Melem (2,5,8-Triamino-tri-
s
-triazine), an Important Intermediate
during Condensation of Melamine Rings to Graphitic Carbon
Nitride: Synthesis, Structure Determination by X-ray Powder
Diffractometry, Solid-State NMR, and Theoretical Studies
Barbara Ju¨rgens,
†
Elisabeth Irran,
‡
Ju¨rgen Senker,
†
Peter Kroll,
§
Helen Mu¨ller,
†
and
Wolfgang Schnick*
,†
Contribution from the Ludwig-Maximilians-UniVersita¨t Mu¨nchen, Department Chemie,
Butenandtstrasse 5-13 (D), D-81377 Mu¨nchen, Germany, Institut fu¨r Chemie - Anorganische
Festko¨rperchemie, Sekr. C2, TU Berlin, Strasse des 17. Juni 135, D-10623 Berlin, Germany, and
Institut fu¨r Anorganische Chemie, RWTH Aachen, Professor-Pirlet-Strasse 1, D-52056 Aachen,
Germany
Received April 24, 2003; E-mail: wolfgang.schnick@uni-muenchen.de
Abstract:
Single-phase melem (2,5,8-triamino-tri-
s
-triazine) C
6
N
7
(NH
2
)
3
was obtained as a crystalline powder
by thermal treatment of different less condensed C-N-H compounds (e.g., melamine C
3
N
3
(NH
2
)
3
,
dicyandiamide H
4
C
2
N
4
, ammonium dicyanamide NH
4
[N(CN)
2
], or cyanamide H
2
CN
2
, respectively) at
temperatures up to 450 °C in sealed glass ampules. The crystal structure was determined ab initio by
X-ray powder diffractometry (Cu KR
1
:
P
2
1
/
c
(No. 14),
a
) 739.92(1) pm,
b
) 865.28(3) pm,
c
)
1338.16(4) pm, β ) 99.912(2)°, and
Z
) 4). In the solid, melem consists of nearly planar C
6
N
7
(NH
2
)
3
molecules which are arranged into parallel layers with an interplanar distance of 327 pm. Detailed
13
C and
15
N MAS NMR investigations were performed. The presence of the triamino form instead of other possible
tautomers was confirmed by a CPPI (cross-polarization combined with polarization inversion) experiment.
Furthermore, the compound was characterized using mass spectrometry, vibrational (IR, Raman), and
photoluminescence spectroscopy. The structural and vibrational properties of molecular melem were
theoretically studied on both the B3LYP and the MP2 level. A structural optimization in the extended state
was performed employing density functional methods utilizing LDA and GGA. A good agreement was found
between the observed and calculated structural parameters and also for the vibrational frequencies of
melem. According to temperature-dependent X-ray powder diffractometry investigations above 560 °C,
melem transforms into a graphite-like C-N material.
Melamine (2,4,6-triamino-s-triazine), C
3
N
3
(NH
2
)
3
1a, repre-
sents an important starting material for several industrial
applications, for example, the syntheses of melamine-formal-
dehyde resins or of fireproof materials.
1,2
Furthermore, it is used
for the architecture of supramolecular structures, for example,
assemblies built up by cyanuric acid C
3
N
3
(OH)
3
1b or melamine
derivatives.
3-5
In the past few years, another interest arose in
melamine as well as in other compounds, C
3
N
3
X
3
1, containing
s-triazine (cyanuric) rings C
3
N
3
, for example, cyanuric chloride
C
3
N
3
Cl
3
1c
6-10
or cyanuric azide C
3
N
3
(N
3
)
3
1d.
11
These are
considered to be suitable molecular precursor compounds for
the synthesis of graphitic forms of carbon nitride (g-C
3
N
4
).
6,12-14
In most of the postulated structures of g-C
3
N
4
, s-triazine ring
systems are linked through trigonal N atoms forming extended
2D sheets 2 (Scheme 1).
Recently, another possible building block for g-C
3
N
4
was
taken into account (Scheme 2): tri-s-triazine rings C
6
N
7
which
are cross-linked by trigonal N atoms 3.
