Multianvil high-pressure/high-temperature preparation, crystal structure, and properties of the new oxoborate β-ZnB4O7

In this work we report about a new oxoborate beta-ZnB4O7 synthesized under high-pressure/high-temperature conditions from zinc oxide ZnO and boron oxide B2O3 with a walker-type multianvil apparatus at 10.5 GPa and 1100 degreesC. Single crystal X-ray structure determination of beta-ZnB4O7 revealed: Cmcm, a = 1085.0(1) pm, b = 648.9(1) pm, c = 517.3(1) pm, Z = 4, R-1 = 0.0182, wR(2) = 0.0478 (all data). The compound exhibits a new structure type which is built up from linked tetrahedral BO4-groups (square) forming a network. The most prominent feature of the tetrahedral network is that there is an oxygen, which is coordinated to three borons. The network exhibits channels formed from four- and six-membered rings running along [001]. The Zn2+ -cations are positioned in the large six-ring channels, whereas the channels built up by four membered rings remain empty. According to the conception of fundamental building blocks beta-ZnB4O7 can be classified with the notation 80 : (30) = (60) = (311). The relation of the crystal structure of the high-pressure phase beta-ZnB4O7 to the normal-pressure phase alpha-ZnB4O7 is discussed. Furthermore we report about temperature-resolved in situ powder diffraction measurements and IR-spectroscopic investigations on beta-ZnB4O7. (C) 2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved.