The crystal structure of synthetic Cs 2 [B 4 O 5 (OH) 4 ]3H 2 O was determined from single-crystal X-ray diffraction data. The compound is monoclinic, space group P2 1 /c; the unit cell parameters are aβ«)2(424.8Ψβ¬ A s , bβ«)3(873.11Ψβ¬ A > , cβ«)5(061.31Ψβ¬ A > , β«Ψβ¬ 92.06(3)Β°; Zβ«.4Ψβ¬ The crystal structure was solved from 6355 reflections until Rβ«;920.0Ψβ¬ it contains isolated [B 4 O 5 (OH) 4 ] 2Ψ polyanions separated by free water molecules and Cs Ψ ions. Although its formula is the same as that of the tincalconite Na 2
which contains only two isolated water molecules. In the cesium and the potassium borates, the [B 4 O 5 (OH) 4 ] 2Ψ anions have not a two-fold axis as in the tincalconite; the shorthand notations of these two kinds of anions shall be noted as: 4: 2 Ψ2T in the first two borates and 4:( ΨT) 2 in the tincalconite, and T being triangular and tetrahedral borons, respectively.Cs 2 [B 4 O 5 (OH) 4 ]3H 2 O indexed X-ray powder diffraction pattern is given. The dehydration of this borate occurs in two close steps and leads to an amorphous phase; this process is well explained considering the structure and especially the change in the Cs Ψ coordination during the heating.