Crystal structures of the fluosilicate hexahydrates of cobalt, nickel and zinc

Structure investigation by neutron diffraction of deuterated cobalt fluosilicate hexahydrate

“…hydrogen or deuterium atoms). Although the parameters of CoSiF6.6D20 in the high-temperature phase are rather similar to those reported by Ray et al (1973) from X-ray data, the present study allows precise determination firstly of the position of D atoms (and thus the conformation of the water molecules) and secondly of the position of the F atoms Table 2. …”

“…2). With the more accurate H/D positions we find that most of the hydrogen-bond lengths are shorter than those given by Ray et al (1973) (Table 2).…”

“…In the case of MgSiF6.6H20 (T___ 300 K) and FeSiF6.6H20 (at room temperature), a structural model involving two types, with equal probability, of ordered domains (space group P3) (Jehanno & Varret, 1975;Chevrier & Jehanno, 1979;Chevrier, Hardy & Jehanno, 1981) can explain the superstructure peaks which were inconsistent with the structure © 1990 International Union of Crystallography ¢ models described by Syoyama &Osaki (1972), andHamilton (1962). In the cases of CoSiF6.6H20, NiSiF6.6HzO and ZnSiF6.6H20, at room termperature, Ray, Zalkin & Templeton (1973) proposed a disordered structure (space group R3) with two completely independent fluorine positions; their occupation was determined as 0.43/0.57 for the cobalt fluosilicate and 0.33/0.67 for the corresponding Ni and Zn salts.…”

“…1). First we tried to refine the structure with two unequal occupancy factors [we used 0.43/0-57 as did Ray et al (1973) in their study, then 0.33/0.66 and 0.66/0.33]. In all cases, the convergence was very difficult to obtain and we noted strong correlations between the rate factors and the y parameters of F (1) and F(2); for instance, after 10 cycles, these parameters were not stabilized [max.…”

A new example of an arrangement of antiphase domains: investigation by neutron diffraction of deuterated manganese fluosilicate

“…The phase transition for our deuterated sample (-244 K) is again at a higher temperature than that reported for the undeuterated compound (-225 K); this significant difference (AT= 19 K) is of the same order of magnitude as that for CoSiF6.6H20 (Ray et aL, 1973;Chevrier & Saint-James, 1990), M = Mg (Chevrier & Jehanno, 1979) and M = Fe (Hamilton, 1962;Chevrier et al, 1981) is 1.680 A].…”