Revision of the structure of Cs₂CuSi₅O₁₂ leucite as orthorhombic Pbca

Abstract

The crystal structure of a hydrothermally synthesized leucite analogue Cs(2)CuSi(5)O(12) has been determined and refined using the Rietveld method from high-resolution synchrotron X-ray and neutron powder diffraction data. This structure is based on the topology and cation-ordering scheme of the Pbca leucite structure of Cs(2)CdSi(5)O(12), and exhibits five ordered Si sites and one ordered Cu tetrahedrally coordinated (T) site. This structure for Cs(2)CuSi(5)O(12) is topologically identical to other known leucite structures and is different from that originally proposed by Heinrich & Baerlocher [(1991), Acta Cryst. C47, 237-241] in the tetragonal space group P4(1)2(1)2. The crystal structure of a dry-synthesized leucite analogue Cs(2)CuSi(5)O(12) has also been refined; this has the Ia3d cubic pollucite structure with disordered T sites.

Crystal structures of K2[XSi5O12] (X = Fe2+, Co, Zn) and Rb2[XSi5O12] (X = Mn) leucites: comparison of monoclinic P21/c and Ia{\overline 3}d polymorph structures and inverse relationship between tetrahedral cation (T = Si and X)—O bond distances and intertetrahedral T—O—T angles

“…Bell et al, 1994a,b;Bell & Henderson, 1996); the uncertainties on bond lengths and bond angles using the former are $ 3 and $ 5 times larger, respectively, than for the synchrotron data. Note also that our earlier combined synchrotron and neutron powder diffraction data for Cs 2 CuSi 5 O 12 (Bell et al, 2010) has uncertainties $ 25% smaller than of those found for purely synchrotron X-ray diffraction; of course this mainly reflects the much greater scattering of oxygen atoms with neutrons rather than X-rays. Thus although the present laboratory XRPD data have significantly higher uncertainties than our earlier data, we will be looking for similar structural trends to those found in our higher resolution experimental work, particularly the neutron diffraction results.…”

“…The Rietveld refinements for dry-synthesized X = Co and Zn and Rb 2 MnSi 5 O 12 leucites were all carried out using the Ia3d tetrahedral cation-disordered structure of dry-synthesized K 2 Comparison of crystal structure parameters for K 2 XSi 5 O 12 P2 1 /c leucite analogues with X = Mg, Fe 2+ , Co and Zn, and with those for the Pbca analogues Cs 2 XSi 5 O 12 with X = Cu and Cd. Bell et al (1994a) This work This work This work Bell et al (2010) Bell et al (1994b Space group…”

“…The structural positions of the O atoms in the samples are most reliably determined using neutron diffraction (see earlier) and we use our published data for Pbca Cs 2 CuSi 5 O 12 (Bell et al, 2010) to establish the trends for the distortions of the different ordered tetrahedral sites. Thus, the data for this compound (Table 2) show that the mean tetrahedral angle variance [ 2 ; Robinson et al (1971)] is smallest (19.1 deg 2 ) for the Q 4 Si(4Si) site, which reflects the fact that this site has the most symmetrical local environment in the framework.…”

“…The mean O-T-O and T-O-T bond angles for the disordered Ia3d cubic K 2 XSi 5 O 12 leucites are given in Table 3, where they are also compared with the data for the Ia3d Rb 2 MnSi 5 O 12 (this work) and Cs 2 CuSi 5 O 12 (Bell et al, 2010) analogues. The tetrahedral angle variance for the disordered Si+Mg sample is very low (10.7 deg 2 ) and the same as that for disordered Si+Zn; the variances are much higher for the disordered Si + Co, Mn or Cu samples.…”

“…K 2 MgSi 5 O 12 ; Bell et al (1994a)] and the structures of these along with cubic Rb 2 MnSi 5 O 12 are also reported. Wider structural properties are discussed based on the new data and those for the most reliable structures from the A 2 X 2+ Si 5 O 12 database (Bell et al, 1994a(Bell et al, ,b, 2010Bell & Henderson, 1996Henderson et al, 1998;2017).…”