Methylsemicarbazide as a Ligand in Late 3d Transition Metal Complexes

Article abstract of DOI:10.1002/chem.201705030

Most ignition and initiation systems nowadays still contain poisonous chemicals such as lead styphnate and lead azide but also chromates and other compounds of high concern. Therefore, methylsemicarbazide (1, MSC), which can be prepared in a one-step reaction and in an extraordinary high yield of 95 %, has been evaluated as ligand in energetic coordination compounds. For the first time 25 new transition metal complexes (Mn²⁺, Ni²⁺, Co²⁺, Cu²⁺, and Zn²⁺) using methylsemicarbazide (1) as the ligand were prepared and comprehensively analyzed by, for example, XRD, IR, EA, UV/Vis and DSC/DTA/TGA. Many show a strong energetic character, which can be tuned by using different anions such as Cl^?, SO₄^2?, NO₃^?, ClO₄^?, picrate or styphnate. Selected compounds were additionally evaluated as lead-free primary explosives in initiation tests (nitropenta filled detonators) and in laser ignition systems. Especially compound 7 showed very promising results during these tests and could be a potential candidate for future applications.

Full text of DOI:10.1002/chem.201705030

A Journal of
Accepted Article
Title: Methylsemicarbazide as Ligand in Late 3d Transition Metal
Complexes
Authors: Joerg Stierstorfer and Norbert Szimhardt
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Chem. Eur. J. 10.1002/chem.201705030
Link to VoR: http://dx.doi.org/10.1002/chem.201705030
Supported by

Chemistry - A European Journal
10.1002/chem.201705030
FULL PAPER
Methylsemicarbazide as Ligand in Late 3d Transition Metal
Complexes
Norbert Szimhardt and Jörg Stierstorfer*
Abstract: Most ignition and initiation systems nowadays still contain
poisonous chemicals such as lead styphnate and lead azide but also
chromates and other compounds of high concern. Therefore;
methylsemicarbazide (1, MSC), which can be prepared in a one-step
reaction and an extraordinary high yield of 95 %, has been evaluated
as ligand in energetic coordination compounds. For the first time 25
(LA) or silver azide are used. Initiation compositions are used e.g.
in millions of commercial detonators for the mining industry but
also in nearly all military warheads.
2+
2+
2+
2+
The use of late first row transition metals (Mn , Fe , Co , Ni ,
2
+
2+
Cu , Zn ) is a good compromise of (i) availability (ii) price (iii)
2
+
2+
2+
2+
density (iv) toxicity (only for Mn , Fe , Cu and Zn ) and (v) the
coordination ability to nitrogen-rich ligands because of low
oxophilicity.
2+
2+
2+
2+
2+
new transition metal complexes (Mn , Ni , Co , Cu , and Zn )
using methylsemicarbazide (1) as the ligand were prepared and
comprehensively analyzed by e.g. XRD, IR, EA, UV/Vis and
DSC/DTA/TGA. Many show a strong energetic character, which can
-
2-
-
-
4 3 4
be tuned by using different anions such as Cl , SO , NO , ClO ,
picrate or styphnate. Selected compounds were additionally
evaluated as lead-free primary explosives in initiation tests (nitropenta
filled detonators) and in laser ignition systems. Especially compound
7
showed very promising results during these tests and could be a
Chart 1
Molecular structures of lead styphnate (LS), mercury fulminate
potential candidate for future applications.
(
MF), lead azide (LA), diazoniumdinitrophenolate (DDNP) and tetrazene.
Useful ECCs contain (a) a metal cation, (b) nitrogen-rich ligands
Introduction
and (c) coordinating or non-coordinating anions (either oxygen-
rich such as NO -
, ClO -
, N(NO
)
-
or nitrogen-rich such as N -
,
The investigation of energetic coordination compounds (ECC) is
one of the most useful strategies in discovering new
environmentally benign materials for ignition and initiation
3
4
2
2
3
tetrazolates or triazolates). Various combinations have been
described in the literature.[
10]
Highly energetic and sensitive
mixtures.[
1-4]
complexes are formed by the combination of hydrazine
derivatives (hydrazine, monomethylhydrazine, dimethylhydrazine,
semicarbazide (SC), carbohydrazide (CHZ) but also N-amino-
azoles) as the ligand with nitrate or perchlorate transition metal
salts.[11,12] One of the most prominent ECCs of this type is NHN
Ignition implies the release and transfer of energy in
the form of heat, flame or subsonic shock waves. This is required
for many different applications such as ammunition or in gas
generators (e.g. airbags, oxygen candles). Igniters mostly contain
a complex mixture of an inorganic pyrotechnic mixture or thermite
as well as a weak primary explosive (often lead styphnate (LS) or
diazodinitrophenol (DDNP)) and a sensitizer (often tetrazene).[5]
Owing to their high toxicity and the related pollution of the
environment, research into possible replacements is strongly
needed.[6-8] Various requirements have to be fulfilled when
synthesizing suitable candidates. The compound should not only
be non-toxic and environmentally friendly but also be easily
produced. Depending on the application, the mixtures can be
ignited by impact, friction, light, electric impulses or heat. In
(
nickel hydrazine nitrate) which has also successfully been tested
in detonators but contains very toxic nickel(II).[
13]
Carbohydrazide (CHZ), which belongs to the group of carbazides
was first synthesized 1894 by Curtius and Heidenreich who
obtained the compound by the reaction of diethyl carbonate with
hydrazine.[14] Since then, many carbazide-based compounds
have been reported (prominent examples in Chart 2a) with
manifold uses for example as precursor of drugs[15] and
herbicides[16]. Also various coordination compounds were
synthesized using carbazide ligands (Chart 2b) which are
proposed to be interesting energetic materials[ . Especially some
of them with possible application as primary explosives[18] and
partly also ignitable by laser irradiation (Chart 2b).[19]
contrast, initiation mixtures produce hypersonic shock waves,
which are able to set of secondary explosives. Until the early 20th
century, mercury fulminate (MF), first applied by Alfred Nobel, was
the initiator of choice (Chart 1).[9] Nowadays, usually lead azide
17]
[
a]
Dr. Jörg Stierstorfer and Norbert Szimhardt, Department of
Chemistry, Ludwig Maximilian University of Munich, Butenandtstr. 5-
13, D-81377 Munich, Germany, Fax: +49-89-2180-77007, E-mail:
jstch@cup.uni-muenchen.de, Homepage: http://www.hedm.cup.uni-
muenchen.de
Supporting information (SI) for this article is available on the WWW
under http://www.eurjic.org/ or from the author. SI contains: X-ray
Diffraction; IR spectroscopy of 11, 12, 15, 18, 20 and 23; DTA plots
of 6–8, 11, 12, 15 and 18; UV-Vis spectra of 6–8, Experimental part
and general methods.
Chart 2
a.) Overview of selected carbazides; b.) energetic coordination
compounds (ECCs) with different carbazide ligands and transition metals.[20]
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201705030
FULL PAPER
Some of the described CHZ and SC compounds are too sensitive
for any potential use. In order to decrease the sensitivity we
synthesized methylsemicarbazide (1, MSC) as a new ligand for
ECCs. MSC has a higher carbon content and has been shown to
be an outstanding ligand for the preparation of new energetic
material complexes with tunable sensitivities and promising
properties.
blocking of
a
coordination site. In this context
methylsemicarbazidium perchlorate
Another observation was the
methylsemicarbazide ( ) in too strongly acidic media, which
(
2
)
was observed.
hydrolysis of
1
is detected by decomposition products like ammonium
perchlorate. Also, in case of the cobalt(II) chloride
complexes, two different species have been observed when
using varying concentrations of acid. These are the blue
water-free compound (16) from concentrated hydrochloric
acid and a red diaqua complex (17) from diluted 2 M acid.
The synthesis of the zinc(II) perchlorate complexes 11 and
Results and Discussion
Synthesis
1
2 strongly depends on the stoichiometry of added ligand
The title compound methylsemicarbazide (1) can be prepared
mainly in two routes starting from different reactants. One way is
the reaction of sodium cyanate with methylhydrazine in
and yields two different coordination compounds with two or
three ligands coordinating to the zinc(II) metal centre,
respectively. The corresponding metal(II) salts for the
hydrochloric acid at 0 °C overnight followed by chromatographic
purification.[
21]
Another route is the high-yielding reaction of
available trimethylsilylisocyanate with
complexes 19–28 were synthesized in situ by reaction of
commercially
metal(II) carbonates and picric/styphnic acid at 70 °C in
water. The colored reaction mixtures were left for
crystallization until a solid appeared. All products were
filtered off, washed with cold ethanol to remove unreacted
starting materials when necessary and dried over night in air.
Most of the compounds were obtained in yields of 28–97 %
directly from the mother liquor in form of suitable crystals for
X-ray determination within hours or days (details are
conducted in the experimental part in the SI). Only
complexes 20 and 23 precipitated as amorphous powders
after the addition of the ligand and all recrystallization
methylhydrazine carried out in dry THF (Scheme 1) at a
temperature of 0 °C.[22] Due to the very hygroscopic character of
(
trimethylsilyl)isocyanate the reaction mixture was held constant
under nitrogen atmosphere. Addition of methanol and heating to
0 °C for 5 hours led to the isolation of 1 with a high yield of 95 %.
4
The acid-base reaction of 1 with picric acid in boiling water
resulted in X-ray suitable crystals of the protonated picrate salt 3.
attempts failed. A complex formula based on elemental
II
analysis of [M (MSC)
3
](PA)
2
is proposed for compounds 20
Scheme 1 Applied synthesis of methylsemicarbazide (1) and its protonated
picrate salt (3).
and 23. The majority of the coordination compounds were
isolated water-free (without crystal water molecules or aqua
ligands) which leads to a higher performance and thermal
stability of the compounds. All compounds, except
could be synthesized and characterized in larger quantities.
For the perchlorate salt and the cobalt(II) chlorido complex
, unfortunately, only a few single crystals could be picked
2 and 16,
Methylsemicarbazide (1) bears no acidic proton, which
allows the inclusion of the neutral molecule to form complex
cations or neutral metal coordination compounds with
endothermic (e.g azides) or oxidizing anions like nitrates,
perchlorates, picrates (PA) or trinitroresorcinates (HTNR).
The selective integration of these anions results in energetic
coordination compounds with adjustable sensitivity and
performance.
2
1
6
between unreacted starting material, decomposition
products and powder bulk material with unknown
constitution. Therefore; only the crystal structures of
2 and
1
6
could be determined which are shown in the SI. The
attempted syntheses of iron(II) and (III) as well as Ag(I)
complexes were unsuccessful.
The coordination compounds
simple reaction of transition metal(II) salts with
corresponding equivalents of methylsemicarbazide ( ) as
4–28 were prepared by the
1
Crystal structures
ligand in water at room or elevated temperatures (Table 1).
Due to the good solubility of the resulting complexes only
small quantities of solvents were used. In some cases
specific amounts of co-solvents like ethanol or acid were
added to the reaction mixture in order to get better
crystallization behavior, improved yields or higher purities.
The concentration of acid used as co-solvent is significant for
the formation of the complexes. Excessive amounts of acid,
especially for the perchlorate complexes can cause
protonation of the methyl-hydrazine moiety and associated
The structures of all complexes (except 20 and 23) were
determined by low temperature crystal X-ray diffraction. Details
on the crystal structures of compounds 5, 6, 9, 15, 19, 21, 24, 25,
27 are given in the SI together with the measurement and
refinement data. Single crystals of the zinc(II), manganese(II) and
nickel(II) perchlorate complexes 11, 12, 15 and 18 were
measured to give an indication of the most likely composition. An
adequate refinement of the data set was not possible because of
the strongly disordered moieties, however elemental analysis
confirmed its preliminary observed structures. The coordination
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201705030
FULL PAPER
compounds 11/15 and 20/23 exhibit the same coordination
environment and their infrared absorptions were therefore
compared by infrared spectroscopy (Figure S11/12) The crystal
structures were deposited to the CSD database[23] and can be
obtained free of charge with the CCDC nos. 1534424 (1),
1574511 (21), 1574509 (22), 1534442 (24), 1534434 (25),
1534437 (26), 1534420 (27), 1534423 (28).
Methylsemicarbazide (1) crystallizes in the monoclinic space
group P2
1
/n with four formula units per unit cell and a calculated
−
3
density of 1.288 g cm at 173 K. Selected bond distances and
1534443 (2), 1574510 (3), 1534422 (4), 1534425 (5), 1534426 (6), angles of the molecule are given in Figure 1. The C–O
1
534428 (7), 1534427 (8), 1580445 (9), 1534421 (10), 1534435
(1.249(2) Å), C1–N1 (1.346(2) Å) and N–N (1.414(2) Å) bonds
are comparable to values found in carbohydrazide and urea.
Lengthening of the C–O double bond comes along with shorter
(
13), 1534440 (14), 1534429 (16), 1534441 (17), 1534429 (19),
Table 1.
Synthesis of transition metal complexes 4–28 with methylsemicarbazide.
C–N and N–N single bond distances and confirms the conjugation
of these atoms.[24,25] In addition, stabilization of the molecular
structure is generated through strong intermolecular hydrogen
bonds formed between the carbonyl function and the neighboring
amino groups (N1–H1BO1 0.93(2), 2.02(2), 2.9428(19) Å,
172(17)°; N3–H3AO1 0.947(18), 2.052(18), 2.9920(19) Å,
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201705030
FULL PAPER
1
71.7(15)°, N3–H3BO1 0.91(2), 2.25(2), 3.148(2) Å,
transition metal. A reorientation of the MSC molecule, already
described in the salts 2 and 3, can be observed in the complexes
(Chart 3). All complexes show a (more or less) octahedral
coordination sphere, which can be explained by the low steric
hindrance of the ligand.
172.5(16)°). These observations are consistent with the almost
planar geometry of the molecule (< (N3–N2–C1–N1) = −5.8(2)°;
(C2–N2–C1–O1) = 6.9(2)°).
<
Figure 1
Molecular structure of methylsemicarbazide (1). Thermal
ellipsoids of non-hydrogen atoms in all structures are set to the 50% probability
level. Selected bond lengths (Å): O1–C1 1.249(2), N1–C1 1.346(2), N2–N3
1
.414(2), N2–C1 1.349(2), N2–C2 1.445(2); selected bond angles (°): N3–N2–
C1 117.81(2), N1–C1–N2 117.26(2), N3–N2–C2 119.20(2), O1–C1–N1
21.40(2), C1–N2–C2 122.26(2), O1–C1–N2 121.28(2); selected torsion angles
°): N3–N2–C1–N1 −5.8(2), C2–N2–C1–O1 6.9(2).
1
(
Chart 3
Reorientation of the MSC molecule after coordination or salt
formation and depiction of the calculated (B3LYP / 6-31G(d,p)) electrostatic
potentials (3D isosurface of electron density) of 1 and its coordinated form.
As described above, parent compound 1 can be protonated under
certain acidic conditions. Protonation takes place on the NH
2
The copper(II) sulfate complex 4 crystallizes in the form of blue
group of the methylhydrazine functional group and causes a
reorientation of half of the molecule. The salts show significantly
higher densities in comparison to the neutral molecule (2: 1.734
g cm−3 (123 K); 3: 1.750 g cm−3 (143 K) vs. 1.288 g cm−3 (173 K)
for 1). The perchlorate compound 2 crystallizes in the monoclinic
rods in the monoclinic space group P2
1
/c with four formula units
−3
per unit cell and a calculated density of 1.857 g cm at 123 K.
The molecular unit shown in Figure 3 consists of a octahedrally
surrounded copper(II) center with two aqua ligands along the
Jahn-Teller distorted axial axis (Cu1–O8 = 2.495(3) Å) and two
bidentaly connected MSC ligands in a plane (Cu1–O5 =
1
space group P2 /c with sixteen formula units per unit cell. On the
other hand the picrate salt 3 crystallizes in the triclinic space group
P−1 with two molecules in the unit cell. Structural parameters and
the molecular structures of both salts are shown in Figure 2. Salt
formation had no significant influence on the bond distances but
rather on the planarity of the methysemicarbazinium cation with a
torsion angle of < (C2–N2–C1–N3) = −30.1(6)° in 3.
1
<
.934(3) Å, Cu1–N2 = 1.977(4) Å, < (O5—Cu1—N2) = 83.28(1)°,
(O5—Cu1—N2) = 96.73(12)°). All complexes described here
i
show higher densities than the non-coordinating MSC molecule
itself.
Figure 3
2 2 2 4
Molecular unit of [Cu(H O) (MSC) ]SO (4). Selected bond
Figure 2
Molecular moieties of the MSC salts 2 (left) and 3 (right). Selected
lengths (Å): Cu1–O5 1.934(3), Cu1–O8 2.495(3), Cu1–N2 1.977(4), S1–O1
bond lengths (Å): 2: N1–C1 1.325(4), N2–N3 1.430(3), N2–C2 1.464(4), N2–C1
1
8
9
.467(3); selected bond angles (°): O5–Cu1–O8 88.03(11), O5–Cu1–N2
1
1
.386(4), C1–O5 1.238(4) Cl1–O1 1.438(2); 3: N1–N2 1.446(5), N2–C1
.405(5), N2–C2 1.457(6), N3–C1 1.322(6), C1–O1 1.228(6); selected bond
3.28(12), O8–Cu1–N2 90.26(12), O5–Cu1–O8i 91.97(11), O5–Cu1–N2i
6.73(12), O1–S1–O2 109.77(16). Symmetry code: (i) −x, −y, −z.
angles (°): 2: N3–N2–C1 111.3(2), N3–N2–C2 112.9(2), C1–N2–C2 124.2(2),
O1–C1–N1 125.1(3), O1–C1–N2 118.0(3); 3: N1–N2–C1 110.5(3), N1–N2–C2
112.9(3), C1–N2–C2 122.9(2), O1–C1–N2 119.7(4), O1–C1–N3 124.3(4);
selected torsion angle (°): 3: C2–N2–C1–N3 −30.1(6).
Complexes 5 (copper(II), green block, Figure S1), 9 (zinc(II),
colorless block, Figure S2) and 16 (cobalt(II), blue block) with
coordinating chlorido ligands crystallize in the monoclinic space
1
The bond distances and most angles of the coordinating MSC
ligands in the examined coordination compounds are similar to
the non-coordinated ligand 1. The carbazide ligand is therefore
not investigated or discussed in more detail in any of the
group P2 /c with two formula units per unit cell showing similar
densities (5: 1.838 g cm at 123 K; 9: 1.799 g cm−3 and 16:
−
3
−
3
1.791 g cm
coordinating chlorido ligands and manganese(II) transition metal
center (colorless block, Figure S3) also crystallizes in
monoclinic space group (P2 /n) with four formula units per unit
at 123 K). The remaining complex 13 with
compounds
crystal
structures
outlined
below.
a
Methylsemicarbazide (1) is bidentate and coordinates through the
carbonyl oxygen and amino-methylhydrazine nitrogen atom to the
1
−
3
cell and exhibits a calculated density of 1.765 g cm at 173 K.
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201705030
FULL PAPER
Every metal(II) center, as illustrated for compound 16 (Figure 4),
shows an octahedral surrounding with two chloridos and two
methylsemicarbazides. On the contrary, the cobalt(II) chloride
complex 17 is composed of two aqua ligands and two MSC
ligands. The chlorides act only as counter-anions (Figure 4). It
From an energetic perspective very interesting, the copper(II)
perchlorate complex 7 is octahedrally coordinated by two
perchlorato ligands in Jahn-Teller distorted axial positions and by
two chelating MSC ligands in a plane (Figure 6). It crystallizes in
1
the form of blue blocks in the monoclinic space group P2 /c with
crystallizes in the monoclinic space group P2
units per unit cell and has a calculated density of 1.735 g cm at
23 K.
1
/n with four formula
two formula units per unit cell and the highest calculated density
of 2.055 g cm−3 at 123 K of all complexes described here.
−
3
1
Figure 4
Complex units of compound 16 (left) and 17 (right). Selected
coordination distances (Å): 16: Co–Cl1 2.4935(6), Co1–O1 2.0396(16), Co1–
N3 2.140(2); 17: Co1–O2 2.1016(17), Co1–N3 2.138(2), Co1–O3 2.0505(16);
selected bond angles (°): 16: Cl1–Co–O1 88.48(5), Cl1–Co–N3 91.22(7), Cl1–
Co–O1i 91.53(5), Cl1–Co–N3 88.78(7), O1–Co–N3 78.46(8), O1–Co–N3
i
i
Figure 6
7). Selected bond lengths (Å): Cu1–O1 2.4730(16), Cu1–O5 1.9257(15), Cu1–
N3 1.994(2), Cl1–O1 1.4472(16); selected bond angles (°): O1–Cu1–O5
4 2 2
Complex unit of the highly energetic complex [Cu(ClO ) (MSC) ]
1
7
1
01.54(8); 17: O2–Co1–O1 91.09(2), O2–Co1–N3 88.67(2), O1–Co1–N3
8.06(2), N3–Co1–O1 101.94(2). Symmetry codes: 16: (i) 1−x, −y, 1−z; 17: (i)
−x, 1−y, 1−z.
(
i
i
9
1.41(6), O1–Cu1–N3 90.07(7), O1–Cu1–O5 88.59(6), O1–Cu1–N3 89.93(7),
i
O5–Cu1–N3 82.83(8), O5–Cu1–N3 97.17(8), O1–Cl1–O2 108.57(11).
Symmetry code: (i) 2−x, −y, 1−z.
The copper(II) and manganese(II) nitrato complexes 6/14
crystallize isotypically in the triclinic space group P−1 with one
−
3
formula unit per unit cell (6: blue block, 1.873 g cm ; 14: colorless
Copper(II) azido complex 8 crystallizes in the form of green
needles in the monoclinic space group P2 /c with four formula
1
block, 1.752 g cm−3 at 173 K). The colorless zinc(II) nitrato
compound 10 crystallizes in the monoclinic space group P2
two formula units per unit cell and a calculated density of
1
with
units per unit cell and a calculated density of 2.016 g cm−3 at
123 K. Every copper(II) center is hexa-coordinated by one
chelating MSC molecule and four bridging azido ligands forming
polymeric chains. It is the only octahedral complex with just one
methylsemicarbazide ligand coordinating to the metal(II) center.
