Unusual Structures
| Element | crystal system | coordination number | notes |
|---|---|---|---|
| Mn | cubic | distorted bcc – unit cell contains Mn atoms in 4 different environments | |
| Zn | hexagonal | distorted from ideal hcp. 6 nearest neighbors in same plane- 6 in adjacent planes 14% farther away | |
| Ga | orthorhombic | each Ga atom has one nearest neighbour at 244 pm, 2 at 270 pm, 2 at 273 pm, 2 at 279 pm. | The structure is related to Iodine. |
| Cd | hexagonal | distorted from ideal hcp. 6 nearest neighbours in the same plane- 6 in adjacent planes 15% farther away | |
| In | tetragonal | slightly distorted fcc structure | |
| Sn | tetragonal | 4 neighbours at 302 pm; 2 at 318 pm; 4 at 377 pm; 8 at 441 pm | white tin form (thermodynamical stable above 286.4 K) |
| Sb | rhombohedral | puckered sheet; each Sb atom has 3 neighbours in the same sheet at 290.8pm; 3 in adjacent sheet at 335.5 pm. | grey metallic form. |
| Hg | rhombohedral | 6 nearest neighbours at 234 K and 1 atm (it is liquid at room temperature and thus has no crystal structure at ambient conditions!) | this structure can be considered to be a distorted hcp lattice with the nearest neighbours in the same plane being approx 16% farther away |
| Bi | rhombohedral | puckered sheet; each Bi atom has 3 neighbours in the same sheet at 307.2 pm; 3 in adjacent sheet at 352.9 pm. | Bi, Sb and grey As have the same space group in their crystal |
| Po | cubic | 6 nearest neighbours | simple cubic lattice. The atoms in the unit cell are at the corner of a cube. |
| Sm | trigonal | 12 nearest neighbours | complex hcp with 9 layer repeat, ABCBCACAB.... |
| Pa | tetragonal | body centred tetragonal unit cell, which can be considered to be a distorted bcc | |
| U | orthorhombic | strongly distorted hcp structure. Each atom has four near neighbours, 2 at 275.4 pm, 2 at 285.4 pm. The next four at distances 326.3 pm and four more at 334.2 pm. | |
| Np | orthorhombic | highly distorted bcc structure. Lattice parameters: a=666.3 pm, b=472.3 pm, c=488.7 pm | |
| Pu | monoclinic | slightly distorted hexagonal structure. 16 atoms per unit cell. Lattice parameters: a= 618.3 pm, b=482.2 pm, c=1096.3 pm, β= 101.79 ° |
Read more about this topic: Periodic Table (crystal Structure)
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