Cs2Gd6N2Te7: The first quaternary nitride telluride of the lanthanides

Article abstract of DOI:10.1016/j.jallcom.2005.08.105

The first quaternary nitride telluride with trivalent gadolinium, Cs₂Gd₆N₂Te₇, was obtained by the reaction of metallic gadolinium with cesium azide, elemental tellurium, and gadolinium trichloride as well as cesium chloride as flux at 900 °C for 7 days in evacuated silica tubes. Single crystals occur as long black needles and crystallize in the monoclinic space group C2/m (a = 2403.1(2) pm, b = 424.03(3) pm, c = 1142.91(7) pm, β = 103.709(4)°, Z = 2). Three crystallographically different Gd³⁺ cations constitute the structure, two are coordinated by one N^3- (d(Gd(1/2)-N) = 217 pm) and five Te^2- anions (d(Gd(1/2)-Te) = 305-326 pm), and the third Gd³⁺ by two N^3- (d(Gd(3)-N) = 244 pm) and four Te^2- anions (d(Gd(3)-Te) = 316-317 pm), all forming distorted octahedra about Gd³⁺. The Cs⁺ cation shows a perfect bicapped trigonal prism (C.N. = 8, d(Cs-Te) = 383-431 pm) as coordination sphere. Two of these polyhedra are condensed via a common (non-capped) rectangular face building up double prisms [Cs₂Te₁₂]^22-. Further linkage via triangular faces (along [0 1 0]) and two of the four caps (along [0 0 1]) results in corrugated layers [Cs₂Te₇]^12- running parallel to (1 0 0). However, the main feature of the crystal structure comprises N^3--centered (Gd³⁺)₄ tetrahedra (d(N-Gd) = 217 pm (2×) and 244 pm (2×); {measured angle}(Gd-N-Gd) = 107° (2 + 2 + 1×) and 121° (1×)), which are connected via two vertices each to build up one-dimensional infinite chains _∞¹{ [ N (Gd 1)_{1 / 1}^t (Gd 2)_{1 / 1}^t (Gd 3)_{2 / 2}^v ]^{6 +} } (t = terminal, v = vertex-shared) along [0 1 0] like in the structure of the M₃NCh₃-type nitride chalcogenides with M = La-Nd, Sm, Gd-Dy, and Ch = S, Se.

Full text of DOI:10.1016/j.jallcom.2005.08.105

Journal of Alloys and Compounds 418 (2006) 68–72
Cs Gd N Te : The first quaternary nitride telluride of the lanthanides
2
6 2
7
∗
Falk Lissner, Thomas Schleid
Institut f u¨ r Anorganische Chemie, Universit a¨ t Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany
Received 12 May 2005; received in revised form 2 August 2005; accepted 2 August 2005
Available online 24 January 2006
Abstract
The first quaternary nitride telluride with trivalent gadolinium, Cs
2
Gd
6
N
2
Te
7
, was obtained by the reaction of metallic gadolinium with
◦
cesium azide, elemental tellurium, and gadolinium trichloride as well as cesium chloride as flux at 900 C for 7 days in evacuated silica
tubes. Single crystals occur as long black needles and crystallize in the monoclinic space group C2/m (a = 2403.1(2) pm, b = 424.03(3) pm,
◦
3+
c = 1142.91(7) pm, β = 103.709(4) , Z = 2). Three crystallographically different Gd cations constitute the structure, two are coordinated by one
3
−
2
−
3+
3
−
N
(d(Gd(1/2)–N) = 217 pm) and five Te anions (d(Gd(1/2)–Te) = 305–326 pm), and the third Gd by two N (d(Gd(3)–N) = 244 pm) and
four Te anions (d(Gd(3)–Te) = 316–317 pm), all forming distorted octahedra about Gd . The Cs cation shows a perfect bicapped trigonal
prism (C.N. = 8, d(Cs–Te) = 383–431 pm) as coordination sphere. Two of these polyhedra are condensed via a common (non-capped) rectangular
2
−
3+
+
2
2−
. Further linkage via triangular faces (along [0 1 0]) and two of the four caps (along [0 0 1]) results
face building up double prisms [Cs
2
Te12
]
1
2
−
3
−
3+
in corrugated layers [Cs
2
Te
7
]
running parallel to (1 0 0). However, the main feature of the crystal structure comprises N -centered (Gd )
4
◦
◦
tetrahedra (d(N–Gd) = 217 pm (2×) and 244 pm (2×); ѯ(Gd–N–Gd) = 107 (2 + 2 + 1×) and 121 (1×)), which are connected via two vertices each
t
t
v
2/2
6
]
+
1
∞
to build up one-dimensional infinite chains {[N(Gd1) (Gd2) (Gd3)
} (t = terminal, v = vertex-shared) along [0 1 0] like in the structure of
1/1
1/1
the M
3 3
NCh -type nitride chalcogenides with M = La–Nd, Sm, Gd–Dy, and Ch = S, Se.
