Crystal structure and thermal behavior of Cs-2[B4O5(OH)(4)]3H(2)O

The crystal structure of synthetic Cs-2[B4O5(OH)(4)]3H(2)O was determined f rom single-crystal X-ray diffraction data. The compound is monoclinic, spac e 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 isol ated [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[B4 O5(OH)(4)]3H(2)O, Cs-2[B4O5(OH)(4)]3H(2)O structure is close to that of syn thetic K-2[B4O5(OH)(4)]2H(2)O which contains only two isolated water molecu les. 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 tw o berates and 4:(Delta+T)(2) in the tincalconite, Delta and T being triangu lar 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 oc curs in two close steps and leads to an amorphous phase; this process is we ll explained considering the structure and especially the change in the Cs coordination during the heating. (C) 1999 Academic Press.