Spontaneous resolution of a triple-stranded dinickel(II) helicate generated via intermolecular transamination reaction of S-methylisothiocarbohydrazide in the presence of Ni2+

Article abstract of DOI:10.1002/ejic.200800605

The reaction of S-methylisothiocarbohydrazide hydroiodide [H ₂NNHC(SCH₃)NNH₂·HI] with NiCl ₂·6H₂O in water at room temperature yielded a triple-stranded dinickel(II) helicate [Ni^II(L¹-L ¹)₃Ni^II]I₄·4H₂O (1⁴⁺·4I^-·4H₂O), where L ¹-L¹ = H₂NNHC(SCH₃)NNC(SCH ₃)NHNH₂, in 35% yield, which spontaneously separates in enantiomers upon crystallization. The enantiomers do not racemize at room temperature, even not after 15 h of heating at 90 °C. X-ray diffraction structures of both enantiomers, chiroptical and magnetic properties of 1 ⁴⁺·4I^-·4H₂O are reported. Demetallation of the complex by treatment with S^2- resulted in 3,6-bis(methylthio)-1,4-dihydro-1,2,4,5-tetrazine (2). Compound 2 undergoes 2-^e- oxidation in air to give the known 3,6-bis(methylthio)-1,2,4,5- tetrazine (3). Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejic.200800605

FULL PAPER
DOI: 10.1002/ejic.200800605
Spontaneous Resolution of a Triple-Stranded Dinickel(II) Helicate Generated
via Intermolecular Transamination Reaction of S-Methylisothiocarbohydrazide
in the Presence of Ni2+
Anatoly Dobrov,[a] Vladimir B. Arion,*[a] Sergiu Shova,[b] Alexander Roller,[a]
Eva Rentschler,[c] and Bernhard K. Keppler[a]
Dedicated to Professor M. T. Reetz on the occasion of his 65th birthday
Keywords: Triple-stranded helicates / Nickel(II) / Spontaneous resolution / Chiroptical properties / Magnetic properties
The reaction of S-methylisothiocarbohydrazide hydroiodide
[H2NNHC(SCH3)NNH2·HI] with NiCl2·6H2O in water at
room temperature yielded a triple-stranded dinickel(II) heli-
of both enantiomers, chiroptical and magnetic properties of
14+·4I–·4H2O are reported. Demetallation of the complex by
treatment with S2– resulted in 3,6-bis(methylthio)-1,4-dihy-
dro-1,2,4,5-tetrazine (2). Compound 2 undergoes 2-e– oxi-
dation in air to give the known 3,6-bis(methylthio)-1,2,4,5-
tetrazine (3).
cate [NiII(L1–L1)3NiII]I4·4H2O (14+·4I–·4H2O), where L1–L1
=
H2NNHC(SCH3)NNC(SCH3)NHNH2, in 35% yield, which
spontaneously separates in enantiomers upon crystallization.
The enantiomers do not racemize at room temperature, even
not after 15 h of heating at 90 °C. X-ray diffraction structures
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
mers can be obtained by spontaneous separation during
crystallization.[12] It should be noted that for the self-as-
sembly labile metal ions are normally employed. As a con-
sequence the enantiomerically pure compounds easily un-
dergo racemization precluding investigation of their chir-
optical properties. Only a few examples of resolved transi-
tion metal helicates have been reported in the literature. In
these particular cases stabilization to racemization was
achieved either by oxidation of the readily assembled co-
balt(II) complex [Co2L3]4+ to the inert cobalt(III) species
Introduction
Transition metal polynuclear double- and triple-stranded
helicates have been the object of interest and intensive stud-
ies for more than 20 years.[1–3] Numerous examples of metal
helicates are now documented in the literature.[4–7] Their
building up in most cases is based on self-organization of
presynthesized one-stranded ligands in the presence of
metal ions with definite stereochemical preferences. The
helicates are usually formed as a racemic mixture of the two
enantiomers, which sometimes can be separated by chiral
chromatographic methods.[8] Separation of enantiomers can
be also achieved by exploring specific interactions between
the helicate and a chiral counterion.[9] In addition, stereose-
lective synthesis of metal helicates can be realized through
enantiopure chiral ligands[5,10] or auxiliary organic chiral
templates that predetermine the stereochemistry of the reac-
tion and can be removed after its termination without sys-
tem racemization.[11] In very rare cases the pure enantio-
[Co2L3]6+ [13]
or by increasing the nuclearity of the triply
,
stranded metal helicate.[14]
Herein we report the synthesis, X-ray diffraction struc-
ture, chiroptical and magnetic properties of an unprece-
dented triple-stranded dinickel(II) helicate [NiII(L1–L1)3-
NiII]4+ (Scheme 1), which spontaneously separates in
enantiomers upon crystallization.
