Melemium Methylsulfonates HC6N7(NH 2)SH2C6N7(NH2)S(SO 3Me)3·H2O and H2C 6N7(NH2)3(SO3Me) 2·H2O

Article abstract of DOI:10.1002/zaac.200900433

Melem C₆N₇(NH₂)₃ was shown to form a variety of adduct phases and salts. Salts of melem can be yielded by reaction of melem with strong acids. We investigated the reaction of melem with methylsulfonic acid, thus identifying two new melemium salts with formulas HC₆N₇(NH₂)₃H₂C ₆N₇(NH₂)₃(SO₃Me) ₃·H₂O (1) and H₂C₆N ₇(NH₂)₃-(SO₃Me)₂· H₂O (2), respectively. The structures of both compounds were elucidated using single-crystal XRD compound 1: (P1 no. 2, Z = 2, a = 10.096(2), b = 12.865(3), c = 13.369(3) A, α = 63.28(3), β = 81.19(3), γ = 72.92(3)°, V = 1461.4(7) A³) compound 2: (P2₁/n, no. 14, Z = 4, a = 8.0757(16), b = 7.6937(15), c = 27.540(6) A, β = 92.03(3)°, V = 1710.6(6) A³). Both compounds are discussed in comparison to structural data from the literature of other melemium salts. We also present new synthetic approaches for the preparation of melem in larger quantities.

Full text of DOI:10.1002/zaac.200900433

ARTICLE
DOI: 10.1002/zaac.200900433
Melemium Methylsulfonates HC6N7(NH2)3H2C6N7(NH2)3(SO3Me)3·H2O and
H2C6N7(NH2)3(SO3Me)2·H2O
Andreas Sattler,[a] Stefanie Schönberger,[a] and Wolfgang Schnick*[a]
Dedicated to Professor Arndt Simon on the Occasion of His 70th Birthday
Keywords: Heptazine; Tri-s-triazine; X-ray diffraction; Sulfonates; Vibrational spectroscopy
Abstract. Melem C6N7(NH2)3 was shown to form a variety of adduct 10.096(2), b = 12.865(3), c = 13.369(3) Å, α = 63.28(3), β = 81.19(3), γ =
phases and salts. Salts of melem can be yielded by reaction of melem with 72.92(3)°, V = 1461.4(7) Å3) compound 2: (P21/n, no. 14, Z = 4, a =
strong acids. We investigated the reaction of melem with methylsulfonic 8.0757(16), b = 7.6937(15), c = 27.540(6) Å, β = 92.03(3)°, V =
acid, thus identifying two new melemium salts with formulas 1710.6(6) Å3). Both compounds are discussed in comparison to structural
HC6N7(NH2)3H2C6N7(NH2)3(SO3Me)3·H2O (1) and H2C6N7(NH2)3- data from the literature of other melemium salts. We also present new
(SO3Me)2·H2O (2), respectively. The structures of both compounds were synthetic approaches for the preparation of melem in larger quantities.
¯
elucidated using single-crystal XRD compound 1: (P1 no. 2, Z = 2, a =
single-crystal XRD only became available in recent years,
mainly due to the low solubility of many heptazines often im-
peding proper crystal growth from solution. The crystal struc-
ture of melem could eventually be elucidated as a part of these
efforts [7].
Introduction
Over the past few years, heptazine (tri-s-triazine) [C6N7]
based molecules have emerged as promising precursors for
condensed carbon nitride materials. Heptazine-based structural
models for graphitic carbon nitride (g-C3N4) have been widely
discussed [1, 2]. Thus, employment of heptazine precursors
turned out to be a promising approach for accessing these com-
pounds. The quest for new ultrahard materials like hypothetical
c-C3N4 [3] also remained a major drive behind ambitions to-
wards synthesis of carbon nitrides. Instead of staying narrowly
focused on the topic of hardness alone, other properties of car-
bon nitrides, like catalytic behavior [4], also turned out to be
most promising. 2,6,10-triamino-s-heptazine (2,6,10-triamino-
tri-s-triazine, C6N7(NH2)3), commonly named melem is one
such precursor compound. The latter compound is usually
yielded by thermal condensation of melamine (2,4,6-triamino-
s-triazine, C3N3(NH2)3). A variety of other compounds, how-
ever, turned out to be suitable starting materials as well (e.g.
cyanamide or dicyandiamide).
