| Abstract/Notes | SynopsisTwo compounds are described which are structurally related to the three salts, metavoltine, Ξ±-Maus' salt, and an unnamed compound here termed βsalt Xβ: The last three salts have structures based on two sheets of composition [K Fe33+O(SO4)6(H2O)3]4β which are essentially intercon-nected via Na atoms in metavoltine, K-atoms in Ξ±-Maus' salt and Na, K, H3O in salt X.Cell parameters and space groups of the new compounds have been determined: as in metavoltine, Ξ±-Maus' salt, and salt X they have a = b β 9.6 Γ
, but the c parameters are β 36 Γ
and β 52 Γ
, i.e. about double and triple that of the other three salts (β 18 Γ
).The salt with c β 36 Γ
was obtained using Van Tassel' recipe at about the same conditions which gave rise to salt X, i.e. from a solution containing Na2SO4Β·10H2O, K2SO4, Fe2(SO4)3Β·nH2O (n β 7H2O) in the ratio 3.40:0.60:4.30. The salt with c β 52 Γ
was formed spontaneously through a topotactic reaction of salt X.It is possible to deduce for these two new salts:(1) The presence of clusters of composition [Fe33+O(SO4)6(H2O)3]5β interconnected via K atoms to build sheets like those found in meta-voltine, Ξ±-Maus' salt, and salt X.Some sheet sequences which may include the correct sequence.The position of Fe3+ atoms belonging to clusters, which are connected by K atoms to form sheets.The similar a and b lattice parameters, as well as the presence of the threefold axis in all the compounds mentioned, suggest strongly that in the two new compounds there are sheets of composition [K Fe33+O(SO4)6(H2O)3]4β which are characterized by a = b β 9.6 Γ
and threefold symmetry. As for the c parameters, examination of possible stacking sequences of the sheets shows which sequences are consistent with the known c parameters and symmetry. The two salts have a parameter and symmetry more similar to metavoltine and salt X than to Ξ±-Maus' salt; moreover, metavoltine and salt X, like the new salts, are more stable than Ξ±-Maus' salt. That is why probably in the two new salts there are two sheets interconnected by Na atoms as in metavoltine and salt X to form a sandwich sheet of composition [Na2K2Fe63+O2(SO4)12(H2O)6]6β. Then, taking into account the c parameters and space groups, possible sequences of these sandwich sheets are considered in order to establish the likely sequence in the new salts.Metavoltine and salt X contain clusters [Fe33+O(SO4)6(H2O)3]5β which are differently oriented: the Fe3+ cation lies at x = 0.17, y = 0.22 or x = 0.22, y = 0.17. These two Fe3+ positions involve an angle rotation for the cluster of about 25Β°. Owing to the similarity in a, b parameters of metavoltine and the salt with c β 52 Γ
on one hand, and of salt X and the salt with c β 36 Γ
on the other, it seems quite probable that the xy coordinates of the Fe3+ cations belonging to the first pair of salts are similar, and similarly for the second pair.(Na, K) Ξ±-Maus' salt effloresces in air, the products being ferrinatrite and goldichite. The transformation (Na, K) Ξ±-Maus' salt β ferrinatrite was clarified when the structure of ferrinatrite was solved. The transition (Na, K) Ξ±-Maus' salt β, goldichite is considered in order to understand how [Fe33+O(SO4)6(H2O)3]5β clusters may be modified to build new structural units such as the corrugated sheets present in goldichite. |
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