Phase equilibria of the system Ce–Zn–Si have been determined for the isothermal section at 600 °C for <33.3 at.% Ce by XRPD and EPMA. This partial section is characterized by the formation of five ...ternary compounds with homogeneity regions at constant Ce-content and partial substitution of Zn/Si: τ
1
-Ce
7
Zn
21
(Zn
1−x
Si
x
)
2
(unique type; 0.45 ≤
x
≤ 0.99), τ
2
-Ce(Si
1−x
Zn
x
)
2
(AlB
2
-type; 0.36 ≤
x
≤ 0.73), τ
5
-CeZn(Zn
1−x
Si
x
)
2
(CeNiSi
2
-type; 0.68 ≤
x
≤ 0.76), τ
6
-CeZn
2
(Si
1−x
Zn
x
)
2
(ThCr
2
Si
2
-type; 0.25 ≤
x
≤ 0.30) and τ
7
-Ce
37
Zn
48
Si
15
(structure unknown). Whereas τ
1
, τ
2
and τ
5
are stable at 600 and 800 °C, the phases τ
6
, τ
7
are unstable at 800 °C. Atom site distribution in the crystal structures of τ
5
, τ
6
and {La,Ce}
7
Zn
21
(Zn
1−x
Ge
x
)
2
have been elucidated from X-ray intensity refinements on single crystals. The small amounts of the stabilizing tetrel element in {La,Ce}
7
Zn
21
Zn
1−x
Si(Ge)
x
2
suggest a hypothetical binary phase “{La,Ce}
7
Zn
23
”. The stabilizing effect of Ge in Ce
7
Zn
23−x
Ge
x
has been elucidated from density functional theory (DFT) calculations discussing the electronic structure in terms of the density of states (DOS) and defining enthalpies of formation for Ce
7
Zn
23−x
Ge
x
(
x
= 0, 0.5, 2) as well as for several neighbouring binary Ce–Zn phases. A Schultz–Scheil diagram for the solidification behaviour in the (Zn,Si)-rich part of the diagram was constructed from DTA measurements in closed silica crucibles along with partial isothermal sections determined in the temperature range from 400 to 900 °C. The phases τ
5
and τ
6
both form in degenerate ternary peritectic reactions: L + CeSi
2
,β-Ce
2
Zn
17
⇔ τ
5
at 865 ± 5 °C and L + τ
5
,CeZn
11
⇔ τ
6
at 695 ± 5 °C, respectively. Magnetic susceptibility, specific heat and resistivity measurements of τ
5
-CeZn(Zn
1−x
Si
x
)
2
revealed Kondo lattice behavior with ferromagnetic ordering below
T
C
= 4.4 K, whereas susceptibility and specific heat studies of τ
6
-CeZn
2
(Zn
0.28
Si
0.72
)
2
revealed Curie–Weiss paramagnetic behaviour down to 3 K. The effective paramagnetic moments of Ce obtained from Curie–Weiss fits of τ
5
(2.50
μ
B
) and τ
6
(2.34
μ
B
) reveal a ground state close to trivalent Ce.
The structure of trigonal ferrinatrite, Na
3
Fe(SO
4
)
3
⋅3H
2
O, from the Hongshan Cu-Au deposit, Eastern Tianshan, NW China was refined in space group
P
3
¯
based on single crystal X-ray ...diffraction data
a
= 15 .553(2),
c
= 8.6616(17 ) Å,
V
= 1814.4(5) Å
3
,
Z
= 6;
R
1
= 0.0535. All hydrogen atoms were located by difference Fourier methods and refined with soft restrictions for distances, but with fixed thermal isotropic displacement parameters. The atomic arrangement in ferrinatrite is based on chains along 001 consisting of isolated FeO
6
-octahedra corner-linked with sulfate groups. All vertices of octahedra link to tetrahedra, and half the tetrahedron vertices link to octahedra. These chains are linked by interstitial Na-ions and H
2
O groups. All Na atoms are coordinated to four oxygen atoms of sulfate groups and to two oxygen atoms of H
2
O molecules within 2.33–2.71 Å; next oxygens are at distances of 2.85–3.00 Å. Among six hydrogen bonds, three acceptor O-atoms of sulfate groups belong to the nearest octahedral-tetrahedral chains, and three acceptor sulfate O-atoms from the neighboring chains, which further strengthen the linkages between octahedral-tetrahedral chains. The O–H···O distances are in the range 2.86–3.13 Å. The O–H stretching frequencies derived from structural data are in good consistence with the known Infrared spectra.
