Chemistry of heterocyclic 2-thiones: In situ generation of 3-(2-thiazolin-2-yl)thiazolidine-2-thione and 1,1′-dimethyl-2,2′- diimidazolyl sulfide and their coordination to CuI and Cu II

Article abstract of DOI:10.1002/ejic.201300676

The chemical reactivity of copper(I) chloride/copper(I) bromide, [Cu ^I(NCCH₃)₄](BF₄), and copper(II) nitrate towards a series of heterocyclic-2-thiones under aerobic conditions is described. Thiazolidine-2-thione (NC₃H₅S₂) in CH₃CN in the presence of copper(I) chloride/bromide and [Cu ^I(NCCH₃)₄](BF₄) was transformed into 3-(2-thiazolin-2-yl)thiazolidine-2-thione (C₃H₄S ₂N-C₃H₄SN) through C-S bond cleavage and the formation of a C-N bond between two heterocyclic rings. This new thio ligand (C₃H₄S₂N-C₃H₄SN) chelates to Cu^I through N,S-donor atoms, and the third site is occupied by the halogen atoms (Cl, Br), which leads to the formation of three-coordinate Cu^I complexes, [Cu^IX(κ²-N,S-C ₃H₄S₂N-C₃H₄SN)] [X = Cl (1), Br (2)], and a four-coordinate N,S-chelated complex, [Cu ^I(κ²-N,S-C₃H₄S ₂N-C₃H₄SN)₂](BF₄) (3), is obtained in the presence of BF₄^-. In each case, the formation of CuSO₄·5H₂O was also observed. Upon reaction of 1-methylimidazoline-2-thione (N₂C₄H ₆S) with [Cu^I(NCCH₃)₄](BF ₄) or copper(II) nitrate in CH₃CN or CH ₃CN/MeOH, respectively, the thio ligand is converted into 1,1′-dimethyl-2,2′-diimidazolyl sulfide (N₂C ₄H₅)₂S (a thioether), which prefers to bind to Cu^II (in situ formed) to yield six-coordinate N,N-chelated octahedral complexes, namely, {Cu^II[κ²-N,N-(N ₂C₄H₅)₂S]₂(κ ¹-OH₂)₂}X₂ [X = BF₄ (6), NO₃ (7)], with water in the axial positions. The transformation of the thio ligand into 1,1′-dimethyl-2,2′-diimidazolyl sulfide is also observed in its copper(I) chloride reaction in acetonitrile, which yields an N,N-chelated chloro-bridged dimer, {Cu^II₂[κ ²-N,N-(N₂C₄H₅)₂S] ₂(μ-Cl)₂Cl₂} (5). Reaction of copper(I) iodide with thiazolidine-2-thione and 1-methylimidazolidine-2-thione (N ₂C₄H₈S) in acetonitrile yields an iodo-bridged dimer, [Cu₂(κ¹-S-NC₃H₅S ₂)₄(μ-I)₂] (4), and a novel polymer, [Cu₄(μ₃-I)₂(μ-I)₂(μ-S- N₂C₄H₈S)₂(κ¹-S- N₂C₄H₈S)]_n (8), respectively. Reactions of copper(I) halides (Cl, Br), [Cu^I(NCCH₃) ₄](BF₄), and copper(II) nitrate with thiazolidine-2- thione, 1-methylimidazoline-2-thione, and imidazolidine-2-thione in different solvents result in C-S bond cleavage and the in situ production of sulfate. For example, thiazolidine-2-thione is transformed into a new thio ligand, 3-(2-thiazolin-2-yl)thiazolidine-2-thione, which forms compounds 1 and 2 depending on the anion. Copyright

Full text of DOI:10.1002/ejic.201300676

FULL PAPER
DOI:10.1002/ejic.201300676
Chemistry of Heterocyclic 2-Thiones: In Situ Generation
of 3-(2-Thiazolin-2-yl)thiazolidine-2-thione and 1,1Ј-
Dimethyl-2,2Ј-diimidazolyl Sulfide and Their Coordination
to CuI and CuII
Tarlok S. Lobana,*[a] Razia Sultana,[a] Ray J. Butcher,[b]
Alfonso Castineiras,[c] Takashiro Akitsu,[d] Francisco J. Fernandez,[e]
and M. Cristina Vega[e]
Keywords: Cleavage reactions / Copper / S ligands / Sulfur heterocycles / N ligands
The chemical reactivity of copper(I) chloride/copper(I) brom-
ide, [CuI(NCCH3)4](BF4), and copper(II) nitrate towards a
series of heterocyclic-2-thiones under aerobic conditions is
described. Thiazolidine-2-thione (NC3H5S2) in CH3CN in the
presence of copper(I) chloride/bromide and [CuI(NCCH3)4]-
(BF4) was transformed into 3-(2-thiazolin-2-yl)thiazolidine-2-
thione (C3H4S2N-C3H4SN) through C–S bond cleavage and
the formation of a C–N bond between two heterocyclic rings.
