Crystal-chemical investigation of Fe₃(PO₄)₂· 8 H₂O vivianite minerals

Theoretical and experimental study of the vibrational spectra of (para)symplesite and hörnesite

“…4, Table 1). The view of the OH stretching spectral region resembles the IR bands observed in the phosphate analogues: vivianite (3460, 3281, 3104 cm À1 ) [23,24] and metavivianite (3350, 3240, 3145 cm À1 ) [7].…”

“….O in the given equation, we have computed the predicted positions of the OH stretching bands in the IR spectra, reflecting the hydrogen bonding pattern (3569, 3561, 3559, 3544, 3519, 3505, 3262, 3158 and 3149 cm À1 for hörnesite and 3571, 3561, 3550, 3536, 3245 and 3218 cm À1 , for parasymplesite (since no structural cif file for symplesite is available). As pointed by Capitelli et al [23] who applied Libowitzky's approach on vivianite minerals, the deviation between the calculated and experimental values could be attributed to the non-perfect resolution of the broad H 2 O stretching band and the fact that some protons are involved in several O-H. . .O bond-like interaction systems.…”

Crystal-chemical study of wavellite from Zbirov, Czech Republic

“…All other strong H bonds are a consequence of the acceptor character of the (PO 4 ) unit, for example Table 5 shows that O8ÀH81_O1 IV is the (Table 5), or also O7ÀH71_O4 and O6ÀH6_O3 I (respectively H_A = 1.995(17) and 1.973(14) Å , D_A = 2.925(2) and 2.860(2) Å , DÀHÀA = 167(5) and 157(2)º (Table 5)), which help to further stabilize the single cationic arrays via (PO 4 ) units, as well as acting as minor interactions such as O7ÀH72_O2 VI and O7ÀH72_O3 VI (Table 5). Lastly, the described strong H bonds can be reviewed as the packing forces that cause the widening of the HOH internal angle at the O7 water molecule, peaking at 125(4)º (while it is 108(3)º at O8, Table 4), a large value already observed in hydrated natural arsenates and phosphates, such as in (Co 2.16 Ni 0.24 Mg 0.60 )(AsO 4 ) 2 ·8H 2 O erythrite (Capitelli et al, 2007) and Fe 3 (PO 4 ) 2 ·8H 2 O vivianite (Capitelli et al, 2012).…”

Babánekite, Cu3(AsO4)2 ∙ 8H2O, from Jáchymov, Czech Republic - a new member of the vivianite group

“…The refined structure of babánekite shows characteristic features of the vivianite-type minerals and synthetic compounds, characterized by the general formula Me 2+ 3 (XO 4 ) 2 •8H 2 O (Me = Mg, Fe, Co, Ni, Zn; X = P, As) (Mori and Ito 1950;Cesbron et al 1977;Hill 1979;Fejdi et al 1980;Giuseppetti and Tadini 1982;Dormann et al 1982;Takagi et al 1986;Riou et al 1989;Bartl 1989;Wildner et al 1996;Yakubovich et al 2001;Capitelli et al 2007Capitelli et al , 2012Assani et al 2010;Yoshiasa et al 2016;Antao and Dhaliwal 2017). Vivianite-type structures consist of MelO 2 (H 2 O) 4 octahedra and dimers of Me2 2 O 6 (H 2 O) 4 octahedra that are linked via XO 4 tetrahedra (where X = P, As and probably can be also V) and hydrogen bonds to form complex layers parallel to (010).…”