Three new compounds Zr(SeO
3
)(SeO
4
), Zr
4
(SeO
3
)(SeO
4
)
7
, and Zr
3
(SeO
3
)(SeO
4
)
5
·2H
2
O were synthesized at low-hydrothermal conditions (Teflon-lined steel vessels, 220 °C) from ...mixtures of Zr
2
O
2
(CO
3
)(OH)
2
, H
2
SeO
4
, and minor contents of water. Colorless single crystals up to several tenth of a mm in size, obtained within 1 week, were studied by single crystal X-ray techniques. Zr(SeO
3
)(SeO
4
) crystallizes in the orthorhombic space group
Pbca
(No. 61), with
a
= 8.291 (2) Å,
b
= 9.458 (2) Å,
c
= 15.357 (3) Å,
V
= 1204.2 (5) Å
3
,
Z
= 8,
R
1 = 0.0322. Zr
4
(SeO
3
)(SeO
4
)
7
is monoclinic, space group
P
2
1
/
n
(No. 14), with
a
= 5.313 (1) Å,
b
= 10.704 (2) Å,
c
= 10.484 (2) Å,
β
= 104.13 (1)°,
V
= 578.2 (1) Å
3
,
Z
= 1,
R
1 = 0.0172. Two independent selenium atoms are present in this structure: one forming a SeO
4
tetrahedron, and the other one exhibiting mixed occupation by ¾ Se
6+
and ¼ Se
4+
; its coordination is, therefore, partially disordered. Zr
3
(SeO
3
)(SeO
4
)
5
·2H
2
O crystallizes in the triclinic space group
P
1 (No. 1), with
a
= 5.273 (1) Å,
b
= 8.079 (2) Å,
c
= 11.959 (2) Å,
α
= 82.60 (1)°,
β
= 88.27 (1)°,
γ
= 89.87 (1)°,
V
= 505.1 (1) Å
3
,
Z
= 1,
R
1 = 0.0235, but exhibits strong centrosymmetric pseudosymmetry; the inversion center is violated only by replacement of one selenate(VI) tetrahedron by a trigonal pyramidal selenite(IV) group as pseudo-centric counterpart. Hydrogen bonds in this compound show donor–acceptor distances within the range of 2.67–2.81 Å. All three framework structures are unique and built up from corner-sharing polyhedra. In all three compounds, mean cation-oxygen bond lengths (Zr
6
: 2.062 and 2.067 Å; Zr
7
: 2.132, 2.137 and 2.139 Å; Se
4+3
: 1.675 and 1.680 Å, excluding the disordered group; Se
6+4
: 1.621–1.641 Å) are comparatively short, resulting in rather high bond valence sums.