−
3
1.860 g cm (123 K). Each metal(II) cation is bonded to two
nitrato ligands in axial positions and two MSC ligands in equatorial
9
positions. As expected, the d -copper(II) center shows Jahn-
9
Teller distortion (elongation in axial direction). Their molecular
motifs are illustrated in Figure 5 and S4.
Due to the d -induced Jahn-Teller distortion, elongation along the
axial sites can be observed, which are occupied by azido ligands
ii
i
(
Cu1–N6 = 2.636(3) Å, Cu1–N9 = 2.479(2) Å). The coordination
environment of the copper(II) cation is depicted in Figure 7a and
shows the small deviation of the ideal coordination sphere caused
by the fixed structure of the azidos and the MSC ligand (< (O1—
ii
Cu1—N3) = 81.52(7)°, < (N3—Cu1—N6 ) = 78.03(10)°). Various
coordination and bridging modes of the azido ligands (1,1; 1,3;
,1,3; 1,1,1 etc.) are possible and known in literature.[ The azido
26]
1
ligand N4—N5—N6 connects two copper(II) centers through cis
,3-coordination while trans 1,3-coordination can be observed for
1
the second azido equivalent N7—N8—N9 (Figure 7b). This end-
on binding situation causes similar bond lengths and almost linear
bond angles within the azido groups (N4–N5 = 1.204(3) Å, N5–
N6 = 1.162(3) Å, N7–N8 = 1.195(3) Å, N8–N9 = 1.160(4) Å, <
Figure 5
Molecular units of compounds 10 (left) and 14 (right). Selected
coordination distances (Å): 10: Zn1–O1 2.061(6), Zn1–O2 2.046(6), Zn1–O3
2.145(9), Zn1–O6 2.351(9), Zn1–N1 2.073(10), Zn1–N4 2.092(9); 14: Mn1–O1
2.2176(17), Mn1–N4 2.268(2), Mn1–O4 2.1392(15); selected bond angles (°):
10: O1–Zn1–O2 169.2(4), O1–Zn1–O3 88.7(3), O1–Zn1–O6 85.8(3), O1–Zn1–
(
N4—N5—N6) = 176.4(3)°, < (N7—N8—N9) = 179.6(3)°).
N1 78.9(4), O1–Zn1–N4 100.5(3), O2–Zn1–O3 102.0(4), O2–Zn1–O6 83.5(4),
O2–Zn1–N1 99.5(4), O2–Zn1–N4 80.3(4), O3–Zn1–O6 172.5(3), O3–Zn1–N1
87.9(4), O3–Zn1–N4 97.1(3), O6–Zn1–N1 86.1(4), O6–Zn1–N4 89.0(3), N1–
Zn1–N4 175.0(4); 14: O1–Mn1–O4 89.53(5), O1–Mn1–N4 83.80(7), O1–Mn1–
O4i 90.47(5), O1–Mn1–N4 96.20(7), O4–Mn1–N4 73.24(6), O4–Mn1–N4
i
i
106.76(6). Symmetry code: 14: (i) 2−x, −y, 2−z.
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201705030
FULL PAPER
metals(II) in compounds 24/25 and 27/28, which crystallize
isotypically in the triclinic space group P−1 with one formula unit
per unit cell and analogous cell parameters. Their densities
2
+
−3
2+
increase in the row of Ni (1.844 g cm ; 173 K) < Co
−
3
2+
−3
2+
(
(
1.852 g cm ; 123 K) < Zn (1.866 g cm , 123 K) < Cu
−
3
1.880 g cm ; 173 K). The molecular unit of the complexes
illustrated in Figure 9 and in the SI are built up by two aqua ligands,
two MSC ligands and two non-coordinating styphnates. The
space group P−1 could also be determined for the water-free
manganese(II) picrate complex 26 (1.892 g cm-3 at 123 K), which
shows a different molecular composition with no aqua ligands, but
two coordinating styphnate ligands instead (Figure 9). A similar
situation that was found for the picrates with distortion along the
MSC bond angle can also be observed for the styphnate
coordination compounds. Each copper(II) complex in 19 and 24
show Jahn-Teller distortion with longer axial bond distances.
Figure 7
a.) Depiction of the octahedral coordination environment of the
copper(II) cation in 8. Selected bond lengths (Å): Cu1–O1 1.957(2), Cu1–N3
.012(3), Cu1–N4 1.963(3), Cu1–N7 1.988(2), Cu1–N6ii 2.636(3), Cu1–N9
.479(2), N4–N5 1.204(3), N5–N6 1.162(3), N7–N8 1.195(3), N8–N9 1.160(4);
i
2
2
selected bond angles (°): O1–Cu1–N3 81.52(9), O1–Cu1–N4 179.24(9), O1–
Cu1–N7 88.72(9), O1–Cu1–N6ii 85.14(9), O1–Cu1–N9 86.59(9), N3–Cu1–N4
i
ii
i
9
9
9
1
2
9.15(10), N3–Cu1–N7 169.26(10), N3–Cu1–N6 78.03(10), N3–Cu1–N9
ii
i
2.01(10), N4–Cu1–N7 90.58(10), N4–Cu1–N6 94.63(11), N4–Cu1–N9
ii
i
ii
ii
3.75(11), N6 –Cu1–N7 96.77(9), N7–Cu1–N9 91.88(9), N6 –Cu1–N9
67.88(8), N4–N5–N6 176.4(3), N7–N8–N9 179.6(3). Symmetry codes: (i)
.5−x, −0.5+y, 0.5−z; (ii) 1.5−x, 0.5+y, 0.5−z; b.) Observed coordination modes
of the azido ligand in 8.
Figure 9
Complex units of compounds 26 (left) and 28 (right). Selected
The water-free copper(II) 19 (green block), manganese(II) 21
coordination distances (Å): 26: Mn1–O1 2.1426(15), Mn1–O2 2.1949(15), Mn1–
N3 2.266(2); 28: Ni1–N3 2.060(3), Ni1–O1 1.9923(15), Ni1–O2 2.143(2);
selected bond angles (°): 26: O1–Mn1–O2 90.51(6), O1–Mn1–N3 73.19(7), O1–
(
yellow block) and cobalt(II) 22 (orange block) picrate complexes
crystallize isotypically to each other in the triclinic space group
P−1 with one formula unit per unit cell exhibiting very similar
calculated densities (19: 1.885 g cm−3 at 123 K; 21: 1.825 g cm−3
i
i
i
Mn1–O2 89.46(6), O1–Mn1–N3 106.81(7), O2–Mn1–N3 91.45(7), O1–Mn1–
i
i
i
O2 89.49(6), O2–Mn1–N3 88.55(7); 28: O1–Ni1–O2 91.30(8), O1–Ni1–N3
i
i
i
9
9.43(8), O2–Ni1–N3 85.23(9), O2–Ni1–N3 94.78(9), O1–Ni1–O2 88.70(8),
and 22: 1.866 g cm−3 at 143 K) and cell dimensions. Their
molecular unit consist of two chelating MSC ligands and two
picrate ligands in axial positions (Figure S5/6 and 8). The picrate
anion binds via its deprotonated phenolate-group to the transition
metal(II) in a monodentate way causing shortening of the MSC
bond angle due to the steric hindrance of the trinitrobenzene
derivative (< (O1—Co1—N3) = 77.42(7)°).
i
i
O1–Ni1–N3 80.57(8). Symmetry codes: 26: (i) 1−x, 1−y, −z; 28: (i) −x, −y, 1−z;
(ii) 1−x, 1−y, 1−z.
