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bonds, two equal distances of 1.165 (b-Zn(N ) ) and 1.168 (g-
pension. The supernatant was separated from the precipitate by
centrifugation and decantation. The residue was dried in vacuo,
3
2
Zn(N ) ) are found in the m2(1,3)-bridging azido ligands. Further-
3
2
which gave almost amorphous a-Zn(N ) as colourless solid (yield
more a strong bending with N -N -N angles of 174.74 for b-
3 2
a
b
g
9
0–95%). Microcrystalline a-Zn(N ) was obtained by heating a sus-
3 2
Zn(N ) and 174.708 for g-Zn(N ) , respectively, is observed.
3
2
3 2
pension of amorphous Zn(N ) in degassed fluorobenzene under
3
2
The structures of a- and b-Zn(OH)N could be solved and re-
3
endogenous pressure at 1208C for 12 h in a sealed glass tube.
After cooling to ambient temperature over a period of one hour,
the tube was opened in air, the suspension was quickly transferred
to a Schlenk tube, and the supernatant was removed by syringe.
[
15]
fined on the basis of the powder X-ray data (see above).
However, since the quality of the Rietveld refinements do not
allow for a detailed discussion of structural parameters, we
[
15]
want to focus only on the basic structural features (Figure 4).
Drying in vacuo at 708C gave microcrystalline a-Zn(N ) suitable
3 2
for powder X-ray diffraction.
In contrast to binary zinc azides, both modifications of basic
zinc azide display the zinc atoms in an octahedral coordination
sphere, which is composed of three hydroxide groups and
three azide units. Thereby, each zinc atom is connected to six
Procedure 2: To a stirred solution of ethereal hydrazoic acid HN
1m, 4.0 mmol, 4.0 mL), a solution of diethyl zinc ZnEt (1m in n-
3
(
2
hexane, 1.5 mmol, 1.5 mL) was added dropwise at 08C over
a period of one minute. The resulting colourless suspension was
stirred for one hour at ambient temperature. The supernatant was
separated from the precipitate by centrifugation and decantation.
The residue was dried in vacuo which gave a-Zn(N ) as colourless
adjacent zinc atoms by m -bridging hydroxide and m3(1,1,1)-bridg-
3
ing azido ligands, leading to the formation of a layer com-
posed of edge-sharing ZnO N coordination polyhedra. As
3
3
3
2
shown in Figure 4, the OH and N units are each bound on op-
3
solid (yield 90–95%).
posite faces of the zinc planes, building an identical sheet
Procedure 3: Neat basic zinc azide (Zn(OH)( (N ) , x=0.8–1.0;
0.124 g, 1.0 mmol) was suspended in an ethereal solution of hydra-
2Àx)
3 x
structure in a- as well as b-Zn(OH)N . Contrarily, both modifica-
3
tions differ with regard to the bridging mode of OH and N3-
units between adjacent layers. While the azide units in a-
Zn(OH)N3 are further connected to three neighboring OH
zoic acid (HN ; 1m, 3.0 mmol, 3.0 mL) at ambient temperature.
3
After stirring for one day, the supernatant was separated from the
precipitate by centrifugation and decantation, and the residue was
re-suspended in an ethereal solution of HN3 (1m, 3.0 mmol,
groups, only one linear OÀH···N
interaction is found for the
azide
3
.0 mL) and stirred at ambient temperature. This procedure was re-
azide units in b-Zn(OH)N , resulting in a slightly larger separa-
3
peated two times. After removal of supernatant, the residue was
tion of the layers in the latter, in agreement with a higher den-
dried in vacuo which gave a-Zn(N ) as colourless solid (yield 90–
3
2
[15]
sity for a-Zn(OH)N (Figure 4).
3
95%).
