The phases La(15)Ge(9)Z, Z = Mn, Fe, Co, Ni, Cu, Ru, C, O, P, have been obtained from reactions of either the elements or suitable binary compounds in sealed Ta containers at 1200-1350 degrees C. All exhibit an ordered root 3a x root 3a x c superstructure of the Mn5Si3 type (La(5)Ge(3)Z, La(5)Ge(3)Z, P6(3)/mcm) in which two-thirds of the slightly distorted confacial chains of trigonal antiprisms (La6/2Ge6/2) have Z bound in alternate, contracted interstitial sites. The room-temperature structures for Z = Mn, Fe, Co, Ni, C, P were refined from single-crystal data (space group P6(3)mc, Z = 2; for the protypical Fe, a = 15.4810(2) Angstrom and c = 6.8768(3) Angstrom). The unit cell lengths and volumes and d(Z-Z) values show notably smaller variations with Z than in La(5)Ge(3)Z or related systems. The buffering effect of empty cavities in the commensurate chains and the weak La-La bonding appear to be responsible. Magnetic susceptibility data and XPS core shifts are reported for the Fe and, in part, the Co and Ni phases La(15)Ge(9)Z. All three are metallic with decreasing moments of similar to 1.83, similar to 0.3, and similar to 0 mu(3), respectively. In contrast, the Fe-richer La5Ge3Fe is a very soft ferromagnet at room temperature. Members of the sequence Fe, La5Ge3Fe, La15Ge9Fe exhibit regularly decreasing moments as well. The Fe 2p(3/2) core levels show a 1.7 eV decrease over the same series, i.e., increasing reduction, while an evidently regular oxidation of La from the element through La5Ge3 and La15Ge9Fe to La(5)e(3)Fe is indicated by a regular overall increase of 2.7 eV in La 3d(5/2) binding energies.