15-17
The possible
condensation of three s-triazine rings and the existence of a
“cyameluric nucleus” C
6
N
7
4 was first postulated by Pauling
†
Ludwig-Maximilians-Universita¨t Mu¨nchen.
‡
TU Berlin.
§
RWTH Aachen.
(1) Allcock, H. R.; Lampe, F. W. Contemporary Polymer Chemistry; Prentice
Hall: New Jersey, 1990.
(2) Kuryla, W. C.; Papa, A. J. Flame Retardancy of Polymeric Materials;
Dekker: New York, 1973-1979; Vols. 1-5.
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Monographs in Supramolecular Chemistry, issue 7; Cambridge: New York,
2000.
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Ltd.: Chichester, New York, Weinheim, Brisbane, Singapore, Toronto,
2000.
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1995, 117, 6360.
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109, 697.
(7) Zhang, Z.; Leinenweber, K.; Bauer, M.; Garvie, L. A. J., McMillan, P. F.;
Wolf, G. H. J. Am. Chem. Soc. 2001, 123, 7788.
(8) Wolf, G. H.; Bauer, M.; Leinenweber, K.; Garvie, L. A. J.; Zhang, Z. NATO
Sci. Ser., II: Mathematics, Physics and Chemistry 2001, 48 (Frontiers of
High-Pressure Research II: Application of High Pressure to Low-
Dimensional NoVel Electronic Materials), 29.
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(10) Khabashesku, V. N.; Zimmermann, J. L.; Margrave, J. L. Chem. Mater.
2000, 12, 3264.
(11) Gillan, E. G. Chem. Mater. 2000, 12, 3906.
(12) Liu, A. Y.; Cohen, M. L. Science 1989, 245, 841.
(13) Teter, D. M.; Hemley, R. J. Science 1996, 271, 53.
(14) Mattesini, M.; Matar, S. F.; Etourneau, J. J. Mater. Chem. 2000, 10, 709.
(15) Komatsu, T. J. Mater. Chem. 2001, 11, 802.
(16) Komatsu, T.; Nakamura, T. J. Mater. Chem. 2001, 11, 474.
(17) Kroke, E.; Schwarz, M.; Horath-Bordon, E.; Kroll, P.; Noll, B.; Norman,
A. D. New J. Chem. 2002, 26, 508.
Published on Web 08/02/2003
10288
9
J. AM. CHEM. SOC. 2003,
125
, 10288-10300 10.1021/ja0357689 CCC: $25.00 © 2003 American Chemical Society
and Sturdivant.
18
On the basis of this complex ring system,
further substitutional derivatives were predicted in analogy to
compounds containing the cyanuric ring, for example, cyame-
luric acid C
6
N
7
(OH)
3
4a which is related to cyanuric acid C
3
N
3
-
(OH)
3
or hydromelonic acid C
6
N
7
(NCNH)
3
4b which represents
the analogue to postulated tricyanomelamine C
3
N
3
(NCNH)
3
1e.
19
Many attempts were performed to synthesize and char-
acterize cyameluric derivatives; however, the existence of the
C
6
N
7
ring system has been proven lately with the crystal
structure of tri-s-triazine C
6
N
7
H
3
4c.
20-21
Very recently, Kroke
et al. described the first functionalized derivative, trichloro-tri-
s-triazine C
6
N
7
Cl
3
4d.
17
In analogy to 2 where 2,4,6-triamino-s-triazine represents the
repeating unit, 2,5,8-triamino-tri-s-triazine 4e can be considered
as the repeating unit of 3. Synonyms for 2,5,8-triamino-tri-s-
triazine are 2,5,8-triamino-1,3,4,6,7,9,9b-heptaazaphenalene or
2,5,8-triamino-1,3,4,6,7,9-hexaazacycl[3.3.3]azine and 2,5,8-
triamino-s-heptazine. The trivial name melem for compound 4e
dates back to Liebig who performed different experiments with
carbon nitrides:
22
While heating potassium thiocyanate with
ammonium chloride, he obtained 1a which he named melamine.