This new thio ligand (C3H4S2N-C3H4SN) chelates to CuI
through N,S-donor atoms, and the third site is occupied by
the halogen atoms (Cl, Br), which leads to the formation of
three-coordinate CuI complexes, [CuIX(κ2-N,S-C3H4S2N-
C3H4SN)] [X = Cl (1), Br (2)], and a four-coordinate N,S-che-
lated complex, [CuI(κ2-N,S-C3H4S2N-C3H4SN)2](BF4) (3), is
obtained in the presence of BF4–. In each case, the formation
imidazoline-2-thione (N2C4H6S) with [CuI(NCCH3)4](BF4)
or copper(II) nitrate in CH3CN or CH3CN/MeOH, respec-
tively, the thio ligand is converted into 1,1Ј-dimethyl-2,2Ј-di-
imidazolyl sulfide (N2C4H5)2S (a thioether), which prefers to
bind to CuII (in situ formed) to yield six-coordinate N,N-che-
lated octahedral complexes, namely, {CuII[κ2-N,N-(N2C4H5)2-
S]2(κ1-OH2)2}X2 [X = BF4 (6), NO3 (7)], with water in the axial
positions. The transformation of the thio ligand into 1,1Ј-di-
methyl-2,2Ј-diimidazolyl sulfide is also observed in its cop-
per(I) chloride reaction in acetonitrile, which yields an N,N-
chelated chloro-bridged dimer, {CuII2[κ2-N,N-(N2C4H5)2S]2-
(μ-Cl)2Cl2} (5). Reaction of copper(I) iodide with thiazolidine-
2-thione and 1-methylimidazolidine-2-thione (N2C4H8S) in
acetonitrile yields an iodo-bridged dimer, [Cu2(κ1-S-
NC3H5S2)4(μ-I)2] (4), and a novel polymer, [Cu4(μ3-I)2(μ-I)2(μ-
of CuSO4·5H2O was also observed. Upon reaction of 1-methyl- S-N2C4H8S)2(κ1-S-N2C4H8S)]n (8), respectively.
exhibited variable bonding modes in neutral and anionic
Introduction
forms, which has led to the formation of mono-, di-, tri-,
Sulfur-containing ligands such as heterocyclic thioam-
and polynuclear complexes.[1] In addition to the diversity of
ides or closely related ligands bearing the –N(H)C(=S)–↔–
N=C(–SH)– or –N(H)C(=S)–N(H)–↔–N=C(–SH)–N(H)–
metal–ligand interactions, the above ligands have caught
the attention of many workers as a result of their applica-
functional groups have shown interaction with a wide range
tions as biomimics in biological systems,[2] as fungicides,[2,3]
of metals owing to the presence of both nitrogen (hard) and
as electric conductors,[4] in the pharmaceuticals industry,[5]
sulfur (soft) donor atoms, and thus, these thio ligands have
as anticancer agents,[6] and in catalysis.[1]
During our studies of the chemistry of copper(I) halides
[a] Department of Chemistry, Guru Nanak Dev University,
in reactions with heterocyclic-2-thioamides (Scheme 1), it
was found that variation of the reaction conditions, includ-
ing solvent and ratio of reactants, produced different types
of products.[7–10] During the course of these reactions, C–S
bond cleavage was observed upon treatment of copper(I)
bromide with 1-methylimidazoline-2-thione (N2C4H6S, II)
and upon treatment of copper(I) chloride/bromide with
imidazolidine-2-thione (N2C3H6S, III)[11] in DMSO. Ad-
ditionally, the reaction of thio ligand II with copper(I)
bromide in acetonitrile/chloroform also involved C–S bond
cleavage with subsequent conversion of II into 2-bromo-1-
methylimidazole (N2C4H5Br).[12] In the literature, cleavage
Amritsar, 143 005, India
E-mail: tarlokslobana@yahoo.co.in
Homepage: www.gndu.ac.in
[b] Department of Chemistry, Howard University,
Washington DC 20059, USA
[c] Departamento De Quimica Inorganica, Facultad de Farmacia,
Universidad de Santiago,
15782- Santiago, Spain
[d] Department of Chemistry, Faculty of Science,
Tokyo University of Science,
Kagurazaka, Shinjuku-Ku, Tokyo 162-8601, Japan
[e] Department of Structural and Quantitative Biology,
Center for Biological Research (CIBeCSIC),
Ramiro de Maeztu 9, 28040 Madrid, Spain
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201300676.
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of C–S bonds by CuII salts under ambient conditions fol- N,S-C3H4S2N-C3H4SN)] (1, Scheme 2). Copper(I) bromide
lowed by in situ aerobic oxidation of sulfur to sulfate has showed similar activity and formed a three-coordinate com-
been observed to a limited extent.[13–18] Apart from copper, plex, [CuIBr(κ2-N,S-C3H4S2N-C3H4SN)] (2). Further, upon
reactions of heterocyclic thioamides with metal carbonyls reaction of a solution of [CuI(NCCH3)4](BF4) with a 2 m
also involve cleavage of C–S bonds by splitting of sulfur, solution of I (acetonitrile), 3-(2-thiazolin-2-yl)thiazolidine-
which subsequently acts as a tri- or tetradentate bridge to 2-thione (C3H4S2N-C3H4SN) was again formed. Owing to
–
generate homo- or heteronuclear clusters.[19a–19f] Activation, the lack of the coordinating ability of the BF4 anion, two
cleavage, and transformations of C–S bonds by using transi- molecules of this thio ligand chelate to CuI present in solu-
tion-metal compounds have found wide interest in synthetic tion to yield a four-coordinate complex, [Cu(κ2-N,S-
chemistry and the petroleum industry[20] and have relevance C3H4S2N-C3H4SN)2](BF4) (3).
in biological reactions.[21–23]
Scheme 1. Different heterocyclic bases.
In continuation of our studies on the chemistry of copper
heterocyclic thioamides,[7–12] in this paper, reactions of cop-
per(I) halides and some other CuI,II salts such as
[Cu(NCCH3)4](BF4) and Cu(NO3)2 with thiazolidine-2-
thione
(NC3H5S2,
I), 1-methylimidazoline-2-thione
(N2C4H6S, II), and 1-methylimidazolidine-2-thione
(N2C4H8S, IV) are described with the sole purpose to deter-
mine the effect of anions and other conditions on the nature
of the products and on C–S bond cleavage.
Results and Discussion
Synthesis Comments
Reactions of copper(I) halides and some other copper
salts with I, II, and IV in different solvents are described.
Except with iodide as the anion, in all cases C–S bond
cleavage and C–N bond formation are observed. The newly
formed ligands then complex either CuI or CuII present in
solution to yield different types of compounds.
Scheme 2. Plausible mechanism for the formation of complexes 1–
3.