Results and Discussion
[a] University of Vienna, Institute of Inorganic Chemistry,
Waehringerstr. 42, 1090 Vienna, Austria
We discovered that the reaction of S-methylisothiocar-
bohydrazide hydroiodide [H2NNHC(SCH3)NNH2·HI] with
NiCl2·6H2O in water at room temperature yielded lilac crys-
tals of [NiII(L1–L1)3NiII]I4·4H2O in 35% yield (Scheme 1).
Recrystallization from water enabled the growth of large
crystals of good quality (see Figure S1, Supporting Infor-
mation) with spontaneous resolution of the enantiomers.
Alternatively the separation of enantiomers of [NiII(L1–L1)3-
Fax: +43-1-427752680
E-mail: vladimir.arion@univie.ac.at
[b] Modova State University, Department of Chemistry,
Mateevici str. 60, 2009 Chisinau, Moldova
[c] University of Mainz, Institute of Inorganic and Analytical
Chemistry,
Duesbergweg 10–14, 55099 Mainz, Germany
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
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Spontaneous Resolution of a Triple-Stranded Dinickel(II) Helicate
Scheme 1.
NiII]I4 was realized via entrainment.[15] An enantiopure nuclear d-block[16] and f-block[17] triple-stranded helicates
crystal was used as a seed for the growth of new crystals of with diphenylmethane spacers.
the same chirality from a racemic solution of 14+·4I–. In
Demetallation of complex 14+·4I–·by treatment with S2–
particular, by using a seed crystal of (M)-14+·4I–, 0.9 g of resulted in 3,6-bis(methylthio)-1,4-dihydro-1,2,4,5-tetrazine
crystals consisting of ca. 90% of (M)-14+·4I– and 10% of 2[18,19] (Scheme 1 and Figure S1a in the Supporting Infor-
(P)-14+·4I– was isolated after 48 h at room temperature mation) as confirmed by X-ray diffraction.[20] This species
from 100 mL of a supersaturate solution containing 3.2 g is presumably formed from L1–L1 by intramolecular trans-
of racemate. A second entrainment procedure afforded 0.3 g amination with expulsion of N2H4 molecule. Compound 2
of pure enantiomer (M)-14+·4I– with [α]D = –1350.
undergoes 2-e– oxidation in air to give the known 3,6-
Spontaneous resolution is the separation of enantiomers bis(methylthio)-1,2,4,5-tetrazine (3)[18] according to X-ray
in conglomerates,[15] the cheapest and most efficient pro- crystallography (see Scheme 1 and Figure S1b).[20] Non-
cedure for separation of enantiomers. The conglomerates innocent behavior has also been reported for a number of
were identified via determination of the crystal structure of metal complexes with ligands based on S-alkylisothio-
both enantiomers in combination with CD spectroscopy semicarbazide.[21,22] The transformations leading to species
and polarimetry of their solutions, as these did not racemize 2 and 3 seem to be suppressed in the presence of nickel(II)
under experimental conditions employed (vide infra). It by shifting the equilibrium towards L1–L1 which is stabi-
should, however, be noted that conglomerate formation is lized as dimetal triple-stranded helicate. Both enantiomers
a rare phenomenon, especially because more than 90% of with iodide as counteranion were easily converted into tet-
compounds crystallize in centrosymmetric space groups.
Microanalytical data and thermal analysis support the prepare mononuclear octahedral nickel(II) complexes with
formulation [NiII(L1–L1)3NiII]I4·4H2O (14+·4I–·4H2O) for S-methylisothiosemicarbazide
[H2NNHC(SCH3)NH],
raphenylborate salt with retention of chirality. Attempts to
the racemic mixture. The positive mode ESI mass spectrum which can be regarded as a half of the molecule L1–L1 and,
shows a large number of peaks (see Exp. Sect.) with isotopic therefore, labeled L1, namely [Ni(L1)3]2+, yielded a square-
distributions, which are in good agreement with those pre- planar complex [Ni(L1)2]2+ (4), in which two S-methyliso-
dicted for ions resulting from fragmentation of [NiII(L1–L1)3- thiosemicarbazide ligands according to X-ray analysis[20]
NiII]I4. Unlike numerous examples reported in the litera- are orientated in antiparallel fashion with two SCH3 groups
ture, the one-stranded ligand with linear “tail-to-tail” ar- trans to each other (Figure 1). In addition, ESI mass spec-
rangement of two identical binding sites linked via an azine tra of the reaction mixture did not show peaks, which may
bridge is generated in situ via intermolecular “transamina- be attributed to [Ni(L1)3]2+
tion reaction” of S-methylisothiocarbohydrazide as shown A racemate crystallizes in one of three ways as (i) a race-
.
