Calcium carbodiimide compounds revisited - Syntheses, single crystal structure determination and vibrational spectra of Ca11N 6[CN2]2, Ca4N2[CN 2] and Ca[CN2]

Article abstract of DOI:10.1515/znb-2008-0509

Single crystals of Ca₁₁N₆[CN₂]₂ (dark red needles, tetragonal, P4₂/mnm (no. 136), a = 1456.22(5), and c = 361.86(2) pm, Z = 2), Ca₄N₂[CN₂] (transparent yellow needles, orthorhombic, Pnma (no. 62), a = 1146.51(11), b = 358.33(4), and c = 1385.77(13) pm, Z = 4) and Ca[CN₂] (transparent, colorless, triangular plates, rhombohedral, R3?m (no. 166), a = 369.00(3), and c = 1477.5(3) pm, Z = 3) were obtained by the reaction of Na ₂[CN₂], CaCl₂ and Ca₃N₂ (if demanded by stoichiometry) in arc-welded Ta ampoules at temperatures between 1200-1400 K. Their crystal structures were re-determined by means of single crystal X-ray structure analyses. Additionally, the Raman spectra were recorded on these same single crystals, whereas the IR spectra were obtained with the KBr pellet technique. The title compounds exhibit characteristic features for carbodiimide units with D_∞h symmetry (d(C-N) = 121.7-123.8 pm and ≮(N-C-N) = 180°). The vibrational frequencies of these units are in the expected range (Ca₁₁N₆[CN₂]₂: v_s = 1230, v_s = 2008; δ = 673/645/624 cm ^-1; Ca₄N₂[CN₂]: v_s = 1230, v_s = 1986; δ = 672/647 cm^-1; Ca[CN ₂]: v_s = 1274, v_s = 2031, δ = 668 cm ^-1). The structural results are more precise than the previously reported data, and with the newly attained Raman spectrum of Ca ₁₁N₆[CN₂]₂ we correct data reported earlier.

Full text of DOI:10.1515/znb-2008-0509

Calcium Carbodiimide Compounds Revisited – Syntheses, Single
Crystal Structure Determination and Vibrational Spectra of
Ca N [CN ] , Ca N [CN ] and Ca[CN ]
11
6
2 2
4
2
2
2
Olaf Reckeweg and Francis J. DiSalvo
Baker Laboratory, Department of Chemistry and Chemical Biology, Cornell University, Ithaca,
NY 14853-1301, USA
Reprint requests to Dr. Olaf Reckeweg. Fax: +1-607-255-4137. E-mail: or22@cornell.edu
Z. Naturforsch. 2008, 63b, 530 – 536; received December 28, 2007
Single crystals of Ca N [CN ] (dark red needles, tetragonal, P4 /mnm (no. 136), a =
1
1
6
2 2
2
1
456.22(5), and c = 361.86(2) pm, Z = 2), Ca N [CN ] (transparent yellow needles, orthorhom-
4 2 2
bic, Pnma (no. 62), a = 1146.51(11), b = 358.33(4), and c = 1385.77(13) pm, Z = 4) and Ca[CN ]
2
¯
(
1
transparent, colorless, triangular plates, rhombohedral, R3m (no. 166), a = 369.00(3), and c =
477.5(3) pm, Z = 3) were obtained by the reaction of Na [CN ], CaCl and Ca N (if demanded
2
2
2
3 2
by stoichiometry) in arc-welded Ta ampoules at temperatures between 1200 – 1400 K. Their crystal
structures were re-determined by means of single crystal X-ray structure analyses. Additionally, the
Raman spectra were recorded on these same single crystals, whereas the IR spectra were obtained
with the KBr pellet technique. The title compounds exhibit characteristic features for carbodiimide
◦
units with D symmetry (d(C–N) = 121.7 – 123.8 pm and ꢀ(N–C–N) = 180 ). The vibrational
∞h
frequencies of these units are in the expected range (Ca N [CN ] : νs = 1230, νs = 2008; δ =
11
6
2 2
−1
−1
6
73/645/624 cm ; Ca N [CN ]: νs = 1230, νs = 1986; δ = 672/647 cm ; Ca[CN ]: νs = 1274,
4
2
2
2
−
1
νs = 2031, δ = 668 cm ). The structural results are more precise than the previously reported data,
and with the newly attained Raman spectrum of Ca N [CN ] we correct data reported earlier.
