Use of melem as a nucleophilic reagent to form the triphthalimide C 6N7(phthal)3-New targets and prospects

Article abstract of DOI:10.1002/chem.201200723

Melem (1), as one of the most important representatives of the tri-s-triazine compounds, can be used as a nucleophilic reagent in reactions with phthalic acid derivatives. The synthesis of 2,5,8-triphthalimido-tri-s- triazine (C₆N₇(phthal)₃, 2) was investigated starting from phthalic anhydride or phthalic dichloride in various solvents, at different temperatures as well as in the solid state. NMR measurements (solution and solid state), IR spectroscopy and elemental analysis indicated the formation of a cyclic imide. Single-crystal structure analysis of a 1:1 adduct of 2 with nitromethane proved the molecular structure expected for a phthalimido-s-heptazine. DFT calculations were performed to obtain a better insight into the structural features of compound 2, especially the interaction of the carbonyl groups with the tri-s-triazine nitrogen atoms. The title compound 2 shows promising properties: it is thermally stable up to 500 °C in air and shows strong photoluminescence with a maximum emission at around 500a nm. The potential of the nucleophilic reaction of melem with other strong electrophiles provides new targets and prospects. Copyright

Full text of DOI:10.1002/chem.201200723

FULL PAPER
DOI: 10.1002/chem.201200723
Use of Melem as a Nucleophilic Reagent to Form the Triphthalimide
C6N7ACHTNUTRGNENG(U phthal)3—New Targets and Prospects
Anke Schwarzer, Uwe Bçhme, and Edwin Kroke*[a]
Abstract: Melem (1), as one of the
the formation of a cyclic imide. Single-
crystal structure analysis of 1:1
adduct of 2 with nitromethane proved
the molecular structure expected for a
phthalimido-s-heptazine. DFT calcula-
tures of compound 2, especially the in-
teraction of the carbonyl groups with
the tri-s-triazine nitrogen atoms. The
most important representatives of the
tri-s-triazine compounds, can be used
as a nucleophilic reagent in reactions
with phthalic acid derivatives. The syn-
thesis of 2,5,8-triphthalimido-tri-s-tria-
a
title compound
2 shows promising
properties: it is thermally stable up to
5008C in air and shows strong photolu-
minescence with a maximum emission
at around 500 nm. The potential of the
nucleophilic reaction of melem with
other strong electrophiles provides new
targets and prospects.
tions were performed to obtain
a
zine (C6N
N
better insight into the structural fea-
starting from phthalic anhydride or
phthalic dichloride in various solvents,
at different temperatures as well as in
the solid state. NMR measurements
(solution and solid state), IR spectro-
scopy and elemental analysis indicated
Keywords: density functional calcu-
lations · luminescence · nitrogen
heterocycles · nucleophilic addition ·
X-ray diffraction
Introduction
cleophilicity of the NH2 groups is low. It is possible to attack
melem nucleophilically with the strong base hydrazine, the
NH2 groups being replaced by hydrazine NHNH2 units.[5a]
On the other hand, reactions involving the amino group
of melem as a nucleophilic reagent are very rare. Spasskaya
et al. described the reaction with formaldehyde[16] leading to
the formation of a methanol-substituted melem derivative.
A second example of a nucleophilic reaction of the amino
groups of melem is the Kirsanov reaction of melem with
PCl5 to form the triphosphinimino derivative [C6N7-
Melem[1–12] (C6N
7ACHTUNGTRENNUNG(NH2)3, 1) is one of the most common and
most important tri-s-triazine (or s-heptazine) derivatives.[1–10]
This group of compounds has recently been suggested for
various innovative applications such as effective flame re-
tardant materials,[1] photocatalysts,[2] organic electronics[3]
and luminescent devices.[4] The synthesis of many tri-s-tria-
zines starts with the synthesis of melem or its polymerised
form melon [C6N7ACHTUNGTRENNUNG
(NH2)(NH)]n.[5–9,13] Reactions of melem
and/or melon have been reported, for example, with potassi-
um hydroxide to give the corresponding cyamelurate K3-
(NPCl2)3].[5c] To the best of our knowledge, reactions of
ACHTUNGTRENNUNG
melem with other electrophiles have not been described so
far. Even in the field of s-triazines, the reaction of melamine
with phthalic acid derivatives is rarely reported.[17] Cyclic
imides like phthalimides or maleimides are known for their
polymorphism,[18] the unusual non-inclusion of solvents in
tricyclic derivatives,[19] as self-healing polymers,[20] and as
host–guest networks.[21] Herein we report the successful syn-
thesis of the triimide 2 by the nucleophilic reaction of 1 with
phthalic acid chloride. The title compound was comprehen-
sively analysed and showed high chemical and thermal sta-
bility and strong photoluminescence.