Graphical abstract
The new compounds Zr(SeO
4
)
2
·H
2
O and Zr(SeO
4
)
2
·4H
2
O were synthesized at low-hydrothermal conditions (teflon-lined steel vessels, 220 °C) from mixtures of Zr
2
O
2
(CO
3
)(OH)
2
, H
2
SeO
4
..., and minor contents of water. Colorless single crystals up to 0.2 mm in length, obtained within 1 week, were studied by single-crystal X-ray techniques. Zr(SeO
4
)
2
·H
2
O crystallizes in the monoclinic space group
P
2
1
/
n
(no. 14), with
a
= 5.332(1) Å,
b
= 7.962(2) Å,
c
= 16.256(3) Å,
β
= 92.19(1)°,
V
= 689.6(3) Å
3
,
Z
= 4, and
R
1 = 0.0195. Zr(SeO
4
)
2
·H
2
O represents a new structure type built from isolated ZrO
7
pentagonal dipyramids, further cornerlinked via SeO
4
groups to a three-dimensional framework. One H
2
O group acts as a ligand of the ZrO
7
coordination. Zr(SeO
4
)
2
·4H
2
O orthorhombic, space group
Fddd
(no. 70), with
a
= 5.651(1) Å,
b
= 11.964(3) Å,
c
= 26.611(6) Å,
V
= 1799.1(4) Å
3
,
Z
= 8, and
R
1 = 0.0177 is isotypic with the compounds
M
(SO
4
)
2
·4H
2
O;
M
= Zr, Hf, Ce, and Pu. The structure is built up by sheets within (001), linked by hydrogen bonds only. The zirconium atom is 8-coordinated to oxygen atoms of four H
2
O molecules and of SeO
4
tetrahedra, forming a distorted tetragonal antiprism. For both structures, mean cation-oxygen bond lengths are in accordance with the literature: Zr
7
: 2.137 Å, Zr
8
: 2.188 Å, and Se
4
: 1.631–1.635 Å. Observed hydrogen bonds show donor–acceptor distances within the range of 2.65–2.79 Å.
Graphical abstract
Cu- and Mn-bearing tourmalines from Brazil and Mozambique were characterised chemically (EMPA and LA-ICP-MS) and by X-ray single-crystal structure refinement. All these samples are rich in Al, Li and ...F (fluor-elbaite) and contain significant amounts of CuO (up to ~1.8 wt%) and MnO (up to ~3.5 wt%). Structurally investigated samples show a pronounced positive correlation between the <
Y
-O> distances and the (Li + Mn
2+
+ Cu + Fe
2+
) content (apfu) at this site with
R
2
= 0.90. An excellent negative correlation exists between the <
Y
-O> distances and the Al
2
O
3
content (
R
2
= 0.94). The samples at each locality generally show a strong negative correlation between the
X
-site vacancies and the (MnO + FeO) content. The Mn content in these tourmalines depends on the availability of Mn, on the formation temperature, as well as on stereochemical constraints. Because of a very weak correlation between MnO and CuO we believe that the Cu content in tourmaline is essentially dependent on the availability of Cu and on stereochemical constraints.
The crystal structure of goldichite KFe(SO
4
)
2
⋅4H
2
O was determined on a single crystal from the Baiyinchang copper deposit, Gansu, China.
P
12
1
/
c
1,
a
= 10.395(2),
b
= 10.475(2),
c
= ...9.0875(18) Å, β = 101.65(3)°,
V
= 969.1(3) Å
3
, Z = 4. All non-H atoms were refined with anisotropic displacement parameters and positions of H-atoms were determined by difference Fourier methods and refined from X-ray diffraction data. The crystal structure of goldichite consists of corrugated sheets parallel to the (100) plane by sharing corners between FeO
6
octahedra and SO
4
tetrahedra. The interstitial potassium atom exhibits a KO
7
(H
2
O)
2
nine-fold coordination, which shares edges to form a column parallel to the
c
-axis and to build a slab with the corrugated sheet. These slabs are linked in the 100 direction through a network of hydrogen bonds. Three types of hydrogen bonds involve links of slabs: O
w
(3)-H(3B)···O(1), O
w
(6)-H(6B)···O(11) and O
w
(9)-H(9B)···O(11). The FTIR spectrum of goldichite shows a strong absorption between ~3384 cm
−1
and ~3592 cm
−1
, which is in accordance with the O-H···O distances derived from structure data.
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