in Scheme 1. The binding sites are twisted to releave S···S mic compound, in which both enantiomers are present in
steric interaction clashes. Full rotation around the central the same crystal; (ii) as a conglomerate, an assemblage of
azine bond is prevented by this interaction. The noted con- crystals, consisting of molecules of the same chirality; (iii)
formational restrictions are of particular importance for in- as a pseudoracemate, in which the crystals contain the two
ducing helicity. It should, however, be noted that a similar enantiomers in a non-ordered arrangement.[15]
principle based on exploiting H···H repulsions has been sys-
[23]
X-ray diffraction studies of [NiII(L1–L1)3NiII]I4
tematically used since two decades for assembly of both bi- showed that the (P)-enantiomer has the composition
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V. B. Arion et al.
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Figure 1. SCHAKAL plot of the structure of the cation in
[NiII(L1)]I2 (4). Selected bond lengths [Å] and angles [°]: Ni–N1
1.9119(16), Ni–N3 1.8624(17), N1–N2 1.427(2), N2–C1 1.350(3),
C1–N3 1.300(2), C1–S 1.7441(19), S–C2 1.801(2) Å, N1–Ni–N3
84.24(7), ΘN1–N2–C1–N3 9.0(2)°.
14+·4I–·2.4H2O and crystallizes in the tetragonal space
group P41212, while the (M)-enantiomer with the formula-
tion 14+·4I–·3.8H2O in P43212 space group. The structures
of the cations (P)-14+ and (M)-14+ are shown in Figure 2.
The cations lie in a special position on a C2 axis running
through the middle of the N6–N6a bond. The helical axis
passes through two symmetry-related nickel(II) ions, which
are homochiral. The Ni···Ni separation is of 3.675 Å in
(M)-14+, the structure of which was determined more accu-
rately. Both structures consist of three strands wrapped
around two metals in a spiral fashion. Two chelate rings
formed by each of the three one-stranded ligands are
twisted around the rotationally flexible central azine bond.
The twist angles can be estimated by torsional angles
Figure 2. Structures of P-enantiomer (top) and of the M-enanti-
omer (bottom); hydrogen atoms were omitted for clarity.
14+·4I– and –1340 for (M)-14+·4I–, which remained un-
changed over 7 d at room temperature. Each of the enantio-
mers was repeatedly recrystallized from boiling water with-
out any sign of racemization.
ΘC1–N3–N9a–C5a
, ΘC3–N6–N6a–C3a and ΘC5–N9–N3a–C1a at
–104.16, –113.24 and –104.16 or ΘNi1–N3–N9a–Ni1a
,
ΘNi1–N6–N6a–Ni1a and ΘNi1–N9–N3a–Ni1a of –35.97, –36.74,
–35.97° in (M)-14+. As already noted the driving force of
the twisting are the intramolecular S···S repulsions. In ad-
dition, the whole structure seems to be stabilized in this
sulfur reach environment (Figure 2). The six sulfur atoms
form almost a regular hexagon (Figure S3) with S···S con-
tacts at 3.825–4.145 Å for (M)-14+, which are longer than
the sum of van der Waals radii (3.600 Å). Each nickel(II)
ion has a distorted octahedral geometry with Ni–N1, Ni–
N3, Ni–N4, Ni–N6, Ni–N7 and Ni–N9 of 2.129(7),
2.059(7), 2.119(8), 2.051(7), 2.118(8) and 2.050(7) Å, respec-
tively for [(M)-14+].
Figure 3. Circular dichroism spectra of the enantiomers of the
[NiII(L1–L1)3NiII]I4 in water: (P)–14+·4I– (black line) and (M)–
14+·4I– (gray line) in the region 200–400 nm. The spectra between
400 and 800 nm are shown in Figure S4.