ACHTUNGTRENNUNG HCTUNGTREN[NUGN C6N7-
[C6N7O3][14] or with KSCN to give the K-melonate K
3A
ACHTUNGTRENNUNG
(NCN)3].[6–9] In addition, melem can be protonated by
strong mineral acids, such as HClO4 or H2SO4, to yield me-
lemium salts.[10] Note that the protonation occurs exclusively
at the ring nitrogen atoms with the NH2 groups remaining
unchanged. The molecular structure[11,12] reveals a planar en-
vironment of the exocyclic nitrogen atoms, as it is already
known from other aromatic amines.[15] Thus, the Brønsted
basicity is lower at these latter nitrogen atoms and the nu-
[a] Dr. A. Schwarzer, Priv.-Doz. Dr. U. Bçhme, Prof. Dr. E. Kroke
Institut fꢀr Anorganische Chemie, TU Bergakademie Freiberg
Leipziger Straße 29, 09599 Freiberg (Germany)
Fax : (+49)3731-394058
Results and Discussion
E-mail: Edwin.Kroke@chemie.tu-freiberg.de
The synthesis of N-phenylphthalimides or analogous malei-
mides is a standardised procedure involving the reaction of
the corresponding anhydride (maleic anhydride, phthalic an-
hydride) with substituted anilines in diethyl ether at room
temperature.[18,22] Condensation of the acyclic amidic inter-
mediates in acetic anhydride gave the target compounds in
Supporting information for this article, including crystallographic
data for 2·CH3NO2, 13C CP/MAS spectrum of 2·CH3NO2, calibration
for the UV/Vis and fluorescence analysis, additional discussion of the
torsion angles at the phthalimide units and their relationship with
BCPs, is available on the WWW under http://dx.doi.org/10.1002/
chem.201200723.
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ative a polar solvent will assist ring formation. Taking this
into account, the low yields of all reactions carried out were
to be expected. The best results were achieved with the
polar o-dichlorobenzene, in which a trace amount of melem
dissolves.
The workup of the crude product was also limited by the
solubility of 1 and 2. Fortunately, the byproducts phthalic
anhydride and acid can be removed by washing with water
and ethanol. IR spectroscopic analysis of the dried crude
product indicates the formation of a cyclic imide with C=O
vibrations at 1804 and 1742 cmꢀ1. In contrast, phthalic acid
gives a single C=O vibration at 1692 cmꢀ1, whereas phthalic
anhydride shows the vibration of a conjugated anhydride at
1854 and 1763 cmꢀ1. Melem is identified by the NH vibra-
tions at 3487 and 3426 cmꢀ1. The separation of the target
compound 2 from melem (1) can be realised by extensive
Soxhlet extraction with nitromethane to give the target com-
pound 2 as a yellow 1:1 adduct.
Scheme 1. Synthesis of triimido-heptazine 2 from melem (1) and phthalic
acid anhydride (PAA) and phthaloyl dichloride (PACl).
In addition to the reaction of melem (1) with PACl in sol-
ution (Table 1), a solid-state reaction was carried out. Al-
though no reaction occurred at 1208C, fast product forma-
tion was observed at 1908C under intensive HCl evapora-
tion. In contrast to the reactions in solution, the separation
of the byproducts is more difficult. In fact, so far it has not
been possible to obtain the pure product 2 by a solid-state
reaction.
moderate-to-good yields (26–73%).[18,22] However, this reac-
tion with melem and phthalic anhydride (PAA) did not give
the desired product (Scheme 1). The nucleophilic strength
of melem towards the carbonyl atoms in PAA is too small.
Even in high-boiling solvents like p-xylene or decalin the re-
action did not succeed (Table 1).