Some adducts and salts containing melem were already de-
scribed, namely the perchlorate salts HC6N7(NH2)3ClO4·
C6N7(NH2)3 [8] and HC6N7(NH2)3ClO4·H2O [9], the sulfate
salt H2C6N7(NH2)3SO4·2H2O [9] and the phosphoric acid ad-
duct C6N7(NH2)3·H3PO4 [9]. All these compounds were syn-
thesized from aqueous solutions of the respective acids, thus
showing that melem is rather insensitive to hydrolysis in acidic
solutions. In alkaline solutions, however, hydrolysis to cyamel-
uric acid is observed relatively fast (cf. Scheme 1 for molecu-
lar structures) [10]. Melemium salts are usually well defined
and well crystalline compounds, which are readily available.
Thus, they are valuable for gaining a solid base of structural
data for heptazine-based compounds. Furthermore, they are
also possible precursors for carbon nitride materials or offer
a way to increase the very low solubility of melem in most
solvents.
Heptazine-based compounds like melem have initially been
described in the mid 19th century [5]. However, its molecular
structure containing the heptazine core (or cyameluric nucleus)
remained unidentified for a remarkably long period of time.
The correct formula was first proposed by Pauling et al. in
1937 [6]. Structural data for heptazine compounds based on
* Prof. Dr. W. Schnick
Fax: +49-89-2180-77440
E-Mail: wolfgang.schnick@uni-muenchen.de
[a] Department Chemie
Lehrstuhl für Anorganische Festkörperchemie
Ludwig-Maximilians-Universität München
Butenandtstraße 5–13 (D)
Scheme 1. Molecular structure of melamine (A), melem (B) and cyam-
eluric acid (C).
81377 München, Germany
476
© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2010, 636, 476–482

HC6N7(NH2)3H2C6N7(NH2)3(SO3Me)3·H2O and H2C6N7(NH2)3(SO3Me)2·H2O
Studying the behavior of melem in solutions of methylsul- bonds in neighborhood to a protonation site and shortening of
fonic acid we identified two new salts on which we report in the bonds adjacent to the elongated bonds is observed. A slight
this contribution.
bending of bond angles at protonation sites can also be found.
The C–N–C angles around protonated nitrogen atoms of the
cyameluric nucleus are generally larger than 120°, whereas the
angles around unprotonated atoms are smaller than 120°. The
planarity of the cyameluric nucleus is not affected by protona-
tion. This was also observed for the other melemium salts as
well [8, 9]. The C–N bonds at the terminal amino groups, how-
ever, are unaffected by proximity to protonation sites and show
a general reduction in bond length by about 2 pm, in compari-
son to melem, instead. This applies to all respective bonds in
all ions. The methylsulfonate ions do not display any unusual
structural features. Both melemium cations are almost planar
and deviation from planarity is mainly caused by hydrogen
atoms in order to allow a more favorable hydrogen bonding
pattern, by increasing the D–H···A angles.
Results and Discussion
The title compounds can be crystallized from aqueous solu-
tions of methylsulfonic acid. Crystals of both salts were grown
by slow cooling of hot saturated solutions. The most important
factor directing the formation of one specific salt is the concen-
tration of the acid. As compound 1 displays a lower overall
protonation of melem it is yielded from less concentrated solu-
tions. An increase in concentration of methylsulfonic acid in
solution resulted in the formation of the higher protonated salt
(2). The structures of both compounds could be solved by us-
ing single-crystal XRD (cf. Table 1). Selected bond lengths
and angles are given in Table 2.
The melemium ions are arranged in hydrogen-bonded
HC6N7(NH2)3H2C6N7(NH2)3(SO3Me)3·H2O (1) crystallizes
in the triclinic space group P1 (no. 2). Additionally to the re-
+
¯
strands with one HC6N7(NH2)3 ion being connected to two
H2C6N7(NH2)32+ ions and vice versa (cf. Figure 2). Bridged by
methylsulfonate ions and crystal water, a corrugated, layer-like
arrangement is assembled (cf. Figure 3). Layers of melemium
ions are running parallel to the plane defined by the b axis and
the face diagonal of the ac plane (cf. Figure 3). The CH3
groups of the methylsulfonate ions all point into the space be-
tween the layers. As proximity of the non-polar groups is fa-
spective three methylsulfonate ions and one crystal water mol-
ecule, the asymmetric unit comprises both a melemium ion
with single and double protonation. The melemium ions ex-
hibit the usual molecular structure of melem, consisting of a
heptazine nucleus and three amino moieties (cf. Figure 1).
