Site-selective As–P substitution and hydrogen bonding in the crystal structure of philipsburgite

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Marco E. Ciriotti
Messaggi: 24481
Iscritto il: ven 25 giu, 2004 11:31
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Site-selective As–P substitution and hydrogen bonding in the crystal structure of philipsburgite

Messaggio da Marco E. Ciriotti » ven 11 mag, 2018 17:15

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Referenza:
▪ Krivovichev, S.V., Zhitova, E.S., Ismagilova, R.M., Zolotarev, A.A. (2018): Site-selective As–P substitution and hydrogen bonding in the crystal structure of philipsburgite, Cu5Zn((As,P)O4)2(OH)6·H2O. Physics and Chemistry of Minerals, 45, (in press).

Abstract:
Philipsburgite, Cu5Zn((As,P)O4)2(OH)6·H2O, from the Middle Pit, Gold Hill Mine, Tooele Co., Utah, USA, was studied by single-crystal X-ray diffraction and scanning electron microscopy. The empirical formula of the studied sample is (Cu4.69Zn1.23)(As0.86P0.18O4)2(OH)5.61·H2O, which agrees well with the previous reports on the mineral. Philipsburgite is monoclinic, P21/c, a = 12.385(6), b = 9.261(4), c = 10.770(5) Å, β = 97.10(1)o, V = 1225.7(9) Å3 (at 100 K), and Z = 4. The crystal structure was refined to R1 = 0.046 for 2563 unique observed reflections with |Fo| ≥ 4σ F . The crystal structure of philipsburgite is isotypic to that of kipushite and can be considered as a complex three-dimensional framework consisting of two types of layers stacked parallel to the a-axis. The A-type layer is formed by the edge-sharing Jahn–Teller-distorted Cuφ6 octahedra [φ = O2−, (OH)−, H2O]. Two adjacent octahedral layers are linked via (As2O4) tetrahedra. The B-type layer is built by corner-sharing (ZnO4) and (As1O4) tetrahedra and is formed by the four- and eight-membered tetrahedral rings. The A:B ratio of the A and B layers is equal to 2:1. The hydrogen bonding network in philipsburgite is rather complex and consists of two- and three-center hydrogen bonds. The As1 site accommodates ca. 18% of P and is a preferable position for the P substitution in philipsburgite. The observed selectivity of the As1 site for P may indicate that, for the intermediate compositions with the P:As ratios close to 1:1, there is a fully ordered species with P prevalent at the As1 site and As prevalent at the As2 site. The intermediate composition would, therefore, be Cu5Zn(AsO4)(PO4)(OH)6·H2O and such a mineral can be considered as a separate species, according to the rules of the International Mineralogical Association (IMA). Philipsburgite should be considered as structurally complex with the Shannon information contents of 4.954 bits/atom and 614.320 bits/cell. The obvious reason for the structural complexity of the mineral is its modularity, i.e., the presence of two structurally distinct modules, the octahedral–tetrahedral (A) and tetrahedral (B) layers.
Marco E. Ciriotti

«Things are interesting only in so far as they relate themselves to other things»

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Marco E. Ciriotti
Messaggi: 24481
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
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Re: Site-selective As–P substitution and hydrogen bonding in the crystal structure of philipsburgite

Messaggio da Marco E. Ciriotti » ven 11 mag, 2018 17:29

I campioni rinvenuti alla ex miniera di Sa Duchessa, Oridda, Domusnovas, sarebbero da re-indagare...
Marco E. Ciriotti

«Things are interesting only in so far as they relate themselves to other things»

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