W. Schnick et al.
after diluting the samples as KBr pellets (2 mg sample, 300 mg KBr,
hand-pressed with a press capacity of 10 kN). Thermoanalytical measure-
ments were carried out under an inert atmosphere (He) on a Thermoana-
lyzer TG-DTA92 (Setaram). The samples were heated in an alumina cru-
maximum operating temperature of >5008C are necessary,
because, at up to 5008C and 0.2 MPa ammonia, melem is
the final de-ammonation product of melamine that can be
synthesized. However, reactions under elevated pressures of
ammonia might be a valuable tool for the synthesis of
melem dimers or oligomers to further elucidate condensa-
tion processes up to polymeric carbon nitrides.
The hydrothermal treatment of melam at up to 3008C did
not induce condensation, but, instead, led to the formation
of melam hydrate, [C3N3ACHTUNGTRNEUNG(NH2)2]2NH·2H2O. Melam hydrate,
which has so far only been known as a multiphase polycrys-
talline compound, was obtained in a crystalline form for the
first time, therefore confirming the high reactivity of super-
critical fluids and their good solvating properties. Since
melam is now accessible in large amounts and with the dem-
onstrated possibility of enhancing the solubility of melam by
hydrothermal or solvothermal treatment, the prerequisites
for exploring the chemistry of melam in terms of acid–base
reactions or coordination chemistry are provided, as well as
commending melam for the synthesis of so-called “organic
alloys”.[42]
cible from RT to 6008C at a heating rate of 5 KminÀ1
.
X-ray diffraction: Powder X-ray diffraction data were collected on a Stoe
STADI P diffractometer by using Ge(111)-monochromated CuKa1 radia-
tion (l=154.06 pm). High-temperature in situ X-ray diffraction was car-
ried out on a STOE Stadi P powder diffractometer (Ge(111)-monochro-
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
mated MoKa1 radiation, l=70.093 pm) with an integrated furnace by
using unsealed quartz capillaries (Ø=0.5 mm) as sample containers. The
samples were measured from 298 K to temperatures around 773 K in
steps of 10 K at a heating rate of 1 KminÀ1 between the scans.
Solid-state NMR spectroscopy: 1D solid-state NMR experiments were
carried out at ambient temperature on an Avance 500 NMR spectrome-
ter (Bruker) with an external magnetic field of 11.7 T at Larmor frequen-
cies of 500.1, 125.7, and 50.7 MHz for 1H, 13C, and 15N nuclei, respective-
ly. The measurements were carried out in a 4 mm standard double-reso-
nance MAS probe (Bruker) at a spinning speed of 10 kHz. The chemical
shifts in the 13C NMR and 15N NMR spectra were referenced to TMS and
nitromethane, respectively. For the 1H13C and 1H15N cross-polarization
(CP) MAS NMR spectra, a ramped-amplitude (RAMP)-shaped pulse on
1H, which was centered on the n=+1 Hartmann–Hahn conditions, and
nutation frequencies of nnut =45 kHz (13C) and 55 kHz (15N) were used;
the 1H RF field varied linearly by about 20% during contact times of
1
1.5 ms (13C) and 7 ms (15N). During the acquisition of the FID H contin-
uous wave (CW), decoupling with nutation frequencies of about 80 kHz
(13C) and 70 kHz (15N) were performed. After the acquisition, a flip-back
(FB)[30,31] pulse was applied on 1H so that the recycle delay became less
Experimental Section
1
dependent on the H T1 relaxation time. The recycle delay was set to 20 s
(13C) and 2 s (15N). About 2500 and 121000 transients were accumulated
for the 13C and 15N experiments, respectively.
Synthesis: Melam. Bulk melam was synthesized by heating dicyandiamide
(1 g, 11.9ꢀ10À3 mol, ꢁ99%, Avocado) in a quartz inlay inside an auto-
clave that was filled with gaseous NH3 (0.2 MPa) at 4508C with a heating
rate of 28C minÀ1. After a tempering time of 1–5 days, the autoclave was
cooled to RT at 18CminÀ1 and opened carefully. Bulk melam was found
at the bottom of the inlay; sublimed melamine was found at the top of
the autoclave. Analytical data for melam: IR (KBr): n˜ =3483 (m), 3466
(m), 3457 (m), 3416 (w), 3306 (s), 3170 (s), 1641 (vs), 1612 (vs), 1590 (vs),
1549 (vs), 1518 (vs), 1454 (vs), 1429 (vs), 1351 (vs), 1252 (m), 1175 (w),
1106 (w), 1070 (w), 1034 (w), 972 (vw), 811 (m), 783 (vw), 748 (vw), 687
(w), 634 cmÀ1 (w).