11
6
2 2
Key words: Calcium, Nitride, Carbodiimide, Cyanamide, Dinitridocarbonate, Crystal Structure,
Raman Spectroscopy
Introduction
Ca[CN ], Ca N [CN ] , and Ca N [CN ] together
2 11 6 2 2 4 2 2
with the complete data of the single crystal struc-
The renaissance of investigations on compounds ture determinations and of Raman and IR spectral
2
−
containing the triatomic [CN2] unit started in 1994 analyses.
with a paper by Schnick et al. [1] reporting the
first reliable structural and spectroscopic data for
Experimental Section
Mg[CN ], Sr[CN ], and Ba[CN ]. Strangely enough,
2
2
2
Ca[CN ] [2 – 5] as the archetype of this class of com- Syntheses
2
pounds was completely left out despite the fact that
the most reliable structure determination dated back
to 1962 [5], and no spectroscopic properties were
known. A few years later, we found out by serendip-
ity that ‘Ca N ’ [6] really is Ca N [CN ] [7] and
All manipulations were performed in a glove box under
purified argon unless stated otherwise. The starting materials
consisted of CaCl (Alfa Aesar, powder, ultradry, 99.99 %),
2
Na CN (Pfaltz & Baur, powder, 97 %, dried and degassed
2
2
1
1
8
11
6
2 2
at 400 K under dynamic vacuum for 2 h; the major impurity
showed on the same occasion the ‘high-temperature
was identified to be NaHCN by its X-ray powder diffrac-
2
form of Ca N ’ (which was also known as γ-
3
2
togram) and thoroughly ground Ca N (Alfa Aesar, pieces,
3
2
Ca N ) [8] to be Ca N [CN ] [9 – 10]. Since the crys-
3
2
4
2
2
9
(
9 %). The reactions were designed to follow the equations
1) – (3).
tallographic data were not completely reported by us
and we found out about an error in our reading of
the Raman spectrum of Ca N [CN ] , we report in
1
1
6
2 2
2
1
CaCl +2 Na [CN ]+3 Ca N
200K,3d
2
2
2
3
2
this paper an alternative synthetic pathway (metathe-
sis reaction) to obtain single crystalline material of
(
1)
−− −−− −→ Ca11N6[CN2]2 +4 NaCl
0
932–0776 / 08 / 0500–0530 $ 06.00 ꢀc 2008 Verlag der Zeitschrift f u¨ r Naturforschung, T u¨ bingen · http://znaturforsch.com
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O. Reckeweg – F. J. DiSalvo · Calcium Carbodiimide Compounds Revisited
531
Table 1. Details of the X-ray single crystal structure determinations of Ca N [CN ] , Ca N [CN ], and Ca[CN ].
11
6
2 2
4
2
2
2
Compound
Ca11N6[CN2]2
Ca4N2[CN2]
Ca[CN2]
¯
Space group (no.), Z
CSD number
Lattice parameter: a, pm
b, pm
P42/mnm (136), 2
418944
1456.22(5)
a
361.86(2)
2.62
Pnma (62), 4
418945
1146.51(11)
358.33(4)
1385.77(13)
2.66
R3m (166), 3
418451
369.00(3)
a
1477.5(3)
2.29
transparent colorless
triangular plate
0.12×0.11×0.04
Bruker X8 Apex II
equipped with a 4 K. CCD
c, pm
−
3
Calculated density, g cm
Crystal color
dark red
needle
transparent yellow
needle
Crystal shape
Crystal size, mm
3
0.12×0.02×0.02
0.12×0.01×0.01
Diffractometer
Stoe IPDS II
Nonius Kappa CCD
Radiation; monochromator
Temperature, K
Ranges, 2θmax; h,k,l
Distance detector-crystal, mm
Number of frames
— MoKα (λ = 71.073 pm); graphite —
293(2)
293(2)
160(2)
◦
◦
◦
52.73 ; ± 18, ± 18, ± 4
52.66 ; ± 14, ± 3, ± 17
73.20 ; −5 → 6, −5 → 6, ± 23
60
25
40
225
154
1078
Exposure time, s
300
LP
3.8
5367
38
LP
3.7
4835
10
LP
2.3
713
Data correction
−
1
µ, mm
Measured reflections
Unique reflections
488
548
129
UR inntique reflections with Fo ≥ 4σ(Fo)
Refined parameters
0.128
43
0.138
55
0.029
8
Weight factors x / y
R1 / wR2 / GooF (all refls.)