The phthalimide 2 crystallises from nitromethane in the
monoclinic space group P21/n with one tri-s-triazine and one
solvent molecule in the asymmetric unit (see Figure 1). The
bond lengths and angles of the heptazine moiety are in the
Table 1. Reaction conditions and yields of compound 2 for reactions of
melem (1) with PAA and PACl under various conditions.
Solvent
Reaction
T
T
Yield
[%]
component
[8C]
[h]
ꢀ
range of the expected values with longer inner C N bonds.
diethyl ether/acetic anhydride
p-xylene[a]
decalin
PAA
PAA
PAA
PAA
PACl
PACl
PACl
PACl
PACl
PACl
25
138
189–191
120
101
189–191
189–191
179
120
190
72
2
2
1
0
0
<1[b]
<1[b]
0
The planarity of the heptazine core is indicated by the rms
deviation of all fitted atoms of 0.0144 ꢂ. The five-membered
imide units are also planar (rms deviation of all fitted
solid state
nitromethane
decalin
0
4
<1[b]
<1[b]
10.2[c]
0
decalin[a]
24
22
1
1,2-dichlorobenzene[a]
solid state
[d]
solid state
0.5
–
[a] Reactions were carried out under inert conditions in argon. [b] The
formation of the product is indicated by the appearance of a yellow
colour and by the IR spectra of the crude product showing the typical
n˜C=O vibrations of a cyclic imide ring. [c] The yield is based on the 1:1
adduct with nitromethane. [d] The crude product could not be purified.
The solid-state reaction between the two components at
1208C revealed the same problem as for the reaction in
higher-boiling solvents: sublimation of the anhydride out of
the reaction mixture. Therefore phthaloyl dichloride (PACl,
Scheme 1) was used, which has a higher reactivity towards
nucleophiles. The results of the reaction of PACl with
melem in several different solvents at different reaction
temperatures and times are presented in Table 1.
The solvent also has an important impact on the forma-
tion of the phthalimide heptazine 2. First, the poor solubility
of melem in all common organic solvents constrained the
possibilities. For the reaction of 1 with a reactive acid deriv-
Figure 1. Molecular structure of compound 2·CH3NO2 showing the
atomic numbering scheme. The thermal displacement ellipsoids of the
non-hydrogen atoms are drawn at the 50% probability level.
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Formation of the Triphthalimide C6N7ACTHNUTRGNEN(UG phthal)3
FULL PAPER
atoms: 0.0070, 0.0057, 0.0099 ꢂ). As expected, the oxygen
atoms of the C=O groups are mainly within the plane of the
five-membered imide ring. The exocyclic nitrogen atoms N8,
N9 and N10 show an almost planar environment (sum of the
angles: 359.3, 359.6, 359.78), as is typical for other melem
derivatives.[23] Melem itself also reveals a planar environ-
ment of the exocyclic nitrogen atoms although with slight
deviations (sum of the angles: 358.5, 359.1, 359.28).[11,12]
In addition, the molecular structure of 2·CH3NO2 can be
weak interactions occur between molecule 2 and the solvent
nitromethane (2.61 ꢂ, 1148 and 2.60 ꢂ, 1538). Stacking inter-
actions can only be observed between the imide unit Cg3
(Cg3 is defined as the centre of gravity of N10, C23, C24,
C29 and C30) and Cg9 (the centre of gravity of the phenyl
ꢀ
ring C24 C29) with
3.883(2) ꢂ (symmetry code: ꢀx, ꢀy, 2ꢀz).
a
centre-to-centre distance of
Quantum chemical calculations were performed to obtain
a better insight into the structural features of compound 2.
Compound 2 crystallises with a C1-symmetric conformation.
Geometry optimisation of this and other possible conforma-
tions revealed that the C3-symmetric conformation repre-
sents the global minimum. The conformation found
in the X-ray structure is only 1.6 kJmolꢀ1 higher in
ꢀ
ꢀ
described by the N C(=O) and Caryl N bond lengths and
the angle between the imide ring and the N-substituted unit,
here the heptazine core (see Table 2). The torsion angle be-
Table 2. Selected geometric parameters of 2·CH3NO2 conjugated[18] and non-conjugat-
ed[19] N-aryl-substituted cyclic imides.