Sensitivities and Thermal Stability
Thermal stability measurements of highly sensitive and
sensitive coordination compounds are very challenging since
quantities larger than ~2 mg can damage the instrument
seriously. On the other hand, endothermic signals such as
melting, vaporization, dehydration or loss of ligand may not
be detected properly when using an inadequate amount.
Approximately 1 mg of the compounds were measured with
a heating rate of 5 °C min−1 via differential thermal analysis
(
DTA) and/or by thermal gravimetric analysis (TGA). Critical
temperatures are give as onset temperatures and are
summarized in Table 2. Additional details on the DTA plots
of
6–8, 11, 12, 15 and 18 are given in the Supporting
Information. The majority of the investigated compounds
have exothermic decomposition events higher or close to
1
80 °C. Losses of water or ligands expressed by
endothermic decomposition points have been observed
partly at lower temperatures. Methylsemicarbazide (
Figure 8
Molecular unit of the cobalt(II) picrate complex 22. Selected bond
lengths (Å): Co1–O1 2.0664(15), Co1–O2 2.1136(13), Co1–N3 2.115(2);
selected bond angles (°): O1–Co1–O2 90.36(6), O1–Co1–N3 77.42(7), O1–
1
)
i
i
i
Co1–O2 89.64(5), O1–Co1–N3 102.58(7), O2–Co1–N3 89.26(7), O2–Co1–N3
0.74(7). Symmetry code: (i) 1−x, 1−y, −z.
showed no exothermic decompositon event in the measured
range of 25–400 °C but had indeed two endothermic points.
9
Compound
1 first melts (60 °C) and vaporizes afterwards at
temperatures above 110 °C, which was determined by
constant weight loss during TGA (Figure 10). This behaviour
In comparison to the picrate compounds discussed so far, the
styphnate counter-anions do not coordinate to the transition
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201705030
FULL PAPER
Table 2.
MSC (1)
Thermal stability measurements of 1, 3–15 and 17–28 by DTA.
could be
a
possible explanation for the exceptional
10 12 14 17 and 18
T
endo2.
T
exo.
(°C)[b]
endothermic peaks observed for
5
,
9
,
,
–
,
endo1. (°C)[a]
T
(
°C)[a]
during DTA measurements. Endothermic loss of
coordinating MSC molecules could lead to the formation of
intermediate species, which decompose in an exothermic
manner at later stages. Numerous decomposition paths and
mechanisms are possible. Similar phenomena have already
60
111
—
MSC
H
PA (3)
O) (MSC)
(MSC) ] (5)
Cu(NO (MSC) ] (6)
Cu(ClO (MSC) ] (7)
Cu(N (MSC)] (8)
ZnCl (MSC) ] (9)
Zn(NO
Zn(H O)
—
144
146
—
—
—
—
—
—
—
—
—
—
187
189
—
—
259
—
—
—
—
—
—
—
—
—
—
—
166
156
166
147
186
121
186
208
231
333
209
208
234
266
258
179
190
190
211
217
179
195
184
205
193
[
[
[
[
[
[
[
[
[
[
[
[
[
[
Cu(H
2
2
2 4
]SO (4)
CuCl
2
2
[
27-29]
been described in the literature.
tendency and the relating bond strengths are strongly
influenced by the metal (Zn(ClO 12) vs. Ni(ClO 18),
Figure S12), anion (Cu(NO ) vs. Cu(ClO4) 19), Figure
S12) and the corresponding coordination environment
Zn(ClO , (11) vs. (12)). The copper(II) azido (Figure 10)
and nitrate complexes and which decompose
exothermically at low temperatures of 121 °C ( ) and 147 °C
) showed the lowest thermal stabilities of all investigated
The ligand vaporization
3
)
2
2
4
)
2
2
—
4
)
2
(
4 2
) (
3
)
2
—
3
)
2
(6
2
(
2
2
171
183
114
123
107
169
96
3
)
2
(MSC)
2
2
] (10)
](ClO
(
4 2
)
2
2
(MSC)
)
4 2
(11)
6
8,
Zn(MSC)
MnCl (MSC)
Mn(NO
Mn(H O)
Co(H O)
Ni(MSC)
3
](ClO
)
4 2
• H
2
O (12)
8
2
2
] (13)
(6
3
)
2
(MSC)
2
2
] (14)
](ClO
coordination compounds. Comparing them to the other
complexes bearing different anions, but the same metal ion,
the decomposition temperatures increase in the following
2
2
(MSC)
4 2
) (15)
2
2
(MSC) ]Cl
2 2
(17)
99
3
](ClO
4
)
2
(18)
252
—
-
-
2-
-
order: N
(
3
(121 °C) < NO
3
(146 °C) < SO
4
(156 °C) < Cl
2 2
[Cu(PA) (MSC) ] (19)
-
-
-
166 °C) < PA (179 °C) ≈ HTNR (179 °C) < ClO
4
(186 °C).
[Zn(MSC) ](PA)2 (20)
—
3
This general trend underlines the importance and correlation
of the decomposition temperature with the anion and
coordination environment.
[Mn(PA)
2
(MSC)
2
] (21)
—
[Co(PA)
2
(MSC)
2
2
] (22)
(20)
—
[Ni(MSC)
3
](PA)
—
[
[
[
[
[
Cu(H
Zn(H
Mn(HTNR)
Co(H O) (MSC)
Ni(H O) (MSC)
2
O)
2
(MSC)
(MSC)
(MSC)
](HTNR)
](HTNR)
2
](HTNR)
](HTNR)
] (26)
2
(24)
119
134
—
2
O)
2
2
2
(25)
2
2
2
2
2
2
(27)
155
172
2
2
2
2
(28)
Onset temperatures at a heating rate of 5 ° min−1 [a] endothermic peak, which
indicates melting, vaporization, dehydration or loss of coordinating MSC
molecules; [b] exothermic peak, which indicates decomposition.
Figure 10
TGA measurements of the free ligand 1 and selected complexes
at a heating rate of 5 ° min−1
.
The water-free metal(II) MSC picrate coordination compounds
showed relatively high thermal stabilities ranging from 179 °C for
1
9 up to 217 °C for 23 (Figure 11). Their exothermic
Figure 11
9–23.
DTA plot (5 ° min−1) comparison of the picrate compounds 3 and
2
+
decomposition temperatures increase in the following order: Cu
1
179 °C) < Zn (190 °C) ≈ Mn (190 °C) < Co (211 °C) < Ni2+
217 °C). For previous complexes analogous trends have been
observed.[
2
+
2+
2+
(
(
30]
Most of the styphnate complexes showed similar thermal
stabilities in comparison with the picrates (Figure 13) but
crystallized in different complex structures. Instead of
coordinating trinitrobenzene derivative ligands, complexes with
two aqua molecules were obtained. Dehydration indicated by an
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201705030
FULL PAPER
endothermic peak in the DTA plots (Figure 12) can be achieved
by heating shown through weight loss during the TGA
measurements (Figure 10).
grain size
IS (J) [a]
FS (N) [b]
ESD (J) [c]
(μm)
1
> 40
> 360
1.50
< 100
3
4
5
6
7
8
9
> 40
> 40
> 40
> 40
2
160
> 360
> 360
324
0.65
1.50
1.50
1.50
0.07
1.50
1.50
1.50
0.30
0.60
1.25
1.00
1.50
0.10
0.30
1.00
0.55
0.30
0.75
0.40
1.00
0.60
1.50
1.50
< 100
< 100
< 100
< 100
< 100
< 100
< 100
< 100
< 100
< 100
< 100
< 100
< 100
< 100
< 100
< 100
< 100
< 100
< 100
< 100
< 100
< 100
< 100
< 100
24
10
> 360
> 360
> 360
160
> 40
> 40
> 40
25
1
0
1
2
4
1
1
1
> 360
> 360
216
40
DTA plots (5 ° min−1) of the styphnate complexes 24–28.
