Crystal structure and thermal behavior of Cs2[B4O5(OH)4]3H2O

The crystal structure of synthetic Cs-2[B4O5(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 a=8.124(2) Angstrom, b=11.378(3) Angstrom, c=13.160(5) Angstrom, beta= 92.06(3)degrees; Z=4, The crystal structure was solved from 6355 reflections until R=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 Na-2[B4O5(OH)(4)]3H(2)O, Cs-2[B4O5(OH)(4)]3H(2)O structure is close to that of synthetic K-2[B4O5(OH)(4)]2H(2)O which contains only two isolated water molecules. In the cesium and the potassium berates, 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: 2 Delta+2T in the first two berates and 4:(Delta+T)(2) in the tincalconite, Delta and T being triangular and tetrahedral borons, respectively. Cs-2[B4O5(OH)(4)]3H(2)O indexed X-ray powder diffraction pattern is given. The dehydration of this berate 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. (C) 1999 Academic Press.