Max. shift / esd, last refinement cycle
Res. electron density: max. / min., e A
0.0234 / 0.4174
0.0797 / 0.0767 / 1.227
< 0.00005
0 / 5.3138
0.0695 / 0.1007 / 1.156
< 0.00005
0.0155 / 0.2111
0.0207 / 0.0444 / 1.193
< 0.00005
a
b
c
˚
−3
0.80 (133 pm to N1) /
0.63 (133 pm to N1) /
−0.66 (163 pm to Ca1)
0.43 (64 pm to N)
−0.45 (71 pm to Ca)
−
0.77 (197 pm to Ca4)
a
R1 = ΣꢀFo| − |Fcꢀ/Σ|Fo|; wR2 = [Σw(Fo2 − Fc ) /Σ(wFo ) ] ; w = 1/[σ (Fo ) + (xP) + yP with P = [(Fo ) + 2F ]/3; GooF:
b
2
2
2
2 1/2
2
2
2
2
2
c
c
2
2
2
1/2
S = [Σw(Fo −Fc ) /(n− p)] , with n being the number of reflections and p being the number of parameters.
CaCl +Na [CN ]+Ca N
2
2
2
3
2
Crystallographic studies
(
2)
1
200K,3d
−
−−−− −→ Ca N [CN ]+2 NaCl
4
2
2
Ca[CN ]: Samples of the reaction mixtures were removed
2
from the glove box in polybutene oil (Aldrich, Mn ∼ 320,
1
200K,3d
CaCl +Na [CN ] −− −−− −→ Ca[CN ]+2 NaCl (3)
2
2
2
2
isobutylene > 90 %) for single-crystal selection. Suitable sin-
The starting materials [Ca N [CN ] : 222 mg (2 mmol) gle crystals of the respective compounds were selected under
11
6
2 2
CaCl , 450 mg (3.04 mmol) Ca N and 172 mg (2 mmol) a polarization microscope, mounted in a drop of polybutene
2
3 2
Na CN ; Ca N [CN ]: 222 mg (2 mmol) CaCl , 300 mg oil sustained in a plastic loop, and placed onto the goniome-
2
2
4
2
2
2
(
2.02 mmol) Ca N2 and 172 mg (2 mmol) Na CN ; ter. A cold stream of nitrogen (T = 160(2) K) froze the poly-
3 2 2
Ca[CN ]: 222 mg (2 mmol) CaCl and 172 mg (2 mmol) butene oil, thus keeping the crystal stationary and protected
2
2
Na CN ] were ground together in an agate mortar and then from oxygen and moisture from the air. Preliminary exam-
2
2
arc-welded into clean Ta containers. The metal containers ination and subsequent data collection were performed on
were sealed into evacuated silica tubes. The tubes were a Bruker X8 Apex II diffractometer equipped with a 4 K
placed upright in a box furnace and heated to the appropriate CCD detector and graphite-monochromatized MoKα radia-
temperature within 12 h. After 3 d the furnace was switched tion (λ = 71.073 pm). All further data processing was per-
off and allowed to cool to r. t. Next to the desired prod- formed with the Bruker SMART software [11].
ucts (Ca N [CN ] : dark red needles; Ca N [CN ]: trans-
Single crystals of Ca N [CN ] and Ca N [CN ] were
11
6
2 2
4
2
2
11 2 2 4 2 2
6
parent yellow needles; Ca[CN ]: transparent, colorless, often selected under a microscope in a glove box and sealed into
2
triangular-shaped plates) the samples contained cube-shaped glass capillaries. A suitable crystal of Ca N [CN ] was
11
6
2 2
crystals of NaCl.