As expected from the findings for other melemium salts, me-
lem is protonated at the nitrogen atoms of the heptazine core.
In comparison to non-protonated melem, elongation of the C–N vorable, only every second interlayer space is filled with CH3
Table 1. Crystallographic data and details of the structure refinement for HC6N7(NH2)3H2C6N7(NH2)3(SO3Me)3·H2O (1) and
H2C6N7(NH2)3(SO3Me)2·H2O (2).
formula
HC6N7(NH2)3H2C6N7(NH2)3 (SO3Me)3·H2O (1)
H2C6N7(NH2)3(SO3Me)2·H2O (2)
formula weight /g·mol–1
742.74
428.43
crystal system
triclinic
monoclinic
¯
space group
lattice parameters /Å, °
P 1(no. 2)
P21/n (no. 14)
a = 8.0757(16)
b = 7.6937(15)
c = 27.540(6)
a = 10.096(2)
b = 12.865(3)
c = 13.369(3)
α = 63.28(3)
β = 81.19(3)
β = 92.03(3)
γ = 72.92(3)
volume /Å3
1461.4(7)
1710.6(6)
4
Z
2
diffractometer
Kappa CCD
radiation, monochromator
temperature /K
Mo-Kα (λ = 71.073 pm), graphite
200
structure solution
structure refinement
corrections applied
extinction coefficient
absorption coefficient /mm–1
calculated density /g·cm–3
data / restraints / parameters
R-indices
SHELXS [18] (direct methods)
SHELXL [18] (full-matrix least-squares on F2)
Lorentz, polarization, extinction, SCALEPACK [17]
0.0054(9)
0.0026(7)
0.342
0.372
1.688
1.664
5343 / 0 / 525
R1 = 0.0572 all data
3786 / 2 / 301
R1 = 0.0988 all data
R1 = 0.0381 FO > 2σ(FO2) (4141 reflections)
R1 = 0.0467 FO > 2σ(FO2) (2432 reflections)
2
2
wR2 = 0.1028 all data
wR2 = 0.1071 all data
2
2
2
2
wR2 = 0.0986 FO > 2σ(FO
)
wR2 = 0.0988 FO > 2σ(FO
)
GooF
weighting Scheme
1.028
1.055
w–1 = σ2(Fo ) + (0.0465P)2 + 0.3351P
w–1 = σ2(Fo ) + (0.0504P)2 + 0.0322P
2
2
2
2
2
2
where P = (Fo + 2Fc ) / 3
where P = (Fo + 2Fc ) / 3
largest peak / deepest hole /e·Å–3
0.282 / –0.395
0.366 / –0.352
Z. Anorg. Allg. Chem. 2010, 476–482
© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
477

A. Sattler, S. Schönberger, W. Schnick
ARTICLE
Table 2. Selected distances (in Å) and angles (in °) for compounds 1 and 2.
HC6N7(NH2)3H2C6N7(NH2)3(SO3Me)3·H2O (1)
C1–N5 1.298(3) C9–N15
C1–N6 1.345(3) C9–N14
C1–N1 1.378(3) C9–N11
1.297(3)
1.347(3)
1.371(3)
N5–C1–N6
N5–C1–N1
N6–C1–N1
N2–C2–N7
N2–C2–N1
N7–C2–N1
N3–C3–N4
N3–C3–N1
N4–C3–N1
N9–C4–N5
N9–C4–N4
N5–C4–N4
120.5(2)
C1–N5–C4
116.74(18) C8–N12–C11
117.48(18)
118.41(19)
122.0(2)
124.13(19) C1–N6–C5
115.33(18) C2–N7–C5
119.91(19) N17–C7–N16
119.56(19) N17–C7–N11
120.53(19) N16–C7–N11
121.78(19) C8–N13–C12
118.23(18) C9–N14–C12
120.77(19) C9–N15–C10
119.59(18) C7–N16–C10
119.64(19) C7–N17–C11
120.15(19) O1–S1–O2
119.21(19) O1–S1–O3
120.64(19) O2–S1–O3
C2–N2 1.314(3) C10–N20 1.303(3)
C2–N7 1.319(3) C10–N15 1.360(3)
C2–N1 1.404(3) C10–N16 1.366(3)
