Polymorf - Knowhwere- Nb3Cl8

MINERALS AND SYNTHETIC COMPOUNDS, A_mX_n, IN WHICH X ATOMS ARE

CLOSE PACKED AND A ATOMS OCCUPY OCTAHEDRAL INTERSTICES

Nb₃Cl₈

click here to see a key to this data bar
octa	3/8	fcc	layer	4 edges	A- 6c; X- 2c, 3c/fcc

structure

The Nb₃Cl₈ structure is adopted by Nb₃X₈ halides in which the X atoms are FCC

and the Nb atoms are present in 75% of the octahedral voids of the occupied layers.

Occupied and unoccupied layers alternate for an overall occupancy rate of 3/8.

Ex. Nb₃Cl₈ ( Nb - A , Cl - X )

Crystal lattice

The FCC lattice model demonstrates that the octahedrally coordinated AX₆ groups

of atoms in the occupied layers link together to form hexagonal rings. Compare

these hexagonal nets with those of corundum and atacamite shown previously. The

fact that the coordination octahedra of Nb₃Cl₈ share four edges with each other while

.

		Figure 90 - Nb₃Cl₈ lattice structure
click image to enlarge


.

those of corundum share only three results in a denser concentration of interstitial

cations and a higher occupancy rate per occupied layer (75% vs. 66.6% respectively).

Note how the hexagonal nets of the occupied layers are staggered relative to each

other so that the X atoms of the AX₆ groups supply all of the close packed atoms

necessary to build the structure including the unoccupied layers.

Polyhedral framework

The above image is looking down on a section of the occupied layer which is

parallel to (111).

Isostructural minerals/compounds

Nb₃X₈ halides

Back to mineral table

Back to Knowhere

Page 59 - Structure matters - Nb₃Cl₈