All three title compounds are moderately sensitive to nor- was centered on a Nonius Kappa CCD diffractometer. The
mounted on a Stoe IPDS II while a specimen of Ca N [CN ]
4 2 2
mal atmosphere and decompose slowly.
quality of the respective crystals were checked, and a set
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532
O. Reckeweg – F. J. DiSalvo · Calcium Carbodiimide Compounds Revisited
Table 2. Atomic coordinates and equivalent isotropic dis-
Atoms
Ca1 – N4
N1
Multiplicity
d
Table 4. Selected bond
lengths (pm) and an-
gles (deg) of Ca N -
2
placement parameters (pm ) of Ca N [CN ] (P4 /mnm),
2×
256.3(9)
258.5(6)
1
1
6
2 2
2
¯
Ca N [CN ] (Pnma) and Ca[CN ] (R3m).
4×
4
2
2
2
11
6
[
CN ] , Ca N [CN ],
2 2 4 2 2
Ca2 – N1
1×
2×
2×
2×
2×
2×
2×
1×
1×
1×
1×
1×
231.7(1)
247.6(4)
263.6(1)
241.6(5)
257.5(8)
290.4(6)
237.8(4)
244.7(6)
286.9(2)
121.7(14)
123.8(13)
180.0(11)
Atom W.-Site
x
y
z
Ueq
and Ca[CN ].
2
N2
Ca1
Ca2
Ca3
Ca4
N1
N2
N3
N4
C
2a
8i
4g
8i
4f
8i
4g
4f
4g
0
0
0
0
0
0
0
0
0
0
0
118(6)
103(4)
133(5)
141(4)
102(17)
135(12)
329(25)
191(20)
135(22)
N3
Ca3 – N1
N4
N2
Ca4 – N2
N2
0.29520(9) 0.52018(9)
0.16733(10) −x
0.39460(10) 0.11703(10)
0.4104(4)
0.6897(4)
0.2437(5)
0.1245(4)
0.1846(5)
x
0.0283(4)
x
x
x
N4
N3
N4
C –
Ca1
Ca2
Ca3
Ca4
N1
N2
N3
N4
C
4c
4c
4c
4c
4c
4c
4c
4c
4c
0.61349(15) 1/4
0.37966(16) 1/4
0.87770(14) 1/4
0.64096(15) 1/4
0.32765(12) 89(6)
0.46003(12) 90(6)
0.61528(12) 99(6)
0.73977(12) 88(6)
ꢀ(N–C–N)
Ca1 – N2
N1
N3
Ca2 – N2
N2
N1
N3
Ca3 – N1
N3
N4
Ca4 – N2
N1
2×
1×
1×
2×
1×
1×
2×
2×
1×
2×
1×
2×
2×
1×
1×
1×
233.4(4)
241.6(7)
252.1(8)
251.1(5)
257.7(7)
261.0(7)
272.2(6)
239.7(5)
252.9(8)
263.7(6)
234.9(7)
242.5(5)
277.1(6)
122.2(12)
122.8(12)
180.0(10)
0.2333(6)
0.4989(6)
0.7682(7)
0.9544(7)
0.8611(8)
1/4
1/4
1/4
1/4
1/4
0.3158(5)
0.6176(5)
0.4569(5)
0.3703(6)
0.4137(6)
99(20)
94(20)
178(23)
204(24)
114(23)
Ca
C
N
12c
18e
36f
0
0
0
0
0
0
0
60(2)
60(5)
1/2
0.41677(11) 78(3)
a
2
Table 3. Anisotropic displacement parameters U (pm ) of
N4
N3
N4
ij
Ca N [CN ] , Ca N [CN ], and Ca[CN ].
