Thiosemicarbazone derivatives of nickel and copper: The unprecedented coordination of furan ring in octahedral nickel(ii) and of triphenylphosphine in three-coordinate copper(i) complexes

Article abstract of DOI:10.1039/c0dt01291b

The influence of substituents at the C² carbon of N ¹-substituted thiosemicarbazones, {C₄H₃X-C ²(CH₃)N³-N²H-C¹(S)N ¹HR²} (X = O, S) on the geometry of nickel(ii) complexes has been investigated. The presence of a methyl group at the C² position of 2-acetylfuran-N¹-substituted thiosemicarbazones {(C ₄H₃O)-C²(CH₃)N³-N ²H-C¹(S)N¹HR², R² = CH₃, HaftscN-Me; C₂H₅, HaftscN-Et; C ₆H₅, HaftscN-Ph} induces unusual coordination by the furan ring and yielded high spin octahedral nickel(ii) complexes, [Ni(κ³-O, N³, S-aftscN-R²)₂], CH₃1, C₂H₅2, and 2[Ni((κ³-O, N³, S-aftscN-Ph)₂] 3 (μ_eff = 2.98, 1; 2.96, 2; 2.92, 3). With 2-acetylthiophene-N¹-substituted thiosemicarbazones, {(C₄H₃S)-C²(CH ₃)N³-N²H-C¹(S)N¹HR ², R² = CH₃, HattscN-Me; C₂H ₅, HattscN-Et; C₆H₅, HattscN-Ph}, N ³, S chelated low spin trans square planar complexes, {[Ni(κ³-O, N³, S-attscN-R²)₂], R² = CH₃, 4; C₂H₅, 5; C ₆H₅, 6} with pendant thiophene rings have been obtained. The bigger sized sulfur atoms of the thiophene rings form short intramolecular contacts with the deprotonated hydrazinic nitrogen atoms (S...N ²) inhibiting its lability for possible coordination to nickel(ii). Complexes have one independent molecule (1) or two independent molecules (2, 3) in their respective crystal lattices. The simultaneous presence of methyl groups at the C² and N¹ atoms of 2-acetylthiophene-N ¹-methylthiosemicarbazone (HattscN-Me) have facilitated the binding of triphenylphosphine in three-coordinate copper(i) halide complexes, [CuX(η¹-S-HattscN-Me)(Ph₃P)] (X, Br, 7; Cl, 8), which represent an unusual donor set of ligands, namely, triphenylphosphine, sulfur of a thio-ligand and a halide.

Full text of DOI:10.1039/c0dt01291b

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PAPER
Thiosemicarbazone derivatives of nickel and copper: the unprecedented
coordination of furan ring in octahedral nickel(II) and of triphenylphosphine in
three-coordinate copper(I) complexes†
Tarlok Singh Lobana,*a Poonam Kumari,a Rekha Sharma,a Alfonso Castineiras,b Ray Jay Butcher,c
Takashiro Akitsud and Yoshikazu Aritaked
Received 27th September 2010, Accepted 7th January 2011
DOI: 10.1039/c0dt01291b
The influence of substituents at the C2 carbon of N1-substituted thiosemicarbazones,
{C4H3X–C2(CH3) N3–N2H–C1( S)N1HR2} (X = O, S) on the geometry of nickel(II) complexes has
been investigated. The presence of a methyl group at the C2 position of 2-acetylfuran-N1-substituted
thiosemicarbazones {(C4H3O)–C2(CH3) N3–N2H–C1( S)N1HR2, R2 = CH3, HaftscN–Me; C2H5,
HaftscN–Et; C6H5, HaftscN–Ph} induces unusual coordination by the furan ring and yielded high spin
3
3
octahedral nickel(II) complexes, [Ni(k -O, N3, S-aftscN–R2)2], CH3 1, C2H5 2, and 2[Ni((k -O, N3,
S-aftscN–Ph)2] 3 (meff = 2.98, 1; 2.96, 2; 2.92, 3). With 2-acetylthiophene-N1-substituted
thiosemicarbazones, {(C4H3S)-C2(CH3) N3-N2H–C1( S)N1HR2, R2 = CH3, HattscN–Me; C2H5,
HattscN–Et; C6H5, HattscN–Ph}, N3, S chelated low spin trans square planar complexes, {[Ni(k -O,
3
N3, S-attscN–R2)2], R2 = CH3, 4; C2H5, 5; C6H5, 6} with pendant thiophene rings have been obtained.
