Preparation, characterization and crystal structure of lead(II) tricyanomethanide

Article abstract of DOI:10.1515/znb-2006-0107

The so far unknown lead tricyanomethanide, Pb[C(CN)₃] ₂, was obtained from a saturated aqueous solution of PbCl₂ and solid AgC(CN)₃. Its IR spectrum and thermal behaviour are described. The crystal structure was determined by single-crystal X-ray diffraction (trigonal, P31m, Z = 3, a = 1414.4(5), c = 409.02(6) pm, R ₁ = 0.0249, wR₂ = 0.0527). Two crystallographically independent ninefold coordinated Pb atoms are connected by planar tricyanomethanide ions in two distinct bridging coordination modes. The Pb-N distances range between 254 and 293 pm.

Full text of DOI:10.1515/znb-2006-0107

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Preparation, Characterization and Crystal Structure of
Lead(II) Tricyanomethanide
Victor M. Deflona, Cassia C. de Sousa Lopesa, Karl E. Besslera, Lincoln L. Romualdob,
and Elke Niquetc
a Instituto de Qu´ımica, Universidade de Bras´ılia, BR-70904-970 Bras´ılia DF, Brazil
b Departamento de Qu´ımica, Universidade Federal de Sa˜o Carlos, BR-13560-970 Sa˜o Carlos SP,
Brazil
c Institut fu¨r Anorganische Chemie der Universita¨t Tu¨bingen, Auf der Morgenstelle 18,
D-72076 Tu¨bingen, Germany
Reprint requests to Prof. Karl E. Bessler. Fax: +55-61-32734149. E-mail: bessler@unb.br
Z. Naturforsch. 61b, 33 – 36 (2006); received October 17, 2005
The so far unknown lead tricyanomethanide, Pb[C(CN)3]2, was obtained from a saturated aque-
ous solution of PbCl2 and solid AgC(CN)3. Its IR spectrum and thermal behaviour are described.
The crystal structure was determined by single-crystal X-ray diffraction (trigonal, P31m, Z = 3,
a = 1414.4(5), c = 409.02(6) pm, R1 = 0.0249, wR2 = 0.0527). Two crystallographically indepen-
dent ninefold coordinated Pb atoms are connected by planar tricyanomethanide ions in two distinct
bridging coordination modes. The Pb−N distances range between 254 and 293 pm.
Key words: Pseudohalide, Lead, Tricyanomethanide, Crystal Structure
Introduction
ponents of comparable intensity at 2207, 2172 and
2134 cm−1, and the C−C≡N out of plane deforma-
tion mode (ν4) exhibits two components at 575 and
The literature reveals little structural information on
binary lead(II) pseudohalides. So far, crystal structures
have been reported only for the thiocyanate [1], the
azide [2] and more recently for the dicyanamide [3, 4].
The crystal structures of two ternary lead tricyano-
methanide complexes were determined [5], while the
structure of the binary lead tricyanomethanide is so far
unknown. The preference of the large Pb2+ cation for
high coordination numbers in combination with multi-
dentate ligands gives rise to interesting network struc-
tures, as was shown in the case of Pb{N(CN)2}2 [3, 4].
The tricyanomethanide ion is able to act in a variety of
coordination modes [6, 7], similar to the dicyanamide.
We supposed that the crystal structure of lead(II) tri-
cyanomethanide should be closely related to that of
lead(II) dicyanamide.
564 cm−1
.
The thermogravimetric analysis of Pb{C(CN)3}2 in
◦
air reveals a smooth degradation from 362◦to 590 C
with a maximum decomposition rate at 524 C. The to-
tal weight loss up to 700 ◦C (42.3%) corresponds to the
solid residue of PbO (calcd. 42.4%), which was iden-
tified by x-ray powder diffraction. We propose the de-
composition reaction as
Pb{C(CN)3}2 +1/2 O2 → PbO+3 (CN)2 +2 CO.