With the help of mass spectrometry, a plausible explana-
tion for the formation of 3-(2-thiazolin-2-yl)thiazolidine-2-
thione and its coordination to CuI in complexes 1–3 is
shown in Scheme 2. Under the experimental conditions, CuI
oxidizes to CuII, which in turn oxidizes A into disulfide B
with concomitant reduction of the metal. This is followed
by the oxidation of B to C (m/z = 268.9; calcd. for
C6H8N2S4O2, m/z = 268.4), which generates copper(II) sulf-
Reactions Involving C–S bond Cleavage/C–N Bond
Formation
Equimolar solutions of copper(I) chloride and
I
(NC3H5S2) in acetonitrile were mixed, and the mixture was ate (m/z = 179.0; calcd. for CuSO4·H2O + 2H, m/z = 179.6)
left undisturbed to react under aerobic conditions at room and E (m/z = 173.0; calcd. for C6H8N2S2, m/z = 172.3) via
temperature. The color of the solution changed from color- D. The interaction of D with A appears to give a new thio
less to greenish brown slowly, and red-brown prismatic ligand, namely, 3-(2-thiazolin-2-yl)thiazolidine-2-thione
crystals of composition C6H8ClCuN2S3 were formed over a (C3H4S2N-C3H4SN, F). The mass spectrometry data sup-
period of 1 week. X-ray analysis of the red-brown crystals port the formation of CuCl(C3H4S2N-C3H4SN) (m/z =
revealed that I (NC3H5S2) was transformed into 3-(2-thia- 304.9, calcd. m/z = 303.3 for complex 1), CuBr(C3H4S2N-
zolin-2-yl)thiazolidine-2-thione
(C3H4S2N-C3H4SN) C3H4SN) (m/z = 346.9, calcd. m/z = 347.8 for complex 2),
through C–S bond cleavage, followed by C–N bond forma- and symmetrical complex 3 (m/z = 470.9, calcd. m/z =
tion (fusion of two thiazolidine-2-thione rings) with ex- 471.0) from the reactions of CuCl and CuBr with I.
trusion of sulfur as sulfate. The C3H4S2N-C3H4SN ligand
Similar to the reactions of I, equimolar solutions of II
subsequently chelated to CuI through N,S-donor atoms, (N2C4H6S) and copper(I) chloride in acetonitrile (or aceto-
and the third site was occupied by a chloride, which led to nitrile/chloroform) were allowed to react under aerobic con-
the formation of a three-coordinate CuI complex, [CuCl(κ2- ditions at room temperature. Green crystals of composition
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C8H10Cl2CuN4S were formed over a period of 2 weeks. X- CuII, which in turn oxidizes G into disulfide H (m/z = 225.5;
ray analysis showed that ligand II was converted into 1,1Ј- calcd. for C8H10N4S2, m/z = 226.0) with concomitant re-
dimethyl-2,2Ј-diimidazolyl sulfide [(N2C4H5)2S] (a thio- duction of the metal. This is followed by the oxidation of
ether), which bonded to CuII through its N,N-donor atoms H to I (m/z = 257.0; calcd. for C8H10N4S2O2, m/z = 258.0).
to yield a dinuclear complex, {CuII2[κ2-N,N-(N2C4H5)2S]2- Species I is transformed into J [(N2C4H5)2S] along with the
(μ-Cl)2Cl2} (5). Further, upon reaction of a solution of formation of CuSO4. Species J combines with CuII in the
[CuI(NCCH3)4](BF4) with a 2 m solution of II (N2C4H6S) presence of halide ions to preferentially generate 5. The
in acetonitrile, dark purple crystals of composition mass spectrometry data for {[(N,N-J)Cu(μ-Cl35)2Cu-
C16H28B2CuF8N8O4S2 were formed over a period of (N,N-J)]·0.5H2O}2+(m/z
1 week, and X-ray analysis showed that II (N2C4H6S) was C16H20N8Cu2S2Cl235·0.5H2O, m/z = 296.5), {[(N,N-J)Cu(μ-
again converted into 1,1Ј-dimethyl-2,2Ј-diimidazolyl sulfide Cl37)2Cu(N,N-J)]·0.5H2O}2+ (m/z
299.0; calcd. for
[(N2C4H5)2S]. Two molecules of this new thio ligand che- C16H20N8Cu2S2Cl237·0.5H2O, m/z = 298.5), {[(N,N-J)Cu(μ-
=
297.0;
calcd.
for
=
lated to CuII in a trans position and two axial sites were Cl35)2Cu(N,N-J)]}2+(m/z
=
292;
calcd.
for
occupied by water molecules, which led to the formation of C16H20N8Cu2S2Cl235, m/z = 292), and {[(N,N-J)Cu(μ-Cl37)2-
37
an octahedral complex, {Cu[κ2-N,N-(N2C4H5)2S]2(κ1- Cu(N,N-J)]}2+ (m/z = 294; calcd. for C16H20N8Cu2S2Cl2
,
OH2)2}(BF4)2·2H2O (6). Interestingly, a blue solution of m/z = 294) support the formation of 5 from J (thioether) as
copper(II) nitrate in methanol turned colorless upon ad- an N,N donor. However, the molecular ion is not observed;
dition of a 2 m acetonitrile solution of II (N2C4H6S) as a rather, these degraded components clearly support various
result of the reduction of CuII to CuI, which then showed species depicted in Scheme 3. Finally, the mass spectrome-
chemical activity similar to that of [CuI(NCCH3)4](BF4) try data for [(N,N-J)Cu(O2SO2)·H2O]+(m/z = 370.0; calcd.
and formed an octahedral complex, {CuII[κ2-N,N- for C8H10N4SCu·SO4·H2O, m/z = 371), and [(N,N-J)Cu-
(N2C4H5)2S]2(κ1-OH2)2}(NO3)2 (7), which is similar to 6; a (μ-Cl)2Cu(O2SO2)]+
(m/z
=
486;
calcd.
for
reaction in nitromethane/methanol also yielded the same C8H10N4SCu2Cl2·SO4, m/z = 486) support the formation of
product.[13]
sulfate, which is in a complexed state.