©
2005 Elsevier B.V. All rights reserved.
Keywords: Lanthanides; Cesium; Gadolinium; Nitrides; Tellurides; Crystal structure
1
. Introduction
this case. The nitride chalcogenides Pr4N2S3 [7] and M4N2Se3
M = Pr, Nd) [6,7] present a layered arrangement, dominated
(
3−
3+
In the last decade, nitride chalcogenides of the lanthanides
by N -centered (M )4 tetrahedra again, which share a com-
mon edge first. Continuing linkage of the resulting bitetrahedral
[N2M6]1 units (also a discrete feature in the crystal struc-
ture of M NSe [8] with M = Pr) via the non-connected vertices
(
and their halide derivatives) have been demonstrated to pos-
2+
sess an extremely rich chemistry of formula and structural
types [1]. However, N3 -centered (M )4 tetrahedra, which
can occur isolated or condensed, provide the main feature in
the crystal structures for all of them. In ternary compounds
such as M3NCh3 (M = La–Nd, Sm, Gd–Dy; Ch = S, Se) [2]
−
3+
5
6
3
+
to layers according to 2 {[N(M) (M )
e
ꢀ v
]
2/2
} forms different
∞
2/2
kinds of tetrahedral nets, which can be described as layers con-
sisting of “four- and eight-rings” for Pr4N2S3 and as layers of
exclusively “six-rings” forPr4N2Se3. Recentlywe could prepare
and characterize the first nitride tellurides of the lanthanides,
M4N2Te3 (M = La–Nd) [9], on the basis of single-crystal X-ray
9+
these [NM4] tetrahedra are connected via two corners form-
ing linear chains 1 {[N(M) (M ) ]} (t = terminal, v = vertex-
t
ꢀ v
∞
2/1
3+
2/2
shared). The ratio N3 : M = 1: 2, realized for the composition
−
3
−
M4N2Ch3 (M = La–Nd, Sm, Tb; Ch = S, Se, Te) [3], requires a
diffraction data. The crystal structure is dominated by N
-
higher degree of linkage of the N3 -centered (M )4 tetrahe-
dra. The crystal structures of Sm4N2S3 [4] and Tb4N2Se3 [5,6]
show also infinite chains, but now by sharing cis-oriented edges
−
3+
3+
centered (M )4 tetrahedra of course, which build up non-
linear infinite chains 1∞{[N(M)
e
]
3+
} by sharing trans-oriented
4/2
edges.
ꢀ e
]
3/3
3
+
according to 1∞{[N(M) (M )
t
} (e = edge-connecting) in
1/1
2
. Experimental data
Cs Gd N Te , the first quaternary nitride telluride with cesium and gadolin-
∗
Corresponding author. Fax: +49 711 685 4241.
2
6
2
7
ium, was obtained by the reaction of elemental gadolinium (Gd: ChemPur;
E-mail address: schleid@iac.uni-stuttgart.de (Th. Schleid).