The bigger sized sulfur atoms of the thiophene rings form short intramolecular contacts with the
deprotonated hydrazinic nitrogen atoms (S ◊ ◊ ◊ N2) inhibiting its lability for possible coordination to
nickel(II). Complexes have one independent molecule (1) or two independent molecules (2, 3) in their
respective crystal lattices. The simultaneous presence of methyl groups at the C2 and N1 atoms of
2-acetylthiophene-N1-methylthiosemicarbazone (HattscN–Me) have facilitated the binding of
1
triphenylphosphine in three-coordinate copper(I) halide complexes, [CuX(h -S-HattscN–Me)(Ph3P)]
(X, Br, 7; Cl, 8), which represent an unusual donor set of ligands, namely, triphenylphosphine, sulfur of
a thio-ligand and a halide.
of the examples of coordination by pendant furan have been
Introduction
observed with alkali/alkaline and main group metals, and only
a few with transition (Ti, Zr, Ag, Ru, Mo)/post transition
(Cd, Lu, Sm, U) metals.3–22 Similarly, free thiophene coordinates
through sulfur (type I) or acts as a S, C- bridge (type II)
Coordination to metals by furan/thiophene through oxy-
gen/sulfur donor atoms can be classified into three broad cat-
egories: as free, pendant or as a part of fused ring as depicted
in Chart 1 (X = O, S). There is only one example in which
free furan coordinates to a metal (namely, Cu) (type I),1 and
again one example in which it acts as an O, C- bridge (namely,
Y) (type II).2 Coordination by pendant furan (type III)3–22 or
fused furan rings (type IV)23–32 make several examples. Most
(X = S) in several complexes,33–40 and likewise coordination by
26a,52c,55–62
pendant thiophene6,38,41–54 or fused thiophene rings
is
also widespread. In this case, complexes of ligands with pendant
thiophene are essentially reported with transition (Cu, Ir, Mo, Pd,
Re, Rh, Sc, Ag)/post transition metals (Hg).41–54
Surprisingly, there is no example of coordination of free or
pendant furan/thiophene rings to nickel(II),1–62 while in a few
complexes, fused furan/thiophene has shown coordination to
nickel(II).25,55c,57 Also, there is no example of coordination by
pendant furan or thiophene in complexes of thiosemicarbazones.63
The impetus to carry out this investigation is primarily due to
our experience in nickel(II)-furan/thiophene thiosemicarbazone
chemistry.64 It was observed that furan/thiophene rings remained
pendant in cis or trans nickel(II) square planar complexes with N1-
substituted thiosemicarbazones (Chart 2, R1 = H).64 This made us
aDepartment of Chemistry, Guru Nanak Dev University, Amritsar, 143 005,
India. E-mail: tarlokslobana@yahoo.co.in; Fax: +91-183-2-258820
bDepartamento De Quimica Inorganica, Facultad de Farmacia, Universidad
de Santiago, 15782, Santiago, Spain
cDepartment of Chemistry, Howard University, Washington DC, 20059, USA
dDepartment of Chemistry, Tokyo University of Science, Tokyo, 1628601,
Japan
† Electronic supplementary information (ESI) available. CCDC reference
numbers 735088 (1), 737163 (2), 771690–771692 (3–5), 783926 (7), 713436
(8) and 771693. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/c0dt01291b
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Chart 1 Coordination to metals by furan/thiophene (X = O, S).
Chart 2 The different ligands used in this work.
curious to investigate coordination by pendant furan/thiophene
rings to nickel(II) by changing substituents at the C2 carbon as
shown in Chart 2.
A series of ligands (R1 = Me, R2 = Me, Et, Ph) have been used
for preparing complexes of nickel(II) in which effect of R1 on the
nature of the complexes is investigated. For R1 = Me at C2 and
R2 = Me at N1, the reactions with copper(I) halides have also
been investigated. The results of the investigations based on these
ligands are herein reported.
absorption bands): 3367 br (n(N1–H)); 3153 m, 2942 m, 2903 m
((C–H)); 1558 s, 1541 s (n(C N) + n(C–C)); 1072 s, 1019 s, 913 s
(n(C–N)); 737 s (n(C–S)). Electronic absorption spectrum (10-4
M
in CH3OH, lmax/nm, e/L mol-1 cm-1): 982 (540), 671 (510), 406
(2.37 ¥ 104), 331 (1.99 ¥ 104), 301 (2.09 ¥ 104), 247 (1.95 ¥ 104). 1H
NMR (d, CDCl3 + DMSO-d6): d 31.86 (1H, s, C6H), 19.58 (1H,
s, C4H), 17.64 (1H, s, C5H), 6.76 (3H, s, CH3(C2)), 6.48 (3H, s,
CH3(N1)), -4.09 (1H, s, N1H) ppm. Magnetic moment: meff = 2.98
BM.
Compounds 2–6 were prepared by a similar method.
Synthesis of [Ni(aftscN–Et)2] 2. Yield: 0.037 g, 76%. Anal.
Calcd. (%) for C18H24N6NiO2S2: C, 45.07; H, 5.01; N, 17.53.