It should be noted that while the optimal coordination
polyhedron for NiII in mononuclear complex [Ni(L1)2]2+ is
a square, the octahedral coordination geometry for NiII is
favored in the case of dinucleating L1–L1 ligand with tail-
Racemization requires breaking of at least 10 Ni–N
to-tail arrangement of two L1 moieties. Thus a better match bonds simultaneously, followed by rotation of half the
between electron-donor and conformational characteristics molecule L1–L1 in only one allowed direction depending on
of the three L1–L1 ligands and preference of nickel(II) for enantiomer identity, clockwise or anticlockwise. The oppo-
octahedral coordination environment[21] is achieved in site rotation is prevented by already mentioned S···S steric
[NiII(L1–L1)3NiII]I4.
clashes. The first step event appears to be highly improba-
Solutions of (P)-14+·4I– and (M)-14+·4I– are indeed op- ble, being in line with high kinetic inertness of enantiomers
tically active and show Cotton effects for both enantiomers to racemization, as anticipated for high-spin octahedral
(see Figures 3 and S4). As expected, they are roughly mirror nickel(II) complex with maximal ligand field stabilization
images over the 200–800 nm region of the spectrum. In ad- energy in a row of bivalent d-block transition metal ions.[24]
dition, they show very large [α]D values of +1355 for (P)- Decomplexation of one ligand with simultaneous break of
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Spontaneous Resolution of a Triple-Stranded Dinickel(II) Helicate
4 Ni–N bonds (seems to be difficult, but evidenced by ESI
mass spectrometric data) makes an opposite rotation
around central azine bond in L1–L1 possible. However, re-
binding of L1–L1 to the [NiII(L1–L1)NiII]4+ moiety needs its
conformational accommodation to stereochemical demands
of the dinickel(II) moiety, preserving in such a way the orig-
inal chirality.
To get evidence for the ligand exchange in [NiII(L1–L1)-
NiII]4+, we have carried out scrambling experiments.[14b,25]
Equimolar amounts of [NiII(L1–L1)3NiII]I4·4H2O and its
deuterated analogue, in which SCH3 groups were replaced
by SCD3 groups {[NiII(L1SCD3–L1SCD3)3NiII]I4·4H2O}
were dissolved in water, and ESI mass spectra measured
immediately after dissolution, thereafter at regular time in-
tervals. Figure S5 shows fragments of the spectra of
[NiII(L1–L1)3NiII]I4, [NiII(L1SCD3–L1SCD3)3NiII]I4 and of
their equimolar mixture immediately and 15 h after disso-
lution and heating at 90 °C. The complexes [NiII(L1–L1)3-
NiII]I4 and [NiII(L1SCD3–L1SCD3)3NiII]I4 give characteris-
tic peaks with m/z 865 and 883, which were attributed to
[NiII(L1–L1)3NiIII–2H]+ and [NiII(L1SCD3–L1SCD3)3NiIII–
2H]+, respectively. These two peaks were also found in the
mass spectrum of the aqueous solution containing both
species with almost equal relative intensities. No peaks be-
tween m/z 865 and 883, which could be attributed to species
[NiII(L1–L1)x(L1SCD3–L1SCD3)3–xNiIII–2H]+ (x = 1, 2) re-
sulted from ligand exchange (ligand dissociation and bind-
ing to nickel-containing ions) were observed in the mass
spectra, in line with extraordinary stability of the separated
enantiomers to racemization.
Figure 4. Electronic absorption spectrum of rac-14+·4I– in water.
NiII ions and a coupling constant of J = 0.35 cm–1, taking
into account the TIP of 280ϫ10–6 cm–1. The simulation of
χmT vs. T with these data is shown in Figure 5 as a solid
line.
The electronic spectrum of rac-14+·4I– in water in the vis-
ible and NIR region (Figure 4) contains three absorption
bands with λmax at 890, 820 and 538 nm (for ε, –1 cm–1,
3
see Exp. Sect.) which can be assigned to A2gǞ3T2g(F),
Figure 5. Magnetic susceptibility data for rac-14+·4I–·4H2O.
3
3A2gǞ1Eg(D) and A2gǞ3T1g(F) transitions, correspond-
ingly.[26] Multiplicity- or spin-allowed transitions are known
to give broad absorption bands, while multiplicity forbid-
den transitions are usually sharp. Cyclic voltammogram of
In conclusion, we reported the synthesis of an unprece-
dented dimetal triple-stranded helicate assembled from
nickel(II) and the ligand generated via transamination of S-
alkylated thiocarbohydrazide. In addition, this is the first
example of dinickel(II) helicate which crystallized under
spontaneous racemate autoresolution with separation of
enantiomers of extraordinary stability to racemization. This
inertness to racemization is due to maximal ligand field sta-
bilization energy for high-spin octahedral nickel(II) in a row
of bivalent d-block transition metal ions, the spatial ar-
rangement of ligand(s) binding sites matching the optimal
coordination polyhedron for the given cation and ad-
ditional stabilization of the complex in a sulfur-rich envi-
ronment.
