
MINERALS AND SYNTHETIC COMPOUNDS, A_{m}X_{n}, WITH CLOSE 
PACKED X ATOMS AND A ATOMS OCCUPYING CUBIC INTERSTICES 


. 
CsCl 
click here to see a key to this data bar

cubic 
100% 
cp 
3d 
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
AX_{8}
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. 
. 






Figure 111  CsCl lattice structure 
click image to enlarge 




. 




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 
. 



linking surfaces 



Figure 112  CsCl polyhedral 
all
faces (CP) 
framework model 

( 66 S, 96 pinges ) 

click image to enlarge 
. 




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 
. 


Page
72  Structure matters  CsCl 