C3–N3 1.293(3) C11–N18 1.311(3)
C3–N4 1.353(3) C11–N12 1.359(3)
C3–N1 1.372(3) C11–N17 1.363(3)
C4–N9 1.296(3) C12–N19 1.304(3)
C4–N5 1.345(3) C12–N13 1.334(3)
C4–N4 1.371(3) C12–N14 1.371(3)
115.55(19)
117.22(18)
116.78(18)
113.75(12)
111.05(11)
110.99(10)
106.13(13)
107.04(14)
107.49(12)
112.38(10)
111.86(10)
110.01(10)
107.75(12)
107.15(14)
107.43(14)
113.15(16)
112.26(13)
111.04(12)
106.42(16)
106.60(17)
106.89(16)
121.3(2)
N12–C8–N13
122.83(19) N12–C8–N11
115.87(19) N13–C8–N11
119.6(2)
118.9(2)
N15–C9–N14
N15–C9–N11
120.5(2)
O1–S1–C13
123.48(19) O2–S1–C13
116.06(19) O3–S1–C13
121.53(18) N14–C9–N11
119.99(19) N20–C10–N15
C5–N10 1.308(3) S1–O1
C5–N7 1.329(3) S1–O2
C5–N6 1.376(3) S1–O3
C6–N8 1.305(3) S1–C13
C6–N2 1.348(3) S2–O6
C6–N3 1.376(3) S2–O5
C7–N17 1.324(3) S2–O4
C7–N16 1.325(3) S2–C14
C7–N11 1.400(3) S3–O9
C8–N12 1.313(3) S3–O8
C8–N13 1.323(3) S3–O7
C8–N11 1.409(3) S3–C15
1.4475(18) N10–C5–N7
1.4523(18) N10–C5–N6
1.4683(17) N7–C5–N6
116.4(2)
118.2(2)
O6–S2–O5
O6–S2–O4
117.6(2)
N20–C10–N16
122.36(19) N15–C10–N16
117.50(19) N18–C11–N12
125.39(19) O5–S2–O4
115.90(19) O6–S2–C14
1.750(3)
N8–C6–N2
1.4534(17) N8–C6–N3
1.4571(16) N2–C6–N3
1.4665(18) C3–N1–C1
117.8(2)
N18–C11–N17
118.0(2)
O5–S2–C14
124.74(19) N12–C11–N17
119.74(18) N19–C12–N13
118.64(17) N19–C12–N14
121.50(18) N13–C12–N14
117.97(18) C9–N11–C7
115.94(19) C9–N11–C8
121.85(19) C7–N11–C8
126.08(19) O4–S2–C14
119.7(2)
118.4(2)
121.9(2)
O9–S3–O8
O9–S3–O7
O8–S3–O7
1.745(3)
1.434(2)
1.443(2)
C3–N1–C2
C1–N1–C2
C2–N2–C6
118.50(17) O9–S3–C15
120.92(18) O8–S3–C15
120.54(18) O7–S3–C15
1.4462(17) C3–N3–C6
1.747(3)
C3–N4–C4
H2C6N7(NH2)3(SO3Me)2·H2O (2)
C1–N2 1.297(3) C5–N2
C1–N7 1.344(3) C5–N3
C1–N1 1.379(3) C6–N9
C2–N3 1.297(3) C6–N5
C2–N4 1.349(3) C6–N4
C2–N1 1.381(3) S1–O1
C3–N5 1.316(3) S1–O2
C3–N6 1.323(3) S1–O3
C3–N1 1.406(3) S1–C7
C4–N10 1.306(3) S2–O5
C4–N6 1.336(3) S2–O6
C4–N7 1.367(3) S2–O4
C5–N8 1.301(3) S2–C8
1.358(3)
1.366(3)
1.305(3)
1.332(3)
1.371(3)
N2–C1–N7
N2–C1–N1
N7–C1–N1
N3–C2–N4
N3–C2–N1
121.2(2)
123.2(2)
115.5(2)
121.1(2)
123.5(2)
115.4(2)
119.8(2)
120.0(2)
120.2(2)
119.9(2)
117.4(2)
122.7(2)
117.4(2)
117.4(2)
N2–C5–N3
N9–C6–N5
N9–C6–N4
C2–N1–C3
C1–N2–C5
C2–N3–C5
C2–N4–C6
C2–N4–H3
C6–N4–H3
C3–N5–C6
C3–N6–C4
C1–N7–C4
O1–S1–O2
N5–C6–N4
125.2(2)
119.1(2)
118.2(2)
C1–N1–C2
C1–N1–C3
O1–S1–O3
116.47(19)
121.6(2)
113.07(11)
111.11(11)
107.11(15)
107.32(15)
106.44(14)
112.25(12)
110.89(14)
111.54(12)
106.68(15)
109.05(14)
106.10(16)
121.89(19) O2–S1–O3
115.9(2)
115.5(2)
121.4(2)
120.8(17)
117.8(17)
118.6(2)
118.0(2)
121.7(2)
O1–S1–C7
O2–S1–C7
O3–S1–C7
O5–S2–O6
O5–S2–O4
O6–S2–O4
O5–S2–C8
O6–S2–C8
1.4503(19) N4–C2–N1
1.458(2) N5–C3–N6
1.4643(18) N5–C3–N1