energy. This leads to the question, what influence
does the conformation of the phthalimide units
have on the total energy of the molecule. For this
purpose 2H-isoindolyl-tri-s-triazine (I) and phthali-
mido-tri-s-triazine (II) were used as model com-
pounds to investigate the rotational barriers of a
single substituent at the heptazine core. (Optimised
geometries are denoted with roman numbers to dis-
tinguish calculated geometries from experimental
data, see Figure 2. Relaxed potential energy surface
(PES)[24] scans were performed for the rotation of
the 2H-isoindolyl and phthalimide groups around
the bond to the heptazine core. We can assume that
all steric and electronic interactions between the
substituent and the heptazine unit are switched off
at a torsion angle of 908. Therefore the torsional
2·CH3NO2
Conjugated
imides[a,b]
Non-conjugated
imides[a,c]
imide/aryl interplanar angle [8]
27.45(15)
34.42(14)
44.62(13)
1.437(5)/1.449(5)
1.433(5)/1.445(5)
1.425(5)/1.435(4)
1.404(5)
59.45
1.409
1.424
73.41
1.404
1.429
ꢀ
N C(=O) [ꢂ]
[d]
ꢀ
Caryl N [ꢂ]
1.397(5)
1.412(5)
[a] Average values are given for comparison.[18,19] [b] “Conjugated imides” refer to flu-
orinated N-phenyl-maleimides, -phthalimides and -tetrafluorophthalimides. [c] “Non-
conjugated imides” refer to the Diels–Alder adducts of fluorinated N-phenylmalei-
mide and 6,6-diphenylfulvenes. [d] Aryl=heptazine core, hydrogen or/and fluorine-
substituted phenyl rings.
tween the two ring systems in 2·CH3NO2 is 35.58 on average.
A comparison with other known derivatives[18,19] with the
same imide unit revealed remarkable differences. In fluori-
nated N-phenyl-substituted maleimides or phthalimides, the
torsion angle of about 598 is a result of the balance between
repulsive and attractive forces between the ortho-substitu-
ents (H,F) and the oxygen atoms and the conjugation of p
electrons over the whole molecular system.[18] In addition,
the non-conjugation of p electrons in Diels–Alder adducts
of the same N-phenylmaleimides led to higher torsion
angles (738).[19] In this study, the heptazine derivative of the
phthalimide 2 does not possess any ortho-substituted atoms.
Hence, it has smaller torsion angles of 27.45(15), 34.42(14)
ꢀ
and 44.62(13)8. The N C(=O) bond is 1.437 ꢂ on average
ꢀ
whereas the C N bond to the heptazine moiety is 1.404 ꢂ.
This is in contrast to the bonding situation found in N-
phenyl-substituted imides (Table 2).[18,19] One possible
reason is the difference in the ortho position: on one hand
hydrogen or fluorine atoms, on the other the lone pair of
the nitrogen atom in the heptazine core.
Figure 2. Illustration of the rotational conformers of I and II. The repul-
sion between the lone pairs of the oxygen and nitrogen atoms in II is
drawn schematically.
In 2·CH3NO2 the packing structure is dominated by very
potentials of I and II are scaled such that both functions in-
tersect at 908 (see Figure 3). It is possible to gain informa-
tion about the different steric interactions of I and II by
comparing these graphs.
ꢀ
weak C H···O/N contacts in the range 2.54–2.60 ꢂ. Only
ꢀ
ꢀ
the C H···O contact in the bifurcated C19 H19···O5/N5 in-
teraction is shorter than 2.5 ꢂ forming a dimer of the hepta-
ꢀ
ꢀ
ꢀ
zine-based molecule (H19 O5=2.40 ꢂ, C19 H19 O5=
1368). The other weak contacts form zigzag chains. Only
There is no steric repulsion between the 2H-isoindolyl
group and the heptazine unit in molecule I. This leads to a
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E. Kroke et al.
density in the molecular geometry of the X-ray structure
shows that there are four repulsive interactions between the
electronic spheres of the phthalimide oxygen atoms and the
nitrogen atoms of the heptazine unit (see Figure 4 and
Table 3). Such interactions occur between O1/N1, O2/N2,
O3/N3 and O4/N4. These atoms are close enough for their
atomic surfaces to come into direct contact. The appearance
of a bond critical point (BCP) between these atoms is asso-
ciated with a fold catastrophe[31,33] and the emergence of an
additional ring critical point (RCP). The BCPs of these
atoms are very close to the corresponding RCPs. If one as-
sumes further rotation of the phthalimide groups towards
higher torsion angles, the BCPs and RCPs merge and anni-
hilate each other. The values of the electron density and the
Laplacian of the electron density at the BCPs are of the
same order of magnitude as in biphenyl[30] and 3-(o-aryl)-5-
methylrhodanines.[32] The BCPs under discussion have low
electron densities of around 0.013 a.u. and small positive
values for the Laplacian of the electron density. Therefore
these interactions can be characterised as non-bonded,
closed-shell interactions.
