The crystal structure and crystal chemistry of mendeleevite-(Ce), (Cs,〈)6(〈,Cs)6(〈,K)6(REE,Ca,〈)30(Si70O175)(H2O,OH,F,〈)35, a potential microporous material.

The crystal structure of mendeleevite-(Ce), (Cs,〈)6(〈,Cs)6(〈,K)6(REE,Ca,〈)30(Si70O175)(H2O,OH,F,〈)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 R1= 4.15% based on 2274 observed [Fo> 4σ|F|] unique reflections measured with Mo-Kα radiationona Bruker P4 diffractometer equipped with a CCD detector. Mendeleevite-(Ce) is cubic, space group Pm3, a21.9148(4) Å, V10525(1) Å3, Z= 2, Dcalc= 3.066 g/cm3. The empirical formula (electron microprobe) is Cs5.94K2.22[(Ce11.35La5.86Nd3.23Pr1.54Sm0.32Gd0.20)Σ22.50(Ca4.68Sr1.00)Σ5.68]Σ28.18Si70.12O203.17H45.67F6.83, Z= 2, calculated onthe basis of 210 (O + F) a.p.f.u., with H2O and OH calculated from structure refinement (OH + F = 17 p.f.u.; H2O = 17.75 p.f.u.).The structural formula is (Cs4.65〈1.35)Σ6(〈4.71Cs1.29)Σ6(〈3.78K2.22)Σ6{[(Ce11.35La5.86Nd3.23Pr1.54Sm0.32Gd0.20)Σ22.50(Ca4.68Sr1.00)Σ5.68]Σ28.18〈1.82}Σ30(Si70O175)[(OH)10.17F6.83]Σ17(H2O)17.75. Simplified and endmember formulae are as follows: (Cs,〈)6(〈,Cs)6(〈,K)6(REE,Ca,〈)30(Si70O175) (H2O,OH,F,〈)35and Cs6(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@] 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. [ABSTRACT FROM AUTHOR]