1.747(3)
1.449(2)
N6–C3–N1
N10–C4–N6
1.4520(18) N10–C4–N7
1.459(2)
1.743(3)
N6–C4–N7
N8–C5–N2
N8–C5–N3
111.42(13) O4–S2–C8
122.7(2)
groups. The interlayer distances are found at 3.3 and 3.5 Å
depending on the presence or absence of methyl groups be-
tween the respective layers (methyl groups slightly increase
the distance).
Figure 1. Molecular structure and hydrogen bonding interactions for Figure 2. Hydrogen bonded strands of melemium ions found in
HC6N7(NH2)3H2C6N7(NH2)3(SO3Me)3·H2O (1). Ellipsoids are drawn HC6N7(NH2)3H2C6N7(NH2)3(SO3Me)3·H2O (1). Ellipsoids are drawn
at 50 % probability level.
at 50 % probability level.
478 www.zaac.wiley-vch.de
© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2010, 476–482

HC6N7(NH2)3H2C6N7(NH2)3(SO3Me)3·H2O and H2C6N7(NH2)3(SO3Me)2·H2O
Figure 3. Layer-like structure of HC6N7(NH2)3H2C6N7(NH2)3
(SO3Me)3·H2O (1). View along b.
Figure 5.
Stacking
pattern
of
melemium
ions
in
H2C6N7(NH2)3(SO3Me)2·H2O (2).
The second salt, H2C6N7(NH2)3(SO3Me)2·H2O (2) crystalli-
2+
zes in the monoclinic space group P21/n. One H2C6N7(NH2)3
ion, two methylsulfonate anions and a crystal water molecule
constitute the asymmetric unit. Taking the molecular structure
of melem and other melemium salts as a reference once again,
the usual structural features found for these compounds are
also observed here. Thus, bond lengths and angles are affected
in the same manner as stated for 1. The melemium ions in 2
are, unlike the findings for lower protonation grades, not
linked to other melemium ions by hydrogen bonding (cf. Fig-
ure 4).
At first glance, projections along the a or b axis might sug-
gest a dominance of hydrogen-bonded layers (cf. Figure 6 and
Figure 7). However, the actual structure is much more compli-
cated, consisting of a complex three-dimensional hydrogen
bonding network. Distinct layer-like structures, found for other
melemium salts, cannot be observed in this case.
Figure 6. Crystal structure of H2C6N7(NH2)3(SO3Me)2·H2O (2). View
along b. Ellipsoids are drawn at 50 % probability level.
Initial hydrogen localization for the title compounds is based
on difference Fourier synthesis (cf. Experimental Section). The
positions found by XRD were very distinct for the reported
melemium methylsulfonate salts. In order to assure the assign-
ment the hydrogen positions at the protonation sites of the hep-
tazine core, were checked for plausibility of hydrogen bonding
interactions and the above-mentioned characteristic effects on
Figure 4. Molecular structure of the melemium ion and hydrogen
bonding interactions for H2C6N7(NH2)3(SO3Me)2·H2O (2). Ellipsoids
are drawn at 50 % probability level.