Later, the formation of melamine by different other experiments
was observed, for example, by heating cyanamide H
2
CN
2
5,
ammonium dicyanamide NH
4
[N(CN)
2
] 6, or dicyandiamide
H
4
C
2
N
4
7 (Scheme 3).
23-25
The pyrolysis of melamine as well as its behavior under
pressure were investigated, and condensation processes (Scheme
4) leading to so-called melam 8, melem 4e, and melon 9 were
postulated.
26-30
For melamine, structural data have been re-
ported. Neither the existence of melam nor the existence of
melem and melon could be confirmed by crystal structure
determinations as yet.
31,32
(18) Pauling, L.; Sturdivant, J. H. Proc. Natl. Acad. Sci. U.S.A. 1937, 23, 615.
(19) Redemann, C. E.; Lucas, H. J. J. Am. Chem. Soc. 1940, 62, 842.
(20) Hosmane, R. S.; Rossman, M. A.; Leonard, N. J. J. Am. Chem. Soc. 1982,
104, 5497.
(21) Shahbaz, M.; Urano, S.; LeBreton, P. R.; Rossman, M. A.; Hosmane, R.
S.; Leonard, N. J. J. Am. Chem. Soc. 1984, 106, 2805.
(22) Liebig, J. Ann. Chem. 1834, 10,1.
(23) Bieling, H.; Radu¨chel, M.; Wenzel, G.; Beyer, H. J. Prakt. Chem. 1965,
28, 325.
(24) Ju¨rgens, B.; Ho¨ppe, H. A.; Irran, E.; Schnick, W. Inorg. Chem. 2002, 41,
4849.
(25) Franklin, E. C. J. Am. Chem. Soc. 1922, 44, 486.
(26) May, H. J. Appl. Chem. 1959, 340.
(27) van der Plaats, G.; Soons, H.; Snellings, R. Proc. Eur. Symp. Therm. Anal.
1981, 2, 215.
(28) Purdy, A. P.; Callahan, J. H. Main Group Chem. 1998, 2, 207.
(29) Ma, H. A.; Jia, X.; Cui, Q. L.; Pan, Y. W.; Zhu, P. W.; Liu, B. B.; Liu, H.
J.; Wang, X. C.; Liu, J.; Zou, G. T. Chem. Phys. Lett. 2003, 368, 668.
(30) Costa, L.; Camino, G. J. Calorim., Anal. Therm. Thermodyn. Chim. 1986,
17, 213.
(31) Larson, A. C.; Cromer, D. T. J. Chem. Phys. 1974, 60, 185.
Scheme 1.
s
-Triazines
Scheme 2.
Tri-
s
-triazines
Study of Melem (2,5,8-Triamino-tri-s-triazine) ARTICLES
J. AM. CHEM. SOC.
9
VOL. 125, NO. 34, 2003 10289
Herein, we report on the synthesis of melem 4e obtained in
preparative amounts, its crystal structure determination, and
spectroscopic investigation. Thus, we confirm the existence of
a fundamental C-N-H molecule, that has been postulated a
long time ago.
Experimental Section
Preparation of Melem C
6
N
7
(NH
2
)
3
. Melem 4e was synthesized by
heating cyanamide 5 (Fluka, g98%) or ammonium dicyanamide 6 (for
preparation, see ref 24) or dicyandiamide 7 (Avocado, 99%) or
melamine 1a (Fluka, purum, g99% (NT)). The commercial products
were used as purchased: 80 mg of starting material (1.90 mmol of 5,
0.95 mmol of 6, 0.95 mmol of 7, or 0.63 mmol of 1a, respectively)
was filled into a glass ampule (outer diameter, 16 mm; inner diameter,
12 mm). The ampule was sealed at a length of 120 mm and heated to
450 °C (heating rate: 1 °C min
-1
). After about5hatthis temperature,
the ampule was slowly (2 °C min
-1
) cooled to room temperature.
After the ampule was opened, the typical smell of ammonia was
detected. At the top of the ampule, colorless crystals were found which
were identified by X-ray powder diffractometry as sublimated melamine.