Figure 3. Schematic representation of PES scans for the rotation of the
2H-isoindolyl (I) and phthalimide (II) groups in the tri-s-triazine unit.
bell-shaped graph with a maximum at 908 and minima at 0
and 1808. The energy difference between the minimum and
maximum is 59.1 kJmolꢀ1 (DE1 in Figure 3). This corre-
sponds to the resonance energy of the molecule when the p
electrons of the two constituent units interact.
The rotational profile of II is more complicated. There is
a local maximum at 908 and higher maxima at 0 and 1808. It
can be concluded from this profile that two opposing effects
operate. Going from 908 to lower or higher torsion angles
leads to an increasing conjugative interaction between the
two parts of the molecule. This lowers the total energy of
the molecule. On the other hand, there is repulsion between
the lone pairs of the oxygen atoms of the phthalimide unit
and the nitrogen atoms of the heptazine in II (see Figure 2).
This leads to higher energies at 0 and 1808. The resulting ro-
tational barrier of II is 13.9 kJmolꢀ1 (DE2 in Figure 3). The
rotational barrier of II is a minimum at a torsion angle of
508 and 1308. This conformation clearly represents the best
compromise between minimal steric repulsion and optimal
conjugative interaction.
If we assume that the resonance energy in compound II is
very similar to that in I, we can estimate the steric repulsion
between the phthalimide and the heptazine unit to be about
67.9 kJmolꢀ1 (DE3 in Figure 3).
The topological analysis of the electron density according
to QTAIM[25] cannot discriminate between attractive and re-
pulsive interactions but tells us that there are interactions
between the atoms. This controversial problem has been dis-
cussed in the recent literature.[26–29] To avoid improper con-
clusions from the topological analysis of the electron densi-
ty, the calculated torsion potentials from above should be in-
cluded in the discussion. We can conclude from these tor-
sion potentials that there are repulsive interactions between
the heptazine core and the oxygen atoms of the phthalimide
unit. Such repulsive interactions have also been analysed in
biphenyl,[30] 2,6-difluoro-substituted biphenyls[31] and 3-(o-
aryl)-5-methylrhodanines.[32] The different torsion angles of
the three phthalimide groups determined from the X-ray
structure of 2 are situated in the broad flat minimum be-
tween 30 and 608 calculated for the model compound II (see
Figure 3). The quantum chemical analysis of the electron
Figure 4. Representation of the BCPs and RCPs of 2. The direction of
view is the same as in Figure 1. For a colour image of the bond and ring
critical points of 2 see the Supporting Information.
Table 3. Selected interatomic distances and values of the topological
properties of the electron density of 2.[a]
Interatomic distance
[ꢂ]
BCP
RCP
1
!2/1
1
!2/1
ꢀ
O1 1
2.767
2.784
2.795
2.832
2.941
2.886
0.0141
0.0137
0.0134
0.0125
0.0574
0.0536
0.0525
0.0508
0.0136
0.0129
0.0129
0.0123
0.0709
0.0683
0.0665
0.0603
ꢀ
O2 N2
ꢀ
O3 N3
ꢀ
O4 N4
ꢀ
O5 N5
ꢀ
O6 N6
[a] Electron density (1) and the Laplacian of the electron density (!21)
are given in atomic units (a.u.).
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Formation of the Triphthalimide C6N7ACTHNUTRGNEN(UG phthal)3
FULL PAPER
The association between tri-s-triazine 2 and solvent was
investigated by TG and DTA analyses under argon and air
(Figure 5). The onset of desorption of the solvent molecule
for the heptazine core are similar to other known 13C CP/
MAS analyses of tri-s-triazine derivatives.[11,13,35,36] The
signal for the solvent nitromethane is observed at d=
63 ppm, as expected.