Scheme 3 shows a plausible explanation for the forma-
tion of 1,1Ј-dimethyl-2,2Ј-diimidazolyl sulfide [(N2C4H5)2-
S], which was arrived at with the help of mass spectrometry
for the reaction of CuCl with II for the formation of 5. As
before, under the experimental conditions, CuI oxidizes to
Reactions with No C–S Bond Cleavage
Equimolar solutions of copper(I) iodide and I in CH3CN
were mixed, and the solution was left undisturbed as done
in the above reactions. Colorless crystals of a dinuclear
complex, [Cu2(κ1-SNC3H5S2)4(μ-I)2] (4), were obtained,
and there was no C–S bond cleavage unlike that in the
above reactions. Introduction of methyl group at the nitro-
Scheme 3. Plausible mechanism of formation of complexes 5–7.
Scheme 4. Rings at S are omitted.
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gen atom yielded IV (N2C4H8S), and it was treated with
copper(I) iodide in the same way as in the above reactions,
but it did not involve C–S bond cleavage. It formed a poly-
meric
product,
[Cu4(μ3-I)2(μ-I)2(μ-SN2C4H8S)2(κ1-
SN2C4H8S)]n (8, Scheme 4). In this polymer, CuI and two
molecules of IV appear to have formed a hetero-bridged
core, Cu(μ-S)(μ-I)Cu, with one terminal iodide bonded to
one Cu and the thio ligand bonded to the second Cu (spe-
cies K). This acts as a building block, and two K units com-
bine through the bridging iodide to form a tetranuclear core
(species L). Two such L cores combined to form an octanu-
clear unit, and the process continues to form the polymer.
Figure 1. UV/Vis spectra of complexes 2, 3, 6, and 7.
Magnetism, Spectroscopy, and Fluorescence
Magnetic susceptibility studies revealed that complexes
5–7 are paramagnetic with μeff values of 1.966 (per Cu),
1.971, and 1.974 BM, respectively, and all of the other com-
plexes are diamagnetic. The IR spectra of these complexes
show the presence of characteristic bands for the ν(C–H),
ν(C–N) + δ(C–H), ν(C–S), and δ(N–CH3) moieties. The
ν(N–H) bands were observed in the spectra of complexes 4
[ν(N–H) = 3206 cm–1; free ligand, 3138 cm–1] and 8 [ν(N–
H) = 3196 cm–1; free ligand, 3272 cm–1], which supports the
fact that the thio ligands in these complexes remained un-
changed; this is in contrast to the C–S bond cleavage that
occurred in the other reactions. The bands resulting from
the BF4– anions in complexes 3 [1030 (s, ν3), 710 (s, ν1), 510
(m, ν4) cm–1] and 6 [1022 (s, ν3), 717 (s, ν1), 502 (m, ν4)
–
cm–1] as well as those that are due to NO3 in 7 [1407 (m,
ν3), 800 (m, ν2), 708 (m, ν4) cm–1] support their ionic na-
Figure 2. Fluorescence spectra of complexes 2 and 3.
1
ture.[24] The H NMR spectrum of complex 4 shows one
broad resonance resulting from the NH proton at δ =
Molecular Structures
10.0 ppm and two sets of signals that are due to C4H at δ
1
= 3.54 ppm and C5H at δ = 4.02 ppm. The H NMR spec-
The formation of 1–3 and 5–7 involved C–S bond cleav-
tra of CuI complexes 1–3 in [D6]DMSO did not show any age and is discussed in this sequence. The in situ generated
signals, and this indicates that these complexes are not 3-(2-thiazolin-2-yl)thiazolidine-2-thione ligand chelates to
stable in DMSO and oxidation to CuII occurred. Complex CuI of complex 1 through its N,S-donor atoms [Cu–S
8 was not soluble in DMSO.
2.187(1) Å, Cu–N 1.989(1) Å] with a N–Cu–S bite angle of
The UV/Vis spectra of CuII complexes 5–7 in DMSO 98.52(6)°. The third position is occupied by a chloride ion
showed intense absorption with λmax values in the range [Cu–Cl 2.150(1)°], which gives rise to a three-coordinate
from 260 to 286 nm (10–4 m solution). To observe d–d tran- complex. The N–Cu–Cl and S–Cu–Cl angles (125.14 and
sitions in the visible region, a 10–3 m solution was used. A 136.30°, respectively) and the N–Cu–S bite angle suggest
very intense absorption occurred in the region of 260 nm a distorted trigonal planar geometry (Figure 3). The bond
for this concentrated solution; however, a weak band at lengths are comparable to literature trends.[1] The bonding
λmax = 739 nm attributed to the d–d transition pertaining and geometry of bromide complex 2 are similar to those of
to CuII was also observed.[31] The UV/Vis spectra of CuI 1, except that there are two independent molecules in the
complexes 1–3 in DMSO showed two absorption bands at same unit cell with slightly different bonding parameters
285 and 312 nm. The band at 312 nm can be attributed to (Figure 4). The S···S contact between two independent units
a charge transfer (SǞCu) transition and that at 285 nm is (4.181 Å) is longer than twice the sum of the van der Waals
due to the πǞ π* transition. Complex 3 showed more in- radii of the sulfur atoms (3.60 Å).[32] In complex 3, two mo-
tense bands owing to the presence of two N,S-chelating thio lecules of the 3-(2-thiazolin-2-yl)thiazolidine-2-thione li-
–
ligands versus one in complex 2[25] (Figure 1). Complexes gand chelate to CuI and the BF4 anion lies outside the
2 and 3 are weakly fluorescent at λem = 344 and 352 nm, coordination sphere. There is a decrease in the N–Cu–S bite
respectively, which corresponds to an excitation wavelength angle [93.8(1)°] in 3 relative to that in 1 or 2, and this is
of 285 nm (Figure 2); other complexes did not show emis- clearly the result of the increase in the coordination number
sion.
of the complex. The Cu–N and Cu–S distances are some-
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what longer than those of the three-coordinate complexes
discussed above (Table S2, Supporting Information). Two
N,S-chelating thio ligands lie in mutually perpendicular pla-
nes in a twisted fashion (Figure 5).