At the bottom, a white-beige powder containing melem was isolated.
The product has formed with a yield of ca. 60%. It is not moisture
sensitive. Anal. calcd for melem: H, 2.75; C, 33.03; N, 64.22. Found:
H, 2.98; C, 32.62; N, 62.04.
Preparation of
15
N-Enriched Samples of Melamine and Melem.
For
15
N MAS NMR investigations, a special synthesis was developed
to prepare
15
N-enriched samples: 54.4 mg (0.20 mmol) of Na
3
[C
6
N
9
]
(for preparation, see ref 33) was heated with 15.1 mg (0.28 mmol) of
sublimated
15
NH
4
Cl (Promochem, 98 at. % enriched) under argon up
to 470 °C (heating rate: 1 °C min
-1
) in a sealed glass ampule (outer
diameter, 16 mm; inner diameter, 12 mm; length, 120 mm). After the
mixture was cooled, NaCl as well as a yellow insoluble polymer
remained at the bottom of the ampule. At the top, a beige reaction
product was found containing melamine. Subsequent sublimation (220
°C, 1 Pa) of this product leads to nearly pure melamine with a
significantly higher content of
15
N within both the amino groups and
the s-triazine ring.
Samples of C
3
15
N
3
(
15
NH
2
)
3
were used to prepare
15
N-enriched melem
C
6
15
N
7
(
15
NH
2
)
3
, which contains
15
N atoms within the tri-s-triazine ring
as well as within the amino groups.
Physical Measurements. X-ray Diffraction. X-ray powder diffrac-
tion data were used for the crystal structure determination because no
single crystals of melem were available. The microcrystalline samples
were enclosed in glass capillaries of diameter 0.3 mm. The diffraction
investigations were carried out in Debye-Scherrer geometry. The
diffraction data were collected on a conventional powder diffractometer
(STOE Stadi P, Cu KR
1
radiation).
Temperature-dependent X-ray powder diffraction experiments were
performed on a STOE Stadi P powder diffractometer (Mo KR
1
) with
a computer controlled STOE furnace: Samples of melamine and of
melem, respectively, were enclosed in silica capillaries and heated from
room temperature to 700 °C in the angular range 3° e 2θ e 30°.
Powder diffraction patterns were recorded in steps of 20 °C. Addition-
ally, a sample of melem was cooled with a 600 Series Cryostream
Cooler (Oxford Cryosystems) from room temperature to -140 °C. The
cooling procedure was interrupted in steps of 20 °C to record diffraction
patterns at constant temperatures.
Thermoanalytical Investigations. A DSC curve of melamine was
recorded with a DSC 141 (Setaram): 17.906 mg (0.142 mmol) of
melamine 1a was filled under argon into a steel pressure crucible and
heated to 500 °C (heating rate: 5 °C min
-1
). Additionally, the thermal
effects during cooling were recorded. The use of special pressure
(32) Varghese, J. N.; O’Connell, A. M.; Maslen, E. N. Acta Crystallogr. 1977,
B33, 2102.
(33) Ju¨rgens, B.; Irran, E.; Schneider, J.; Schnick, W. Inorg. Chem. 2000, 39,
665.
Scheme 3.
Formation of Melamine 1a
Scheme 4.
Postulated Condensation of Melamine 1a
ARTICLES Ju¨rgens et al.
10290 J. AM. CHEM. SOC.
9
VOL. 125, NO. 34, 2003
crucibles was necessary because conventional alumina crucibles burst
due to evolution of ammonia.
Solid-State MAS NMR Spectroscopy.
13
C and
15
N MAS NMR
spectra of melamine and melem were recorded at room temperature
with a conventional impulse spectrometer DSX 500 Avance (Bruker)
operating at 500 MHz. For recording the
15
N MAS NMR spectra,
15
N-
enriched samples of both compounds were used.
The samples were filled into zirconia rotors with a diameter of 4
mm and mounted in a standard double-resonance MAS probe (Bruker).
The signals were referenced to trimethylsilane (TMS) (
13
C) and
nitromethane (
15
N), respectively. Rotation frequencies between 3 and
7 kHz were chosen.