The UV/Vis spectrum of 2 in nitromethane shows a
shoulder at 394 nm (eAbs =314 Lmolꢀ1 cmꢀ1) and a band of
low intensity at 413 nm (eAbs =339 Lmolꢀ1 cmꢀ1, Figure 6). In
addition, the fluorescence spectrum shows a strong emission
at 490 nm (lexc =416 nm, eEm =107500 Lmolꢀ1 cmꢀ1).
Figure 6. Absorption (dashed) and emission (solid) spectra of 2 in nitro-
methane solution at 298 K, corrected and standardised to 1 (Abs: absorp-
tion; Em: emission). For a colour image of the strong luminescence of 2
in nitromethane under UV excitation at 254 nm, see the table-of-contents
entry for this paper.
Figure 5. TG (solid) and DTA (dashed) curves of 2·CH3NO2 under a) a
flow of Ar (2.729 mg) and b) a flow of air (2.476 mg), measured with a
heating rate of 5 Kminꢀ1
.
Conclusions
In this paper we have reported on the reactions of melem,
as a nucleophilic reagent, with carbonyl compounds. The
low yields are due to the low reactivity of melem 1 as well
as the low solubility of 1 and the resulting triimido-hepta-
zine 2.
occurs in the range of 128–1738C, which is significantly
higher than the boiling point of nitromethane (1018C). As
known from other heptazine derivatives,[11,14,34] decomposi-
tion starts above 5008C. Analogous thermal gravimetric
measurements under air revealed a similar picture (Fig-
ure 5b). The nitromethane desorbs in the range of 111–
1738C, which indicates a slightly lower thermal stability. De-
composition of the tri-s-triazine molecule also occurs above
5008C, but is complete at 6508C, in contrast to the analysis
performed under argon in which the heptazine has not en-
tirely decomposed even at 8008C. In summary, the organic
title compound 2 is stable up to very high temperatures of
around 5008C in air.
Quantum chemical calculations have shown that the
phthalimide units in compound 2 are able to adopt different
conformations due to a broad flat minimum in the potential
energy surface. Non-bonding, closed-shell interactions exist
between the oxygen atoms of the phthalimide unit and the
peripheral nitrogen atoms of the heptazine core. These in-
teractions prevent the formation of a completely planar
molecule. The results of the calculations correspond well
with the experimental findings, especially the structural data
obtained from the single-crystal structure analysis of 2.
Compound 2 is the first example of a new class of imido
derivatives of melem. These novel tri-s-triazines may find
applications in photo- or electroluminescent devices.
Future investigations will focus on improving the yields
by using higher temperatures and even stronger electro-
philes. The reactions with various reactants showing very
strong Lewis acidity, such as various element halides, should
In addition, solid-state 13C MAS NMR spectroscopy anal-
ysis revealed the crystallinity of 2·CH3NO2 (see Figure S1 in
the Supporting Information). In the range of d=166–
160 ppm several peaks are observed in the spectrum arising
from the carbonyl and tri-s-triazine carbon atoms. The phe-
nylene moiety also shows several peaks in the range of d=
142–123 ppm, which indicates the non-equality of the
carbon atoms in the solid state. The chemical shifts observed
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E. Kroke et al.
internal coordinates. In these cases, the specific torsion angle was
changed in steps of 58. The geometry of the molecule was completely op-
timised at every step, restricting only the torsion angle to the specified
value. This method allows access to a defined section of the potential
energy surface.
yield products derived from nucleophilic attack of the NH2
groups of melem if suitable reaction conditions are applied.
The AIM analysis[25] of 2 was performed at the B3LYP/6-311+G
ACHTUNGTRENNUNG(d,p)
Experimental Section
level of theory with the geometry taken from the X-ray structure analysis
without further optimisation. The wavefunction files for the AIM analysis
were generated in Cartesian coordinates with a basis set containing 6d
functions. The option SCF=Tight was used to prevent “charge leakage”
as described by Popelier.[43] The electron density topology was analysed
by using AIM2000.[44]
General: All solvents were purified and dried according to general proce-
dures. Commercially available chemicals were of p.a. quality and used as
obtained from the suppliers. IR spectra were recorded in the range 400–
4000 cmꢀ1 at room temperature with a Nicolet 380 FT-IR spectrometer.