Figure 5. Molecular structure of [Cu(κ2-N,S-C3H4S2N-C3H4SN)2]-
(BF4) (3).
The 1,1Ј-dimethyl-2,2Ј-diimidazolyl sulfide [(N2C4H5)2S]
ligand is a thioether that is chelated to CuII in complexes
5–7. Complex 5 is a chloride-bridged dimer in which the
Cu(μ-Cl)2Cu core is a parallelogram with unequal Cu–Cl
bond lengths [2.2931(1), 2.7159(1) Å; Figure 6]. The
Cu···Cu separation of 3.665(3) Å is longer than the sum of
the van der Waals radii of the Cu atoms (2.80 Å).[26] As re-
gards complexes 6 and 7 (Figure 7), both have identical oc-
tahedral cations, and in these complex cations, copper(II)
is bonded to N,N-chelating 1,1Ј-dimethyl-2,2Ј-diimidazolyl
sulfide ligands in the basal plane with a pair of water mole-
cules occupying the axial positions. Considering the O–Cu–
O bond angle of 180° as the z axis, other angles in the
square plane formed by the CuN4 core are nearly 90° and
the trans N–Cu–N bond angles are again 180°.
Figure 3. Molecular structure of [CuCl(κ2-N,S-C3H4S2N-C3H4SN)]
(1).
Complexes 4 and 8 did not involve C–S bond cleavage.
Dinuclear complex 4 is an iodide-bridged complex with
four terminally bonded thiazolidine-2-thione (NC3H5S2, I)
ligands. The central Cu(μ-I)2Cu core is a parallelogram
with unequal Cu–I bond lengths [2.713(5), 2.757(5) Å],
which are longer than those observed in iodo-bridged com-
plexes reported in the literature.[20,21] The bond angles
around each Cu atom vary in the range from 98.59(2) to
123.29(4)°, which results in severe distortion from a tetrahe-
dral geometry (Table S2, Supporting Information). In com-
Figure 4. Molecular structure of [CuBr(κ2-N,S-C3H4S2N-
C3H4SN)] (2).
Figure 6. Molecular structure of complex {CuII2[κ2-N,N-(N2C4H5)2S]2(μ-Cl)2Cl2} (5).
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bonds. The CuII ions in salts such as copper(II) nitrate ini-
tially undergo reduction to CuI upon the addition of a thio
ligand. Thus, in all cases we preferred to use CuI salts, as
the reactions appeared to proceed through CuI. The CuI
ions in solution in the presence of a thio ligand slowly react
under aerobic conditions through oxidation–reduction reac-
tions, which yields a variety of products as described above.
–
The higher polarity of the Cu–X bond (X = Cl–, Br–, BF4 ,
–
NO3 ) results in easy bond cleavage and the formation of
CuII ions, which are believed to oxidize the thio ligand
through a variety of probable steps, as proposed in the
mechanism cited in the above discussion. The more bulky
iodide is reducing nature, which tends to stabilize the CuI
state, and the redox reactions are slow or do not occur.
Figure 7. Structure of {Cu[κ2-N,N-(N2C4H5)2S]2(κ1-OH2)2}(BF4)2·
2H2O (6).
plex 8 (Figure 8), two Cu–I and two 1-methylimidazolidine-
2-thione (IV) moieties appear to have formed a hetero-
bridged Cu(μ-S)(μ-I)Cu core in which one terminal iodide
is bonded to one Cu atom and the thio ligand is bonded to
the second Cu atom. This acts as a building block, and two
such units combine through the bridging iodide to form a
tetranuclear core. Two such tetranuclear cores combine to
form an octanuclear unit, and the process continues to form
an infinite polymeric zigzag chain. An interesting feature of
this chain is the existence of alternate Cu(μ-S)(μ-I)Cu and
Cu(μ-I)2Cu cores. Further, variation in the Cu cores follows
the trend ···AABBAABB··· (A = CuS2I2, B = CuSI3). The
Cu···Cu distance in the Cu(μ-I)2Cu core is 2.787(2) Å,
which is less than the sum of the van der Waals radii of the
Cu atoms (2.80 Å).[26] Notably, the imidazolidine-2-thione
forms six- or eight-membered repeating units, Cu3(μ-S)3 or
Cu4(μ-S)4, to construct polynuclear compounds, namely,
[Cu6(μ3-SN2C3H6)2(μ-SN2C3H6)4X2(μ-X)4]n (X = Cl, Br, I),
[Cu6(μ3-SN2C3H6)4(μ-SN2C3H6)2(μ-I)2I4]n, and [Cu8(μ3-
The new 3-(2-thiazolin-2-yl)thiazolidine-2-thione (VI)
thio ligand has one N atom and one thione sulfur atom as
donor atoms, and they prefer to bind to CuI. It is well
known that thiones prefer to bind to CuI, and if thiones are
treated with CuII, they reduce it to CuI. Thus, ligand VI
binds to CuI ions. The ethereal sulfur does not show bind-
ing to either of the ions. In contrast, ligand VII has two
ring nitrogen atoms that prefer to bind to CuII. This can
also be understood in terms of hard–soft acid–base theory:
soft–soft and hard–hard preferences.
Conclusions
[21,22]
SN2C3H6)4(μ-SN2C3H6)4(κ1-Cl)8]n
Reactions of copper(I) halides and other copper salts
with five-membered heterocyclic thiones under aerobic con-
ditions were studied. Interesting chemical reactivity was ob-
served, and some important points are summarized here.