A ramped cross-polarization sequence was employed to excite both
13
C and
15
N nuclei via the proton bath where the power of the
1
H
radiation was linearly varied about 50%. A CPPI (cross-polarization
combined with polarization inversion) experiment was performed to
investigate the bonding and the position of the hydrogen atoms of
melamine and melem, respectively. For these experiments, rotation
frequencies of 3.7 kHz (melamine) and 5 kHz (melem) and an initial
contact time of 30 ms before inverting the sign of the
1
H radiation
were used. The data collection of all experiments was performed
applying broadband proton decoupling via a TPPM sequence.
34
Vibrational Spectroscopy. FTIR spectra of melamine and melem
were obtained at room temperature by using a Bruker IFS 66v/S
spectrometer with DTGS detector. The samples were thoroughly mixed
with dried KBr (5 mg of sample, 500 mg of KBr). The preparation
procedures were performed in a glovebox under dried argon atmosphere.
The spectra were collected in a range from 400 to 4000 cm
-1
with a
resolution of 2 cm
-1
. During the measurement, the sample chamber
was evacuated.
For FT-Raman measurements, samples of melamine and melem were
filled into glass capillaries of 0.5 mm diameter. The spectra were excited
by a Bruker FRA 106/S module with a Nd:YAG laser (λ ) 1064 nm)
scanning a range from 0 to 3500 cm
-1
.
Photoluminescence Spectroscopy. Photoluminescence spectra were
recorded with a spectrofluorimeter FL900 (Edinburgh Instruments) with
a Xe lamp as the light source and a Hamamatsu photomultiplier.
BaMgAl
10
O
17
:Eu which has a quantum efficiency of 90% at 254 nm
was used as reference. The transfer function of the spectrometer has
been calibrated over the entire frequency range of the measurements
utilizing reference phosphors.
Mass Spectrometry. Mass spectra were obtained with a JEOL
MStation JMS 700. The source was operated at a temperature of
200 °C.
Calculations. Methods. The theoretical assessment of the structural
properties of C
6
N
7
(NH
2
)
3
is based on a detailed comparison of
computational results for both the molecular and the extended state.
The molecular-orbital calculations were performed using the Gaussian
quantum chemistry software package.
35
Beckes three-parameter hybrid
functional (B3LYP)
36,37
was employed as well as the second-order
Møller-Plesset perturbation theory (MP2).
38
Dunning’s correlation-
consistent basis set (cc-pVDZ) was used.
39
A Pople-type basis set (6-
311++G**) yielded very similar results.
The structural optimizations in the extended state were done using
the Vienna ab initio simulation package (VASP).
40-43
Ultrasoft pseudo-
potentials were employed for the atoms, and the exchange-correlation
energy of the valence electrons was treated at the DFT level using both
the local density approximation (LDA)
44
and the generalized-gradient
approximation (GGA).
45
The wave function was expanded into a plane
wave basis set using a cutoff energy of 400 eV; for the integration
over the Brillouin Zone, a Monkhorst-Pack 2 × 2 × 2 k-point mesh
was used.
46
Initial positions of atoms were the crystal coordinates
supplied by the refinement of the X-ray diffraction data. During
relaxation, all crystal coordinates were optimized while keeping space
group symmetry and experimental lattice constants fixed. Releasing
the latter constraint showed the usual trends of LDA and GGA tending
to smaller and larger volumes, each by 4%, respectively.
(34) Bennett, A. E.; Rienstra, C. M.; Auger, M.; Lakshimi, K. V.; Griffin, R.
G. J. Chem. Phys. 1995, 103, 6951.
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A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A., Jr.; Stratmann,
R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels, A. D.; Kudin,
K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone, V.; Cossi, M.; Cammi,
R.; Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford, S.; Ochterski, J.;
Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma, K.; Malick, D. K.;
Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Cioslowski, J.; Ortiz,
J. V.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.;
Gomperts, R.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng,
C. Y.; Nanayakkara, A.; Gonzalez, C.; Challacombe, M.; Gill, P. M. W.;
Johnson, B. G.; Chen, W.; Wong, M. W.; Andres, J. L.; Head-Gordon,
M.; Replogle, E. S.; Pople, J. A. Gaussian 98, revision A.11; Gaussian,
Inc.: Pittsburgh, PA, 1998.