Found: C, 45.12; H, 4.98; N, 17.54. IR (KBr, cm-1, selected
absorption bands): 3372 br (n(N1–H)); 3081 m, 2975 m, 2875 m
(n(C–H)); 1558 s, 1507 s (n(C N) + n(C–C)); 1065 s, 1021 s, 916 s
Experimental Section
General. Ni(OAc)2·4H2O, CuSO4·5H2O, 2-acetylfuran-2-
carbaldehyde, 2-acetylthiophene-2-carbaldehyde, N-methyl-,
N-ethyl- and N-phenyl-thiosemicarbazides were procured from
Sigma-Aldrich Ltd. The ligands HaftscN–Me, HaftscN–Et,
HaftscN–Ph, HattscN–Me, HattscN–Et and HattscN–Ph were
synthesized by conventional procedures.65 Copper(I) halides were
prepared by reducing an aqueous solution of CuSO4·5H2O using
SO2 in the presence of NaX (X = Cl, Br, I) in water.66
(n(C–N)); 735 s (n(C–S)). Electronic absorption spectrum (10-4
M
in CH3OH, lmax/nm, e/L mol-1 cm-1): 983 (410), 675 (380), 405
(2.37 ¥ 104), 331 (1.99 ¥ 104), 301 (2.09 ¥ 104), 248 (1.95 ¥ 104).1H
NMR (d, CDCl3 + DMSO-d6): d 29.38 (1H, s, C6H), 18.04 (1H, s,
C4H), 16.64 (1H, s, C5H), 5.02 (5H, s, CH3(C2) + CH2(N1)), 3.94
(3H, s, CH3(N1)), -3.01 (1H, s, N1H) ppm. Magnetic moment:
meff = 2.96 BM.
Synthesis of [Ni(aftscN–Me)2] 1. To a light yellow solution
of the HaftscN–Me ligand (0.039 g, 0.200 mmol) in methanol
(15 mL) solid Ni(OAc)2 (0.025 g, 0.100 mmol) was added. The
color of the solution changed to dark brown and it was stirred
for about 4 h. The clear solution after filtration was left for
crystallization. During slow evaporation of the solution, a brown
colored compound was separated, which was recrystallized in a
dichloromethane and methanol mixture (3 : 1 v/v). Yield: 0.034 g,
75%. Anal. Calcd (%) for C16H20N6NiO2S2: C, 42.55; H, 4.43; N,
18.62. Found: C, 42.38; H, 4.65; N, 18.46. IR (KBr, cm-1, selected
Synthesis of [Ni(aftscN–Ph)2] 3. Yield: 0.044 g, 77%. Anal.
Calcd. (%) for C26H24N6NiO2S2: C, 54.23; H, 4.17; N, 14.60.
Found: C, 54.56; H, 4.78; N, 14.40. IR (KBr, cm-1, selected
absorption bands): 3394 br (n(N1–H)); 3103 m, 3023 m, 2950
m (n(C–H)); 1554 s, 1520 s (n(C N) + n(C–C)); 1085 s, 1023 m,
917 s (n(C–N)); 731 s (n(C–S)). Electronic absorption spectrum
(10-4 M in CH3OH, lmax/nm, e/L mol-1 cm-1): 986 (390), 678 (350),
408 (2.39 ¥ 104), 330 (1.98 ¥ 104), 301 (2.09 ¥ 104), 248 (1.94 ¥ 104).
3220 | Dalton Trans., 2011, 40, 3219–3228
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1H NMR (d, CDCl3 + DMSO-d6): d 24.40 (1H, s, C6H), 15.91
(1H, s, C4H), 14.17 (1H, s, C5H), 9.79 (2H, s, o-H(Ph)), 7.91 (3H,
s, p-H+m-H(Ph)), 7.05 (3H, s, CH3(C2)), -1.12 (1H, s, N1H) ppm.
Magnetic moment: meff = 2.92 BM.
w, 2765 m n(C–H); 1640 m, 1575 m n(C N) + n(C C); 1095 s
1
n(P–CPh); 1029 s n(C–N); 795 s n(C S). H NMR (d, CDCl3):
11.30 s (1H, s, N2H), 7.35–7.53 (18H, m, C4,6H + PPh3 + N1H),
7.01 (1H, dd, C5H), 3.12 (3H, d, CH3(C2)), 2.56 (3H, d, CH3(N1))
ppm. 31P NMR (d, CDCl3): 30.8 ppm, Dd (dcomplex - dligand) 35. 4
ppm.
Synthesis of [Ni(attscN–Me)2] 4. Yield: 0.036 g, 74%, Anal.
Calcd. (%) for C16H20N6NiS4: C, 39.72; H, 4.13; N, 17.38. Found:
C, 39.65; H, 4.15; N, 16.93. IR (KBr, cm-1, selected absorption
bands): 3395 br (n(N–H)); 3056 m, 2905 m (n(C–H)); 1558 s, 1507
s (n(C N) + n(C C)); 1069 s, 1025 m, 978 s (n(C–N)); 713
s (n(C–S)). Electronic absorption spectrum (10-4 M in CH3OH,
Physical measurements. Elemental analyses for C, H and N
were carried out using a thermoelectron FLASHEA1112 analyser.
