Figure 2 Coordination polyhedra of the different Pb cations. Displacement ellipsoids are drawn at the 50% probability level. The labeling scheme for symmetry-related atoms is the following: (i) 0.5-x,0.5 + y,1.5-z (ii) x,1 + y,z (iii) -x,-y,1-z (iv) 0.5-x,-0.5 + y,1.5-z (v) x,-1-y,0.5 + z (vi) x,-y,0.5 + z.