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(39) Dunning, T. H. J. Chem. Phys. 1989, 90, 1007.
(40) Kresse, G.; Hafner, J. Phys. ReV.B1993, 47, 558.
(41) Kresse, G.; Hafner, J. Phys. ReV.B1994, 49, 14251.
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(43) Kresse, G.; Furthmu¨ller, J. Phys. ReV.B1996, 54, 11169.
(44) Perdew, J. P.; Zunger, A. Phys. ReV.B1981, 23, 5048.
(45) Perdew, J. P. In Electronic Structure of Solids ‘91; Eschrig, P. H., Ed.;
Akademie Verlag: Berlin, 1991.
(46) Monkhorst, H. J.; Pack, J. D. Phys. ReV.B1976, 13, 5188.
Figure 1.
Observed (crosses) and calculated (line) X-ray powder diffraction patterns as well as difference profiles of the Rietveld refinement of melem 4e
(STOE Stadi P, λ ) 154.06 pm).
Study of Melem (2,5,8-Triamino-tri-s-triazine) ARTICLES
J. AM. CHEM. SOC.
9
VOL. 125, NO. 34, 2003 10291
Results and Discussion
Powder Diffractometry and Structure Refinement. The
diffraction pattern of a room-temperature measurement of melem
was indexed with a monoclinic unit cell (Figure 1, Table 1).
The extinction rules unequivocally indicated the space group
P2
1
/c. A structure solution with direct methods was not possible.
To solve the structure, the profile and lattice constants were
refined by the LeBail method. For these calculations and also
for the Rietveld refinement, the program GSAS was employed.
47
The crystal structure was solved by a combination of trial-and-
error and rigid-body methods. The atomic positions of the
molecule neglecting the outermost NH
2
groups were calculated
in a random position in the unit cell. The distances between
the atoms were restrained with a very high weight, so that nearly
a rigid body was formed. As a reference for the atomic distances,
the data of C
6
N
7
Cl
3
4d were taken from Kroke et al.
17
The
positions of all atoms were refined simultaneously. When the
refinement reached a local minimum (R
F
2
≈ 60%), the weight
of the restraints was reduced to zero, and therefore the atoms
randomized and were released to positions of high electron
density. The weight was then increased again so the molecule
was formed again. This procedure was repeated twice, and then
the molecule reached a position where it gave a low R
F
2
value
(∼20%). Refinement with a low weight gave an R-value of
about 15%. A subsequent Fourier map clearly revealed the
positions of the N atoms of the outermost NH
2
groups. This
result nicely illustrates the reliability of the position and
orientation of the melem molecule in the cell. The H atoms of
the NH
2
groups could not be found by difference Fourier
synthesis. Their positions were calculated by the program
SHELX
48
and refined with restraints. Details of the structure
determination and refinement are listed in Table 1, and the
refined atomic coordinates are given in Table 2. In Scheme 5,
the labeling of the different C and N positions of the melem
molecule is illustrated.
Crystal Structure. Solid melem 4e consists of C
6
N
7
(NH
2
)
3
molecules interconnected by extended hydrogen bridges. Com-
parable to the situation found in tri-s-triazine and trichloro-tri-
s-triazine, each molecule contains a cyameluric nucleus C
6
N
7
of three anellated s-triazine rings. In the case of melem, the
structure is completed by three terminal N atoms bound to
positions 2, 5, and 8 of the tri-s-triazine C
6
N
7
nucleus.
In the asymmetric unit, there is one complete C
6
N
7
(NH
2
)
3
molecule (Figure 2). Two differently orientated layers of parallel
molecules alternate along the direction of the c-axis. The planes
of the planar molecules are slightly tilted to the (10-1) plane.