15
10
Figure 12
17
18
19
20
21
22
23
24
25
26
27
28
> 40
10
> 360
< 60
30
> 360
360
The sensitivities toward impact, friction and electrostatic
discharge for the compounds were determined according to BAM
standards. In addition, the compounds have been classified in
accordance to the “UN Recommendations on the Transport of
Dangerous Goods” using the measured values. An overview of
the sensitivities is given in Table 3. The uncoordinated free ligand
10
9
288
5
288
10
> 360
> 360
> 360
324
> 40
> 40
25
1
can be considered as “insensitive” with values greater than 40 J
for impact, greater than 360 N for friction and an ESD value of
.50 J. For complete energetic categorization of compound 1, we
> 40
> 40
> 360
> 360
1
−
1 [31]
calculated the enthalpy of formation to be −205 kJ mol . So the
compound is formed exothermically in contrast to the condensed
phase heat of formation of monomethylhydrazine (54.1 kJ
[a] Impact sensitivity according to the BAM drophammer (method 1 of 6); [b]
friction sensitivity according to the BAM friction tester (method 1 of 6); [c]
electrostatic discharge sensitivity (OZM ESD tester); Impact: insensitive > 40 J,
less sensitive ≥ 35 J, sensitive ≥ 4 J, very sensitive ≤ 3 J; Friction: insensitive >
−
1 [32]
mol ).
3
60 N, less sensitive = 360 N, sensitive < 360 N and > 80 N, very sensitive ≤
0 N, extremely sensitive ≤ 10 N. According to the UN Recommendations on
8
the Transport of Dangerous Goods.
The sulfate, chloride and nitrate complexes are insensitive
against impact, friction and ESD (except compound 6, which is
sensitive toward friction). In most cases, substitution of these
anions with perchlorates, azides, picrates or styphnates causes
higher sensitivities toward impact, friction and ESD (impact: 2–
40 J, friction: 24–360 N; ESD: 0.07–1.50 J). All water-free
compounds with coordinating picrates or styphnates are more
sensitive toward mechanical stimuli than their aqua ligand-
containing analogs. Compound 7, which behaves like a primary
explosive, can be classified as very sensitive toward impact and
friction, but it is still safe to handle, which makes it a very suitable
initiating substance. The sensitivity toward impact of the
II
II
[
M (PA)
2
(MSC)
2
]/[M (MSC)
3
+
](PA)
2
2+
complexes (Figure 14)
Figure 13
Comparison of the exothermic decomposition temperatures of
increases in the order: Cu < Zn < Ni < Mn2+ < Co2+ and in the
2
2+
picrate complexes with styphnate coordination compounds.
following order toward friction: Cu ≈ Ni2+ < Zn2+ < Mn2+ < Ni .
Incorporation of aqua ligands in the styphnate complexes 24/25
and 27/28 leads to an increase in stability toward mechanical
stimuli but decreases its energetic character compared to the
relating water-free picrate complexes (Figure 14).
2
+
2+
Table 3.
Sensitivities toward impact, friction and ESD of 1, 3–12, 14–15
and 17–28.
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201705030
FULL PAPER
Based on the positive results of the hot needle and hot plate
tests, the initiation capability of compound
7 toward
pentaerythritol tetranitrate (PETN) as secondary explosive
was investigated. A copper shell with a diameter of 7 mm and
length of 88 mm was filled with 200 mg sieved PETN (grain
size 100–500 μm) and pressed with a weight of 8 kg. 50 mg
of the primary explosive was subsequently loosely filled on
top of the main charge. To examine the influence of pressing
of the primary explosive on the initiation capability, two
experiments were conducted a.) with pressing and b.)
without. The shell was sealed by an insulator, placed in a
retaining ring, which was soldered to a copper witness plate
with a thickness of 1 mm and finally initiated by a type A
electrical igniter (Figure 16).
Figure 16
Schematic test setup (left); copper shell and plate before the
initiation capability test (right).
A positive test is indicated by a hole in the copper plate and
fragmentation of the shell caused by a deflagration-to-detonation
transition (DDT) of the secondary explosive. In the case of
compound 7, two different results are observed depending on the
pressing of the sample and the related loading density (Figure 17).
A negative test, represented by a nearly undamaged copper plate,
was obtained after loosely filling the primary into the shell.
Pressing of the sample on top of the main charge led to a positive
result and complete detonation of PETN proofed by a hole in the
plate.
Figure 14
9–28.
Stabilities of the picrate and styphnate coordination compounds
1
Hot needle and hot plate tests of the most promising
compound showed a sharp deflagration in both tests
Figure 15). The sample was fixed on a copper plate
7
(
underneath adhesive tape and initiated by a red hot needle.
Strong deflagration or detonation of the compound usually
indicates a valuable primary explosive. The safe and
straightforward hot plate test shows only the behaviour of the
unconfined sample toward fast heating on a copper plate. It
does not necessarily allow any conclusions on a compound´s
capability as a suitable primary explosive.
Figure 17
Negative (left) and positive (right) results of the PETN initiation
tests.
Toxicity
The toxicity of compound 1 was determined using the known
luminescence marine bacterium Vibrio fischeri in order to
estimate the potential toxicological impact of the corresponding
complexes.[33] With a value of 1.48 g L−1 for the half maximal
Figure 15
Moment of deflagration of compound 7 during the hot needle test
(left) and hot plate test (right).
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201705030
FULL PAPER
effective concentration EC50 after 30 min, the compound can be
considered as non-toxic (toxicity level after 30 min incubation:
0.10 g L ; toxic 0.10–1.00 g L−1; non-toxic
>
−
1
very toxic
<
[34]
−
1
1.00 g L ).
Laser initiation
Figure 18
Moment of detonation of compound 7.
In recent years, more and more research groups all over the world
have been working intensively on new laser ignitable energetic
materials.[35-37] The laser initiation shows many advantages
compared to conventional methods like mechanical stimuli or heat
and investigated compounds do not require high sensitivities
toward the customary stimuli. Consequently, laser ignitable
explosives with high performance, high thermal stability and no
impact on the environment can be used as insensitive but
powerful energetic materials to allow much safer handling and
prevent undesired initiations. About 15 mg of the carefully pestled
complex to be investigated were filled into a transparent plastic
cap, pressed with a pressure force of 1 kN and sealed by a UV-
curing adhesive. The laser initiation experiments were carried out
with a 45 W InGaAs laser diode operating in the single-pulsed
mode. The diode was connected to an optical fiber with a core
diameter of 400 μm and a cladding diameter of 480 μm. The
optical fiber was coupled via a SMA type connecter directly to the
laser and to a collimator. This collimator was linked to an optical
lens, which was positioned in its focal distance (f = 29.9 mm) to
the sample. The lens was protected from the explosive by a
sapphire glass. The confined samples were irradiated at a
wavelength of 915 nm, a voltage of 4 V and varying parameters
regarding pulse length (0.1 ms or 15 ms) and current (8 A or 9 A).
