Preparation and Crystal Structure of Li
4
[TaN
3
]
R. Niewa*, D. A. Zherebtsov, H. Borrmann, and R. Kniep
Dresden, Max-Planck-Institut für Chemische Physik fester Stoffe
Received June 21st, 2002.
Dedicated to Professor Dieter Fenske on the Occasion of his 60
th
Birthday
Abstract. The new lithium nitridotantalate(V), Li
4
[TaN
3
], was pre-
pared by reaction of Li
15
[CrN
4
]
2
N with the wall of a welded Ta
ampoule in the presence of metallic Li at 1470 K. Li
4
[TaN
3
]forms
colourless single crystals (platelets, space group Ibca, No. 73, a ⫽
491.85(4) pm, b ⫽ 973.59(6) pm, c ⫽ 1415.0(1) pm, Z ⫽ 8, R1 ⫽
0.0288). The crystal structure is described as Li
2
O superstructure
Synthese und Kristallstruktur von Li
4
[TaN
3
]
Inhaltsübersicht. Das neue Lithiumnitridotantalat(V) Li
4
[TaN
3
]
wurde durch Umsetzung von Li
15
[CrN
4
]
2
N mit der Wand einer Ta-
Ampulle bei 1470 K einkristallin erhalten. Li
4
[TaN
3
] kristallisiert
in Form von farblosen Plättchen (Raumgruppe Ibca, Nr. 73, a ⫽
491,85(4) pm, b ⫽ 973,59(6) pm, c ⫽ 1415,0(1) pm, Z ⫽ 8, R1 ⫽
Introduction
In the last decade, the study of ternary and higher nitrido-
metalates has been a rapidly growing field of inorganic solid
state chemistry [1⫺3]. As one branch, ternary lithium nitri-
dometalates have attracted considerable attention. The reac-
tion product(s) in many nitride-systems often strongly de-
pend not only on the reaction conditions, but also on the
starting materials chosen [2]. For some time now, we are
trying to prepare new nitridocompounds from ternary nitri-
dometalates via decomposition reactions in different atmos-
pheres [4, 5], or by conversion reactions starting from ter-
nary nitridocompounds [6, 7]. These approaches already
were successful to gain products that can not be prepared
by direct reactions from the respective binaries or elements,
or to yield samples of higher purity. Here we report on a
new lithium nitridotantalate(V), Li
4
[TaN
3
], prepared by re-
dox-reaction of a ternary nitridochromate(VI) and elemen-
tal tantalum in the presence of excess lithium.
Experimental
All manipulations were carried out in an argon filled glove box
(p(O
2
,H
2
O) < 0.1 ppm). Single crystals of Li
4
[TaN
3
] were prepared
* Dr. R. Niewa
MPI für Chemische Physik fester Stoffe
Nöthnitzer Str. 40
D-01187 Dresden
e-mail: niewa@cpfs.mpg.de
Z. Anorg. Allg. Chem. 2002, 628, 2505⫺2508 WILEY-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002 0044⫺2313/02/628/2505⫺2508 $ 20.00⫹.50/0 2505
with ordered occupation of the tetrahedral sites by Li and Ta. The
resulting arrangement leads to infinite chains
1
⬁
[TaN
2
N
2/2
4⫺
] run-
ning along [100].
Keywords: Nitrides; Tantalum; Lithium; Crystal structure
0,0288). Die Kristallstruktur wird als Li
2
O-Überstruktur mit ge-
ordneter Besetzung der Tetraederlücken einer kubisch dichten Pa-
ckung aus N beschrieben. Die gefundene Anordnung führt zu un-
endlichen Ketten
1
⬁
[TaN
2
N
2/2
4⫺
], welche entlang [100] verlaufen.
from Li
15
[CrN
4
]
2
N [8] in a welded Ta ampoule in presence of excess
Li. This assembly was heated in Ar atmosphere to 1470 K for 20 h
and then slowly cooled (100 h to 870 K), before the furnace was
switched off and allowed to cool down naturally. Li
15
[CrN
4
]
2
Nwas
synthesized from Li
3
N (prepared from Li metal, Roth 99.99 %, in
flowing N
2
, Messer-Griesheim 99.999 %, additionally purified by
passing over molsieve, Roth 3 A
˚
, and BTS-catalyst, Merck) and Cr
(powder, Alfa, 99,9 %) in flowing N
2
for 20 h at 1070 K. The final
oxygen content in Li
15
[CrN
4
]
2
N was less than 0.01 % (LECO ana-
lyzer TC-436 DR, hot extraction technique). After synthesis of
Li
4
[TaN
3
] the excess Li metal was extracted with liquid ammonia.
The only products observed after the reaction are chromium den-
drites and colourless plates of Li
4
[TaN
3
], both up to 1 mm in size.
The solids could be separated manually. Li
4
[TaN
3
] is sensitive
against moisture by rapid formation of ammonia.
For powder X-ray diffraction measurements, the purified samples
of the ternary nitride were ground and sealed in glass capillaries
(diameter 0.2 mm). The measurements were performed on a Huber
image plate Guinier camera in the 2θ-range of 10°-100° (expose
time 3 ⫻ 8 h) using CuKα
1
-radiation. Fig. 1 presents the powder
diagram together with the calculated intensity profile. Differences
in intensities are most likely due to preferred orientation of the
crystallites with the shape of platelets (esp. the reflections (002),
(004), (006) and (008) exhibit intensities in the experimental pattern
too high compared with the calculated diagram).
X-ray diffraction intensity data of a single crystal (0.1 mm ⫻
0.1 mm ⫻ 0.05 mm sealed in a glass capillary) were collected on a
MSC-Rigaku CCD applying MoKα-radiation. Initial indexing of
the powder pattern and the data from the single crystal resulted in
an orthorhombic unit cell with the dimensions a ⫽ 491.85(4) pm,
b ⫽ 973.59(6) pm, c⬘⫽707.5(1) pm (Guinier data). Close inspec-
tion of the powder pattern revealed one weak unindexed peak call-
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