The use of a lower metal-to-ligand ratio prevented C–S
bond cleavage and the CuI oxidation state seemed to be
stabilized; thus, a 1:1 molar ratio was optimum to perform
reactions at room temperature. Cleavage of the C–S bond
–
–
occurred in the presence of Cl–, Br–, BF4 , and NO3
anions. More polar solvents assisted Cu–X bond cleavage,
which involves Cu–X···solvent interactions, and allowed the
ready formation of Cu+ ions. Similarly, DMSO and DMF
coordinated to the metal center in Cu–X, but the electro-
negative O donor atom of DMSO did not stabilize the CuI
state. The more readily that CuI could be formed, the
greater was the tendency to induce C–S bond cleavage. The
use of copper(II) salts also involved initial reduction to CuI
with similar products; thus, reactions were performed with
copper(I) halides. The bulky iodide stabilized CuI, which
prevented cleavage under the experimental conditions.
Figure 8. Structure of [Cu4(μ3-I)2(μ-I)2(μ-S-N2C4H8S)2(κ1-S-
N2C4H8S)2]n (8).
Effect of Anions on C–S Bond Cleavage and Preferential
Binding to CuI or CuII
During these investigations, it was found that anions Upon the addition of a metal salt to a stirred solution of
–
–
such as Cl–, Br–, BF4 , and NO3 support cleavage of C–S the thione ligand, there was a general tendency to form a
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(10–4 m in DMSO): λmax (ε, Lmol–1 cm–1) = 286 (2.592ϫ 104),
310 nm (1.946ϫ 104). Fluorescence (10–4 m in DMSO): λex
precipitate, which prevented crystal formation. However, if
a mixture of the metal salt and the thione ligand was left
undisturbed, crystalline products were obtained.
=
285 nm, λem = 352 nm. IR: ν = 3077–2920 (w, C–H); 1532 (s), 1497
˜
(sh.) (C–N + δC–H); 1030 (s), 710 (s), 510 (m) (BF4); 930 (m,
C=S) cm–1.
Synthesis of [Cu2(κ1-S-NC3H5S2)4(μ-I)2] (4): To a solution of cop-
per(I) iodide (0.025 g, 0.13 mmol) in acetonitrile was added a solu-
tion of I (0.015 g, 0.13 mmol) in acetonitrile. The reaction mixture
was left undisturbed. After 1 week, slow evaporation of the solu-
tion at room temperature resulted in colorless crystals of 4, yield
0.072 g, 64%, m.p. 120–125 °C. C12H20Cu2I2N4S8 (857.68) calcd. C
16.79, H 2.33, N 6.53, S 29.84; found C 16.94, H 2.41, N 6.62, S
28.90. UV/Vis (CHCl3, partially soluble): λmax = 280, 330 nm. IR:
Experimental Section
Materials: Copper(I) halides were prepared by the reduction of
CuSO4·5H2O by using SO2 in the presence of stoichiometric
amounts of NaCl, NaBr, and NaI in water.[27] [Cu(NCCH3)4](BF4)
was prepared by the slow addition of HBF4 to a suspension of
copper(I) oxide in acetonitrile until the solution was colorless.
[Cu(NCCH3)4](BF4) was extracted by using diethyl ether. Cop-
per(II) nitrate, thiazolidine-2-thione (I), 1-methylimidazoline-2-
thione (II), and 1-methylimidazolidine-2-thione (IV) were procured
from Aldrich Sigma, Ltd., and used as such.
ν = 3206 (br., N–H); 3018–2943 (w, C–H); 1522 (s), 1456 (m) (C–
˜
N + δC–H); 994 (s, C=S) cm–1. 1H NMR (CDCl3): δ = 10.0 (br., 1
H, NH), 3.54 (t, 2 H, C4H), 4.02 (t, 2 H, C5H) ppm.
Methods: Elemental analyses for C, H, and N analysis were ob-
tained with a Thermoelectron Flash EA1112 CHNS analyzer. UV/
Vis spectra were recorded by using a UV-1601PC Shimadzu spec-
trophotometer. Fluorescence spectra were recorded by using a RF-
1501 Shimadzu spectrophotometer (10–4 m concentration at 20 °C).
IR spectra were recorded by using KBr pellets in the 4000–400 cm–1
range with a Varian 660-IR FTIR spectrophotometer. Melting
points were determined with a Gallenkamp electrically heated ap-
paratus. Magnetic moments were determined by using a magnetic
susceptibility balance (Johnson Matthey, Catalytic Systems Divi-
sion Equipment).
Synthesis of {CuII2[κ2-N,N-(N2C4H5)2S]2(μ-Cl)2Cl2} (5): To a solu-
tion of copper(I) chloride (0.025 g, 0.25 mmol) in acetonitrile was
added a solution of II (0.029 g, 0.25 mmol) in acetonitrile, and the
solution was left undisturbed. The color of the solution changed
to greenish brown in 4–5 d. After about 2 weeks, green prismatic
crystals of 5 as well as light blue crystals of CuSO4·5H2O (0.008 g,
13%) were formed. The products were separated manually. Data
for 5: yield 0.044 g, 58%, m.p. 233–237 °C. C16H20N8S2Cu2Cl4
(657.44) calcd. C 29.20, H 3.04, N 17.04, S 9.73; found C 29.00, H
3.26, N 16.90, S 9.55. UV/Vis (10–4 m in DMSO): λmax (ε,
Lmol–1 cm–1) = 261 nm (2.889ϫ 103). UV/Vis (10–3 m in DMSO):
Synthesis of [CuCl(κ2-N,S-C3H4S2N-C3H4SN)] (1): To a solution
of copper(I) chloride (0.025 g, 0.25 mmol) in acetonitrile was added
a solution of I (0.030 g, 0.25 mmol) in acetonitrile. The reaction
mixture was left undisturbed. The color of the solution started to
change to greenish brown after about 3–4 d, and after about
1 week, red-brown prismatic crystals of 1 along with light bluish
crystals of CuSO4·5H2O were formed and then manually separated.
