Yttrium pyrogermanate, Y(2)Ge(2)O(7).

The structure of diyttrium digermanate, Y(2)Ge(2)O(7), has been determined in the tetragonal space group P4(3)2(1)2. It contains one Y, one Ge (both site symmetry 1 on general position 8b) and four O atoms [one on special position 4a (site symmetry ..2) and the remaining three on general positions 8b]. The basic units of the structure are isolated Ge(2)O(7) groups, sharing one common O atom and displaying a Ge-O-Ge angle of 134.9 (3) degrees , and infinite helical chains of pentagonal YO(7) dipyramids, parallel to the 4(3) screw axis. The crystal investigated here represents the left-handed form of the tetragonal R(2)Ge(2)O(7) compounds (R = Eu(3+), Tb(3+), Er(3+), Tm(3+) and Lu(3+)).