C –
1
1
6
2 2
4
U22
U11
113(7)
U11
2
2
2
Atom U11
U33
U23
U13
U12
ꢀ
(N–C–N)
Ca1
Ca2
Ca3
Ca4
N1
N2
N3
N4
C
109(9)
110(7)
157(7)
161(8)
139(16)
86(7)
84(11)
103(7)
39(41)
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
4(10)
Ca –
C –
N
N
6×
2×
1×
246.14(8)
123.0(2)
180
−12(5)
a
62(8)
Angle fixed, linearity
set by symmetry.
a
ꢀ
(N–C–N)
159(7)
−58(5)
−16(30)
−5(24)
−163(48)
−52(37)
15(39)
133(24) U11
124(30) 149(30) 133(32)
344(37) U11
186(28) U11
137(30) U11
For all three compounds, the intensity data were corrected
for Lorentz and polarization effects, but since all compounds
are poor X-ray absorbers, no absorption correction was
299(62)
202(51)
129(58)
applied. The crystallographic coordinates of Ca[CN ] [5],
2
Ca1
Ca2
Ca3
Ca4
N1
N2
N3
N4
C
92(9)
91(10) 97(16)
82(9)
76(8)
105(35) 97(65)
73(34) 114(64)
177(43) 217(72) 140(40)
139(41) 261(76) 212(43)
189(49) 16(72)
64(17)
111(9)
81(9)
0
0
0
0
0
0
0
0
0
27(7)
0
0
0
0
0
0
0
0
0
Ca N [CN ] [7] and Ca N [CN ] [7], respectively, were
11
6
2 2
4
2
2
−2(6)
used as starting models which were refined by full-matrix
least-squares techniques with SHELXL-97 [14]. The refine-
ments converged and resulted in stable models for the crystal
structures of Ca[CN2], Ca11N6[CN2]2 or Ca4N2[CN2] cor-
roborating the previous models. Additional crystallographic
details are summarized in Table 1. Atomic coordinates and
equivalent isotropic displacement coefficients are shown in
Table 2, and Table 3 displays the anisotropic displacement
parameters. Selected bond lengths and angles are listed in
Table 4.
113(16) 103(9)
83(16)
−2(7)
106(9)
95(39)
70(36)
−4(7)
−11(29)
−16(29)
10(32)
−2(34)
−66(40)
135(45)
Ca
C
N
60(2)
42(7)
87(5)
U11
U11
U11
60(2)
97(11)
60(7)
0
0
0
0
0
0
1/2 ×U11
21(4)
44(3)
a
The anisotropic displacement factor takes the form:
Further details of the crystal structure investiga-
tions can be obtained from the Fachinformationszen-
trum Karlsruhe, 76344 Eggenstein-Leopoldshafen, Ger-
2
2
∗2
2
∗2
2
∗2
∗ ∗
Uij = exp[−2π (h a U11 + k b U22 + l c U33 + 2klb c U23 +
∗ ∗
∗ ∗
2hla c U13 +2hka b U12)].
of intensity data was collected for Ca N [CN ] [7] and many (fax: (49) 7247-808-666; e-mail: crysdata@fiz-karls-
11
6
2 2
Ca N [CN ] at r. t. The following processing of the inten- ruhe.de), on quoting the deposition number CSD-418944
4
2
2
sity data was performed with the software package that came for Ca N [CN ] , CSD-418945 for Ca N [CN ] and
11
6
2 2
4
2
2
with the respective diffractometer [12, 13].
CSD-418451 for Ca[CN2].
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O. Reckeweg – F. J. DiSalvo · Calcium Carbodiimide Compounds Revisited
533
(a)
(b)
(c)
Results and Discussion
Crystal structures
6
45
5
50
δ
The crystal structures of the title compounds can
be seen as part of the pseudo-binary system Ca N -
6
24 / 673
νasym = 2008
δ = 1312 / 1352
3
2
νsym = 1230
CaCN . The crystal structure of Ca N is well-
2 3 2
2
known [9] and can be described as an ordered defect
[4t]
[6o]
variant of the CaF type with Ca N2
(Fig. 2a).
2
3
Since the typical coordination environment of nitro-
gen consists of six Ca contacts, the coordination of
the cations are not well met with this structure. The
5
00
1000
1500
Wavenumber (cm–1
2000
2500
)
crystal structure of Ca[CN ] is adopted by many
2
ternary carbodiimides containing divalent cations such
2
+
2+
2+
2+
as Mg [1], Sr [15], Mn [16] or Cd [17].
