A2, body-centered cubic

Structural typeA2
Common namebody-centered cubic (bcc)
Prototype W
Pearson symbolcI2
Space group229 Im-3m Oh9
Chemical formulaA
Bondingmetallic
Atomic positions A (2a)  0  0  0
Coordination8cb + 6o with r2/r1=2/sqrt(3)≈1.15
PDB filesA2, voids (4t/6by at 12d/6b by H)
SubstructuresAa tetragonal distortion, Ai rhombohedral distortion
Substancesalkali and some other metals (see the table below), many metals before melting

δ=sqrt(27/32)≈.92 increases at tetragonal distortions and decreases at rhombohedral distortions.

Aa
α-Fe2.8665T<1180K
Cr2.8848
V3.0282
Mo3.1474
W3.1652 
Nb3.2941
Ta3.3025
Li3.5023
Na4.282
Eu4.572
Ba5.019
K5.247
Rb5.70
Cs6.141