The combined current and pulse length result in an approximately
energy output of 0.20 mJ (0.1 ms/8A) and 34 mJ (15 ms/9A).
Only selected compounds with promising properties (7, 8 and 18)
were tested toward laser irradiation and showed different
responses depending on the used metal(II) and anion. A summary
of the test results is given in Table 4. All investigated complexes
could be initiated showing detonations for 7 and 18 (Figure 18)
and decomposition for compound 8 under the applied laser
parameters.
UV-Vis spectroscopy
In order to get a deeper insight into the laser initiation mechanism
of energetic materials solid state UV-Vis spectra for the
coordination compounds 7, 8 and 18 were recorded in the
wavelength region 350–1000 nm (Figure 19). In addition, the
influence of different anions on the absorption for copper(II)
complexes was investigated and compared to each other (Figure
S13). An overview of the observed optical properties is given in
Table 5.
Figure 19
UV-Vis spectra in the solid state of complexes 7, 8 and 18. The
step in the absorption intensity at 800 nm in the spectra is caused by a detector
change. The UV-Vis spectra have only qualitative character.
Table 4
Results of the laser ignition tests.
0
.1 ms/8 A
15 ms/9 A
All analyzed complexes showed characteristic absorptions in the
near-infrared, visible and UV region correlating with their
observed complementary colors. Depending on the transition
7
8
det.
dec.
x
–
–
18
det.
2+
2+
metal (Cu vs. Ni ) or coordination environment (blue Cu(ClO
4 2
)
(
7) vs. green Cu(N (8)) different d-d transitions can be found.
3 2
)
(
–: not tested, x: no ignition, dec.: decomposition, deflag.: deflagration, det.:
detonation). Operating parameters: current 8–9 A; voltage 4 V;
theoretical maximal output power Pmax = 45 W; theoretical energy Emax = 0.20–
4 mJ; wavelength λ = 915 nm; pulse length τ = 0.1–15 ms.
As expected, the blue copper(II) complexes 4–7 differ only
minimally from each other, which can be explained by their similar
coordination environment.
I
=
U =
3
Different laser initiation thresholds could be observed for the
complexes expressed by varying outcomes and required energy
inputs. Copper(II) complex 7 detonated at the lowest possible
initiation energy configurable in the settings of the laser device.
The compound exhibits slightly increased sensitivities against
mechanical stimuli but is still safe to handle and therefore a
promising candidate for future laser ignition systems.
Table 5
Optical properties of 14-27, 31 and 36.
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201705030
FULL PAPER
[
a]
915/λd-d[b]
λ
measurements. Thermal gravimetric analysis (TGA) of selected
compounds gave new insights into possible decomposition
pathways at elevated temperatures. Highest stabilities toward
temperature were observed for nickel(II) and cobalt(II) complexes,
while highest stabilities toward physical stress for manganese(II)
and zinc(II) complexes. Additionally, low temperature X-ray
structure elucidation for 22 compounds was achieved and allowed
the correlation between crystal structure and mechanical
stabilities (e.g. the bridging azido ligand in the low-performing
copper(II) complex 8 vs. the highly sensitive perchlorato complex
M
color
λ
d-d
CuII
CuII
CuII
CuII
CuII
NiII
4
5
6
7
8
blue
blue
blue
blue
green
blue
646
642
0.51
0.51
0.46
0.40
0.89
0.98
603
602
786
18
581, 952
[
a] absorption intensity maximum wavelength, which can be assigned to
electron d-d excitations in the measured range of 350–1000 nm; [b] quotient of
the absorption intensity at the laser wavelength and the intensity at the d-d
absorption wavelength.
7). All investigated picrate complexes crystallized water-free and
showed higher sensitivities in comparison to their diaqua
containing styphnate analogs. Compound 7 has a high thermal
stability (186 °C) and shows manageable sensitivities for a
primary explosive. Further investigation in a PETN filled copper
shell proofed its suitability as lead-free alternative. The successful
ignition (observing detonation) of PETN makes copper(II)
complex 7 to an interesting candidate for future primary explosive
applications. It can be prepared by a simple, low-cost and
upscalable reaction. Also, non-classical initiation tests by laser
irradiation at a wavelength of 915 nm showed detonation of
complex 7 after irradiation at the lowest applicable energy input of
the laser setup (0.2 mJ).
The nature of the laser ignition process (e.g. thermally,
electronically or combined) and the related requirements of
compounds to be laser ignitable are still not fully understood.[38]
Looking at the absorption intensity of the coordination compounds
at the irradiated wavelength of 915 nm (Figure 19), one could
possibly derive a direct connection to the performed laser ignition
since all complexes could be initiated. However, the laser initiation
capability depends not only on the absorption but also on multiple
other factors like crystal structure or the coordination
environment.[
29]
It can be concluded that deflagration or
detonation of the complexes after exposure to laser irradiation
occurs possibly if the compounds posses high mechanical
sensitivities. Because of the influence of the metal, anion and
ligand on the laser initiation process, as well as the mechanism Acknowledgements
itself has not been clarified yet, future investigations will be
needed to fully understand the laser initiation of energetic
materials.
We acknowledge the financial support of this work, which
was provided by the Ludwig-Maximilian University of Munich
(LMU). The authors also want to thank Mr. Stefan Huber for
sensitivity measurements, Mrs. Cornelia Unger for toxicity
assessments, Mr. Josh Bauer for proofreading and Mrs.
Chantal von der Heide for contribution. In addition, the
authors are indebted to Prof. Thomas M. Klapötke and
gratefully acknowledge his financial and technical support.
Conclusions
Methylsemicarbazide (1, MSC),
a
methyl derivative of
semicarbazide and member of the prominent carbazide family,
was prepared in a facile one-step reaction by treatment of
trimethylsilylisocyanate with methylhydrazine in a high yield of
Keywords: methylsemicarbazide • coordination chemistry •
transition metal complexes • primary explosives • laser ignition
95%. Toxicity determination showed no toxicity of 1 toward
aquatic life, which makes it a suitable candidate as ligand in
environmental benign complexes for various applications. In
comparison to hydrazine and methylhydrazine as ligands (both
show high toxicities), significantly less sensitive compounds are
obtained which might be a reason of the negative heat of
[
1]
T. W. Myers, K. E. Brown, D. E. Chavez, R. J. Scharff, J. M. Veauthier,
Inorg. Chem. 2017, 56, 2297–2303.
[2]
[3]
S. Seth, K. A. McDonald, A. J. Matzger, Inorg. Chem. 2017, 56, 10151–
10154.
−
1
M. Freis, T. M. Klapötke, J. Stierstorfer, N. Szimhardt, Inorg. Chem.
formation (−205 kJ mol ) of 1. In the present extensive study 25
new coordination compounds, with 1 as the ligand, were
2017, 56, 7936–7947.
[4]
[5]
[6]
S. Li, Y. Wang, C. Qi, X. Zhao, J. Zhang, S. Zhang, S. Pang, Angew.
Chem., Int. Ed. 2013, 52, 14031–14035.
synthesized
and
investigated.
Coordination
causes
intramolecular rotation of the bidentate ligand and leads to an
increase in density in comparison to the free compound 1.
Obtained complexes are composed of a 3d transition metal (Mn,
K. D. Oyler, in Green Energetic Materials, John Wiley & Sons, Ltd, 2014,
pp. 103–132.
Y. Tang, C. He, L. A. Mitchell, D. A. Parrish, J. M. Shreeve, Angew.
Chem., Int. Ed. 2016, 55, 5565-5567.