2
+
In these compounds, the M cations form a cubic
close packing. The coordination can be expressed as
[
6o] [2l] [4t]
Ca [C
N
2] (Fig. 2d). This geometry is closer
to the typical coordination requirements of each ion.
This is also mirrored by the increased stability of
Ca[CN ] compared to Ca N against air and moisture.
2
3
2
Ca N [CN ] and Ca N [CN ] can structurally and
1
1
6
2 2
4
2
2
chemically be seen as calcium nitride compounds with
an increasing Ca[CN ] fraction.
2
According to this view, the 3D structure of Ca N
3
2
is broken up into the open channel structures of
Ca N [CN ] and Ca N [CN ] before the 2D struc-
1
1
6
2 2
4
2
2
ture of Ca[CN ] is assumed. This can also be seen by
2
the Ca and N coordination found in these two com-
pounds. In Ca N [CN ] or – to emphasize the sto-
1
1
6
2 2
ichiometry – (Ca N ) (Ca[CN ] ), all nitrogen atoms
3
2 3
2 2
not within bonding distance to carbon are coordinated
by a distorted octahedron of Ca atoms while the ni-
trogen atoms in the carbodiimide unit are surrounded
by four Ca atoms and – of course – by one carbon
atom. The coordination number of the Ca by N aver-
ages to 4.9 and ranges from 4 to 6. A similar picture
can be seen for Ca N [CN ] or (Ca N )(Ca[CN ]),
Fig. 1. Raman and IR spectra of Ca N [CN ] (a), Ca N
2
1
1
6
2 2
4
[
CN ] (b), Ca[CN ] (c) (for details, see text).
2 2
Vibrational spectroscopy
4
2
2
3
2
2
The crystals used for the single crystal structure refine- but here the Ca N : Ca[CN ] ratio is decreased to 1 : 1
3
2
2
ments were washed with hexane and sealed in Lindemann compared to 3 : 2 in Ca N [CN ] . We also find in
1
1
6
2 2
capillaries under an Ar atmosphere. The Raman investiga-
tions were performed on a microscope laser Raman spec-
trometer from Jobin Yvon (4 mW, excitation line at λ =
Ca N [CN ] that all nitrogen atoms not within bond-
4
2
2
ing distance to carbon are coordinated by distorted oc-
tahedra of Ca atoms while the nitrogen atoms in the
carbodiimide unit are surrounded by four Ca atoms
and by one C atom. The average coordination number
of Ca by N in Ca N [CN ] increases not significantly
6
32.817 nm (HeNe laser), 20× magnification, 3 × 60 s ac-
cumulation time).
IR investigations of all three title compounds and for
4
2
2
‘
Ca N ’ were done with a Bruker AFS 66 FT-IR spectrom-
3 2
to 5.0 and still ranges from 4 to 6. The coordination
of the [CN2] moiety is more open to one side since
eter. About 1 – 5 mg of the respective product was ground in
an agate mortar with 450 – 500 mg of thoroughly dried KBr
2
−
and pressed into a pellet. The results of the optical measure- the channels start to break down if one considers the
ments are displayed in Fig. 1.
transition being made from Ca N to Ca[CN ].
3
2
2
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534
O. Reckeweg – F. J. DiSalvo · Calcium Carbodiimide Compounds Revisited
(a)
(b)
(c)
(d)
(a) Ca11N6[CN2]2
(b) Ca4N2[CN2]
(c) Ca[CN2]
Fig. 2. Perspective view of the unit cells of Ca N (a),
3
2
Ca N [CN ] (b), Ca N [CN ] (c), and Ca[CN ] (d). The
1
1
6
2 2
4
2
2
2
3−
coordination octahedra about isolated N are drawn as grey,
hatched octahedra, C and N are displayed as crossed light
grey, black and white circles, respectively. Displacement el-
lipsoids are drawn at the 95 % probability level.
Fig. 3. Coordination envi-
2
−
ronment of the [N=C=N]
anions in Ca N [CN ] ,
11
6
2 2
Ca N [CN ], and Ca[CN ].
