Suitable reactions of KI, La, LaI3, and Os in niobium tubes at 800-850 degrees C result in black, air- and moisture-sensitive crystals of the quaternary tide phase. Isostructural K(4)Pr(6)I(14)Z also exist for Z = Fe, Ru. The title phase was characterized by single-crystal X-ray diffraction (tetragonal, P4/ncc (No. 130), Z = 4; a = 13.117(3), c = 25.17 (1) Angstrom at 23 degrees C). The important structural feature is the constitution (K4I)(3+)(La6I13Os3-) with a new type of 3D anion network of [(La6Os)(I8I4/2i-aI4/2a-iI2/2a-a)-I-i] clusters that are connected into puckered layers through Ii-a and Ia-i atom pairs that bridge diagonally in the a-b plane. These cluster layers are further interlinked along (c) over bar at trans-vertexes through simple bridging Ia-a. The 14th iodine atom occurs in the unique K4I3+ ions which lie in columns that interpenetrate the La6OsI13 network along c. The present 16-e(-) clusters, in contrast with the optimal 18-e(-) octahedral cluster configuration, exhibit an uncommon tetragonal elongation and evidently become closed shell, with only a small temperature-independent (van Vleck-like) paramagnetism, similar to 4 x 10(-4) emu mol(-1).