The samples (KBr pellets) were prepared under N2 atmosphere. Standard
1H and 13C NMR spectra were recorded on an AVANCE DPX 400 spec-
trometer at 293 K [1H (400 MHz), 13C (101 MHz) NMR]. Chemical shifts
are reported relative to tetramethylsilane. CP/MAS 13C NMR (101 MHz)
studies were performed on a Bruker DSX Avance 400 conventional im-
pulse spectrometer with a rotation of 10 kHz and a ramp of 80%. Ele-
mental analyses were performed with a Vario Micro CHNS analyser.
UV/Vis spectra were recorded with a JASCO V-650 spectrophotometer
at room temperature. Emission spectra were recorded on a JASCO FP-
6500 instrument at room temperature with an excitation wavelength of
416 nm. Calibration curves were determined with the following concen-
trations: 446.6, 361.3, 290.8, 307.7, 177.7, 44.7 and 29.1 mmol using
307.7 mmol as sample. The thermogravimetry measurements were per-
formed with a Seiko SSC 5200 TG/DTA 22 instrument (Seiko Instru-
ments) with a heating rate of 5 Kminꢀ1, argon or air flow rate of
300 mLminꢀ1 and a maximum temperature of 8008C.
Crystal structure determination: Crystals of compound 2·CH3NO2 suita-
ble for X-ray crystallography were obtained from a solution of 2 in nitro-
methane by slow evaporation of the solvent at room temperature. Data
collection of 2·CH3NO2 was performed on a STOE IPDS-2 diffractome-
ter (image plate) equipped with a low-temperature device [T=100(2) K]
with graphite-monochromatised MoKa radiation (l=0.71073 A8) using w
and f scans. Reflections were corrected for background, Lorentzian and
polarisation effects. Preliminary structure models were derived by direct
methods[45] and the structures were refined by full-matrix least-squares
calculations based on F2 for all reflections using SHELXL.[45] All hydro-
gen atoms were included in the models in calculated positions and were
refined as constrained to the bonding atoms. The crystal data and param-
eters pertinent to the data collection and structure refinement of
2·CH3NO2 are summarised in Table 4 and selected bond lengths and
angles are presented in Table 2.
Preparation of melem (1):[11,37] Melem was obtained by following the
published procedure. In brief, melamine (25 g) was heated in a glass tube
to 3858C. At about 2508C, violent gas (ammonia) liberation began,
which continued for about 9 h. The heating at 385–3908C was continued
for 60 h. Thereafter the reaction mass was allowed to cool to room tem-
perature. Pure melem was obtained as a white-to-beige powder. Yield:
CCDC 868710 (for 2·CH3NO2) contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via www.ccdc.cam.
ac.uk/data_request/cif.
Table 4. Crystallographic and structure refinement data for 2·CH3NO2.
2·CH3NO2
ꢀ
16.87 g, 95.5%; IR (KBr): n˜ =3490, 3430 (N H), 1620, 1310 (n˜ass hepta-
zine ring), 1480, 805 cmꢀ1 (heptazine ring); elemental analysis calcd (%)
for C6N7ACHTUNGTRENNUNG(NH2)3 (218.08): C 33.03, H 2.77, N 64.20; found: C 31.93, H
2.68, N 63.47%.
chemical formula
formula mass
colour
C30H12N10O6·CH3NO2
669.54
yellow
Preparation of 2,5,8-triphthalimido-tri-s-triazine (2): Under inert condi-
tions, melem (3 g, 13.75 mmol) and phthaloyl dichloride (11.17 g,
55.03 mmol) were heated under reflux in dry 1,2-dichlorobenzene
(200 mL) for 22 h. Suction filtration of the cooled reaction mixture gave
the crude product including phthalic anhydride and unreacted melem.