0
925-8388/$ – see front matter © 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2005.08.105

F. Lissner, Th. Schleid / Journal of Alloys and Compounds 418 (2006) 68–72
69
Table 1
Cs2Gd6N2Te7: crystallographic data and their determination
Table 3
◦
Cs2Gd6N2Te7: selected internuclear distances, d (pm), and angles, ѯ( )
Formula
Cs2Gd6N2Te7
Cs Gd1 Gd2
Crystal system
Space group
Formula units (Z)
Lattice constantsa
Monoclinic
C2/m (no. 12)
2
a = 2403.12(15) pm, b = 424.03(3) pm,
c = 1142.91(7) pm, β = 103.709(4)
340.68(4)
6.254
–Te3 (2×) 383.2
–N (1×)
217.0
–Te4 (2×) 305.3
–N (1×)
217.1
307.1
317.3
318.2
–Te4 (2×) 393.8
–Te3 (2×)
–Te2 (2×)
ꢀ
–Te4 (2×) 400.6
–Te2 (1×) 319.2
ꢀ
ꢀ
–Te1 (1×) 414.0
–Te2 (2×) 326.9
–Te3 (1×)
◦
–Te2 (1×) 430.5
3
−1
)
)
Molar volume, Vm (cm mol
Calculated density, Dx (g cm
F(0 0 0)
Gd3
N
−
3
–
N (2×)
244.1
–Gd1 (1×) 217.0 Gd1–N–Gd3 (2×) 107.0
–Gd2 (1×) 217.1 Gd2–N–Gd3 (2×) 107.2
–Gd3 (2×) 244.1 Gd1–N–Gd2 (1×) 107.3
1744
–
–
–
Te3 (1×) 315.5
Diffractometer/wavelength
Kappa-CCD (Nonius)/λ = 71.07 pm
Te1 (2×) 316.1
Te4 (1×) 317.3
(Mo-K␣)
ꢀ
Gd3–N–Gd3 (2×) 120.6
Index range
± hmax = 32, ± kmax = 5, ± lmax = 15
◦
Θmax ( )
28.3
Absorption coefficient, µ
29.33
−
1
(
mm
)
Data corrections
Background, polarization and Lorentz
factors; numerical absorption correction:
program X-SHAPE [11]
Collected reflections/unique ones
Rint/Rσ
13978/1590
0.092/0.053
Structure solution and refinement
Scattering factors
R1 (with 4σ barrier)
Program package SHELX-93 and -97 [12]
International Tables, vol. C [13]
0.037 (for 1386 reflections)
0.050/0.061/1.122
R1/wR2/Goodness of Fit (GooF)
(
for all reflections)
Extinction (g)
0.00022(3)
Residual electron density, ρ
1.91 (max.), −1.72 (min.)
−
6
3
(
e
× 10 pm )
a
Single crystal data, further details of the crystal structure investigation
can be obtained from the Fachinformationszentrum (FIZ) Karlsruhe, D-
6344 Eggenstein-Leopoldshafen, Germany (fax: +49 7247 808 666; e-mail:
7
crysdata@fiz-karlsruhe.de), on quoting the depository number CSD-391315 for
Cs2Gd6N2Te7.
Table 2
Cs2Gd6N2Te7: atomic coordinates and anisotropic thermal displacement para-
2
a
meters, Uij (pm )
Atom
Wyckoff position
x/a
y/b
z/c
Cs
4i
4i
4i
4i
4i
2a
4i
4i
4i
0.06636(4)
0.16467(2)
0.21612(2)
0.41009(2)
0.1386(4)
0
0.24075(3)
0.33622(3)
0.42506(3)
0
0
0
0
0
0
0
0
0
0.69714(9)
0.39163(5)
0.13008(5)
0.86393(5)
0.1964(9)
0
0.66158(8)
0.05830(8)
0.59543(8)
Gd1
Gd2
Gd3
N
Te1
Te2
Te3
Te4
Atom
U11
U22
U33
U23
U13
U12
Cs
307(5)
144(3)
112(3)
104(3)
81(41)
167(6)
160(4)
134(4)
163(4)
300(5)
150(3)
136(3)
141(3)
163(51)
148(6)
153(4)
154(4)
164(4)
313(5)
140(3)
170(3)
162(3)
115(50)
374(8)
163(4)
171(4)
227(5)
0
0
0
0
0
0
0
0
0
28(4)
19(2)
44(2)
23(2)
−3(37)
−104(6)
13(3)
0
0
0
0
0
0
0
0
0
Gd1
Gd2
Gd3
N
Te1
Te2
Te3
Te4
38(3)
81(3)
a
2
2
2
Defined as temperature factor according to: exp[−2π (U11h a* +
Fig. 1. Coordination polyhedra [(Gd1)NTe5], [(Gd2)NTe5], and [(Gd3)N2Te4]
(top to bottom) in the crystal structure of Cs2Gd6N2Te7.
2
2
2
2
U22k b* + U33l c* + 2U23klb*c* + 2U13hla*c* + 2U12hka*b*)].