–
rac-14+·4BPh4 in acetonitrile displayed one irreversible
electron-transfer wave at 0.90 V relative to Fc+/Fc couple,
–
which is unambiguously attributed to oxidation of BPh4
anion.
The magnetic properties of a polycrystalline (racemic)
sample of rac-14+·4I–·4H2O in the temperature range 2–
300 K in a field of 1 T is shown in Figure 5. At room tem-
perature the observed value for χmT is 2.27 cm3 Kmol–1,
which is only slightly higher than the theoretical value of
2.0 cm3 Kmol–1 for a dinuclear unit of two non-interacting
S = 1 NiII ions with g = 2. With lowering temperature the
value remains almost constant at 2.27–2.28 cm3 Kmol–1.
Further temperature decrease is accompanied by sharp in-
crease of χmT to 2.44 cm3 Kmol–1 at 5 K. This implies that
the main spin exchange interaction in rac-14+·4I–·4H2O is
Experimental Section
General: All reagents were used as received from Aldrich. S-Meth-
ferromagnetic in nature. The coupling constant was ex- ylisothiocarbohydrazide hydroiodide was prepared according to a
literature procedure.[27]
tracted by modeling the data as a dinuclear system of inter-
[NiII(L1–L1)3NiII]I4·4H2O (14+·4I–·4H2O):
NiCl2·6H2O (0.48 g, 2.0 mmol) and S-methylisothiocarbohydrazide
A
solution of
acting S = 1 ions by applying the spin Hamiltonian H =
–2JS1·S2. Best fit to the experimental data down to low
temperature was obtained by using g values of 2.13 for the hydroiodide (1.5 g, 6.0 mmol) in water (4 mL) was allowed to stand
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V. B. Arion et al.
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at room temperature. After 7 d the product precipitated as lilac
crystals. It was filtered off, recrystallized from water, and dried in
carbon disk working electrode, probed by a Luggin capillary con-
nected to a silver-wire pseudo-reference electrode, and a platinum
air; yield 0.32 g (24%). C12H44I4N18Ni2O4S6 (1322.00): calcd. C auxiliary electrode. Measurements were performed by cyclic vol-
10.90, H 3.35, N 19.07, S 14.45; found C 10.91, H 2.90, N 18.78,
S 13.96. Weight loss at 110 °C is 5.5%. ESI-MS (positive): m/z =
tammetry (CV) at room temperature using an EG & G PARC 273A
potentiostat/galvanostat. Deaeration of solutions was ac-
1121 [Ni2(L1–L1)3I3]+, 993 [Ni2(L1–L1)3I2 – H]+, 865 [Ni2(L1–L1)3I complished by passing a stream of high-purity nitrogen through
– 2H]+, 785 [Ni2(L1–L1)2I2 – H]+, 739 [Ni2(L1–L1)3 – 3H]+, 657 the solution for 10 min prior to the measurements and then main-
[Ni2(L1–L1)2I – 2H]+, 601 [Ni2(L1–L1)2I]+, 529 [Ni2(L1–L1)2
–
taining a blanket atmosphere of nitrogen over the solution during
the measurements. The potentials were measured in 0.15 
[nBu4N][BF4]/CH3CN using the [Fe(η5-C5H5)2]0/+ (E1/2 = +0.66 V
vs. NHE) as internal standard. Magnetic susceptibility measure-
ments were carried out with a Quantum Design MPMS SQUID
magnetometer between 2 and 290 K in an applied field of 1 T. Dia-
magnetic correction of –500ϫ10–6 cm3 mol–1 for rac-14+ 4I–·4H2O,
was estimated from Pascal’s constants.[29]
3H]+, 473 [Ni(L1–L1)2 – H]+, 393 [Ni(L1–L1)I]+, 265 [Ni(L1–L1) –
H]+, 209 [(L1–L1)H]+. UV-Vis of P–14+·4I– in water: λmax, nm (ε,

–1 cm–1): 225 (78000), 250 sh (25000), 538 (58), 820 (96), 890 (99).
