Reactions of the elements within welded Ta containers at similar to600 degreesC followed by slow cooling give new A(8)Tl(11)Pd(x) products from an apparently continuous encapsulation of Pd atoms into the pentacapped trigonal prismatic anions in the isotypic rhombohedral (R (3) over barc) A(8)Tl(11) phases. All systems also produce other phases at x < 1 as well, the simplest being the cesium system in which only trigonal Pd13Tl9 is also formed. Cs8Tl11Pd0.84(1) was characterized by single-crystal means as close to the upper x limit in that system (R (3) over barc, Z = 6, a = 10.610(1) Angstrom, c = 54.683(8) A). The Pd insertion causes an expansion of the D-3 host anion, particularly about the waist, to generate a trigonal bipyramidal PdTl5 unit (d(Pd-Tl) similar to 2.6-2.8 A) centered within a somewhat larger Tl-6 trigonal prism, the remainder of the Tl-11 cluster. Strong Tl cage bonding is retained. Extended Huckel calculations show significant involvement of all Tl 6s, 6p and Pd 4d, 5s, 5p orbital sets in the central and cage bonding. The last valence electron is considered to be delocalized in a conduction band, as in A(8)Tl(11) examples, rather than occupying an antibonding e" LUMO across a gap of similar to2.4 eV.