7
0
F. Lissner, Th. Schleid / Journal of Alloys and Compounds 418 (2006) 68–72
9
9
9.9%) with cesium azide (CsN3: Ferak; 99.9%), tellurium (Te: ChemPur;
9.9999%) as well as gadolinium trichloride (GdCl3: prepared from Gd2O3
3. Structure description and discussion
In the crystal structure of Cs2Gd N2Te7 there are three crys-
(
Johnson–Matthey;99.999%)bytheammonium-chlorideroute[10])andcesium
6
chloride (CsCl: ChemPur; 99.9%) as flux. In attempts to obtain Gd4N2Te3 with
a crystal structure isotypic to the M4N2Te3-type homologues with M = La–Nd
3+
tallographically different Gd cations present, two of them
3
−
2−
coordinated by one N and five Te anions, the third by two
[
9] according to
3−
2−
N
and four Te anions, forming distorted octahedra about
each Gd3 (Fig. 1, top to bottom). The distances d(Gd –N
3−
)
+
3+
3
4 Gd + 6 CsN3 + 27 Te + 2 GdCl3 → 9 Gd4N2Te3 + 6 CsCl
3+
2−
amount to 217–244 pm and d(Gd –Te ) to 305–327 pm,
respectively, as shown in Table 3. These values are in good
agreement with the Gd–N distances in the crystal structures of
Gd3NS3 (220–232 pm) [2] or Gd2NCl3 (226–228 pm) [14] and
the reactants (Gd, CsN3, Te, GdCl3) were handled under the inert argon atmo-
sphere of a glove box (M. Braun, Garching) and then heated to 900 C for 7 days
in evacuated silica tubes. Single crystals occur as long black needles in amounts
of at least 50% and turned out to possess a heretofore unknown basis-centered
monoclinic unit cell (space group: C2/m) with parameters like a = 2403.1(2) pm,
◦
Gd3NCl (224–231 pm) [15] as well as with the Gd–Te distances
6
◦
b = 424.03(3) pm, c = 1142.91(7) pm and β = 103.709(4) . Complete single-
in gadolinium sesquitelluride Gd2Te3 [16] with U2S3-type
structure (311–323 pm, C.N. = 7) or Cs3Gd7Te12 (304–322 pm,
crystal X-ray diffraction data refinement (Tables 1 and 2) results in the first
quaternary nitride telluride with cesium and gadolinium: Cs2Gd6N2Te7. In order
to increase the yield of this new nitride telluride the stoichiometric mixtures of
the educts were changed according to
+
C.N. = 6) [17]. The Cs cation shows a perfect bicapped trigonal
prism (C.N. = 8) as coordination figure due to its site symmetry
+
2−
m with distances d(Cs –Te ) of 383–431 pm (Fig. 2, above).
The binary telluride Cs2Te [18] (in contrast to most of the
other alkali-metal chalcogenides, A2Ch, with no anti-CaF2-type
structure) shows distances that again agree well (371–378 pm,
C.N. = 4 and 5) with the title compound and the same is true
for the Cs–Te distances in the ternary telluride Cs3Gd7Te12
5
8 Gd + 6 CsN3 + 63 Te + 12 CsCl → 9 Cs2Gd6N2Te7 + 4 GdCl3
◦
for reactions at 900 C of 1 week. Under these circumstances Cs2Gd6N2Te7
became the single-phase nitride telluride product in almost quantitative yields.
It was not possible to isolate a pure sample of this nitride telluride so far,
however, because by rinsing off the water-soluble by-products (GdCl3 and the
fluxing agent CsCl) Cs2Gd6N2Te7 begins to decompose by hydrolysis after
1
5−
(368–414 pm, C.N. = 6 and 7) [17]. Two of these [CsTe8]
polyhedra (Fig. 2) are condensed via a common (non-capped)
10–15 min, leaving behind black tellurium and colourless gadolinium hydrox-
2
2−
.
ide after ammonia evolution.
rectangular face building up double prisms [Cs2Te12]
Fig. 2. Coordination polyhedron [CsTe8] (above) and its condensation to corrugated layers 2∞{([Cs(Te4) (Te3)f (Te1)v (Te2)t ] )12−} (below) in the crystal
f
4/4
2/2
1/2
1/1
2
structure of Cs2Gd6N2Te7.