CD [λ, nm (∆ε/–1 cm–1)], for 14+·4I–: band 1 (c = 6ϫ10–6 ): 219
(44), 251 (–35), 282 (18); (c = 1.2ϫ10–2): 550 (0.90); for 14+·4I–:
band 2 (c = 6ϫ10–6 ): 219 (–65), 251 (27), 278 (–27); (c =
1.2ϫ10–2): 550 (–0.88). [α]D for (P)–14+·4I–: +1355; for (M)–
14+·4I–: –1340. IR (P)–14+·4I–·2.4H O: ν = 3421, 3203, 3111, 1601,
˜
2
Supporting Information (see also the footnote on the first page of
this article): ORTEP views of molecular structures of 2 (a) and 3
(b) (Figure S1), details of data collection and refinement for 2–4,
crystals of enantiomers grown from water (Figure S2), projection
of the structure of the (M)-[NiII(L1–L1)3NiII]4+ cation along the
Ni···Ni vector, showing the arrangement of the sulfur atoms (Fig-
ure S3), circular dichroism spectra of the enantiomers of the
[NiII(L1–L1)3NiII]I4 in water (Figure S4), ESI mass spectra of
[NiII(L1–L1)3NiII]I4 and its SCD3 analogue (Figure S5).
1526, 1485, 1422, 1261, 1168, 1108, 1022, 899 cm–1. IR (M)–
14+·4I–·3.8H O: ν = 3436, 3212, 3116, 1601, 1531, 1487, 1426, 1263,
˜
2
1172, 1110, 1025, 901 cm–1.
–
[NiII(L1–L1)3NiII][BPh4]4 (14+·4[BPh4]4 ): To a solution of [NiII(L1–
L1)3NiII]I4·4H2O (0.6 g, 0.45 mmol) in water/ethanol, 2:1 (90 mL)
was added a solution of NaBPh4 (0.64 g, 1.87 mmol) in water
(20 mL). The precipitate formed was filtered off, washed with water
and dried in air; yield 0.80 g (87%). C108H116B4N18Ni2S6 (2019.22):
calcd. Ni 5.81, N 12.49, S 9.53; found Ni 5.86, 5.90, N 12.51, S
9.43. ESI-MS (positive): m/z = 1697 [Ni2(L1–L1)3(BPh4)3]+, 1377
[Ni2(L1–L1)3(BPh4)2 – H]+, 1057 [Ni2(L1–L1)3(BPh4) – 2H]+, 849
[Ni2(L1–L1)2(BPh4) – 2H]+, 793 [Ni2(L1–L1)2(BPh4)]+, 739 [Ni2(L1–
L1)3 – 3H]+, 529 [Ni2(L1–L1)2 – 3H]+, 473 [Ni2(L1–L1) – H]+, 265
[Ni(L1–L1) – H]+, 209 [(L1–L1)H]+.
Acknowledgments
This work was supported by the University of Vienna. Mr. P. Walla
is kindly acknowledged for measurement of the CD spectra.
3,6-Bis(methylthio)-1,4-dihydro-1,2,4,5-tetrazine (2): To a solution
of [NiII(L1–L1)3NiII]I4·4H2O (0.1 g, 0.07 mmol) in 0.2  hydrochlo-
ric acid (1 mL) at 60 °C was added a solution of Na2S·9H2O
(0.12 g, 0.5 mmol) in water (2 mL). The black precipitate formed
(NiS) was filtered off and washed with water. The filtrate produced
colorless crystals suitable for X-ray diffraction[20] upon evapora-
tion.
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Angew. Chem. Int. Ed. 1999, 38, 302–322.
3,6-Bis(methylthio)-1,2,4,5-tetrazine (3): An aqueous solution of
[NiII(L1–L1)3NiII]I4·4H2O was allowed to stand at room tempera-
ture for one month and then evaporated under reduced pressure.
The collected solvent contained a small amount of volatile com-
pound, which made it slightly red colored. This was extracted by
chloroform and allowed to crystallize by slow evaporation at room
temperature. The red crystals formed were suitable for X-ray dif-
fraction study.[20]
[Ni(L1)2]I2 (4): To a solution of Ni(CH3COO)2·4H2O (1.3 g,
5.0 mmol) in ethanol (10 mL) was added a solution of S-methyliso-
thiosemicarbazide hydroiodide (3.45 g, 15.0 mmol) in ethanol
(20 mL). The blue solution generated red crystals of X-ray diffrac-
tion quality.[20] Compound with the same composition was already
reported in the literature.[28]
[6] C. J. Matthews, S. T. Onions, G. Morata, L. J. Davis, S. L.
