The title compounds, LiKB4O7 and LiRbB4O7, are newly developed non-linear o
ptical crystals containing two kinds of anionic groups, namely (B3O8)(7-) a
nd (B5O10)(5-). The (B3O8)(7-) groups form infinite spiral chains parallel
to the [100] direction, which are interconnected by sharing O atoms with (B
5O10)(5-) groups.