X-ray structure determination: Single-crystal X-ray diffraction data of
melam hydrate were collected at 293 K on a Kappa CCD diffractometer
by using monochromated MoKa radiation (l=71.073 pm). The diffraction
intensities were scaled by using the SCALEPACK software package.[43]
No additional adsorption correction was applied. The crystal structure
was solved by using direct methods with the SHELXS-97 software pack-
age and refined against F2 by applying the full-matrix least-squares
method (SHELXL-97).[44–46] Positions of the hydrogen atoms could be de-
termined from difference Fourier syntheses and were refined isotropical-
ly. All non-hydrogen atoms were refined anisotropically.
Melam–melem adduct phase: The melam–melem adduct phase was syn-
thesized by heating dicyandiamide (1 g, 11.9ꢀ10À3 mol, ꢁ99%, Avocado)
in a quartz inlay inside an autoclave that was filled with gaseous NH3
(0.2 MPa) at 4508C with a heating rate of 28C minÀ1. After a tempering
time of 9–10 days, the autoclave was cooled to RT at 18CminÀ1 and
opened carefully. The adduct was found at the bottom of the inlay; sub-
limed melamine at the top of the autoclave. Analytical data for the
melam–melem adduct phase: IR (KBr): n˜ =3482 (w), 3466 (w), 3452 (w),
3387 (w), 3306 (m), 3141 (s), 1635 (vs), 1592 (vs), 1548 (vs), 1475 (vs),
1456 (vs), 1428 (vs), 1352 (s), 1309 (m), 1255 (m), 1105 (w), 1037 (w), 811
(w), 798 (w), 769 (vw), 759 (vw), 741 (vw), 641 (vw), 717 (w), 700 (vw),
631 (vw), 610 cmÀ1 (vw).
CCDC-901046 (melam hydrate) contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of charge
c.uk/data_request/cif.
Acknowledgements
We gratefully acknowledge financial support from the Deutsche For-
schungsgemeinschaft (DFG; project nos SCHN377/15-1, SE1417/5-1, and
SFB840) and the Fonds der Chemischen Industrie (FCI, scholarship to
E.W.). We also thank Dr. Charlotte Martineau and Dr. Francis Taulelle
(Tectospin, Institut Lavoisier de Versailles, Universitꢅ de Versailles Saint-
Quentin-en-Yvelines) for measurement time on the Avance 500 Bruker
Spectrometer.
Melam hydrate. Single crystals of melam hydrate that were suitable for
X-ray diffraction analysis were synthesized under hydrothermal condi-
tions by heating a suspension of melam (100 mg, 0.36ꢀ10À3 mol) in water
(30 mL) in a quartz inlay inside an autoclave. The autoclave was heated
for 24 h at 3008C, then cooled to RT at 0.058C minÀ1. Analytical data for
melam hydrate: IR (KBr): n˜ =3451 (s), 3348 (s), 3139 (s), 1656 (vs), 1628
(vs), 1585 (vs), 1552 (vs), 1524 (vs), 1466 (s), 1430 (vs), 1350 (vs), 1265
(m), 1187 (w), 1031 (vw), 810 (m), 774 (w), 740 (vw), 635 (vw), 616 cmÀ1
(w).
General techniques: MS was performed on a Jeol MStation JMS-700 gas-
inlet system by using direct insertion (DEI+). Elemental analysis was per-
formed on Vario EL and Vario Micro elemental analyzers (Elementar
Analysensysteme GmbH). FTIR measurements were carried out on a
Bruker IFS 66v/S spectrometer. Spectra of the samples were recorded in
an evacuated cell under ambient conditions between 400 and 4000 cmÀ1
[6] E. Horvath-Bordon, R. Riedel, P. F. McMillan, P. Kroll, G. Miehe,
P. A. van Aken, A. Zerr, P. Hoppe, O. Shebanova, I. McLaren, S.
2048
ꢃ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2013, 19, 2041 – 2049