melting point	1,937 °C (3,519 °F; 2,210 K)[1]
Solubility	slightly soluble in HCl insoluble in nitric acid
Structure[2]
Crystal structure	Cubic, cP6
Space group	Pm3m, No. 221
Lattice constant	a = 0.4211 nm
Formula units (Z)	3
Thermochemistry[3]
Heat capacity (C)	41.3 J/(mol·K)
Std molar entropy (S⦵298)	48.1 J/(mol·K)
Std enthalpy of formation (ΔfH⦵298)	−405.85 kJ/mol
Gibbs free energy (ΔfG⦵)	−378.6 kJ/mol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

Structure and electronic properties

NbO adopts an unusual cubic structure, similar to the rock salt structure but with some missing atoms compared to it, so that both niobium and oxygen atoms have square planar coordination geometries. The niobium centers are arranged in octahedra, and there is a structural similarity to the octahedral niobium clusters in lower halides of niobium. In NbO the Nb–Nb bond length is 298 pm which compares to 285 pm in the metal.^[2] One study of the bonding concludes that strong and nearly covalent bonds exist between the metal centers.^[4]

It is a superconductor with a transition temperature of 1.38 K.^[5] It is used in capacitors where a layer of Nb₂O₅ is formed around NbO grains as the dielectric.^[6][7][8]

Preparation

NbO can be prepared by reduction of Nb₂O₅ by H₂. More typically, it is prepared by comproportionation:^[9]

Nb₂O₅ + 3 Nb → 5 NbO