DEHYDRATION PROCESS OF TLB5O6(OH)(4)CENTER-DOT-2H(2)O AND CRYSTAL-STRUCTURE OF TLB5O8

The dehydration of TIB5O6(OH)(4) . 2H(2)O leads to a loss of water in one step, forming anhydrous TIB5O8, which is amorphous to X-ray diffra ction, This can be explained by structural considerations; a decrease in oxygenated coordination of thallium ions occurs during the heating. TIB5O8 crystallizes at about 450 degrees C and melts at 660 degrees C , By slow cooling from the melt, single crystals were obtained. TIB5O8 is orthorhombic, space group Pbca, with unit cell parameters a = 7.55 7(3) Angstrom, b = 11.925(6) Angstrom, c = 14.734(19) Angstrom; Z = 8, The structure was solved from 1113 reflections until R = 0.023 and R- w = 0.026, The structure consists of two separate interlocking three-d imensional networks of pentaborate groups, which form large empty tunn els, Nine oxygen atoms belonging to four different pentaborate groups surround each thallium ion. Except for the presence of pentaborate gro ups with almost the same geometry, there is no relation between the st ructure of TIB5O8 and that of its hydrated precursor, TIB5O6(OH)(4) . 2H(2)O; the shorthand notation of polyborate anions in these compounds is 5:infinity(3)(4 Delta+T) and 5:4 Delta+T, respectively. (C) 1998 A cademic Press.