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The hollandite-related structure La1.16Mo8O16, Mr = 1184.66, tetragonal, PI4 1, a = 9.983 (1), c = 2.8890 (5) Å, V = 287.9 Å3, Z = 1, Dx = 6.83 g cm-3, \lambda(Mo K[alpha]) = 0.71069 Å, [mu] = 126 cm-1, F(0000) = 530, room temperature, R = 0.041 for 1145 unique reflections with I\geq3[sigma](I). At room temperature the compound exhibits a one-dimensional incommensurate modulated structure with a modulation wavevector q* = 0.608 (1)c*. Both a displacive modulation wave, acting on La, Mo and O atoms, and a modulation wave governing the occupancy probability of La sites inside the tunnels are involved in the crystal. Within the superspace group PI4 1, the final R values of main reflections (477) and first- and second-order satellite reflections (523 and 145) are 0.030, 0.050 and 0.133 respectively. The more spectacular modulation features are the occurrence of La-La pairs in the tunnels and the formation of Mo3 triangular clusters in the double chains of edge-sharing octahedra. Contrary to previous descriptions based upon rigid tunnels in structures of the hollandite type, the tunnels in the crystal studied are distorted in a periodic way along [001] ([lambda] = 4.75 Å), giving rise to alternate contractions and expansions. The distortion of the double octahedral chains is considerable and probably created via the La-O(1) bonds by insertion of La atoms inside two adjacent tunnels.

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