The melting points were determined with a Gallenkamp electri-
cally heated apparatus. UV-visible spectra were recorded using a
UV-1601PC Shimadzu spectrophotometer. Magnetic susceptibil-
ity was recorded using Magnetic Susceptibility balance procured
from Johnson Matthey, Catalytic Systems Division Equipment.
The IR spectra of the ligands and their complexes were recorded
using KBr pellets in the range 4000–400 cm-1 on the FTIR-
SHIMADZU 8400 Fourier Transform Spectrophotometer. 1H
NMR spectra were recorded on a JEOL AL-300 FT spectrometer
operating at a frequency of 300 MHz in CDCl3 with TMS as the
internal reference. 31P NMR spectra were recorded at 121.5 MHz
with (CH3O)3P as the external reference taken as zero position.
l
max/nm, e/L mol-1 cm-1): 412 (0.40 ¥ 104), 337 (1.28 ¥ 104), 270
(1.10 ¥ 104), 229 (1.09 ¥ 104). 1H NMR (d, CDCl3): d 7.45 (1H, t,
C6H), 6.91 (1H, s, N1H), 6.57 (1H, s, C4H), 6.22 (1H, s, C5H), 3.81
(3H, s, CH3(C2)), 1.56 (3H, s, CH3(N1) + DMSO) ppm.
Synthesis of [Ni(attscN–Et)2] 5. Yield: 0.038 g, 74%. Anal.
Calcd. (%) for C18H24N6NiS4: C, 42.24; H, 4.69; N, 16.43. Found:
C, 42.17; H, 5.00; N, 16.48. IR (KBr, cm-1, selected absorption
bands): 3357 br (n(N1–H)); 3093 m, 3056 m, 2987 m, 2871 (n(C–
H)); 1560 s, 1507 s (n(C N) + n(C C)); 1074 s, 1046 m, 1002 m
(n(C–N)); 737 s (n(C–S)). Electronic absorption spectrum (10-4
M
in CH3OH, lmax/nm, e/L mol-1 cm-1): 410 (0.40 ¥ 104), 343 (1.41 ¥
X-ray crystallography. The single crystals of compounds were
mounted on Bruker X8 KappaAPEXII (1–5) and CCD area
detector (7 and 8) diffractometer, equipped with a graphite
1
104), 269 (1.26 ¥ 104), 231 (1.18 ¥ 104). H NMR (d, CDCl3): d
7.37 (1H, dd, C6H), 6.71 (1H, d, C4H), 6.47 (1H, d, C5H), 6.10
(1H, s, N1H), 4.24 (2H, s, CH2), 2.20 (3H, s, CH3(C2) + DMSO),
1.26 (3H, s, CH3(N1)) ppm.
˚
monochromator and Mo-Ka radiation (l = 0.71073 A). The unit
cell dimensions and intensity data were measured at 100(2) K
for 1–5, and at 294(2) and 173(2) K for 7 and 8 respectively.
The data were processed with APEX267a (1–5), Bruker SMART67b
(7, 8) (data collection, cell refinement), Bruker SAINT67b (7, 8)
(data reduction) corrected for absorption using SADABS67c (1–5)
(transmissions factors: 1.000–0.871). The structure was solved by
direct methods using the program SHELXS-9767d and refined by
full-matrix least-squares techniques against F2 using SHELXL-
97.67e Compounds 2 and 5 present a chiral crystal structure. For
2 (space group P21) the structure was refined as a racemic twin
with components 0.31(6) and 0.67(6) for the Flack parameter
(absolute structure parameter), and for 5 (space group C2) the
Flack parameter was calculated to be 0.03(2) for the present
structure and 0.98(2) for the inverted structure. Criteria of a
satisfactory complete analysis were the ratios of “rms” shift to
standard deviation less than 0.001 and no significant features
in the final difference maps. Atomic scattering factors from
“International Tables for Crystallography”.67f Molecular graphics
from PLATON67g (1–5), Bruker SHELXTL67h (7 and 8). Table 1
contains crystal data for complexes 1–5, 7 and 8. Crystallographic
data of ligand (HaftscN–Me) and bond distances and other
data for complexes 1–5, 7 and 8 are placed as supplementary
information.†
Synthesis of [Ni(attscN–Ph)2] 6. Yield: 0.035 g, 58%. Anal.
Calcd. (%) for C26H24N6NiS4: C, 51.43; H, 3.96; N, 13.84. Found:
C, 50.92; H, 3.84; N, 13.32. IR (KBr, cm-1, selected absorption
bands): 3408 m (n(N1–H)); 3088 m, 2930 m, 2857 m (n(C–H));
1558 s, 1507 s (n(C N) + n(C C)); 1050 s, 1025 m (n(C–N)); 752
s (n(C–S)). Electronic absorption spectrum (10-4 M in CH3OH,
l
max/nm, e/L mol-1 cm-1): 415 (0.52 ¥ 104), 343 (1.89 ¥ 104), 264
(2.28 ¥ 104), 213 (1.50 ¥ 104). 1H NMR (d, CDCl3): d 8.88 (1H, d,
N1H) 7.46 (2H, m, o-H(Ph)), 7.37 (1H, d, C6H), 7.30 (m, p-H(Ph)
+ CDCl3), 7.14 (1H, t, C4H), 7.04 (2H, m, m-H(Ph)), 6.92 (1H, q,
C5H), 2.80 (3H, s, (CH3(C2)) ppm.
