Crystal Structure and Thermal Behavior of Cs2[B4O5 (OH)4]3H2O

The crystal structure of synthetic Cs2[B4O5(OH)4]3H2O was determined from single-crystal X-ray diffraction data. The compound is monoclinic, space groupP21/c; the unit cell parameters area=8.424(2) ?,b=11.378(3) ? ,c=13.160(5) ? ,beta=92.06(3)°;Z=4. The crystal structure was solved from 6355 reflections untilR=0.029; it contains isolated [B4O5 (OH)4]2-polyanions separated by free water molecules and Cs+ions. Although its formula is the same as that of the tincalconite Na2[ B4O5(OH)4]3H2O, Cs2[B4O5(OH)4]3H2O structure is close to that of synthetic K2[B4O5(OH)4]2H2O which contains only two isolated water molecules. In the cesium and the potassium borates, the [B4O5(OH)4]2-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: 2delta+2T in the first two borates and 4:(delta+T)2in the tincalconite, deltaand T being triangular and tetrahedral borons, respectively. Cs2[B4O5(OH)4]3H2O 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+coordination during the heating.