Heath, D. J. Price, Angew. Chem. 2003, 115, 3274–3277; Angew.
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[7] C. Piquet, G. Bernardinelli, G. Hopfgartner, Chem. Rev. 1997,
97, 2005–2062.
[8] G. Rapenne, B. T. Patterson, J.-P. Sauvage, F. R. Keene, Chem.
Commun. 1999, 1853–1854.
[9] a) R. M. Yeh, M. Ziegler, D. W. Johnson, A. J. Terpin, K. N.
Raymond, Inorg. Chem. 2001, 40, 2216–2217; b) R. M. Yeh,
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2005, 5690–5692.
[11] a) C. R. Woods, M. Benaglia, F. Cozzi, J. S. Siegel, Angew.
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[12] F. E. Hahn, C. Schulze Isfort, T. Pape, Angew. Chem. 2004, 116,
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[13] L. J. Charbonnière, M.-F. Gilet, K. Bernauer, A. F. Williams,
Chem. Commun. 1996, 39–40.
IR spectra were recorded on a Bruker FTIR VERTEX70 instru-
ment in the region 4000–400 nm. Circular dichroism spectra were
recorded in thermostatted (Ϯ0.5 °C) quartz cuvettes (1 cm path
length) on a CD6 circular dichrograph (I.S.A. Jobin-Yvon). Optical
rotation was measured on Perkin–Elmer Polarimeter Model 341.
UV/Vis spectra were recorded on a Perkin–Elmer Lambda 20 UV/
Vis spectrophotometer. Electrospray ionization mass spectrometry
was carried out with a Bruker Esquire 3000 instrument Bruker Dal-
tonic, Bremen, Germany. Predicted and experimental isotope dis-
tributions were compared. Cyclic voltammograms were measured
in a two-compartment three-electrode cell using a 0.5-mm-diameter
[14] a) R. Krämer, J.-M. Lehn, A. De Cian, J. Fisher, Angew. Chem.
1993, 105, 764–767; Angew. Chem. Int. Ed. Engl. 1993, 32, 703–
706; b) L. J. Charbonnière, A. F. Williams, U. Frey, A. E. Mer-
bach, P. Kamalaprija, O. Schaad, J. Am. Chem. Soc. 1997, 119,
2488–2496.
4144
www.eurjic.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 4140–4145

Spontaneous Resolution of a Triple-Stranded Dinickel(II) Helicate
[15] L. Pérez-Garcia, D. B. Amabilino, Chem. Soc. Rev. 2002, 31,
342–356.
refined parameters], Flack parameter 0.07(10). Crystal data for
(M)–[Ni2(L1–L1)3]I4·3.8H2O: C12H43.6I4N18Ni2O3.80S6, Mr
1318.43, tetragonal, space group P43212, a = b = 14.8489(3), c
=
[16] a) A. F. Williams, C. Piquet, G. Bernardinelli, Angew. Chem.
1991, 103, 1530–1532; Angew. Chem. Int. Ed. Engl. 1991, 30,
1490–1492; b) M. J. Hannon, C. L. Painting, A. Jackson, J.
Hamblin, W. Errington, Chem. Commun. 1997, 1807–1808.
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1992, 104, 1626–1628; Angew. Chem. Int. Ed. Engl. 1992, 31,
1624–1626.
=
20.4632(3) Å,
V
=
4511.93(14) Å3,
Z
=
4, ρcalcd.
=
=
1.941 gcm–3, Mo-Kα radiation (λ
=
0.71073 Å,
µ
3.891 mm–1), T = 100 K, R = 0.0512 (F2 Ͼ 2σ), Rw = 0.1442
[for 171651 data, 4607 unique reflections (Rint = 0.0931) and
230 refined parameters], Flack parameter –0.01(4). A single
crystal of suitable size was attached to a glass fiber using
acrylic resin and mounted on a goniometer head 40 mm off
the detector. Data were collected on a Nonius Kappa CCD
diffractometer using graphite-monochromated X-radiation
(λ = 0.71073 Å) at 100 and 243 K. 2667 and 664 frames were
measured, each for 20 and 50 s over 1° scan width. The data
were processed using SAINT software. The structure was
solved by direct methods and refined by full-matrix least-
squares techniques using the SHELX program. Non-hydrogen
atoms were refined with anisotropic displacement parameters.