Synthesis of [CuBr(HattscN–Me)(Ph3P)] 7. To copper(I) bro-
mide (0.025 g, 0.174 mmol) in 15 mL acetonitrile, the ligand
HattscN–Me (0.037 g, 0.174 mmol) was added, and the contents
stirred for 3–4 h. It formed yellow precipitates and addition of Ph3P
(0.046 g, 0.174 mmol) followed by stirring for 5–10 min formed
a clear solution, which on slow evaporation at room temperature
yielded yellow crystals. Yield: 0.063 g, 72%. Anal. Calcd. (%) for
C26H26CuBrN3S2P: C, 50.44; H, 4.20; N, 6.79. Found: C, 50.57; H,
4.26; N, 6.73. IR (KBr, cm-1, selected absorption bands): 3365 s
n(N1H); 3129 m n(N2H); 2925 m, 2789 w, 2755 m n(C–H); 1642 m,
1570 m n(C N) + n(C C); 1093 s n(P–CPh); 1029 s n(C–N); 801
1
s n(C S). H NMR (d, CDCl3): 11.42 (1H, s, –N2H), 7.31–7.57
Results and discussion
(18H, m, C4,6H + PPh3 + N1H), 7.02 (1H, dd, C5H), 3.22 (3H,
d, –CH3(C2)), 2.60 (3H, d, CH3(N1)) ppm. 31P NMR (d, CDCl3):
31.2 ppm, Dd (dcomplex - dligand) 35. 8 ppm.
(a) Nickel complexes
Synthesis and coordination by furan rings. Nickel(II) acetate
with heterocyclic N1-substituted thiosemicarbazones {C4H3X–
C2(R1) N3–N2H–C1( S)N1HR2, X = O, S} in methanol formed
square planar complexes of stoichiometry, [NiL2] (L = ftscN-R2,
ttscN-R2), for R1 as a hydrogen substituent at the C2 carbon
(Scheme 1).64 Furan or thiophene rings remained pendant and
Complex 8 was prepared by a similar method.
Synthesis of [CuCl(HattscN–Me)(Ph3P)] 8. Yield: 0.079 g,
67%. Anal. Calcd. (%) for C26H26CuClN3S2P: C, 54.35; H, 4.56;
N, 7.31. Found: C, 54.17; H, 4.56; N, 7.22. IR (KBr, cm-1, selected
absorption bands): 3360 s n(N1H); 3119 m n(N2H); 2920 m, 2788
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Scheme 1 Synthesis of complexes with R1 = H substituent at the C2
carbon.
did not show any coordination for different substituents at the N1
nitrogen (R2 = Me, Et, Ph). For R1 as a methyl substituent at the
C2 carbon in place of hydrogen, a series of new complexes, namely,
[NiL2] {L = aftscN–R2, R2 = Me 1, Et 2, Ph 3, attscN–R2, R2 = Me
4, Et 5, Ph 6} have been isolated (Scheme 2).
Scheme 2 Synthesis of complexes with R1 = CH3 substituent at the C2
carbon.
The IR and NMR spectral data of the complexes have shown
disappearance of the hydrazinic protons (N2–H) and it reveals that
thio-ligands are coordinating as uninegative anions. The electron
absorption spectral data (d-d transitions and charge transfer
transitions)68a and m values support octahedral geometry for the
furan complexes and a square planar geometry for the thiophene
complexes. The paramagnetism of complexes 1–3 revealed that
the furan ring is probably coordinating to nickel(II) metal. A
single crystal X-ray study (vide infra) later confirmed octahedral
geometry for complexes with coordinated furan rings (1–3), and
square planar for complexes with pendant thiophene rings (4–6)
(Scheme 2).
Molecular structures. Molecular structures of complexes
1–3 are shown in Fig. 1–3 respectively. In these complexes, the
uninegative thio-ligands are coordinated to the nickel metal center.