Co, Ni, Cu, Zn), methylsemicarbazide and varying anions (SO
4
2−,
−
−, ClO
−, N
−, picrates, styphnates). Attempts using Fe(II)
Cl , NO
3
4
3
[7]
D. G. Piercey, D. E. Chavez, B. L. Scott, G. H. Imler, D. A. Parrish,
Angew. Chem., Int. Ed. 2016, 55, 15315–15318.
and Fe(III) salts failed. The concept of energetic coordination
compounds (ECCs), which are obtained by including nitrate,
perchlorate, nitrophenolates and azide anions, is a brilliant,
inexpensive and simple strategy in order to find new laser-
ignitable and eco-friendly primary explosives. Energetic and
optical properties can be easily adjusted by variation of the
building blocks (metal, ligand, anion). Most of the complexes
showed exothermic decomposition temperatures higher or close
to 180 °C during differential thermal analysis (DTA)
[
8]
9]
R. Haiges, K. O. Christe, Inorg. Chem. 2013, 52, 7249-7260.
R. Matyás, J. Pachman, in Primary Explosives, Springer, Heidelberg
[
2
013.
10] M. A. Ilyushin, I. V. Tselinsky, I. V. Shugalei, Cent. Eur. J. Energ. Mater.
012, 9, 293–327.
[
[
2
11] M. Joas, T. M. Klapötke, J. Stierstorfer, N. Szimhardt, Chem. - Eur. J.
2013, 19, 9995–10003.
[12] J. Zhang, Y. Du, K. Dong, H. Su, S. Zhang, S. Li, S. Pang, Chem. Mat.
016, 28, 1472–1480.
2
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201705030
FULL PAPER
[13] B. Hariharanath, K. S. Chandrabhanu, A. G. Rajendran, M. Ravindran,
C. B. Kartha, Def. Sci. J. 2006, 56/3, 383–389.
[
[
[
[
14] T. Curtius, K. Heidenreich, Chem. Ber. 1894, 27, 55.
15] M. B. Labib, P. F. Lamie, Med. Chem. Res. 2016, 25, 2607–2618.
16] R. J. W. Cremyln, J. L. Turner, J. Chem. Soc., C 1970, 2629–2631.
17] W.-C. Tong, J.-C. Liu, Q.-Y. Wang, L. Yang, T.-L. Zhang, Z. Anorg. Allg.
Chem. 2014, 640, 2991–2997.
[
18] a.) V. P. Sinditskii, A. E. Fogelz´ang, M. D. Dutov, V. V. Serushkin, S. P.
Yarkov, B. S. Svetlov, Zh. Neorg. Khim. 1986, 31, 1759–1765; b.) V. P.
Sinditskii, A. E. Fogelz´ang, M. D. Dutov, V. I. Sokol, V. V. Serushkin, B.
S. Svetlov,, M. A. Porai-Koshits, Zh. Neorg. Khim. 1987, 32, 1944–1949;
c.) M. B. Talawar, A. P. Agrawal, J. S. Chhabra, S. N. Asthana, J. Hazard.
Mater. 2004, 113, 57–65.
[
[
[
[
19] M. Joas, T. M. Klapötke, Propellants, Explos., Pyrotech. 2015, 40, 246–
2
52.
20] C. Sitong, G. Weiming, Z. Bo, Z. Tonglai, Y. Li, Polyhedron 2016, 117,
10–116.
1
21] X. Fu, F. He, Y. Li, L. Liu, Y. Mi, Y.-C. Xu, G. Xun, Z. Yu, J. Y. Zhang, M.
Dai, Novartis AG, Switz. 2011, p. 143pp.
22] A. Shibayama, R. Kajiki, M. Kobayashi, T. Mitsunari, A. Nagamatsu,
Kumiai Chemical Industry Co., Ltd., Japan; Ihara Chemical Industry Co.,
Ltd. 2012, p. 226pp.
[
23] Crystallographic data for the structures have been deposited with the
Cambridge Crystallographic Data Centre. Copies of the data can be
obtained free of charge on application to The Director, CCDC, 12 Union
Road, Cambridge CB2 1EZ, UK (Fax: int.code_(1223)336-033; e-mail for
inquiry:
deposit@ccdc.cam.ac.uk).
24] P. Domiano, M. A. Pellinghelli, A. Tiripicchio, Acta Crystallogr., Sect. B
972, 28, 2495–2498.
25] J. E. Worsham, Jr., H. A. Levy, S. W. Peterson, Acta Crystallogr. 1957,
0, 310–323.
26] A. Cabort, B. Therrien, K. Bernauer, G. Süss-Fink, Inorg. Chim. Acta
003, 349, 78–84.
fileserv@ccdc.cam.ac.uk;
e-mail
for
deposition:
(
[
[
[
1
1
2
[
[
[
27] K. C. Patil, J. Chem. Sci., 1986, 96, 459–464.
28] R. A. F. Sherriff and A. K. Galwey, J. Chem. Soc. A, 1967, 1705–1708.
29] J. Stierstorfer, N. Szimhardt, M. H. H. Wurzenberger, L. Daumann, A.
Beringer, J. Mater. Chem. A, 2017, 5, 23753–23765.
[
30] M. Joas, PhD thesis; Ludwig-Maximilians Universität München, 2014.
31] a) CBS-4M was applied for the electronic enthalpy; atomization method
for conversion to gas phase enthalpy of formation and Trouton’s rule for
computing the sublimation enthalpy; b) T. Altenburg, T. M. Klapötke, A.
Penger, J. Stierstorfer, Z. Anorg. Allg. Chem. 2010, 636, 463–471.
32] NIST http://webbook.nist.gov/cgi/cbook.cgi?ID=C302012&Mask=1E9F,
Accessed October 2017.
[
[
[
33] G. I. Sunahara, S. Dodard, M. Sarrazin, L. Paquet, G. Ampleman, S.
Thiboutot, J. Hawari, A. Y. Renoux, Ecotoxicol. Environ. Saf., 1998, 39,
185−194.
[34] C. J. Cao, M. S. Johnson, M. M. Hurley, T. M. Klapötke, JANNAF J.
Propuls. Energet., 2012, 5, 41–51.
[35] T. W. Myers, J. A. Bjorgaard, K. E. Brown, D. E. Chavez, S. K. Hanson,
R. J. Scharff, S. Tretiak, J. M. Veauthier, J. Am. Chem. Soc. 2016, 138,
4
685−4692.
36] M. A. Ilyushin, I. V. Tselinksi, Zh. Prikl. Khim. (S.-Petersburg, Russ. Fed.)
000, 73, 1233−1240.
37] M. Freis, T. M. Klapötke, J. Stierstorfer, N. Szimhardt, Inorg. Chem. 2017,
6, 7936−7947.
[
[
[
2
5
38] E. D. Aluker, A. G. Krechetov, A. Y. Mitrofanov, D. R. Nurmukhametov,
M. M. Kuklja, J. Phys. Chem. C, 2011, 115, 6893−6901.
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201705030
FULL PAPER
Entry for the Table of Contents
FULL PAPER
Methylsemicarbazide (MSC) was
Norbert Szimhardt, Jörg Stierstorfer*
successfully
demonstrated
as
suitable building block in the
formation of 25 new energetic
coordination compounds (ECC). The
further clever selection of late 3d
metals, co-solvents and anions
yielded a wide choice of different
functional materials partly suitable for
laser ignition or as classical primary
explosive.
Page No. – Page No.
Methylsemicarbazide as Ligand in
Late 3d Transition Metal Complexes
This article is protected by copyright. All rights reserved.