At comparable conditions the decomposition of
◦
K{C(CN)3} occurs in a wide range from 241 to 666 C
◦
with a maximum decomposition rate at 605 C. In this
case the total weight loss up to 700 ◦C (46.4%) is in ac-
cord to K2CO3 as solid residue (calcd. 46.5%), which
was identified by IR spectroscopy. The probable de-
composition reaction can be formulated as
Results and Discussion
Infrared spectrum and thermal behaviour
K{C(CN)3}+3/2 O2 → 1/2 K2CO3 +3/2 (CN)2.
The IR spectrum of Pb{C(CN)3}2 (nujol mull)
shows the characteristic features of the tricyanometh-
anide ion [8]. The existence of distinct coordination
modes of the {C(CN)3}− ions leads to a significant
splitting of several vibrational frequencies. So, the
Crystal structure
The unit cell of Pb{C(CN)3}2 is shown in Fig. 1.
C≡N stretching mode (ν6) is split into three com- As anticipated, the crystal structure is strongly related
c
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V. M. Deflon et al. · Lead(II) Tricyanomethanide
Fig. 1. View of the unit cell
of Pb{C(CN)3}2 along the c-
axis (DIAMOND) [15].
Table 1. Crystallographic data and refinement parameters.
Empirical formula
Mw [g mol−1
C8N6Pb
387.33
]
Crystal size [mm]
Diffractometer
Radiation; λ [pm]
Temperature [K]
Crystal system
Space group
Lattice constants
a [pm]
0.35×0.05×0.05
Enraf Nonius CAD4
Mo-Kα ; 71.073
208(2)
trigonal
P31m
1414.4(5)
c [pm]
409.02(6)
708.7(4)
3
2.723
17.827
516
Fig. 2. Coordination modes of the two independent tri-
cyanomethanide units (right hand side unit 1, left hand side
unit 2).
Volume [×106 pm3]
Z
ρ Calcd. [g cm−3
]
Abs. Coefficient [mm−1
F(000)
]
to that of Pb{N(CN)2}2 [3, 4]. Two crystallograph-
ically independent lead atoms are situated on spe-
cial positions (0, 0, z) and (2/3, 1/3, z). Both lead
atoms are ninefold coordinated by the N-atoms of
the {C(CN)3}− ions in irregular holodirected arrange-
ments. There is no evidence for a stereochemically
active lone pair on the Pb2+ ion [9, 10]. The tri-
cyanomethanide ion is found in two distinct coordi-
nation modes (Fig. 2). One of them (unit 1) exhibits
one terminal coordinating and two bridging N-atoms,
while the other one (unit 2) coordinates via one bridg-
ing and two terminal N-atoms. The bridging angles
Pb–N–Pb are close to 90◦. Pb atoms of two different
layers are connected by the bridging N atoms of the
tricyanomethanide ions. The Pb–N distances range be-
tween 254 and 293 pm and are comparable to those
Diffraction range (deg)
Index range
3.33 ≤ 2θ ≤ 31.00
−1 ≤ h ≤ 20,
−20 ≤ k ≤ 18,
−5 ≤ l ≤ 5
ω scans
Scan type
Collected reflections
Independent reflections
Observed reflections
Refined parameters
Absorption correction
Min./max. transmission
Structure solution
Structure refinement
Molecular graphics
Refinement method
4946
1591 (Rint = 0.0414)
1445 [I > 2σ(I)]
79
DELABS
0.88276/0.96106
SHELXS-97 [13]
SHELXL-97 [14]
DIAMOND [15]
2
full-matrix least-squares on F
−0.005(14)
Absolute structure parameter
Goodness-of-fit on F2
R Indices [I > 2σ(I)]
1.029
R1 = 0.0249, wR2 = 0.0527
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V. M. Deflon et al. · Lead(II) Tricyanomethanide
35
Table 2. Atomic coordinates and equivalent isotropic dis-
placement parameters (pm2 × 10−1) for Pb{C(CN)3}2.