F. Lissner, Th. Schleid / Journal of Alloys and Compounds 418 (2006) 68–72
71
Fig. 3. Infinite chain 1∞{[N(Gd1) (Gd2)t (Gd3)v
t
]
2/2
6+} of vertex-connected [NGd4]9+ tetrahedra along [0 1 0] in the crystal structure of Cs2Gd6N2Te7.
1/1
1/1
Table 4
Cs2Gd6N2Te7: motifs of mutual adjunction [21]
3 3
chalcogenides M NCh (M = La–Nd, Sm, Gd–Dy; Ch = S, Se)
1
6+
[
2] already. These strands {[NGd3] } reside in the commen-
∞
2
6−
N
Te1
Te2
Te3
Te4
C.N.
surate layer {[CsTe3.5] } and assure the three-dimensional
∞
interconnection to a framework as well as the charge balance
for electroneutrality. Fig. 4 shows a view of the complete crystal
structure of Cs2Gd6N2Te7 along [0 1 0].
Cs
0/0
1/1
1/1
2/2
4
1/2
0/0
0/0
2/4
6
1/1
3/3
2/2
0/0
6
2/2
0/0
3/3
1/1
6
4/4
2/2
0/0
1/1
7
8
6
6
6
Gd1
Gd2
Gd3
C.N.
With the intention to prepare ternary lanthanide(III) nitride
tellurides, we only could successfully obtain the M4N2Te3-type
representatives for M = La–Nd [9] regardless of the nitrogen
source (NaN3 or CsN3) and the flux (NaCl or CsCl). Efforts
Further linkage via triangular faces (along [0 1 0]) and two of
the four caps (along [0 1 0]) results in the formation of cor-
3+
3+
to synthesize isotypic nitride tellurides with Sm and Eu
failed, but resulted in the formation of SmTe and EuTe (NaCl-
type structure) with the divalent cations instead. For the heav-
ier lanthanides starting with gadolinium and using NaN3 as
nitrogen source (and NaCl as flux) only the ternary sodium tel-
lurides NaMTe2 (M = Gd–Lu) have been detected. These very
stable compounds crystallize with the ␣-NaFeO2-type structure,
which has been well-investigated mainly for the sulfides NaMS2
(M = Gd, Ho–Lu) [19]. Upon replacement of the sodium com-
pounds (NaN3 and NaCl) by CsN3 and CsCl, in the case of
12−
rugated layers 2 {([Cs(Te4) (Te3)f (Te1)v (Te2)t ] )
f
}
∞
4/4
2/2
1/2
1/1
2
(
t = terminal, v = vertex-connecting, f = face-connecting; com-
pare also Table 4). However, the main feature of the crystal
3
−
3+
structure comprises N -centered (Gd )4 tetrahedra which are
fused via two (Gd3)3 vertices to build up one-dimensional infi-
+
6+
nite chains 1 {[N(Gd1) (Gd2)t (Gd3)v
t
]
2/2
} (t = terminal,
∞
1/1
1/1
v = vertex-sharing) along [0 1 0] (Fig. 3). The longest Gd–Gd
distance within this chain is 424 pm ( a), which corresponds
well to the large deviation of the corresponding tetrahedral angle
+
3−
gadolinium (and also terbium), Cs and N were incorpo-
rated into quaternary tellurides such as Cs2Gd N2Te7 (or iso-
◦
9+
ѯ(Gd–N–Gd) = 121 . This kind of [NM4] -tetrahedral linkage
6
is well-known from the crystal structure of the ternary nitride
typic Cs2Tb N2Te7 [20], a = 2394.8(2) pm, b = 421.35(3) pm,
6
Fig. 4. View of the complete crystal structure of Cs2Gd6N2Te7 along the b-axis.

7
2
F. Lissner, Th. Schleid / Journal of Alloys and Compounds 418 (2006) 68–72
◦
c = 1140.49(7) pm, β = 104.031(4) ). The corresponding com-
[2] F. Lissner, Th. Schleid, Z. Anorg. Allg. Chem. 619 (1993) 1771–1776;
F. Lissner, M. Meyer, R.K. Kremer, Th. Schleid, Z. Anorg. Allg. Chem.,
in preparation;
pounds Cs2M N2Te7 with M = Dy–Lu do obviously not exist,
6
but again the formation of ternary alkali-metal tellurides
CsMTe2 (M = Dy–Lu) [19] with the ␣-NaFeO2-type structure
was found to take place.