Procedure 4 (large crystals of a-Zn(N ) ): Neat Zn(N ) (any phase,
3
2
3 2
0
(
.299 g, 2.0 mmol) was suspended in an aqueous solution of HN3
5m, about 0.1 mL) at ambient temperature. The stirred suspension
was heated to 60–708C and aqueous HN (5m, about 0.3 mL) was
Conclusion
To summarize, a comprehensive study was carried out on the
3
added dropwise, until a colourless solution was obtained. Slow
cooling to ambient temperature (and further cooling to 58C) re-
sulted in the deposition of colourless needle-like crystals. Removal
of supernatant by syringe, and drying in vacuo at 708C gave a-
Zn(N ) as colourless crystals (yield 30–40%). The same procedure
synthesis of pure a-Zn(N ) , along with the isolation of two
3
2
labile polymorphs, b- and g-Zn(N ) . While all binary zinc azides
3
2
could be structurally characterized for the first time, the crys-
tallographic and analytical data indicate that a-Zn(N3)2 was
most likely first prepared by Wçhler and Martin as early as
3
2
could be applied using basic zinc azide (Zn(OH) (N ) , x=0.8–
(
2Àx)
3 x
14
1
917. Contrarily, we could demonstrate that several later re-
1
.0). M.p. 335–3388C; N NMR (300 K, [D ]DMSO, 36.14 MHz): d=
6
ports of pure Zn(N ) are doubtful or even wrong.
À136 (N , Dn =62 Hz), À283 ppm (N , Dn =290 Hz); IR (ATR,
3
2
b
1/2
g
1/2
3
2
2 scans): n˜ =3465 (w), 3403 (w), 3367 (w), 2658 (w), 2598 (w),
540 (w), 2141 (s), 2120 (s), 1417 (w), 1368 (m), 1304 (m), 1277 (s),
À1
Experimental Section
1174 (w), 1154 (w), 675 (m), 587 (m), 579 cm (m); Raman
(
2
1
785 nm, 10 mW, 258C, 10 acc., 30 sec.): n˜ =2187 (0.1), 2170 (1.3),
140 (0.3), 2120 (0.2), 1375 (0.5), 1317 (0.7), 1289 (0.7), 1277 (1.0),
180 (0.3), 1159 (0.3), 683 (0.5), 588 (0.5), 580 (0.5), 402 (0.6), 328
Caution! Covalent azides are potentially hazardous and can de-
compose explosively under various conditions! Especially dry, crys-
talline Zn(N ) is extremely sensitive to shock and friction and can
3
2
(
7
0.8), 286 (1.3), 201 (1.4), 138 (5.5), 121 (8.6), 108 (7.5), 91 (10),
explode violently upon the slightest provocation. Appropriate
safety precautions (safety shields, face shields, leather gloves, pro-
tective clothing) should be taken.
À1
3 cm (6.6); elemental analysis calcd (%) for N Zn: N 56.24,
6
Zn 43.76; found Zn 42.5.
b-Zn(N3)2
a-Zn(N3)2
Polycrystalline b-Zn(N ) : Neat amorphous Zn(N ) (from dehydrat-
Procedure 1: A Schlenk flask containing a mixture of sodium azide
3
2
3 2
ed Zn(N ) ·2.5H O, about 0.01 g) was sealed in a small glass tube
(
NaN ; neat, 0.228 g, 3.5 mmol) and stearic acid (C H CO H; neat,
3 2
2
3
17 35
2
under argon at ambient pressure. The sample was slowly heated
0
.996 g, 3.5 mmol) was connected to a second flask containing
À1
up to 1508C (heating rate 208Cmin ) and then cooled to ambient
a frozen (and degassed) solution of diethyl zinc (ZnEt ; 0.124 g,
2
À1
temperature (cooling rate 308Cmin ), which gave b-Zn(N ) as
1
.0 mmol) in n-hexane (5 mL). The whole apparatus was evacuated
in vacuo. The sodium azide/stearic acid mixture was heated to
08C and the semi-solid mixture was further heated to 1308C
3 2
polycrystalline, colourless solid (quantitative yield).
7
Crystalline b-Zn(N ) (suitable for X-ray): Neat amorphous Zn(N )
3 2
3
2
within three hours while the hydrazoic acid HN was continuously
(from dehydrated Zn(N ) ·2.5 H O, about 0.001 g) was sealed in
3 2 2
3
condensed on the frozen ZnEt2 solution. The colourless mixture
was warmed to ambient temperature, resulting in a colourless sus-
a small glass tube under argon at ambient pressure. The sample
was slowly heated up to 3458C (heating rate 208Cmin ), resulting
À1
Chem. Eur. J. 2016, 22, 2032 – 2038
2037
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