U(eq) is defined as one third of the trace of the orthogonal-
ized Ui j tensor.
Crystallographic data for Pb{C(CN)3}2 have been
deposited with the Cambridge Crystallographic Data
Centre (CCDC 267368). Copies of the data can be
obtained free of charge on application to CCDC, 12
Union Road, Cambridge CB2 1EZ, UK, (fax +44-
1223-336033 or e-mail: deposit@ccdc.cam.ac.uk).
Atom W.-symbol
x
0
2/3
0.3761(7)
0.2812(7)
0.2071(6)
0.4731(5)
0.5517(5)
0
y
0
1/3
x
x
z
U(eq)
22(1)
20(1)
25(2)
26(2)
34(2)
26(1)
32(1)
Pb(1)
Pb(2)
C(1)
1a
2b
3c
3c
3c
6d
6d
3c
3c
3c
6d
6d
0.4638(2)
0.6241(1)
1.2230(20)
1.3490(20)
1.4490(20)
Experimental Section
C(11)
N(11)
C(12)
N(12)
C(2)
x
Reagents were used as purchased without further purifi-
cation. IR spectra were recorded on a BOMEM model 100
FT-IR spectrometer in the range 4000 – 400 cm−1 from Nu-
jol mulls. The thermogravimetric analyses were performed
on a Shimadzu Thermogravimetric Analyzer TGA-50 in alu-
mina crucibles at a heating rate of 5 ◦C/min in air.
0.3741(5) 1.1560(14)
0.3710(5) 1.1048(15)
0.2893(7) −0.2380(30) 26(2)
C(21)
N(21)
C(22)
N(22)
0
0
0.2028(6) −0.0850(20) 23(2)
0.1272(6) 0.0265(19)
28(2)
−0.0998(5) 0.2824(5) −0.3242(15) 26(1)
−0.1786(5) 0.2801(6) −0.4004(16) 41(1)
Synthesis
Table 3. Selected bond lengths [pm] and angles [deg] for
Pb{C(CN)3}2.
Ag{C(CN)3}. Silver tricyanomethanide was prepared ac-
C(1)–C(11)
143.9(14)
141.3(8)
141.3(8)
112.4(13)
115.3(9)
137.4(12)
141.1(7)
141.1(7)
116.2(12)
114.2(9)
120.9(4)
118.3(8)
119.9(4)
120.1(8)
179.8(14)
178.9(7)
176.1(10)
177.6(8)
Pb(1)–N(21)
Pb(1)-N(21)h
Pb(1)-N(21)a
253.7(8)
253.7(8)
253.7(8)
292.2(9)
292.2(9)
292.2(9)
293.0(9)
293.0(9)
293.0(9)
276.8(6)
264.8(6)
264.8(6)
264.8(6)
276.8(6)
276.8(6)
288.2(6)
288.2(6)
288.2(6)
cording to Trofimenko [11].
C(1)–C(12)
C(1)–C(12)a
Pb{C(CN)3}2. A solution of 0.278 g PbCl2 (1 mmol) in
40 ml H2O was stirred with 0.594 g Ag{C(CN)3} (3 mmol)
for 24 h on a water bath. The solution was filtered from insol-
uble silver salts and the filtrate evaporated to dryness, yield-
ing 350 mg crude Pb{C(CN)3}2 (90%). Colorless crystal
needles. Solubility in water 100 g/l at 25 ◦C. IR (Nujol mull):
i
C(11)–N(11)
C(12)–N(12)
C(2)–C(21)
Pb(1)-N(21)
Pb(1)-N(21)c
j
Pb(1)-N(21)
C(2)–C(22)
Pb(1)-N(11)e
C(2)–C(22)b
Pb(1)-N(11)k
l
C(21)–N(21)
C(22)–N(22)
Pb(1)-N(11)
˜
ν = 2207 s, 2172 vs, 2134 s, 1269 vw, 1243 w, 1233 vw,
Pb(2)–N(12)
Pb(2)-N(22)m
Pb(2)-N(22)n
Pb(2)-N(22)o
Pb(2)-N(12)p
Pb(2)-N(12)q
Pb(2)-N(12)r
Pb(2)-N(12)s
Pb(2)-N(12)e
685 vw, 660 vw, 607 w, 575 m, 564 m, 493 vw cm−1
.