The sulfur and furan ring oxygen atoms occupy cis positions of
the octahedron and the azomethine nitrogen atoms occupy trans
positions. The furan rings form short O–Ni–O bite angles in com-
plexes, {73.26(4), 79.89(10), and 80.03(13)◦ respectively}, other
angles surrounding nickel(II) suggest severely distorted octahedral
geometry. Nickel–furan bond distances (Ni–O) lie in the range
˚
2.202(3) –2.358(11) A, which are close to the bond distances
˚
(2.093–2.120 A) observed in the tetrakis(m2-(4-methoxyphenyl)
dithiophosphonato- O, S, S¢)-tetra-aquatetrakis(tetrahydrofuran)-
tetra-nickel(II) complex68b and 2.184, 2.139 A observed in nickel(II)
˚
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Fig. 1 Molecular structure of complex [Ni(aftscN–Me)2] 1.
complexes involving fused furan ring coordination.25 An analysis
of the X-ray structure of one of the furan ligands (HaftscN–Me,
Fig. 4) revealed that H ◊ ◊ ◊ H contact between the methyl hydrogen
at the C2 carbon (numbering is C3 in ligand’s structure, Fig. 4) and
4
6
˚
the furan ring hydrogen (C –H ◊ ◊ ◊ H–C , 2.110 A) is increased {C–
˚
H ◊ ◊ ◊ H–C: 2.452, 2.486, 2.407 A in complexes 1–3 respectively}.
Complex 1 exists as a single molecule (Fig. 1) and complexes 2
and 3 exist as two independent molecules in their respective crystal
lattices (Fig. 2 and 3).
Fig. 3 Molecular structure of complex of [Ni(aftscN–Ph)2] 3.
Complexes 4–6 do not show coordination by the thiophene ring
and have trans square planar geometries (Fig. 5). These complexes
exist as single molecules in their respective crystal lattices, a
behavior different from that of furan complexes. It is found
that the bigger sized sulfur atoms of thiophene rings form short
intramolecular contacts with the deprotonated hydrazinic nitrogen
atoms (S ◊ ◊ ◊ N2) inhibiting its lability for possible coordination to
nickel(II). These S ◊ ◊ ◊ N2 interactions in complexes 4 and 5 (2.63,
Fig. 4 Molecular structure of the ligand HaftscN–Me.
˚
2.65 A respectively) are much shorter than the sum of the van der
69
˚
Waals radius of S and N, 3.35 A.
of a similar interaction (O ◊ ◊ ◊ N2) for the furan derivatives leads to
a different pattern of bonding and intermolecular interactions.
In complex [Ni(aftscN–Me)2] 1, the deprotonated hydrazinic
nitrogen atom (–N2–) of one molecule interacts with hydrogen
Packing interactions. An analysis of the packing diagrams
of complexes 1–5 reveals interesting trends of inter- and intra-
molecular interactions which are influenced by the presence of the
substituents at the C2 and N1 atoms of thiosemicarbazones. The
sulfur atoms of thiophene rings are exhibiting short intramolecular
contacts with the deprotonated hydrazinic (–N2–) nitrogen atom
which lowers the fluxional ability of the thiophene rings. The lack
1
2
1
˚
atom (at N ) of the adjacent molecule {N ◊ ◊ ◊ H–N , 2.33 A}.
This leads to the formation of a zig-zag 1D chain. Between these
1D chains there are (furan)C–H ◊ ◊ ◊ N (2.58 A) and (furan)C–
H ◊ ◊ ◊ p(C N ) (2.85 A) interactions, thus a 2D polymeric sheet
2
˚
2
˚
Fig. 2 Molecular structure of complex [Ni(aftscN–Et)2] 2 showing the enantiomers A (Ni1) and B (Ni2) present in the asymmetric unit.
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From above it is noted that the lack of a methyl substituent at C2
resulted in square planar complexes with the furan or thiophene
rings remaining pendant.64 The presence of a methyl group at C2
has induced coordination by the furan ring, but thiophene still
remains pendant. It appears that weak Lewis basicity of the furan
ring is enhanced by the inductive effect of the methyl substituent
at the C2 carbon. Further, there is an increase in electron density
around the nickel center by N3, S- chelation which appears
to assist in the formation of nickel(II)–furan ring coordination.
Stereochemically, it has been found that H ◊ ◊ ◊ H contact between
the methyl hydrogen at the C2 carbon and the furan ring hydrogen
is increased in complexes 1–3. Thus both the electronic and steric
factors appear to be responsible for furan ring coordination. As
regards the thiophene ring, it is found that the bigger sized sulfur
atoms of thiophene rings form short intramolecular contacts with
the deprotonated hydrazinic nitrogen atoms (S ◊ ◊ ◊ N2) inhibiting
its lability for possible coordination to nickel(II). The formation
of Ni–O is also favored in terms of the HSAB principle over Ni–S
bonds.
Fig. 5 Molecular structure of complex [Ni(attscN–Me)2] 4 (complex 5
has a similar structure).
is formed (Fig. 6). In contrast in complex [Ni(aftscN–Et)2] 2,
hydrogen at the N1 nitrogen of one molecule interacts with the
1
˚
sulfur atom of the adjacent molecule {N –H ◊ ◊ ◊ S–C, 2.73 A}. This
interaction forms a 1D zig-zag chain. The interaction between
chains {(furan)C–H ◊ ◊ ◊ N , 2.72 A and (furan)C–H ◊ ◊ ◊ ·p(C N2),
1
˚
˚
2.81 A} results in the formation of 2D sheet (see supplementary
information†).
In complex [Ni(aftscN–Ph)2] 3, there are two independent
molecules (Type I and Type II) in the crystal lattice. Type
I molecules interact with one another through furan–phenyl
(b) Copper complexes
˚
{(furan)C–H ◊ ◊ ◊ p(phenyl), 3.004 A) and amino–methyl {H–
1
2
˚
N ◊ ◊ ◊ H–CH2(C ), 2.618 A} groups. Type II molecules interact
with this arrangement from its top and bottom through C–S,
CH3 and phenyl moieties {C–S ◊ ◊ ◊ H–CH2(C2), 2.827, C–S ◊ ◊ ◊ H–
As an extension, the thiosemicarbazones under investigation
were reacted with copper(II) salts, which however reduced CuII
to CuI. This observation was in line with our previous re-
actions of thiosemicarbazones with copper(II) halides, wherein
thiosemicarbazones, {C4H3X–C2(H) N3–N2H–C1( S)N1HMe,
X = O, S} reduced copper(II) halides to copper(I) halides and
˚
C(furan), 2.957, (phenyl)C–H ◊ ◊ ◊ p(phenyl), 2.861 A} as shown in
Fig. 7. This unit of six molecules interacts with a similar unit via
2
1
˚
(phenyl)C–H ◊ ◊ ◊ N , 2.661 and C–S ◊ ◊ ◊ H–N , 2.660 A (Fig. 8a).
This unit of twelve molecules in the ab plane forms the basic core
which interacts with similar units along the c-axis resulting in the
formation of a 3D sheet.
1
formed dinuclear copper(I) halide complexes, [Cu2X2(m-S–L)2(h -
S–L)2] in which furan or thiophene rings remained pendant.70
Thus in this section reactions of 2-acetylthiophene-N1-methyl
thiosemicarbazone directly with copper(I) halides in the presence
of Ph3P have been carried out.
In complex [Ni(attscN–Me)2] 4, a hydrogen atom (at N1) of one
molecule interacts with a sulfur atom of the adjacent molecule {C–
1
˚
S ◊ ◊ ◊ H–N , 2.73 A} and this process continues to form a linear
The reactions of 2-acetylthiophene-N1-methyl thiosemicar-
bazones (R1 = Me, R2 = Me) with copper(I) halides in the presence
of triphenylphosphine have formed complexes of stoichiometry
{CuX(HattscN–Me)(Ph3P)} (X = Br, Cl). The IR spectra con-
firmed the presence of characteristic n(N–H), n(C S) and n(P–
CPh) bands of HattscN–Me and Ph3P ligands in complexes. The
1H NMR spectra revealed the presence of N1H, N2H, methyl
and phenyl signals and support the view that complexes have
1D chain. The chains then interact with one another through a
second set of sulfur and hydrogen atoms (at N1) resulting in the
formation of a 2D sheet. In complex 5, a 1D chain is similarly
1
˚
formed {C–S ◊ ◊ ◊ H–N , 2.82 A 5} and these chains link to one
2
1
˚
another through C ◊ ◊ ◊ H–CH–N (2.85 A), C–S ◊ ◊ ◊ H–CH2CH2–
1
˚
N (2.83 A) interactions and form a 2D sheet (see supplementary
information†).
Fig. 6 Packing diagram of complex 1, showing 2D network.
3224 | Dalton Trans., 2011, 40, 3219–3228 This journal is
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Fig. 7 Interactions of Type I and II molecules with one another.
Fig. 8 Packing diagram of complex 3 showing a 2D (a) and 3D network (b).
neutral thio-ligands. A single crystal X-ray study has shown the
formation of three-coordinate complexes, [CuX(h -S-HattscN–
Me)(Ph3P)] (X = Br 7, Cl 8) (Scheme 3). Recently, it has been
demonstrated that the substituents at the C2 and N1 atoms of
thiosemicarbazones influence the nuclearity and nature of bonding
of metal complexes.63,71–77 For example, in the case of thiophene
thiosemicarbazones, a sulfur-bridged dimer (type A) was obtained
when R1 and R2 were hydrogens (I, Chart 3).73 With a methyl
group at the C2 carbon (R1 = Me, R2 = H), again a type A
dimer was formed. Further, when hydrogen at the N1 atom was
replaced by a methyl group (R1 = H, R2 = Me), the sulfur-bridging
changed to halogen-bridging (type B, Chart 3).74 Interestingly, for
1
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Scheme 3
Chart 4 (a) P = (Ph)2PC6H4CHO, (b) P = Ph3P, N = (p-tolyl)2N, (c) P =
(cyhexl)3P, N = 1, 10 phen.
copper–phosphorous bond distances {Cu–Br, 2.3725(6); Cu–S,
63,69–71
˚
2.2180(11); Cu–P, 2.2225(10) A} (Fig. 9A).
Fig. 9B shows
how three-coordinate molecules of complex 7 are interlinked in the
crystal lattice. Two molecules are linked to one another through an
intermolecular interaction between the hydrogen of a methyl group
at the C2 carbon and bromine, which form an H-bonded dimer.
The H-bonded dimers are linked to one another through p ◊ ◊ ◊ p
interactions leading to the formation of a 1D chain. Complex 8
has a similar molecular structure and intermolecular interactions
(see supplementary information†).
Chart 3 P = Ph3P, X = Cl, Br, I.
R1 and R2 as methyl groups, neither a sulfur-bridged dimer A
nor a halogen-bridged dimer B were formed as anticipated, rather
three coordinate complexes were obtained. Therefore, the presence
of methyl groups at both the C2 and N1 atoms of thiophene
thiosemicarbazones (R1 = R2 = Me) has played an important role in
stabilizing a coordination number of three with a new combination
of ligands. It is reported that triphenylphosphine coordinates to
copper(I) in a tetrahedral environment.78–81
Three coordinate copper(I) complexes with cores, [CuXP2] (a),82
[CuNP2)] (b),85 and [CuP(N–N)]BF4 (c)86 (Chart 4) have displayed
interesting photophysical luminescence.82–88 Here, in case (b), Ph3P
is bonded in a three coordinate environment with (o-tolyl)2N- as
the anion and cases (a) or (c), are exhibited by Ph2PCH2CHO and
(cyhexl)2P- respectively. Finally, tri-o-tolylphosphine formed three
coordinate copper(I) complexes with heterocyclic thioamides.83
The geometry around copper(I) is distorted trigonal planar
for complex 7, {S–Cu–P, 125.98(4); S–Cu–Br, 122.37(3); P–Cu–
Br, 111.53(3)◦}, with usual copper–halogen, copper–sulfur and
It is important to understand the interactions which may
have assisted in the formation of three coordinate copper(I)
complexes of triphenylphosphine. In complex 7, there are intra-
molecular interactions involving amino hydrogen–imido nitrogen
◦
1
3
˚
{CH3N H ◊ ◊ ◊ N , 2.168 A, 107.74 }, methyl hydrogen–sulfur
◦
˚
{H2CH ◊ ◊ ◊ S, 2.646 A, 107.92 } and imino hydrogen–bromine
◦
2
˚
atoms {N H ◊ ◊ ◊ Br, 2.587 A, N–H ◊ ◊ ◊ Br, 153.60 } (Scheme 4). The
bromine atom is also involved in intermolecular interactions. The
methyl substituent at N1 is engaged in H-bond formation with the
◦
˚
coordinated sulfur {H2CH ◊ ◊ ◊ S, 2.646 A, C–H ◊ ◊ ◊ S, 107.92 }, and
in a way blocking the possibility of dimerization through the sulfur
donor atom. Likewise, the methyl substituent at the C2 carbon is
involved in an intermolecular interaction with the bromine atom
{H2CH ◊ ◊ ◊ Br, 2.847 A, 162.84 }. The bromine is also H-bonded
to hydrogen at the N2 atom thus making it difficult for bromine to
act as a bridge. All the intra- and inter-molecular interactions are
strong as these distances are less than the sum of van der Waals
◦
˚
69
˚
radii {H, Br, 3.00–3.45; H, S, 3.00–3.45; H, N, 2.75–3.00 A}.
Fig. 9 Structure of complex 7 with atomic numbering scheme (A). Packing diagram of complex 7 showing a 1D chain (B).
3226 | Dalton Trans., 2011, 40, 3219–3228 This journal is The Royal Society of Chemistry 2011
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12 (a) C. Turta, S. Melnic, M. Bettinelli, S. Shova, C. Benelli, A.
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Scheme
4
Various intra- and inter-molecular interactions of
1
[CuBr(h -S-HattscMe)(Ph3P)] 7.
Conclusions
21 R. Fischer, H. Gorls and D. Walther, Z. Anorg. Allg. Chem., 2004, 630,
1387.
In this investigation, two different five membered heterocyclic rings
at the C2 carbon of N1-substituted thiosemicarbazone ligands,
{C4H3X–C2(R1) N3–N2H–C1( S)N1HR2, X = O, S; R2 = Me,
Et, Ph} have shown different behavior in their interaction with
nickel(II) acetate. For R1 = Me at the C2 carbon in place of H
(R2 = Me, Et, Ph), furan ring coordination has been observed
resulting in the formation of octahedral complexes. However,
for R1 = Me at C2, the thiophene ring remained pendant and
formed N3, S- chelated square planar complexes. The formation
of a tunnel in complex 3 is unprecedented (phenyl substituent
at the N1 nitrogen). The methyl groups at the C2 and N1 atoms
of 2-acetylthiophene-N1-methyl thiosemicarbazone favor three-
coordinate complexes in which copper(I) is bonded to a thio-
ligand, a halogen and triphenylphosphine.
22 P. Neugebauer, U. Klingebiel and M. Z. Noltemeyer, Naturforsch. B:
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Acknowledgements
Financial support from CSIR, New Delhi (Scheme no.
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