Layers of C
6
N
7
(NH
2
)
3
molecules are formed which are parallel
to this plane. Neighboring molecules form an angle of about
40°. The interlayer distance is 327 pm. This value is comparable
to the respective distances in melamine (320 pm - 340 pm), in
the C-N polymer [C
6
N
9
H
4
]Cl (322 pm), as well as in pure
graphite (334 pm). The relatively short interlayer distance
observed in melem may be explained by intermolecular π‚‚‚π
interactions between the aromatic C
6
N
7
nuclei.
The ring system of C
6
N
7
(NH
2
)
3
is quite planar; the sums of
the bond angles around each atom are 360°. The rings are
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(48) Sheldrick, G. M. SHELXTL, V 5.10 Crystallographic System; Bruker AXS
Analytical X-ray Instruments Inc.: Madison, 1997.
Table 1.
Crystallographic Data for Melem C
6
N
7
(NH
2
)
3
formula H
6
C
6
N
10
M
r
/g mol
-1
218.18
crystal system monoclinic
space group P2
1
/c (no. 14)
powder diffractometer Stoe STADI P
radiation; λ/pm Cu KR
1
; 154.06
temperature/°C22
lattice parameters
a/pm 739.92(1)
b/pm 865.28(3)
c/pm 1338.16(4)
β/deg 99.912(2)
V/10
6
pm
3
843.95(4)
Z 4
F
calc
/g cm
-3
1.717
profile range 5° e 2θ e 80°
no. of data points 7500
observed reflections 515
structural parameters 68
profile parameters 18
χ
2
0.883
structure refinement Rietveld refinement (GSAS)
47
R-values
wR
p
0.056
R
p
0.042
R
F
0.079
Table 2.
Atomic Coordinates and Displacement Factors (in pm
2
)
for Melem C
6
N
7
(NH
2
)
3
; All Atoms in Wyckoff Position 4
e
atom xy zU
iso
a
C(i)1 0.765(2) 0.203(2) 0.447(1) 440(20)
C(i)2 0.675(2) -0.069(2) 0.453(1) 440(20)
C(i)3 0.867(2) 0.046(2) 0.593(1) 440(20)
C(e)4 0.602(2) 0.093(1) 0.3119(9) 440(20)
C(e)5 0.773(2) -0.195(1) 0.5924(9) 440(20)
C(e)6 0.959(2) 0.294(1) 0.5903(8) 440(20)
N(i)1 0.771(1) 0.065(2) 0.5019(9) 320(10)
N(c)2 0.695(1) 0.221(1) 0.3509(7) 320(10)
N(c)3 0.581(1) -0.044(1) 0.3644(8) 320(10)
N(c)4 0.659(1) -0.196(1) 0.5017(8) 320(10)
N(c)5 0.870(1) -0.083(1) 0.6515(9) 320(10)
N(c)6 0.956(1) 0.169(1) 0.6443(8) 320(10)
N(c)7 0.883(1) 0.315(1) 0.4956(7) 320(10)
N(t)8 0.511(1) 0.1046(8) 0.2226(6) 320(10)
N(t)9 0.766(1) -0.3282(9) 0.6460(7) 320(10)
N(t)10 1.056(1) 0.413(1) 0.6356(7) 320(10)
H1 0.542(5) 0.164(4) 0.183(1) 250
H2 0.427(3) 0.047(3) 0.204(1) 250
H3 0.679(4) -0.384(4) 0.633(2) 250
H4 0.846(3) -0.349(2) 0.692(2) 250
H5 1.081(5) 0.416(2) 0.696(7) 250
H6 1.091(4) 0.479(2) 0.602(1) 250
a
U
iso
is defined as exp(-8π
2
U
iso
sin
2
θ/λ
2
); U
iso
values of H atoms are
not refined.
Scheme 5.
One Melem Molecule in the Crystal Structure of
C
6
N
7
(NH
2
)
3
a
a
The labeling of the atoms is indicated. The molecule adopts ap-
proximately symmetry D
3h
.
ARTICLES Ju¨rgens et al.
10292 J. AM. CHEM. SOC.
9
VOL. 125, NO. 34, 2003