This corresponds to the situation observed for the bond lengths and angles within the cyameluric nucleus. Find-
2+
H2C6N7(NH2)3 ions found in H2C6N7(NH2)3SO4·2H2O [9]. ings here were in line with expectation. The hydrogen atoms
The molecular structure of the methylsulfonate ions is as ex- of H2O as well as NH2 and CH3 groups were also located
pected. The three-dimensional arrangement is mainly governed accordingly and accepted, as they displayed no remarkable fea-
by hydrogen bonding interactions. The resulting structure com- tures. All observed hydrogen bonding interactions for
prises strand like motifs alternating in an A A' B B' stacking HC6N7(NH2)3H2C6N7(NH2)3(SO3Me)3·H2O (1) and H2C6N7-
pattern (cf. Figure 5).
(NH2)3(SO3Me)2·H2O (2) are summarized in Table 3.
Z. Anorg. Allg. Chem. 2010, 476–482
© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
479

A. Sattler, S. Schönberger, W. Schnick
ARTICLE
similar situation was already discussed for the tautomers of the
dihydrogencyamelurate anion [11].
2+
Scheme 2. Tautomers found for the H2C6N7(NH2)3 ion. The higher
symmetric ion (left) found in H2C6N7(NH2)3SO4·2H2O and in
H2C6N7(NH2)3(SO3Me)2·H2O (2) is of C2v symmetry, whereas the
lower symmetric one in HC6N7(NH2)3H2C6N7(NH2)3(SO3Me)3·H2O
(1) (right) expresses Cs symmetry.
We observed rather short contacts between the S=O groups
of methylsulfonate ions and certain atoms (mostly carbon at-
oms) of the cyameluric nucleus in the title salts. These contacts
range from 2.82 to 2.95 Å for 1 and 2.93 to 2.96 Å for 2.
Although we did not conduct any further investigations con-
cerning this point, we would propose to attribute this finding
primarily to electrostatic interactions of the cyameluric nucleus
with the S=O groups.
The pKb values for melem were reported [12] as pKb1 = 12,
pKb2 = 13 and pKb3 = 16. Methylsulfonic acid is a strong acid
displaying a pKs value of –0.6 [13]. The composition of crys-
talline phases, however, is a poor tool for making reliable state-
ments concerning the basicity of melem, since the effect of
Figure 7. Crystal structure of H2C6N7(NH2)3(SO3Me)2·H2O (2). View
along a. Ellipsoids are drawn at 50 % probability level.
Table 3. Hydrogen bonding interactions (in Å) and angles (in °) for
compounds 1 and 2.
HC6N7(NH2)3H2C6N7(NH2)3(SO3Me)3·H2O (1)
D–H···A
<D–H···A D···A D–H···A
<D–H···A D···A
N9–H1···N17 174.41
N9–H2···O3 173.40
N6–H3···O4 165.54
N10–H4···O6 178.89
N10–H5···O1 165.87
N8–H6···N12 169.04
N8–H6···N13 135.83
N8–H7···O8 166.91
N4–H8···N16 174.50
2.991 N20–H9···O8
2.910 N20–H10···N3
2.674 N18–H11···O2
2.844 N18–H12···N2
2.831 N19–H13···O7
133.17
171.00
163.48
171.90
167.07
2.762
2.927
2.849
3.031
2.769
2.860
2.659
2.952
2.803
3.067 N19–H14···O10 161.83
3.396 N14–H15···O5
2.924 O10–H25···O4
2.875 O10–H26···O3
166.14
166.95
179.06
H2C6N7(NH2)3(SO3Me)2·H2O (2)
N8–H1···O1 164.46
N8–H2···O7 160.19
N4–H3···O4 172.48
N9–H4···O6 158.95
N9–H5···O5 166.80
N10–H6···O2 114.17
2.982 N10–H6···O1
159.72
173.36
164.51
169.22
163.25
131.56
3.397
2.810
2.763
2.867
3.224
3.128
2.794 N10–H7···O2
2.640 N7–H8···O3
2.933 O7–H15···O5
2.973 O7–H16···N6
3.018 O7–H16···N5
2+
The H2C6N7(NH2)3 ion found in HC6N7(NH2)3H2C6N7-
(NH2)3(SO3Me)3·H2O (1) exhibits different protonation posi-
tions than the ions found in H2C6N7(NH2)3(SO3Me)2·H2O (2)
and H2C6N7(NH2)3SO4·2H2O [9]. The two different tautomers
of the diprotonated melemium ion found in melemium salts
show different symmetry (cf. Scheme 2). The tautomer real-
ized in H2C6N7(NH2)3SO4·2H2O [9] and in H2C6N7(NH2)3
(SO3Me)2·H2O (2) has C2v symmetry (for the idealized mole-
cule). The other tautomer found in HC6N7(NH2)3-
H2C6N7(NH2)3(SO3Me)3·H2O (1) displays idealized Cs sym-
metry. Energetic differences between the two tautomeric forms
of the cation seem to be low, allowing other effects like hydro-
Figure 8. Comparison of measured and calculated XRD patterns for
the melemium methylsulfonates (1) and (2). Side-phase reflections are
gen bonding to determine the formation of one tautomer. A marked with *.