C(11)–C(1)–C(12)
C(12)–C(1)–C(12)a
C(21)–C(2)–C(22)
C(22)–C(2)–C(22)b
C(1)–C(11)–N(11)
C(1)–C(12)–N(12)
C(2)–C(21)–N(21)
C(2)–C(22)–N(22)
X-ray structure determination
Colorless needles were obtained by recrystallization of
the title compound from H2O. The cell constants were cal-
culated from 25 reflections measured under a wide range of
2θ. The intensity data were collected by the ω scan tech-
nique, on an Enraf Nonius CAD4 diffractometer at 208 K
with graphite-monochromated Mo-Kα radiation. Orientation
was monitored every 300 measurements and intensity was
checked every hour with 3 standard reflections. Intensity
fluctuations remained within 3.3%. The program HELENA
(PLATON) was used for the data reduction [12]. The Laue
symmetry and the systematic absences were consistent with
the trigonal space groups P312 (acentric), P31m (acentric)
and P31m (centric), with much lower probability for the
last one [12]. The structure could be successfully solved in
the acentric space group P31m by direct methods [13]. All
atoms were refined with anisotropic displacement parame-
ters [14], with final indices R1 = 0.0249 and wR2 = 0.0527
for I > 2σ(I), and the absolute structure was confirmed by
a Flack parameter of −0.005(14). A DELABS (PLATON)
empirical absorption correction was performed [12]. More
detailed information related to the crystallographic data and
the structure refinement is given in Table 1.
Symmetry operations used to generate equivalent atoms: a (y,x,z);
b
f
c
d
e
(−x,−x+y,z);
(x,y,1+z);
(y,x,1+z),
(x,y,−1+z);
g
h
i
(−1+x,y,−1+z); (y,x,−1+z); (−y,x−y,z); (y,x,1+z);
j
k
l
(−y,x−y,1+z);
(−x+y,−x,−1+z);
(−y,x−y,−1+z);
m
p
s
n
o
(1+x,y,1+z);
(−x+y,−x,1+z);
(1−y,1+x−y,1+z);
(1−y,x−y,−1+z);
q
r
(1−x+y,1−y,z);
(1−y,x−y,z);
(1−x+y,1−x,−1+z).
found for (C≡N)–Pb in Pb[N(CN)2]2 (269– 282 pm)
in which the Pb atoms exhibit a similar coordination
sphere (c. n. 9) [3, 4]. The {C(CN)3}− ions have al-
most ideal planar D3h geometry with mean deviations
from planarity of 0.38 pm for unit 1 and 3.23 pm for
unit 2. The two symmetry independent tricyanometh-
anide groups are inclined to each other by 24.3(2)◦ and
are stacked in columns parallel to the crystallographic
c axis. Bond lengths and angles within the {C(CN)3}−
ion (Table 3) are similar to those found in other tricyan-
omethanides [7].
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V. M. Deflon et al. · Lead(II) Tricyanomethanide
Acknowledgements
and Prof. M. J. de Arau´jo Sales for the thermogravimet-
ric analyses. Financial support from the Brazilian Agen-
cies CNPq and FAPDF is gratefully acknowledged. CCSL
is grateful to CNPq for a scholarship.
The Authors would like to thank Prof. Dr. Dr. h.c. J. Stra¨hle
(Univ. Tu¨bingen) for providing X-ray diffraction facilities
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