The superstructure of the double layer mineral wermlandite [ Mg 7 ( Alo . 57
نویسنده
چکیده
The structure of wermlandite, [Mg7(Alo.57Feo.43h(OH)ls]2+ [(CaO.6' Mgo.4) (S04h(H20)u]2has been determined and refined to an R value of 7.2 % based on 779 symmetry-independent reflections, of which 224 are unobserved (weighted R=6.1%). The cell dimensions are a=b=9.303(3), c=22.57(1) A, the space group is pjc1 with Z=2 ~nd Dx=1.96 cm-3. The double layer structure ofwermlandite is similar to those ofpyroaurite and sj6grenite. In these compounds the excess positive charge in the brucitelike main layer is compensated by additional anions in the interlayers. Main and interlayer are connected by 0 H. . .0 hydrogen bonds ~ 2.91 A. The network of hydrogen bonds could be evaluated. The reflections of type h,k = 3n, 1= 2n are especially strong and indicate the existence of an eighteenfold trigonal superstructure. The superstructure was solved using partial Fourier and Patterson syntheses.
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