F. Lissner, Th. Schleid, Z. Anorg. Allg. Chem. 630 (2004) 1741.
[
[
3] F. Lissner, Th. Schleid, Z. Kristallogr. Suppl. 21 (2004) 171.
4] F. Lissner, Th. Schleid, Z. Anorg. Allg. Chem. 620 (1994) 2003–2007.
A comparison of the Madelung Part of the Lattice Energy
MAPLE according to Hoppe [21]) for Cs2Gd N2Te7 with
6
[5] F. Lissner, Th. Schleid, Z. Anorg. Allg. Chem. 628 (2002) 2179.
[
[
[
[
6] F. Lissner, Th. Schleid, Z. Anorg. Allg. Chem. 629 (2003) 1027–1032.
7] F. Lissner, Th. Schleid, Z. Anorg. Allg. Chem. 631 (2005) 427–432.
8] F. Lissner, O. Janka, Th. Schleid, Z. Kristallogr. Suppl. 22 (2005) 166.
9] F. Lissner, Th. Schleid, Z. Anorg. Allg. Chem. 631 (2005) 1119–1124.
(
the sum of the formally underlying three binary compo-
nents Cs2Te [18], Gd2Te3 (U type) [16], and GdN (NaCl
type) [22] also gives a convincing result. By taking 1×
[
10] G. Meyer, Inorg. Synth. 25 (1989) 146–150.
4
34 + 2× 2666 + 2× 2092 kJ/mol a value of 9950 kJ/mol
[11] W. Herrendorf, H. B a¨ rnighausen, HABITUS: program for the opti-
mization of the crystal shape for numerical absorption correction in
X-SHAPE (Version 1.06, Fa. Stoe, Darmstadt 1999), Karlsruhe, Gießen,
for the sum (MAPLE(Cs2Te) + 2× MAPLE(Gd2Te3) + 2×
MAPLE(GdN)) emerges, which only deviates by −0.7%
1993, 1996.
from MAPLE of Cs2Gd N2Te7 (10016 kJ/mol) itself. This
6
[
12] G.M. Sheldrick, SHELX-97: program package for crystal structure deter-
mination and refinement from diffraction data, G o¨ ttingen, 1997.
[13] A.J.C. Wilson (Ed.), International Tables for Crystallography, vol. C,
Kluwer Academic Publishers, Dordrecht, Boston, London, 1992.
[14] U. Schwanitz-Schueller, A. Simon, Z. Naturforsch. 40 b (1985) 705–709.
15] A. Simon, T. Koehler, J. Less-Common Met. 116 (1986) 279–292.
16] J.S. Swinnea, H. Steinfink, L.R. Danielson, J. Appl. Crystallogr. 20
is all the more astonishing, because a structure in which
3
−
3+
N
(
anions octahedrally surrounded by Gd cations as GdN
d(N3 –Gd ) = 250 pm, 6×) [22] has to compete with such a
−
3+
3−
one (Cs2Gd N2Te7) containing tetrahedrally coordinated N
6
[
[
anions (d(N3 –Gd ) = 217–244 pm, C.N. = 4).
−
3+
(
1987) 102–104.
Acknowledgements
[17] O. Touga ˆı t, H. No e¨ l, J.A. Ibers, Solid State Sci. 3 (2001) 513–518.
[
[
18] I. Schewe-Miller, P. Boettcher, Z. Kristallogr. 196 (1991) 137–151.
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The authors gratefully acknowledge the funding of the
Fonds der Chemischen Industrie” (FCI: Frankfurt a. M.,
1
215–1220;
Th. Schleid, F. Lissner, Eur. J. Solid State Inorg. Chem. 30 (1993)
29–836;
“
Germany), of the “Deutsche Forschungsgemeinschaft” (DFG:
SPP 1166 “Lanthanoidspezifische Funktionalit a¨ t in Molek u¨ l
und Material”; Bonn, Germany), and the State of Baden-
W u¨ rttemberg (Stuttgart, Germany).
8
F. Lissner, Th. Schleid, Z. Anorg. Allg. Chem. 629 (2003) 1895–1897;
K. St o¨ we, C. Napoli, S. Appel, Z. Anorg. Allg. Chem. 629 (2003)
1925–1928.
[
[
20] F. Lissner, Th. Schleid, Acta Crystallogr. E, in preparation.
21] R. Hoppe, Angew. Chem. 78 (1966) 52–63;
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