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MINERALS AND SYNTHETIC COMPOUNDS, A_mX_n, WITH CLOSE

PACKED X ATOMS AND A ATOMS OCCUPYING CUBIC INTERSTICES

CsCl

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cubic	100%	cp	3-d	all faces	A- 8c, X- 8c/cp

structure

In the CsCl structure the X atoms are packed CP (simple cubic or cubic primitive)

and the A atoms occupy all of the cubic interstices. As a result the A atoms are

coordinated with eight X atoms and vice versa. The CsCl structure is exhibited by

ionic compounds where the cations and anions have equal but opposite charge and

nearly equal ionic radii.

Ex. CsCl ( cesium chloride ) ( Cs - A , Cl - X )

Crystal lattice

The crystal structure could be modeled as a CP lattice with the understanding

that each cube represents an AX₈ coordination group of atoms and the vertices

represent the locations of the CP packed X atoms. However since both the A and

X atoms have the same coordination it is more informative to model the structure as

two interpenetrating CP lattices. That is, the vertices of one lattice represent the X

atoms and the vertices of the other lattice represent the A atoms. The following

image shows how the successive layers alternate between A atoms and X atoms.

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		Figure 111 - CsCl lattice structure
click image to enlarge


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The X atoms are located at the intersections of the solid green square grid and the

A atoms are positioned at the intersections of the solid purple grid.

Polyhedral framework

The polyhedral framework could be modeled as a simple CP structure or as two

interpenetrating CP frameworks as pictured here. The X atoms are located at the

vertices of the green 2^o cube and the A atoms at the vertices of the purple 2^o cube.

The interpenetrating model demonstrates the topological equivalency of the atoms.

Isostructural minerals/compounds

AgCd, AgMg, AgZn, AuMg, AuZn, BeCo, BeCu, BePd, CaTl, CoAl, CsBr, CsI, CuPd,

CuZn, LiAg, LiHg, TiTl, MgHg, MgSr, MgTl, NiAl, NiTi, SrTl, TlBi, TlBr, TlCl, TlI, TlSb

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