Refinement of the crystal structure of gallium oxide hydroxide, GaO(OH)

Abstract

and available on-line February 2, 2003; CSD-No. 409671 microporous materials. These materials have attracted intense interest due to their industrial applications in catalysis, sorption, ion-exchange processes, and gas separation [3-8]. GaO(OH) can also be used to produce ceramics such as ZnGaiCU and LaGaC>3 [9] for luminescent phosphor application in vacuum fluorescent or field emission displays. It has also been employed with HBr as a novel chemical wet etchant for the fabrication of 1-D laser waveguides [10]. There are several approaches to prepare gal-lium oxide hydroxide: by heating either a-Ga2C>3 or (5-Ga2C>3 in wet atmosphere [11], by heating gallium metal with water in an autoclave at 200 °C, by dehydration of gallium trihydroxide at 100 °C, or by hydrolysis of gallium salts (e.g. chloride, nitrate, and Perchlorate) [12], In addition, sonochemical reaction can yield excellent scroll-like cylindrical GaO(OH) nanoparticles [13]· To date, two different crystal structures have been reported for the title compound. The deuteriohydroxide, GaO(OD), crystallizes in the space group Pbnm (a = 4.516 A ,b = 9.779 A, c = 2.966 A), as determined by a profile analysis of powder neutron diffraction data [11]. Another one belongs to the space group Fddd (a = 10.140 A, b = 8.321 À, c = 7.010 Â) [14], This leads to the speculation that deuterium and hydrogen would make the difference in the structure. In this report, we present a refinement of the oxide hydroxide compound. The refinement shows that the oxide hydroxide has the same structure as that of the oxide deuteriohydroxide. During the refinement , the hydrogen position could be located via the difference map of electron density. The hydrogen atom is attached to 02, which is bonded to three Ga atoms at distances 2.054 A, 2.054 Â and 2.055 A. This is to be compared to 01, which is also bonded to three Ga atoms, but at distances 1.929 Á, 1.929 Á and 1.934 Â. The bonding geometry around Ol is more flat, as the three 01-Ga bonds make angles of 100.8°, 123.4° and 123.4°. The bonding geometry around 02 is more puckered, and the three 02-Ga bonds have angles of 92.7°, 103.7° and 103.7°. Abstract GaH0 2 , orthorhombic, Pnma (No. 62), a = 9.7907(8) Á, b = 2.9732(2) Â, c = 4.5171(4) Â, V= 131.5 À 3 ,Z = 4, R g t(F) = 0.0403, wR lei (F 2) = 0.081, Τ = 293 Κ. Source of material The title compound was one of several phases synthesized by a hydrothermal reaction of metal gallium, CdCh, iodine, DMF and ammonia in sealed teflon-lined stainless steel autoclave at 448 Κ for 2 days. Transparent prism-like crystals were recovered by filtration. Discussion Gallium oxide hydroxide GaO(OH), also known as gallium oxyhydroxide, oxyhydrate or monohydrate with the diaspore structure [1-2], is widely used to synthesize various gallophos-phates, a new family of three-dimensional open-framework Table 1. Data collection and handling. Crystal: Wavelength: μ: Diffractometer, scan mode: 2ö[nax : N(hkl) me asured, N(hkl) U mque' Criterion for / 0 bs, N(hkl) g t. N(param) refined: Programs: colorless fragment, size 0.02 χ 0.02 χ 0.02 mm Mo Ka radiation (0.71073 Â) 202.77 cm" 1 Siemens SMART CCD, ω 61.98° 1466, 234 Us > 2 a(Iobs), 233 23 SHELXL-97 [15], SADABS [16]