Syntheses of the title compounds result from appropriate reactions of the elements and LaI3 in sealed Nb or Ta containers at 800 degrees C. These exhibit a new structural type with an unusual metal-rich layered structure, detailed for La2INi2 by single-crystal X-ray diffraction : hexagonal P (6) over bar m2, Z = 1, a = 4.1387 Angstrom, c = 8.814 Angstrom (23 degrees C). This is related to the Gd2IFe2-type structure known for La(2)IZ(2) for Z Fe, Co, and others. Both structures contain AlB2-like slabs, namely, graphite-like Z(2) (Z Ni, Fe) layers between eclipsed pairs of La layers, but these are instead separated by single iodine layers. The La2INi2 structure differs in that the iodine positions along (c) over bar project onto only one Z position instead of both and the cell is half as large. An additional set of very weak reflections and streaks revealed in widely varying amounts by precession photographs suggests a superstructure in c or intergrowths by small amounts of disordered components, but a reasonable model could not be derived beyond some possible short-range disordering in the iodine layers. Comparisons..of La2INi2 with La2IFe2 in terms of electronic band structures show that filling of antibonding states occurs in the Ni layers. Integrated overlap populations in the Fe vs Ni compounds show corresponding decreases for Z-Z and La-Z bonding and a smaller strengthening of La-La bonding in the layers, while the a lattice parameter increases and the trigonal prismatic La(6)Z units decrease in height. These conflicts are reflected in the Z-layer puckering and the doubled c dimension found in La2IFe2 and other phases with the Gd2IFe2-type structure.