H atoms were placed in calculated positions and refined as
riding atoms with isotropic displacement parameters, set to be
a multiple of that of the parent atoms. CCDC-680517 (for 4),
-680518 [for (M)–14+·4I–·3.8H2O], -680519 [for (P)–
14+·4I–·2.4H2O], -680520 (for 3), -680521 (for 2) contain the
supplementary crystallographic data for this paper. These data
can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
[18] J. Sandstrom, Acta Chem. Scand. 1961, 15, 1575–1582.
[19] F. A. Neugebauer, C. Krieger, H. Fischer, R. Siegel, Chem. Ber.
1983, 116, 2261–2274.
[20] Crystal data for 2: C4H8N4S2, Mr = 176.26, monoclinic, space
group C2/c, a = 11.3538(8), b = 7.0853(8), c = 10.5678(10) Å,
β
=
118.514(8)°,
V
=
747.01(12) Å3,
Z
=
4, ρcalcd.
=
=
1.567 gcm–3, Mo-Kα radiation (λ
=
0.71073 Å,
µ
0.639 mm–1), T = 100 K, R = 0.0245 (F2 Ͼ 2σ), Rw = 0.0654
(for 7018 data and 50 refined parameters). Crystal data for 3:
C4H6N4S2, Mr = 174.25, monoclinic, space group P21/c, a =
8.5962(12),
b = 10.2017(12), c = 8.6899(12) Å, β =
100.435(10)°, V = 749.46(17) Å3, Z = 4, ρcalcd. = 1.544 gcm–3,
Mo-Kα radiation (λ = 0.71073 Å, µ = 0.636 mm–1), T = 100 K,
R = 0.0412 (F2 Ͼ 2σ), Rw = 0.1169 (for 17559 data and 91
refined parameters). Crystal data for 4: C4H14I2N6S2, Mr
=
522.84, monoclinic, space group P21/n, a = 4.3552(1), b =
18.7024(6), c = 8.6247(3) Å, β = 100.828(2)°, V = 690.00(4) Å3,
Z = 2, ρcalcd. = 2.517 gcm–3, Mo-Kα radiation (λ = 0.71073 Å,
[24]
[25]
R. A. Henderson, The Mechanisms of Reactions of Transition
Metal Sites, OUP, Oxford, 1993, p. 27–28.
S. P. Palii, K. M. Indrichan, N. V. Gerbeleu, V. B. Arion, D. V.
Zagorevsky, Yu. S. Nekrasov, Org. Mass Spectrom. 1990, 25,
151–153.
M. A. Robinson, J. D. Curry, D. H. Busch, Inorg. Chem. 1963,
2, 1178–1181.
E. S. Scott, L. F. Audrieth, J. Org. Chem. 1954, 19, 1231–1237.
V. Leovac, M. Babin, C. Canic, N. V. Gerbeleu, Z. Anorg. Allg.
Chem. 1980, 471, 227–232.
For diamagnetic corrections (Pascal’s constants) see, for exam-
ple: R. L. Carlin, Magnetochemistry, Springer, Heidelberg,
1986.
µ = 6.164 mm–1), T = 100 K, R = 0.0157 (F2 Ͼ 2σ), Rw
=
0.0313 (for 20968 data and 86 refined parameters). Details of
data collection and structure refinement are given as Support-
ing Information
[21] U. Knof, T. Weyhermüller, T. Wolter, K. Wieghardt, E. Bill, C.
Butzlaff, A. T. Trautwein, Angew. Chem. 1993, 105, 1701–1704;
Angew. Chem. Int. Ed. Engl. 1993, 32, 1635–1638.
[26]
[27]
[28]
[22] N. V. Gerbeleu, V. B. Arion, J. Burgess, Template Synthesis of
Macrocyclic Compounds, Wiley-VCH, Weinheim, 1999.
[23] Crystal data for (P)–[Ni2(L1–L1)3]I4·2.4H2O: C12H40.8I4N18-
Ni2O2.40S6, Mr = 1293.21, tetragonal, space group P41212, a =
b = 14.825(1), c = 20.201(1) Å, V = 4439.8(5) Å3, Z = 4, ρcalcd.
[29]
=
1.935 gcm–3, Mo-Kα radiation (λ
= 0.71073 Å, µ =
3.950 mm–1), T = 243 K, R = 0.0997 (F2 Ͼ 2σ), Rw = 0.2391
[for 88427 data, 3953 unique reflections (Rint = 0.1154) and 215
Received: April 18, 2008
Published Online: August 4, 2008
Eur. J. Inorg. Chem. 2008, 4140–4145
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4145