480 www.zaac.wiley-vch.de
© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2010, 476–482

HC6N7(NH2)3H2C6N7(NH2)3(SO3Me)3·H2O and H2C6N7(NH2)3(SO3Me)2·H2O
fraction patterns (XRPD) were recorded with a Huber G670 Guinier
solubility also has to be taken into account. Double and single
protonation of melem occurs in compound (2). Our results are
thus well in line with the finding that pKb1 and pKb2 for melem
are not extremely different.
Imaging Plate. Measurements were conducted using Cu-Kα1 radiation
at room temperature. Theoretical powder diffraction patterns were sim-
ulated from single-crystal data using the Win XPOW software package
[16].
Phase pure samples of H2C6N7(NH2)3(SO3Me)2·H2O (2)
were readily available as can be seen by comparison of meas-
ured powder XRD data with XRD pattern simulated from sin-
gle-crystal data (cf. Figure 8). For lower concentrations of
methylsulfonic acid, however, the existence ranges of a multi-
tude of phases overlap. A pure bulk sample of the methylsulfo-
nate salt HC6N7(NH2)3H2C6N7(NH2)3(SO3Me)3·H2O (1) could
not be prepared. Impurities either are 2 (cf. Figure 8) or other
salts presumably expressing lower overall protonation than 1.
These species could, however not be structurally characterized
so far.
As reported in our prior contributions, melem was prepared
by heating melamine in sealed glass ampoules [7]. In order to
allow the synthesis of larger quantities of melem, we devel-
oped an alternative synthesis, based on synthetic protocols
used for the polymer melon and observations for the synthesis
of melem in open systems [12, 14]. Melamine is heated in a
loosely covered crucible. In contrast to the synthesis of melon,
pure melem is rarely ever yielded this way. Additional purifi-
cation is possible by boiling in water (or dilute acetic acid) to
remove unreacted melamine and yielding melem as a hydrate.
We already identified this compound, but were unfortunately
unable to solve its crystal structure yet [15]. We might add that
the synthesis of suitable melem samples in this way requires
some adjustments of synthetic conditions, first of all furnace
temperature, size and form of the crucible etc.
Single-crystal XRD
The diffraction data of the melemium salts was measured with a No-
nius Kappa-CCD diffractometer. The measurements were conducted at
a temperature of 200 K. The diffraction intensities were scaled using
the SCALEPACK software package [17]. No additional absorption
correction was applied. The crystal structure was solved by direct
methods (SHELXS-97) and refined against F2 on all data by full-ma-
trix-least-squares (SHELXL-97) [18]. Hydrogen atoms were located
by difference Fourier synthesis and refined with isotropic thermal dis-
placement parameters. Restraints were applied wherever necessary.
Crystallographic data is summarized in Table 1. Selected distances and
angles are presented in Table 2. Further details on the crystal structure
can be obtained free of charge on application to Cambridge Crystallo-
graphic Data Centre (CCDC-738615 (HC6N7(NH2)3H2C6N7(NH2)3-
(SO3Me)3·H2O) and CCDC-738616 (H2C6N7(NH2)3(SO3Me)3·H2O) 12
Union Road, Cambridge CB2 1EZ, UK (Fax: +44-1223-336-033; E-
Mail: fileserv@ccdc.cam.ac.uk)
Melem: Melem was synthesized by heating melamine (Fluka, purum)
in a porcelain crucible covered with a lid. A temperature of 425 °C
was maintained overnight. Subsequently, the mixture was suspended
in water and boiled under reflux for several hours to remove impurities.
The resulting product was dried at room temperature. It is actually a
hydrate of melem, analysis of which suggests the formula
C6N7(NH2)3·1.5H2O.