Data for 1: yield 0.019 g, 63%, m.p. 172–175 °C. C6H8ClCuN2S3
(303.31): calcd. C 23.74, H 2.64, N 9.23, S 31.65; found C 23.53,
λmax (ε, Lmol–1 cm–1) = 261 (very intense), 739 nm (117). IR: ν =
˜
3026–2948 (w, C–H); 1525 (s), 1481 (s) (C–N + δC–H); 870 (s,
C=S); 763 (s, δN–CH3) cm–1. Magnetic moment: 1.97 BM per cop-
per.
Synthesis of {Cu[κ2-N,N-(N2C4H5)2S]2(κ1-OH2)2}(BF4)2·2H2O (6):
To a solution of [Cu(NCCH3)4](BF4) (0.050 g, 0.16 mmol) in aceto-
nitrile was added a solution of II (0.036 g, 0.32 mmol) in acetoni-
trile. The reaction mixture was left undisturbed. The color of the
solution changed to brownish green in 3–4 d and dark blue pris-
matic crystals of 6 were formed in about 1 week along with light
blue crystals of CuSO4·5H2O (0.006 g, 14%). Data for 6: yield
0.049 g, 49%, m.p. 220–223 °C. C16H28B2CuF8N8O4S2 (697.74)
calcd. C 27.51, H 4.01, N 16.05, S 9.17; found C 27.64, H 4.10, N
16.10, S 8.30. UV/Vis (10–4 m in DMSO): λmax (ε, Lmol–1 cm–1) =
H 2.55, N 9.57, S 30.21. IR: ν = 2922–2855 (m, C–H); 1587 (s),
˜
1480 (sh.) (C–N
+
δC–H); 942 (s, C=S) cm–1. Data for
CuSO4·5H2O: yield 0.010 g, 16% (see the Supporting Information
for analytical data).
Synthesis of [CuBr(κ2-N,S-C3H4S2N-C3H4SN)] (2): To a solution
of copper(I) bromide (0.025 g, 0.17 mmol) in acetonitrile was
added a solution of I (0.021 g, 0.25 mmol) in acetonitrile. The reac-
tion mixture was left undisturbed. After 2–3 d, the color of the
solution changed to yellow. Slow evaporation of the solution at
room temperature led to red-violet plates of 2 along with light blue
crystals of CuSO4·5H2O (0.008 g, 18%), which were manually sepa-
rated. Data for 2: yield 0.031 g, 68%, m.p. 187–190 °C.
C6H8BrCuN2S3 (347.80): calcd. C 20.70, H 2.30, N 8.06, S 25.5;
found C 20.55, H 2.40, N 8.19, S 25.3. UV/Vis (10–4 m in DMSO):
λmax (ε, Lmol–1 cm–1) = 285 (1.153ϫ 104), 312 nm (8160). Fluores-
286 nm (1.152ϫ 104). IR: ν = 3444 (br., OH); 3101–2947 (m, C–
˜
H); 1547 (s), 1458 (sh.) (C–N + δC–H); 1022 (s), 717 (s), 502 (m)
(BF4); 883 (m, C–S); 782 (s, δN–CH3) cm–1. Magnetic moment:
1.971 BM.
Synthesis of {Cu[κ2-N,N-(N2C4H5)2S]2(κ1-OH2)2}(NO3)2 (7): To a
solution of copper(II) nitrate (0.025 g, 0.10 mmol) in methanol was
added a solution of II (0.024 g, 0.20 mmol) in acetonitrile. The blue
color of the copper(II) nitrate solution changed to colorless upon
the addition of the thio ligand, as a result of the reduction of CuII
into CuI by the thio ligand. The reaction mixture was left undis-
turbed. The color of the solution again changed to greenish blue
in about 5–6 d. Blue prismatic crystals of 7 were obtained after
2 weeks along with blue crystalline CuSO4·5H2O (0.006 g, 18%).
Data for 7: yield 0.032 g, 52%, m.p. 173–175 °C. C16H24CuN10O8S2
(612.11): calcd. C 31.37, H 3.92, N 22.87, S 10.45; found C 31.50,
H 4.03, N 23.00, S 9.83. UV/Vis (10–4 m in DMSO): λmax (ε,
cence (10–4 m in DMSO): λex = 285 nm, λem = 344 nm. IR: ν =
˜
2995–2817 (m, C–H); 1584 (s), 1450 (sh.) (C–N + δC–H); 940 (s,
C=S) cm–1.
Synthesis of [Cu(κ2-N,S-C3H4S2N-C3H4SN)2](BF4) (3): To a solu-
tion of [Cu(CH3CN)4](BF4) (0.050 g, 0.16 mmol) in acetonitrile
was added a solution of I (0.038 g, 0.32 mmol) in acetonitrile. The
color of the solution changed to greenish brown in 3–4 d. After
1 week, dark purple needles of 3 were formed along with blue crys-
tals of CuSO4·5H2O (0.006 g, 14%). Data for 3: yield 0.048 g, 52%,
m.p. 210–213 °C. C12H16BCuF4N4S6 (559.00): C 25.76, H 2.86, N
10.01, S 34.34; found C 25.84, H 3.00, N 10.16, S 33.20. UV/Vis
Lmol–1 cm–1) = 264 nm (1.477ϫ 104). IR: ν = 3432 (br., OH);
˜
3107–2935 (m, C–H); 1570 (s), 1483 (sh.) (C–N + δC–H); 1407
(m), 800 (m), 708 (w) (NO3); 887 (m, C–S); 770 (s, δN–CH3) cm–1.
Magnetic moment (BM): 1.974.
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Synthesis of [Cu4(μ3-I)2(μ-I)2(μ-S-N2C4H8S)2(κ1-S-N2C4H8S)2]n (8): (data collection, refinement, and reduction) with XSCANS[28] and
To a solution of copper(I) iodide (0.025 g, 0.13 mmol) in acetoni-
trile was added a solution of IV (0.015 g, 0.13 mmol) in acetonitrile.
