The systems A=Ca, Sr, Ba, Eu, Yb and Pn=As, Sb, Bi form isostructural A(16)Pn(11) phases for all but Ba-As and Yb-As when the elements are reacted in Ta containers at about 1100 degrees C and then annealed at 825-900 degrees C or slowly cooled. It is important to run particularly the Ae(16)Sb(11) reactions for Ae=Ca, Sr, Ba either under dynamic vacuum or to previously remove the pervasive hydrogen impurity from these metals. The tetragonal structure type was defined for Ca16Sb11 (, Z=2, a=12.253(3) Angstrom, c=11.313(4) Angstrom). The complex structure is built of pairs of confacial W5Si3-like slabs intergrown with single square-prismatic slabs along <(c)over arrow> in which Ca atoms in both define the polyhedra centered by Sb. This structure is the missing n=2 member of the homologous series A(5n+6)B(3n+5)(Parthe) with n:1 ratios of intergrown slabs. Four of five Ae(16)(Sb,Bi)(11) examples studied are diamagnetic (Ba16Sb11 excepted), and Ca16Sb11 is a poor semiconductor. Accommodation of these Zintl-phase characteristics in the Ca16Sb11 structure requires that 50% of the Sb atom pairs centering the confacial square antiprisms be bonded (d=3.40 Angstrom) on a random basis. Ellipsoids on these atoms are elongated along the proposed bonds.