HC6N7(NH2)3H2C6N7(NH2)3(SO3Me)3·H2O (1): Melem hydrate
(400 mg, 1.63 mmol) was suspended in a solution of methylsulfonic
acid (10 mL) in water (35 mL). Active carbon was added to the sus-
pension. The mixture was heated under reflux for a short time and
passed through a sintered glass filter under suction. The resulting solu-
tion was cooled to 4 °C for 12 h. Afterwards, the colorless product
was removed by suction (298 mg, 49 %). The product usually con-
tained small amounts of (2). FT-IR (reflection, 25 °C): ν = 3443 s,
3237 s br, 2600 sh br, 1611 m, 1510 w, 1467 m, 1204 w, 1320 w,
1185 m, 1148 m, 1042 m, 962 w, 779 m cm–1.
Conclusions
Melemium methylsulfonates were synthesized and structur-
ally characterized. Knowledge of these compounds and their
structure allows a better understanding of the structural fea-
tures possible for melemium salts in general. The obtained data
suggest the existence of differently protonated melemium ions
in one salt to occur quite often. Non-protonated melem was
+
found
along
with
HC6N7(NH2)3
ions
in
HC6N7(NH2)3ClO4·C6N7(NH2)3 [8] whereas the newly discov-
Colorless needle shaped crystals of (2) could best be collected after
slow cooling/evaporation of a hot solution containing melem hydrate
(150 mg), methylsulfonic acid (10 mL) and water (30 mL).
ered salt HC6N7(NH2)3H2C6N7(NH2)3(SO3Me)3·H2O (1) incor-
+
2+
porates both HC6N7(NH2)3 and H2C6N7(NH2)3 ions. By re-
vealing the existence of two different tautomers of the
2+
H2C6N7(NH2)3 ion we showed that there is significant struc- H2C6N7(NH2)3(SO3Me)2·H2O (2): Melem hydrate (900 mg,
3.67 mmol) was suspended in a solution of methylsulfonic acid
(20 mL) in water (30 mL). Active carbon was added to the suspension.
The mixture was heated under reflux for a short time and passed
through a sintered glass filter under suction. The resulting solution was
cooled to 4 °C for 12 h. Afterwards, the colorless product was removed
by suction (278 mg, 18 %). FT-IR (reflection, 25 °C): ν = 3558 m,
3302 m, 3063 s br, 2703 m br, 1717 w, 1650 s, 1619 s, 1541 m,
1494 m, 1437 m, 1410 m, 1342 w, 1312 w, 1150 s, 1127 s, 1040 s,
983 w, 964 w, 779 m cm–1.
tural variability as the tautomerism of this ion can possibly be
directed by relatively weak non-covalent interactions. We also
found hints at a possible interaction between the cyameluric
nucleus and the S=O moieties of the methylsulfonate ion.
Experimental Section
General Methods
FT-IR spectra were recorded with a Spektrum BX II FT-IR spectrome- Colorless needle shaped crystals of (2) could best be collected after
ter (Perkin–Elmer) equipped with a DuraSampler diamond-ATR. The slow cooling/evaporation of a hot solution containing melem hydrate
measurements were conducted at room temperature. X-ray powder dif- (150 mg), methylsulfonic acid (20 mL) and water (30 mL).
Z. Anorg. Allg. Chem. 2010, 476–482
© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
481

A. Sattler, S. Schönberger, W. Schnick
ARTICLE
[7] a) B. Jürgens, E. Irran, J. Senker, P. Kroll, H. Müller, W. Schnick,
J. Am. Chem. Soc. 2003, 125, 10288; b) A. Sattler, W. Schnick,
Z. Anorg. Allg. Chem. 2006, 632, 238.
Acknowledgement
The authors would like to thank Dr. P. Mayer, Department Chemie und
Biochemie, LMU München, for collecting the X-ray diffraction data.
Financial support by the Deutsche Forschungsgemeinschaft (DFG)
(project SCHN 377/12) as well as the Fonds der Chemischen Industrie
(FCI) is gratefully acknowledged.
[8] A. Sattler, W. Schnick, Z. Anorg. Allg. Chem. 2008, 634, 457.
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[10] a) A. Sattler, W. Schnick, Z. Anorg. Allg. Chem. 2006, 632, 1518;
b) E. Horvath-Bordon, E. Kroke, I. Svoboda, H. Fueß, R. Riedel,
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Received: September 9, 2009
Published Online: February 11, 2010
482
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© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2010, 476–482