4
2
2
2
The same color code as in
In Fig. 2 this view is emphasized by displaying
Fig. 2 is employed.
all compounds with [NCa ] octahedra, while Fig. 3
6
shows the different coordination environments of the
gle crystal structure analyses and the vibrational spec-
tra are consistent.
2
−
triatomic [CN2] unit which basically all show the
carbodiimide structure with D∞h symmetry within
one standard deviation despite the unsymmetrical co-
ordination environment found in Ca N [CN ] and
The symmetric stretching mode for Ca N [CN ]
1
1
6
2 2
reported by us in a previous paper [7] turned out to be
wrong. In the course of our previous research, we used
samples which obviously were not clean with respect
to reaction by-products. This time the Raman measure-
ment was done on single crystals cleaned thoroughly
1
1
6
2 2
Ca N [CN ].
4
2
2
Vibrational spectra
The IR and Raman spectra show the fundamental vi- with n-hexane before the measurement.
2
−
brations expected for a [CN2] unit with D∞h symme-
try [18]. Since the C–N distances are equal within the
accuracy of the measurements, and the N–C–N angles
Discussion
Ca N [CN ] was first mistaken as ‘Ca N ’ [6].
1
1
6
2 2
11
8
show no significant deviations from linearity, the sin- Only small amounts of carbon need to be incorporated,
Unauthenticated
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O. Reckeweg – F. J. DiSalvo · Calcium Carbodiimide Compounds Revisited
535
The formation of the compounds seems to be enhanced
by the increasing vapor pressure of Ca N with in-
3
2
creasing temperature. Small amounts of carbon im-
purities and relatively low reaction temperatures are
sufficient to form the compound, but if the reaction
temperature chosen is too low, the crystallinity of
Ca N [CN ] is poor. If the reaction temperature is
1
1
6
2 2
increased to improve the crystal quality, Ca N [CN ]
4
2
2
formation begins. Another problem arises from the
needle shape in which most crystals of Ca N [CN ]
1
1
6
2 2
and also of Ca N [CN ] are formed. This needle
4
2
2
shape of Ca N [CN ] and Ca N [CN ] is not unex-
1
1
6
2 2
4
2
2
pected considering the crystal structure of these com-
clearly the asymmetric stretching mode (at 2006 cm ) of pounds.
Ca N [CN ] .
Fig. 4. IR spectrum of ‘pure’ Ca N2 which shows
3
−1
11
6
2 2
Conclusion
e. g. from CaCO formed on the surface of the Ca metal
3
The compounds Ca N [CN ] , Ca N [CN ] and
1
1
6
2 2
4
2
2
used as an educt or by residues of carbon from the syn-
thesis of the metal by electrolysis between carbon elec-
trodes. If such a contaminated Ca metal is used for the
synthesis of Ca N , small amounts of Ca N [CN ]
Ca[CN ] were synthesized in good yields by
2
Na [CN ] metathesis reactions with CaCl which is
2
2 2
2
an alternative to the methods employing Li [CN ] [19]
2
2
3
2
11
6
2 2
or Zn[CN ] [20]. Complete structural characterization
2
are formed which are hard to detect by X-ray methods
or by chemical analyses. We took an IR spectrum (KBr
pellet technique) of such a ‘pure’ (according to pow-
der X-ray diffraction) Ca N sample and found despite
of Ca N [CN ] and Ca N [CN ] is reported for the
1
1
6
2 2
4
2
2
first time. Especially in the case of Ca[CN ] data of
higher precision are provided.
2
3
2
The title compounds show the typical geometrical
strong absorption of the main compound and some
2
−
features of carbodiimide [CN2] units with D∞h sym-
metry. The vibrational spectroscopy data yielded sym-
metric and asymmetric stretching modes as well as the
bending modes which are in the expected range [18].
The previously reported symmetric stretching mode
has been corrected.
CO interferences the asymmetric stretching vibration
2
−
1
of Ca N [CN ] with νasym = 2006 cm (Fig. 4). By
heating this ‘pure’ Ca N under flow-through condi-
1
1
6
2 2
3
2
tions, Ca N [CN ] forms and sublimes away. Going to
4
2
2
even higher temperatures, Ca[CN ] is finally formed.
2
For flow-through reactions with N this can be put in
2
some simple scheme:
Acknowledgements
It is a pleasure to thank Prof. Dr. h. c. mult. Arndt Simon
(MPI-FKF, Stuttgart, Germany) for hospitality and for the
opportunity to do work and research in his lab. Thanks are
also due to Mr. Armin Schulz for the Raman measurement
(MPI-FKF, Stuttgart, Germany) and to Prof. Dr. Th. Schleid
and Dr. F. Lissner (Inst. f u¨ r Anorg. Chemie, Universit a¨ t
Stuttgart, Germany) for the collection of intensity data on
Ca4N2[CN2].
◦
4
80−800 C
1
1 Ca+2 C −− −−−− −→ Ca N [CN ]
1
1
6
2 2
N2
◦
8
00−1200 C
−
−−−−−− −→ 2 Ca N [CN ]
4
2
2
−Ca3N2
◦
1
200−1400 C
−
−−−−−−−→ 2Ca[CN ]
2
2 Ca3N2
[
1] U. Berger, W. Schnick, J. Alloys Compds. 1996, 206,
79.
[6] Y. Laurent, J. Lang, M. Th. Le Bihan, Acta Crystallogr.
1969, B25, 199.
1
[
[
[
2] U. Dehlinger, Z. Kristallogr. 1927, 65, 286
3] M. A. Bredig, J. Am. Chem. Soc. 1942, 64, 1730.
4] Y. Yamamoto, K. Kinoshita, K. Tamaru, T. Yamanaka,
Bull. Chem. Soc. Jap. 1958, 31, 501.
[7] O. Reckeweg, F. J. DiSalvo, Angew. Chem. 2000, 112,
397; Angew. Chem. Int. Ed. 2000, 39, 412.
[8] Y. Laurent, J. David, J. Lang, C. R. Acad. Sci. Paris
1964, C259, 1132.
[
5] N.-G. Vannerberg, Acta Chem. Scand. 1962, 16, 2263.
Unauthenticated
Download Date | 8/18/18 10:41 AM

536
O. Reckeweg – F. J. DiSalvo · Calcium Carbodiimide Compounds Revisited
[
9] O. Reckeweg, F. J. DiSalvo, Z. Anorg. Allg. Chem.
[15] W. Liao, R. Dronskowski, Acta Crystallogr. 2004, E60,
2001, 627, 371.
i124.
[
10] P. H o¨ hn, R. Kniep, GDCh-Tagung Anorganische Funk-
tionsmaterialien, M u¨ nster (Germany) 2000; P. H o¨ hn,
R. Niewa, R. Kniep, Z. Kristallogr. (NCS) 2000, 215,
[16] W. Liao, M. Krott, P. M u¨ ller, C. Hu, H. Lueken,
R. Dronskowski, Inorg. Chem. 2005, 44, 3001.
[17] G. Baldinozzi, B. Malinowska, M. Rakib, G. Durand,
J. Mater. Chem. 2002, 12, 268.
323.
[
[
[
[
11] SMART, Bruker Analytical X-ray Instruments Inc.,
Madison, Wisconsin (USA) 2004.
12] I. PDS II-Software, Stoe & Cie GmbH, Darmstadt
[18] O. Reckeweg, A. Simon, Z. Naturforsch. 2003, 58b,
1097.
[19] K. Gibson, M. Str o¨ bele, B. Blaschkowski, J. Glaser,
M. Weisser, R. Srinivasan, H.-J. Kolb, H.-J. Meyer, Z.
Anorg. Allg. Chem. 2003, 629, 1863.
[20] M. Becker, M. Jansen, Acta Crystallogr. 2001, C47,
347; W. Liao, M. Krott, P. M u¨ ller, C. Hu, H. Lueken,
R. Dronskowski, Inorg. Chem. 2005, 44, 3001.
(Germany) 2004.
13] Nonius Kappa-CCD Software, Nonius BV, Delft (The
Netherlands) 1997.
14] G. M. Sheldrick, SHELXL-97, Program for the Refine-
ment of Crystal Structures, University of G o¨ ttingen,
G o¨ ttingen (Germany) 1997.
Unauthenticated
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