Stirring in water for 30 min, suction filtration, washing with ethanol and
extensive Soxhlet extraction gave 2 as an intense yellow 1:1 adduct with
nitromethane. Yield: 0.94 g, 10.2%; m.p. >3008C; 1H NMR
([D6]DMSO): d=8.06–7.96 (m, 12H, 5-H, 6-H), 4.41 ppm (s, 3H,
CH3NO2); 13C NMR ([D6]DMSO): d=163.94 (C-3), 163.13 (C-2), 161.46
(C-1), 136.12 (C-6), 131.41 (C-4), 124.68 (C-5), 63.69 ppm (CH3NO2);
13C CP/MAS NMR: d=166.2, 164.1, 161.9, 160.3 (C=O, C6N7), 142.2,
138.1, 135.3, 131.4, 129.7, 127.2, 126.1, 123.4 (phenylene moiety),
63.4 ppm (CH3NO2); IR (KBr): n˜ =3100, 3062, 2963 (CArH), 1804, 1742
(n˜C=O), 1618, 1610 (n˜assheptazine, n˜C=CAr), 1525 (n˜C=CAr), 1470, 1329
crystal system
space group
a [ꢂ]
b [ꢂ]
c [ꢂ]
monoclinic
P21/n
7.4314(3)
25.8162(13)
14.6322(6)
93.177(3)
2802.9(2)
4
b [8]
V [ꢂ3]
Z
F
N
1368
]
1.587
m
G
]
0.120
data collection temperature [K]
q range [8]
h, k, l range
no. of coll./unique refl.
Rint
100(2)
1.58–25.00
ꢀ8/7, ꢁ30, ꢁ17
18972/4934
0.0809
ꢀ ꢀ
(heptazine ring), 1395, 1112 (s, n˜C N C), 828, 812 (heptazine ring),
710 cmꢀ1 (dC=O); UV/Vis (CH3CH2OH): l (e)=271 (2484), 236 (3004),
209 nm (2484 Lmolꢀ1 cmꢀ1); elemental analysis calcd (%) for
C30H12N10O6·CH3NO2 (669.54): C 55.61, H 2.26, N 23.01; found: C 55.35,
H 2.25, N 23.04%.
no. of refl. with [Iꢂ2s(I)]
no. of refined parameters/restraints
R1(F)[a]/wR2(F2) (all data)[b]
S (goodness of fit on F2)[c]
2937
452/0
0.0595/0.1685
1.056
Quantum chemical calculations: Quantum chemical calculations were
carried out by using the Gaussian 09 series of programs.[38] Geometries
were fully optimised by DFT using Beckeꢃs three-parameter hybrid-ex-
change functional and the correlation functional of Lee, Yang and Parr
(B3LYP).[39,40] Geometry optimisations and harmonic frequencies were
final D1max
/
[eꢂꢀ3
]
0.251/ꢀ0.327
min
CCDC number
868710
1
2
2
[a] R1=SjFo jꢀjFc j/SjFo j. [b] wR2=[Sw
G
(Fo )2] =
,
w=[s2-
2
2
2
G
(Fo ,0)+2Fc2]/3. [c] GoF=[Sw-
1
calculated for all elements with the polarised 6-311+GACHTUNTRGNEU(GN d,p) basis set for
2
(Fo ꢀFc2)2/(nobsꢀnparam)] =
2
the different conformations of 2.[41,42] The stationary points were charac-
terised by zero imaginary frequencies.
Relaxed potential energy surface scans of I and II were performed with
the Opt=ModRedundant utility in Gaussian 09 at the B3LYP/6-311+G-
ACHTUNGTRENNUNG(d,p) level of theory. This option includes the specification of redundant
&
6
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ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!

Formation of the Triphthalimide C6N7ACTHNUTRGNEN(UG phthal)3
FULL PAPER
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Received: March 4, 2012
Revised: June 1, 2012
[18] A. Schwarzer, E. Weber, Cryst. Growth Des. 2008, 8, 2862–2874.
Published online: && &&, 2012
Chem. Eur. J. 2012, 00, 0 – 0
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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ÞÞ
These are not the final page numbers!

E. Kroke et al.
Nucleophilic tri-s-triazine: Melem
Nucleophilic Reagents
reacts as a nucleophile with phthaloyl
dichloride to form the title triphthali-
mide C6N7ACTHNUTRGNEUNG(phthal)3. Comprehensive
analysis and ab initio calculations have
provided useful insights into its molec-
ular structure and properties: it is
stable in air up to 5008C and shows
strong photoluminescence (see figure).
A. Schwarzer, U. Bçhme,
E. Kroke* ..................... &&&& — &&&&
Use of Melem as a Nucleophilic
Reagent to Form the Triphthalimide
C6N
U
pects
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www.chemeurj.org
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
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These are not the final page numbers!