The crystal structure and crystal chemistry of mendeleevite-(Ce), (Cs,square)(6)(square,Cs)(6)(square,K)(6)(REE,Ca,square)(30)(Si70O175)(H 2O,OH,F,square)(35), a potential microporous material

作者：Sokolova E^*; Hawthorne F C; Pautov L A; Agakhanov A A; Karpenko V Yu

来源：Mineralogical Magazine, 2011, 75(5): 2583-2596.

DOI：10.1180/minmag.2011.075.5.2583

• mendeleevite-(Ce)
• new mineral
• silicate cluster
• silicate framework
• electron microprobe analysis
• crystal structure
• microporous material
• Darai-Pioz glacier
• Tajikistan

The crystal structure of mendeleevite-(Ce), (Cs,square)(6)(square,Cs)(6)(square,K)(6)(REE,Ca,square)(30)(Si70O175) (H2O,OH,F,square)(35), a new mineral from the moraine of the Darai-Pioz glacier, the Alai mountain ridge, Tien-Shan mountains, northern Tajikistan, was solved by direct methods and refined to R-1 = 4.15% based on2274 observed [F-o > 4 sigma|F|] unique reflections measured with Mo-K alpha radiationona Bruker P4 diffractometer equipped with a CCD detector. Mendeleevite-(Ce) is cubic, space group Pm (3) over bar, a 21.9148(4) angstrom, V 10525(1) angstrom(3), Z = 2, D-calc = 3.066 g/cm(3). The empirical formula (electronmicroprobe) is Cs5.94K2.22[(Ce11.35La5.86Nd3.23Pr1.54Sm0.32Gd0.20)(Sigma 22.50)(Ca4.68Sr1.00)(Sigma 5.68)](Sigma 28).(18) Si70.12O203.17H45.67F6.83, Z = 2, calculated onthe basis of 210 (O + F) a.p.f.u., with H2O an d OH calculated from structure refinement (OH + F = 17 p.f.u.; H2O = 17.75 p.f.u.).
The structural formula is (Cs-4.65 square(1.35))(Sigma 6)(square Cs-4.71(1.29))(Sigma 6)(square K-3.78(2.22))(Sigma 6){[(Ce11.35La5.6Nd3.23 Pr1.54Sm0.32Gd0.20)(Sigma 22.50)(Ca4.68Sr1.00)(Sigma 5.68)](Sigma 28.18)square(1.82)}(Sigma 30)(Si70O175)[(OH)(10.17)F-6.83](Sigma 17)(H2O)(17.75). Simplified and endmember formulae are as follows: (Cs,square)(6)(square,Cs)(6)(square,K)(6)(REE,Ca,square)(30)(Si70O175) (H2O,OH,F,square)(35) and Cs-6(REE22Ca6)(Si70O175)(OH,F)(14)(H2O)(21). The crystal structure of mendeleevite(Ce) is an intercalation of two independent Si-O radicals and an M framework of (REE, Ca) polyhedra. The Si-O radicals are an(Si104O260)(104-) framework and an (Si36O90)(36-) cluster which do not link directly. The M framework is located betweenthe Si-O framework and the Si-O clusters. Interstitial cations occupy two types of cages and channels. Cages I and II are 78 and 22% occupied by Cs. Channels along [100(sic)] contain K atoms and H2O groups. Mendeleevite-(Ce) has no natural or synthetic structural analogues. Mendeleevite-(Ce) is a framework mineral with large cavities and it has the potential to be used as a model for the synthesis of microporous materials of industrial interest.

• 出版日期2011-10