After 2–3 d, colorless prismatic crystals of 8 were obtained, yield
SHELXTL-PC (for 7), CrysAlisPro (for 1, 3, 5, 6, 7), SMART and
SAINT (for 2), and APEX2 (for 4, 8)[29,30] and corrected for ab-
sorption by using SADABS.[31] The structures of 1–8 were solved
0.005 g, 32%, m.p. 157–160 °C. C4H8CuIN2S (306.62): calcd. C by direct methods by using SIR-92 (for 5) and SHELXS-97 (for 1–
15.65, H 2.61, N 9.13, S 10.44; found C 15.76, H 2.70, N 9.17, S
4, 6–8)[32] and refined by full-matrix least-squares techniques based
9.84. IR: ν = 3272 (m, N–H); 2930–2878 (w, C–H); 1536 (s), 1503 on F2 by using SHELXL-97[32] All non-hydrogen atoms were re-
˜
(m) (C–N + δC–H); 1190 (m, C=S); 958 (m, δN–CH3) cm–1.
fined anisotropically. The crystallographic data are given in
¯
Tables 1 and 2. For complex 2, if higher symmetry (P1) was intro-
Crystal Structure Determinations: Single crystals of 1–8 were
mounted on glass fibers and data were collected by using Xcalibur
R (for 1, 3, 6, 7), Bruker X8 Kappa APEXII (for 4), Siemens P4
(for 5), and Bruker SMART APEXII CCD area detector (for 2, 8)
diffractometers, each equipped with a graphite monochromator
and Mo-Kα radiation (λ = 0.71073 Å). The unit cell dimensions
duced, refinement was not performed finely. So we employed lower
symmetry (P1) without centrosymmetry in an exact sense. How-
ever, the chemical formula was defined, as elemental analysis was
calculated regardless of discrepancy between actually bridged
structures and crystallographically asymmetric unit.
and intensity data were measured at 296 (for 2, 5), 123(2) (for 1, CCDC-852658 (for 1), -852659 (for 2), -852660 (for 3), -880493 (for
7), 110(2) (for 3, 6), and 100(2) (for 4, 8). The data were processed
4), -769469 (for 5), -852657 (for 6), -852661 (for 7), and -880492
Table 1. Crystallographic data for complexes 1–4.
1
2
3
4
Empirical formula
Formula weight
T [K]
C6H8ClCuN2S3
303.31
123(2)
C6H8BrCuN2S3
347.80
296
C12H16BCuF4N4S6
559.00
110(2)
C12H20Cu2I2N4S8
857.68
100(2)
Crystal system
Space group
triclinic
P1
triclinic
P1
monoclinic
C21
triclinic
P1
¯
¯
a [Å]
b [Å]
c [Å]
α [°]
7.3104(4)
8.5765(6)
9.4759(8)
67.830(7)
68.854(6)
82.517(5)
513.14(6)
2
7.4773(7)
8.5574(8)
9.5302(9)
70.051(1)
67.410(1)
84.450(1)
528.82(9)
2
18.67(4)
4.93(1)
12.35(3)
90
120.17(3)
90
983.3(4)
2
1.888
7.5969(2)
9.2259(3)
9.6091(3)
96.511(2)
109.542(1)
90.080(2)
630.04(3)
1
β [°]
γ [°]
V [Å3]
Z
Dcalcd. [gcm–3]
1.963
2.949
2.184
6.388
2.261
4.810
μ [mm–1]
1.792
All reflections collected
Unique reflections, Rint
Observed reflections
Final R indices
R1
7565
7569, 0.000
3763
3034
2611, 0.0100
2284
3469
2652, 0.0319
2094
14476
2486, 0.0368
2244
2
0.0426
0.1135
0.024
0.0809
0.0652
0.1833
0.0271
0.0598
wR2 (all)
Table 2. Crystallographic data for complexes 5–8.
5
6
7
8
Empirical formula
Formula weight
C16H20Cl4Cu2N8S2
657.44
C16H28B2CuF8N8O4S2
697.74
C16H24CuN10O8S2
612.11
C4H8CuIN2S
306.62
T [K]
Crystal system
Space group
296(2)
monoclinic
P21/n
110(2)
monoclinic
P21/n
123(2)
monoclinic
P21/n
100(2)
triclinic
¯
P1
a [Å]
b [Å]
c [Å]
α [°]
9.053(1)
8.402(1)
15.754(3)
90
94.28(1)
90
1195.0(3)
2
1.827
7.6059(2)
13.7908(4)
13.1488(4)
90
96.807(3)
90
1369.47(7)
2
1.692
8.6442(3)
13.6041(4)
10.3827(3)
90
100.382(3)
90
1200.98(7)
2
1.693
9.386(2)
9.584(2)
10.00(2)
111.38(3)
96.05(3)
105.42(3)
786.7(3)
4
β [°]
γ [°]
V [Å3]
Z
Dcalcd. [gcm–3]
μ [mm–1]
2.589
36.533
2.425
1.045
1.149
All reflections collected
Unique reflections, Rint
Observed reflections
Final R indices
R1
2365
2219, 0.0193
1859
9021
4506, 0.0258
3421
9180
3975, 0.0249
2929
14651
2817, 0.0296
2791
0.0344
0.0929
0.0377
0.1017
0.0296
0.0703
0.0350
0.1207
wR2 (all)
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[10]
[11]
[12]
[13]
Supporting Information (see footnote on the first page of this arti-
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molecular structure of 4; packing network of the complexes; tables
of hydrogen bonds, bond lengths, and bond angles.
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Financial assistance from the University Grant Commission
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is gratefully acknowledged. The authors thank Shikha Indoria and
Amanpreet Kaur Junior Research Fellows for preliminary assist-
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[16]
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© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim