Synthesis, structures and antimicrobial activity of copper derivatives of N -substituted imidazolidine-2-thiones: Unusual bio-activity against Staphylococcus epidermidis and Enterococcus faecalis

Article abstract of DOI:10.1039/c8nj00206a

The main objective of this study was to explore the antimicrobial activity of several copper(i) complexes with N,S-donor thio-ligands against Gram positive bacteria, namely Staphylococcus aureus (MTCC 740), Staphylococcus epidermidis (MTCC 435), and Enter

Full text of DOI:10.1039/c8nj00206a

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DOI: 10.1039/C8NJ00206A.
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Synthesis, structures and antimicrobial activity of copper
derivatives of N-substituted imidazolidine-2-thiones :
unusual bio-activity against Staphylococcus epidermidis and
Enterococcus faecalis†
Tarlok S. Lobanaa,*, Jaspreet K. Aulakha, Heena Soodb, Daljit S. Arorab, Isabel Garciaꢀ
Santosc, Manpreet Kaurd, Courtney E. Duffd and Jerry P. Jasinskid
The main objective of this study was to explore the antimicrobial activity of several
copper(I) complexes with N,Sꢀ donor thioꢀligands against Gram positive bacteria,
namely, Staphylococcus aureus (MTCC 740), Staphylococcus epidermidis (MTCC 435),
Enterococcus faecalis (MTCC 439), Gram negative bacteria Shigella flexneri (MTCC
1457), Escherichia coli (MTCC 119) and yeast Candida tropicalis (MTCC 230). New
copper complexes were prepared from copper(I) halides and imidazolidineꢀ2ꢀthiones (Lꢀ
NR, R = Et; Prn; Bun; Ph) with triphenylphosphine as a coꢀligand. Complexes are
mononuclear, [CuX(LꢀNR)(PPh3)2] (X, R: Cl, Prn, 1; Br, Prn, 2; Cl, Bun, 3; I, Bun, 4; I, Ph,
6), [CuBr(LꢀNPh)2(PPh3)] 5 and halogenꢀbridged dinuclear, [Cu2(ꢁꢀX)2(LꢀNR)2(PPh3)2]
(Br, Et, 7; Cl, Prn, 8; Br, Prn, 9; I, Prn, 10; Br, Ph, 11;I, Ph, 12). These complexes were
1
characterized using analytical data, IR, HꢀNMR spectroscopy, single crystal Xꢀray
crystallography, electron spray ionization mass spectrometry (ESIꢀMS) and techniques
for antimicrobial study (agar diffusion, agar dilution, MTT assay). All of the complexes
are found to be bactericidal against Staphylococcus aureus. A most significant outcome
of this investigation is that several complexes have shown significant activity against
1

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Staphylococcus epidermidis and Enterococcus faecalis, which is higher than that of the
standard drug Gentamicin. Finally, these complexes were nearly inactive against
Shigella flexneri, Escherichia coli and yeast Candida tropicalis.
aDepartment of Chemistry, Guru Nanak Dev University, Amritsar-143 005, India
bDepartment of Microbiology, Guru Nanak Dev University, Amritsar-143 005, India
cDepartamento de Quimica Inorganica, Facultad de Farmacia, Universidad de Santiago,
15782-Santiago, Spain
dDepartment of Chemistry, Keene State College, Keene NH 03435–2001 USA
* Corresponding author E-mail address: tarlokslobana@yahoo.co.in; Fax: +91ꢀ183ꢀ2258820
†Electronic supplementary information (ESI) available: ESIꢀMS data. CCDC 1814805–1814816
for complexes 1ꢀ12 respectively
1 Introduction
Coordination chemistry of copper with heterocyclicꢀ2ꢀthiones, an interesting class of N,S donor
thioꢀligands, has invited interest of several researchers in the past for several decades.1ꢀ5 Among
heterocyclicꢀ2ꢀthiones, 1,3ꢀimidazolidineꢀ2ꢀ thione and its derivatives have been used for the
investigation of their interaction with metals.1ꢀ8 The ligands, 1,3ꢀimidazolidineꢀ2ꢀthione and its
derivatives with mono substitution at one nitrogen (LꢀNR, R = H, Me, Et, nPr, iPr) with copper(I)
halides / pseudo halides have yielded trigonal planar complexes, [CuX(LꢀNR)2] (X = Cl, Br, I,
NCS),9ꢀ17 tetrahedral complexes,18 dinuclear, or polynuclear complexes.17, 19ꢀ21 Further, 1,3ꢀ
2

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imidazolidineꢀ2ꢀthione and its derivatives (Chart 1) in their reactions with copper(I) halides at
ambient conditions have shown unusual chemical transformations involving CꢀS rupture forming
a variety of novel compounds.22, 23
5
4
1
3
PrnꢀN
NꢀH BunꢀN
NꢀH PhꢀN
NꢀH
MeꢀN
NꢀH
NꢀH EtꢀN
NꢀH
HꢀN
2
S
S
S
S
S
S
LꢀNPrn
LꢀNBun
LꢀNEt
LꢀNH
LꢀNPh
LꢀNMe
Chart 1 Imidazolidineꢀ2ꢀthiones ligands (LꢀNR).
The coordination chemistry of heterocyclicꢀ2ꢀthiones is important from the bioinorganic
perspective as well. To illustrate, a few examples of bioꢀactivity of copper complexes are cited
below. The antimicrobial activity of copper(I) halide complexes with Nꢀsubstituted
benzothiazoleꢀ2ꢀthione24, 25 and pyrimidineꢀ2ꢀthione26 with triphenylphosphine as a coꢀligand has
been studied against Gramꢀpositive (Staphylococcus aureus, Bacillus subtilis and Bacillus
cereus) and Gramꢀnegative (Escherichia coli and Xanthomonas campestris) bacteria. The ability
of complexes to interact with native calf thymus DNA (CTꢀDNA) in vitro as well as their antiꢀ
inflammatory activity have also been investigated.24,26 Heteroꢀmetallic complexes of CuꢀNi, Cuꢀ
Co, CuꢀCoꢀNi with 2ꢀthiouracil have been screened in vitro against Staphylococcus aureus
(Gramꢀpositive bacteria), Escherichia coli (Gramꢀnegative bacteria), Aspergillus flavus
(filamentous fungi) and Candida albicans (yeast).27 Similarly, another set of copper(I) halide
complexes with 5ꢀcarbethoxyꢀ2ꢀthiouracil and PPh3 as a coꢀligand have been evaluated for in
vitro antitumor properties.28 Copper(II) halide complexes of Nꢀ(2ꢀpyridyl)imidazolidinꢀ2ꢀones,
N,N'ꢀbis(2ꢀpyridyl)imidazolidinꢀ2ꢀones, NꢀacylꢀN'(2ꢀpyridyl)imidazolodinꢀ2ꢀones and Nꢀ
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Complexes (2ꢀpyridyl)imidazolidineꢀ2ꢀthiones have shown high antiꢀtumor activity with
promising results for developing anticancer agents.29
The antimicrobial activity of imidazolidineꢀ2ꢀthione (LꢀNH, Chart 1) is limited to some metal
complexes of Hg, Ag, Cd, Fe, Pd and Zn which have shown activity against various
microorganisms, namely, Heterotrotropic Plate Counts (HPC), Pseudomonas aeruginosa, Fecal
Streptococcus, Escherichia coli, Klebsiella pneumoniae, Salmonella typhi, Staphylococcus
aureus, Bacillus cereus, Enterobacter aerogenes, Serratiam arescens, Salmonella enteric, molds
(Aspergillus niger, Penicillium citrinum), and yeasts (Candida albicans, Saccharomyces
cerevisiae). However, there are limited systematic investigations in literature, generally
preliminary accounts of bioꢀactivity.30ꢀ39
Recently we have investigated several copper(I)ꢀimidazolidineꢀ2ꢀthione complexes (trigonal
planar, dinuclear, tetranuclear and hexanuclear) for their antimicrobial activity against S. aureus,
(MRSA, K. pneumoniae 1, S. typhimurium 1 and a yeast C. albicans. These complexes have
shown high antimicrobial activity and in a few cases the in-vitro cell viability was high (95%).17
In this paper we are reporting the synthesis, spectroscopy, molecular structures and antimicrobial
activity of copper(I) halide complexes with Nꢀsubstitutedꢀimidazolidineꢀ2ꢀthiones (LꢀNR, R= Et,
Prn, Bun, Ph, Chart 1) using PPh3 as a coꢀligand.
2 Experimental section
2.1. Materials and techniques
Copper(I) halides were prepared by the reduction of CuSO4·5H2O using SO2 in the presence of
stoichiometric amounts of corresponding NaCl, NaBr or NaI salts in water.40 The thioꢀligands
used, namely, 1ꢀethylꢀimidazolidineꢀ2ꢀthione (LꢀNEt), 1ꢀnꢀpropylꢀimidazolidineꢀ2ꢀthione (Lꢀ
4

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NPrn), 1ꢀnꢀbutylꢀimidazolidineꢀ2ꢀthione (LꢀNBun), and 1ꢀphenylꢀimidazolidineꢀ2ꢀthione (Lꢀ
NPh) were prepared by the method as reported in the literature.18,41 The melting points were
determined by using an Gallenkamp electrically heated apparatus. Elemental analyses (C, H, N,
1
S) were carried out using a THERMO FINNIGAN FLASH technique. The H NMR spectra
were recorded in CDCl3 / DMSO using a Bruker Advance II 400 NMR spectrometer at 400 MHz
and a Bruker Ascend 500 NMR spectrometer at 500 MHz using TMS as an internal reference.
The IR spectra were recorded using KBr pellets on a Varian 660 FT IR Spectrometer in the
4000ꢀ400 cmꢀ1 range. The ESIꢀmass spectra were recorded in DMSO or chloroform solvents
using a Bruker Daltonik LSꢀMS high resolution micro TOFꢀQ II 10356 spectrometer.
2.2. Synthesis of complexes
[CuCl(LꢀNPrn)(PPh3)2] 1. To a solution of copper(I) chloride (0.025 g, 0.25 mmol) in 10 mL
of acetonitrile was added triphenylphosphine (0.13 g, 0.50 mmol), followed by stirring for 2 h at
room temperature. To the white precipitates formed was added 1ꢀpropylꢀ1, 3ꢀimidazolidineꢀ2ꢀ
thione (0.036 g, 0.25 mmol), it was stirred until a clear solution was obtained. Slow evaporation
of the solution at room temperature gave colorless crystals of 1. Yield (70 %). M.p 105ꢀ107 ˚C.
Elemental analysis for C42H42CuClN2P2S: calcd. C 65.64; H 5.47; N 3.64; S 4.16 %; found: C
65.31; H 5.65; N 3.70; S 4.22 %. Complexes 2ꢀ4, 6 were prepared similarly.
[CuBr(LꢀNPrn)(PPh3)2] 2. Colorless compound (yield 70 %, M.p 140ꢀ142 ˚C). Elemental
analysis for C42H42CuBrN2P2S: calcd. C 62.05; H 5.17; N 3.45; S 3.94 %; found: C 62.02; H
5.22; N 3.49; S 3.65 %.
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[CuCl(LꢀNBun)(PPh3)2] 3. Colorless compound (yield 70 %, M.p 135ꢀ137 ˚C). Elemental
analysis for C43H44CuClN2P2S: calcd. C 66.06; H 5.63; N 3.58; S 4.09 %; found: C 65.75; H
5.49; N 3.40; S 3.73 %.
[CuI(LꢀNBun)(PPh3)2] 4. Colorless compound (yield 75 %, M.p 120ꢀ122 ˚C). Elemental
analysis for C43H44CuIN2P2S: calcd. C 59.14; H 5.04; N 3.20; S 3.66 %; found: C 59.12; H 5.24;
N 3.31; S 3.80 %.
[CuBr(LꢀNPh)2(PPh3)] 5. To a solution of copper(I) bromide (0.025 g, 0.17 mmol) in 10 mL
of acetonitrile was added 1ꢀphenylꢀ1,3ꢀimidazolidineꢀ2ꢀthione (0.062 g, 0.34mmol), followed by
stirring for 2 h at room temperature. To the white precipitates formed was added
triphenylphosphine (0.045 g, 0.17 mmol) and it was heated followed by addition of
dichloromethane to it (v/v:: 1:1). Slow evaporation of the solution at room temperature gave
colorless crystals of 5 (yield 65 %, M.p 147ꢀ149 ˚C). Elemental analysis for C36H35CuBrN4PS2:
calcd. C 56.73; H 4.59; N 7.35; S 8.40 %; found: C 56.97; H 4.69; N 7.41; S 8.05 %.
[CuI(LꢀNPh)(PPh3)2] 6. Colorless compound (yield 70 %, M.p 148ꢀ150 ˚C). C45H40CuIN2P2S:
calcd. C 60.45; H 4.47; N 3.13; S 3.58 %; found: C60.78; H 4.68; N 3.19; S 3.64 %.
[Cu2(µꢀBr)2(LꢀNEt)2(PPh3)2] 7. To a solution of copper(I) bromide (0.025 g, 0.17 mmol) in
10 mL of acetonitrile was added triphenylphosphine (0.045 g, 0.17 mmol), followed by stirring
for 2 h at room temperature. To the white precipitate formed was added solid 1ꢀethylꢀ1,3ꢀ
imidazolidineꢀ2ꢀthione (0.020 g, 0.17 mmol) and it was heated until a clear solution was
obtained, then 1 mL of methanol was added to it. Slow evaporation of the solution at room
temperature gave colorless crystals of 7 (yield 70 %, M.p 148ꢀ150 ˚C). Elemental analysis for
6

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C46H50Cu2Br2N4P2S2: calcd. C 51.54; H 4.66; N 5.22; S 5.97 %; found: C 51.32; H 4.71; N 5.45;
S 6.00 %. Complexes 8, 9, 11 and 12 were prepared similarly.
[Cu2(µꢀCl)2(LꢀNPrn)2(PPh3)2] 8. Colorless compound (yield 75 %, M.p 123ꢀ125 ˚C).
Elemental analysis for C48H54Cu2Cl2N4P2S2: calcd. C 65.71; H 5.47; N 3.65; S 4.17 %; found: C
65.36; H 5.78; N 3.73; S 4.20%.
[Cu2(µꢀBr)2(LꢀNPrn)2(PPh3)2] 9. Colorless compound (yield 69 %, M.p 95ꢀ98 ˚C). Elemental
analysis for C48H54Cu2Br2N4P2S2: calcd. C 52.36; H 4.90; N 5.09; S 5.82 %; found: C 52.61; H
5.00; N 5.13; S 5.75%.
[Cu2(µꢀI)2(LꢀNPrn)2(PPh3)2] 10. To a solution of copper(I) iodide (0.025 g, 0.13 mmol) in 10
mL of acetonitrile was added 1ꢀpropylꢀ1,3ꢀimidazolidineꢀ2ꢀthione (0.037 g, 0.26 mmol),
followed by stirring for 2 h at room temperature. To the white precipitates formed was added
triphenylphosphine (0.034 g, 0.13 mmol) and it was heated followed by addition of
dichloromethane (v/v :: 1:1). Slow evaporation of the solution at room temperature gave colorless
crystals of 10 (yield 65 %, M.p 100ꢀ102˚C). Elemental analysis for C48H54Cu2I2N4P2S2: calcd. C
48.24; H 4.52; N 4.69; S 5.36%; found: C 48.57; H 4.64; N 4.75; S 5.21 %.
[Cu2(µꢀBr)2(LꢀNPh)2(PPh3)2] 11. Colorless compound (yield 67 %, M.p 155ꢀ157 ˚C).
Elemental analysis for C54H50Cu2Br2N4P2S2: calcd. C 55.48; H 4.28; N 4.79; S 5.47%; found: C
55.53; H 4.26; N 4.61; S5.25 %.
[Cu2(µꢀI)2(LꢀNPh)2(PPh3)2] 12. Colorless compound (yield 69 %, M.p 135ꢀ137 ˚C).
Elemental analysis for C54H50Cu2I2N4P2S2: calcd. C 51.39; H 3.96; N 4.44; S 5.07 %; found: C
51.63; H 4.02; N 4.52; S 4.87 %.
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2.3. Xꢀray crystallography
Single crystals of complexes were mounted on polymer loops and data for these complexes
were measured on a RigakuꢀOxford Diffraction Eos, Gemini –CCD auto diffractometer at 173(2)
(1, 3, 4ꢀ12) and 293(2) (2) K. The diffractometer was equipped with a graphite monochromator
with Mo–Kα radiation (λ = 0.71073 Å; 3, 11, 6), or CuꢀKα radiation (λ = 1.54178 Å; 1, 2, 4, 5,
7, 8, 10, 12). The structures were solved by direct methods and refined using fullꢀmatrix leastꢀ
squares techniques based on F2 using ShelXLꢀ2014. In all the structures, the nonꢀhydrogen
atoms were refined anisotropically and hydrogens were fixed geometrically except for the ones
attached to the imidazole nitrogens. Further it was checked that none of these structures in
question (1ꢀ7, 10) have any disorder in their refinement. Table 1 contains crystal data.
Table 1 Crystallographic data for complexes 1–12
1
2
3
4
Empirical
formula
M
C42H42ClCuN2P2S
C42H42BrCuN2P2S
C43H44ClCuN2P2S
C43H44CuIN2P2S
767.76
812.22
780.78
873.24
T /K
173(2)
293(2)
173(2)
173(2)
Crystal system
Space group
a(Å)
Monoclinic
P 21/n
Monoclinic
P 21/n
Monoclinic
P 21/n
Monoclinic
P 21/n
13.0220(4)
20.5063(5)
14.8412(5)
90
13.0009(2)
20.8461(4)
14.7070(3)
90
13.0881(4)
20.2471(5)
15.2533(4)
90
12.8975(3)
21.2368(4)
15.1545(3)
90
b(Å)
c(Å)
α (º)
β (º)
105.560(4)
105.105(2)
105.139(3)
105.562(2)
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γ (º)
V(Å3)
Z
90
90
90
90
3817.8(2)
4
3848.13(13)
3901.77(19)
4
3998.66(15)
4
4
D
calcd (g.cmꢀ3)
1.336
0.813
1.40
3.550
1.329
1.451
ꢀ (mmꢀ1)
F(000)
0.797
8.317
1600
1672
1628
1776
Reflns collected 31662
15911
32675
17017
Unique reflns.
12752
7353
13050
7650
(Rint, 0.0352)
(Rint, 0.0420)
7353/0/444
(Rint, 0.0368)
13050/43/472
(Rint, 0.0559)
7650/0/453
Data/ restraints / 12752/0/443
parameters
Reflecs. with
[I>2σ(I)]
9523
6325
9625
6852
Final R indices
[I>2σ(I)]
R1 = 0.0468
R1 = 0.0416
R1 = 0.0416
R1 = 0.0522
wR2 = 0.1005
wR2 = 0.1102
wR2 = 0.0885
wR2 = 0.1373
Final R indices
(all data)
R1 = 0.0722
wR2 = 0.1152
0.987 and
ꢀ0.487
R1 = 0.0488
wR2 = 0.1168
0.570 and
ꢀ0.512
R1 = 0.0693
wR2 = 0.1026
0.539 and
ꢀ0.436
R1 = 0.0570
wR2 = 0.1427
2.065 and
ꢀ1.790
Largest diff.
Peak/ hole e.Åꢀ3
5
6
7
8
Empirical
formula
M
C36H35BrCuN4PS2
C45H40CuIN2P2S
C46H50Br2Cu2N4P2S2 C48H54Cl2Cu2N4P2S2
762.22
173(2)
Triclinic
Pī
893.23
173(2)
Triclinic
Pī
1071.86
173(2)
Triclinic
Pī
1010.99
173(2)
Triclinic
Pī
T /K
Crystal system
Space group
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a(Å)
b(Å)
c(Å)
α (º)
β (º)
γ (º)
V(Å3)
Z
9.9322(4)
10.6993(4)
17.6677(8)
76.569(3)
80.316(4)
69.508(4)
1702.79(13)
2
10.5257(4)
12.8802(5)
15.7569(5)
76.632(3)
79.082(3)
79.691(3)
2020.19(13)
2
9.1793(5)
9.4283(5)
10.2484(7)
13.4319(9)
79.123(6)
73.321(5)
69.953(6)
1131.33(14)
1
10.2759(7)
13.1681(10)
78.871(6)
73.632(5)
70.704(5)
1148.27(14)
1
D
calcd (g.cmꢀ3)
1.487
1.468
1.573
1.462
ꢀ (mmꢀ1)
F(000)
4.116
1.470
2.907
1.242
780
904
544
524
Reflns collected 11854
27355
13541
13314
Unique reflns.
6451
13280
7448
7559
(Rint, 0.0376)
(Rint, 0.0302)
13280/0/469
(Rint, 0.0285)
7448/0/263
(Rint, 0.0490)
7559/0/273
Data/ restraints / 6451/0/407
parameters
Reflecs. with
[I>2σ(I)]
6036
9097
6134
6276
Final R indices
[I>2σ(I)]
R1 = 0.0387
R1 = 0.0476
R1 = 0.0330
R1 = 0.0457
wR2 = 0.1052
wR2 = 0.1145
wR2 = 0.0726
wR2 = 0.1150
Final R indices
(all data)
R1 = 0.0411
wR2 = 0.1079
0.651 and
ꢀ0.517
R1 = 0.0804
wR2 = 0.1357
0.854 and
ꢀ1.111
R1 = 0.0467
wR2 = 0.0787
0.487 and
ꢀ0.649
R1 = 0.0570
wR2 = 0.1275
0.520 and
ꢀ0.544
Largest diff.
Peak/ hole e.Åꢀ3
9
10
11
12
10

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Empirical
formula
M
C48H54Br2Cu2N4P2S2 C48H54Cu2I2N4P2S2
C54H50Br2Cu2N4P2S2 C54H50Cu2I2N4P2
1099.91
173(2)
1193.89
1167.94
1261.92
173(2)
T /K
173(2)
173(2)
Crystal system
Space group
a(Å)
Triclinic
Pī
Triclinic
Pī
Monoclinic
P 21/c
Monoclinic
P 21/c
9.4815(6)
10.3547(6)
13.2247(8)
79.062(5)
73.412(6)
70.630(5)
1167.40(13)
1
9.6418(12)
10.5247(8)
13.4048(12)
79.580(7)
72.802(9)
70.907(9)
1222.6(2)
1
10.5137(3)
20.7529(6)
11.7654(3)
90
10.7515(2)
20.6834(4)
11.9733(3)
90
b(Å)
c(Å)
α (º)
β (º)
103.798(3)
90
106.826(2)
90
γ (º)
V(Å3)
Z
2493.00(12)
2
2548.61(10)
2
D
calcd (g.cmꢀ3)
1.565
1.622
1.556
1.644
ꢀ (mmꢀ1)
2.819
2.320
2.645
12.212
F(000)
560
596
1184
1256
9026
Reflns collected 13822
14548
19058
Unique reflns.
7700
8056
8252
4872
(Rint, 0.0400)
(Rint, 0.0306)
8056/0/273
(Rint, 0.0407)
8252/2/99
(Rint, 0.0376)
4872/0/299
Data/ restraints / 7700/0/273
parameters
Reflecs. with
[I>2σ(I)]
5909
6449
6208
4527
Final R indices
[I>2σ(I)]
R1 = 0.0410
R1 = 0.0343
R1 = 0.0416
R1 = 0.0425
wR2 = 0.0865
wR2 = 0.0748
wR2 = 0.0859
wR2 = 0.1063
11

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Final R indices
(all data)
R1 = 0.0609
wR2 = 0.0966
0.519 and
ꢀ0.778
R1 = 0.0487
wR2 = 0.0832
0.738 and
ꢀ0.710
R1 = 0.0664
R1 = 0.0454
wR2 = 0.0979
0.656 and
ꢀ0.620
wR2 = 0.1103
1.670 and
ꢀ1.139
Largest diff.
Peak/ hole e.Åꢀ3
2.4. Antimicrobial studies
Test organisms and inoculum preparation. The reference strains of bacteria and yeast were
obtained from Microbial Type Culture Collection (MTCC), Institute of Microbial Technology
(IMTECH), Chandigarh, India. Reference strains included Gram positive bacteria:
Staphylococcus aureus (MTCC 740), Staphylococcus epidermidis (MTCC 435), Enterococcus
faecalis (MTCC 439), Gram negative bacteria Shigella flexneri (MTCC 1457), Escherichia coli
(MTCC 119) and yeast Candida tropicalis (MTCC 230). A loopful of broths bacterial and yeast
colonies were inoculated into 5 mL of their respective medium and incubated at 37 °C and 25
°C, respectively for 4 h. This was used as inoculum after adjusting the turbidity as per the
McFarland turbidity standard. This turbidity is equivalent to approximately (1 to 2) ×108 colony
forming units per mL (CFU/mL). The inoculums thus prepared were used for further testing. In
relation to live subject statement it is submitted here that the study has been carried out as per
Institutional Bioethics Committee and National Guidelines .It is further stated it did not involve
any experimentation on live animals or Humans.
Antimicrobial screening. A 100 ꢁL of activated test organism (prepared as above) sample
was inoculated onto suitable medium plates by the spread plate method. Wells measuring 8 mm
in diameter were cut out in the medium using a sterilized stainless steel borer. A stock solution
12

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of each test complex of concentration 50 mg/mL was prepared in DMSO and each well was
filled with 0.1 mL of this test complex and kept for incubation in an upright position for 18–24 h.
Sensitivity was measured in terms of a diameter of the zone of inhibition. Any organism with a
clear zone of inhibition ≤12 mm was considered to be resistant to the compound.42
Minimum inhibitory concentration (MIC). Minimum inhibitory concentration of the
selected coordination compound dissolved in DMSO was worked out by the agar dilution
method for their antimicrobial activity against the sensitive microorganisms. From the stock
solution, the concentration of a complex in the range (0.001–2 mg/mL) was mixed with a Muller
Hinton agar medium and then poured on plates. These plates were then inoculated with 0.1 mL
of the activated bacterial and yeast strains by streaking with a sterile swab. The plates were
incubated at 37°C for bacteria and 25 °C for yeast for 24 h each. The minimum concentration of
the extract causing inhibition of the visible growth was taken as MIC. The results were compared
with that of DMSO as a control.
MTT toxicity assay. In order to check the level of cellular toxicity of the test compounds,
MTT [3ꢀ(4, 5ꢀdimethylthiazolꢀ2ꢀyl)ꢀ2, 5ꢀdiphenyl tetrazolium bromide] assay was performed43
as follows. Ten milliliter of sheep blood was taken into an injection syringe containing 3 mL of
Alsever's solution (anticoagulant) and transferred to sterile centrifuge tube. The blood was
centrifuged at 16,000 rpm at room temperature (25 °C) for 20 min so as to separate the plasma
from the cells. The supernatant was discarded and 6 mL phosphate buffer saline (PBS) was
added and it was again centrifuged. The blood cells were washed thrice with PBS by
centrifugation and the pellet was reꢀsuspended in 6 mL of PBS. Various dilutions of these cells
were prepared using PBS and counted with the help of a hemocytometer under a light
microscope so as to obtain cells equivalent to 1× 105 cells/mL. One hundred microliters (100 ꢁL)
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of this diluted suspension was added in each well and incubated at 37 °C for overnight. The
supernatant was removed carefully and 200 ꢁL of the sample solution (contains 10 mg/mL) was
added and incubated further for 24 h. The supernatant was removed again and 20 ꢁL MTT
solution (5 mg/mL) was added to each well and incubated further for 3.5 h at 37 °C on an orbital
shaker at 60 rpm. After incubation, the supernatant was removed without disturbing the cells and
50 ꢁL of DMSO was added to each well to dissolve the formazan crystals. The absorbance was
measured at 590 nm using an automated microplate reader (Biorad 680ꢀXR, Japan). The wells
with untreated cells served as a control. Reduction of MTT can only occur in metabolically
active cells, as MTT is converted into formazan crystals and hence the absorbance directly
represents the viability of the cells (% viability = (optical density (OD) of Treated/ OD of
Control) × 100). If the percent viability of the blood cells is quite high, then the compounds are
nonꢀcytotoxic in nature.
3 Results and discussion
3.1. Synthetic comments. Scheme 1 depicts formation of complexes 1ꢀ12. Reactions of
copper(I) halides with imidazolidineꢀ2ꢀthiones (LꢀNR) having bulky substituents (R = Prn, Bun,
Ph) at one nitrogen atom of an imidazolidine ring in the presence of PPh3 as a coꢀligand have
yielded mononuclear [CuX(PPh3)2(LꢀNR)] (R, X: Prn, Cl, 1; Prn, Br, 2; Bun, Cl, 3; Bun, I, 4; Ph,
I, 6) and dinuclear [Cu2(µꢀX)2(PPh3)2(LꢀNR)2] (R, X: Et, Br, 7; Prn, Cl, 8; Prn, Br, 9; Prn, I,
10;Ph, Br, 11;Ph, I, 12) complexes. Mononuclear complexes 1ꢀ4, 6, were formed by reacting a
mole of copper(I) halide with two moles of PPh3 in organic solvents followed by reaction with
one mole of the respective LꢀNR thioꢀligand (Cu : PPh3 : LꢀNR : : 1 : 2 : 1 molar ratio).
14

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Similarly, dinuclear complexes 7, 9, 11 and 12 were obtained by reacting a mole of copper(I)
halide with a
X
Cu
PPh3
RNꢀL
PPh3
1-4, 6
(i) m = 2, n = 1
PPh3
LꢀNR
X
X
RNꢀL
Ph3P
(ii) m = 1, n = 1, 2
Cu
Cu
CuX +mPPh3
+ nLꢀNR
X
(iii) m = 1, n = 2
7-12
Cu
LꢀNR
LꢀNR
Ph3P
5
Scheme 1. Synthesis of complexes; (i) CH3CN, 6; CH3CNꢀMeOH, 1- 4;
(ii) CH3CNꢀMeOH, 7; CH3CN, 8; CH3CNꢀCH2Cl2 9-12;
(iii) CH3CNꢀCH2Cl2 5
mole of PPh3 and a mole of thioꢀligand (Cu : PPh3 : LꢀNR : : 1 : 1 : 1 molar ratio). Dinuclear
complex 10 could not be obtained by a similar equimolar reaction owing to a turning of the
reaction mixture green and no product could be characterized. Thus complex 10 was obtained by
reacting first copper(I) iodide with LꢀNPrn followed by addition of PPh3 in 1 : 2 : 1 molar ratio
(Cu : LꢀNPrn : PPh3). Here, an excess of LꢀNPrn thioꢀligand appears to have stabilized the Cu(I)
oxidation state. A similar reaction of copper(I) bromide with LꢀNPh and PPh3 in 1 : 2 : 1 molar
ratio (Cu : LꢀNPh : PPh3) did not yield a complex similar to 10, rather it formed a mononuclear
complex, [CuBr(PPh3)(LꢀNPh)2] 5, with less common stoichiometry.44 This thioꢀligand, LꢀNPh,
15

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was previously reported to form [CuBr(PPh3)2(LꢀNPh)] with PPh3 coordinated.18 It is added here
that reaction of copper(I) chloride/bromide with the thioꢀligands under discussion in the absence
of PPh3 involved C–S rupture forming copper(II) sulfate, but other products could not be
identified. Thus generally the order of reaction followed binding of copper(I) halides to PPh3
followed by binding to thio ligands.18
In literature several thioꢀligands,45ꢀ51 similar to 1, 3ꢀimidazolidineꢀ2ꢀthione, such as 2ꢀ
45
thiohydantoin,
5,5ꢀdiphenylꢀ2ꢀthiohydantoin,45 imidazolidineꢀ2ꢀthione,46,50 Nꢀmethylꢀ
Nꢀmethylꢀimidazolidineꢀ2ꢀthione,18 Nꢀethylꢀimidazolidineꢀ2ꢀ
imidazolineꢀ2ꢀthione,47,48,51
thione,18 Nꢀphenylꢀimidazolidineꢀ2ꢀthione,18 and imidazolidineꢀ2ꢀthione49 on reaction with
copper(I) halides have also yielded analogous mononuclear,18,45,46,50,47,48,49 halogenꢀbridged
dinuclear18 and sulfurꢀbridged dinuclear18,51 complexes.
3.2. IR and NMR spectroscopy. All of the complexes have shown IR stretching and bending
bands within a range of 4000 – 400 cmꢀ1, varying in intensity from weak to strong (See
Supporting Information, Fig.S35 ꢀ Fig.S51 for IR Spectra of complexes / ligands ). The ν(NꢀH)
bands occur in the region 3142ꢀ3241cmꢀ1 (strong to medium in intensity) in complexes (Table 2)
and this presence confirms the coordination of a thioꢀligand to a metal center as a neutral ligand.
In comparison to the uncoordinated thioꢀligands [ν(NꢀH): 3191s, ν(LꢀNEt); 3207 s, ν(LꢀNPrn); 3196 s,
ν(LꢀNBun); 3203 s, ν(LꢀNPh)], these ν(NꢀH) bands have been found to be shifted either to a low
energy region (1, 3, 6, 8) or to a high energy region (2, 4, 5, 7, 9, 10ꢀ12). Compounds containing
thioamide group HꢀNꢀC=S give rise to four characteristic thioamide bands in their IR spectra.52
Thioamide band I has contribution from δNH + δCꢀH + υC=N, band II from υC–N + δNH +
δCH + υC=N, band III from υC–N + from υC–S and band IV from υC–S. Thioamide bands III
and IV which contain main contribution from υ(C–S), undergo red shift of 8ꢀ12 cmꢀ1 and 7ꢀ63
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cmꢀ1 in complexes as compared to the free ligand. This red shift indicates the metalꢀsulphur
bonding. Band I and band II have main contribution from δNH + υCꢀN + υC=S, remain nearly
unshifted which imply that there is no coordination through nitrogen atom of thioamide group.
The appearance of ν(PꢀCPh) bands in the region 1084ꢀ1099 cmꢀ1 (weak to medium in intensity)
confirm the presence of coordinated PPh3 in the complexes .
Table 2 IR spectral bands of complexes and free thioꢀligands
Complexes/
ν(NꢀH)
ν(PꢀCPh)
Band I
Band II
Band III
Band IV
Free thioꢀligand
[CuCl(LꢀNPrn)(PPh3)2] (1)
[CuBr(LꢀNPrn)(PPh3)2] (2)
[CuCl(LꢀNBun)(PPh3)2] (3)
[CuI(LꢀNBun)(PPh3)2] (4)
[CuBr(LꢀNPh)2(PPh3)] (5)
[CuI(LꢀNPh)(PPh3)2] (6)
[Cu2(µꢀBr)2(LꢀNEt)2(PPh3)2] (7)
[Cu2(µꢀCl)2(LꢀNPrn)2(PPh3)2] (8)
[Cu2(µꢀBr)2(LꢀNPrn)2(PPh3)2] (9)
[Cu2(µꢀI)2(LꢀNPrn)2(PPh3)2] (10)
[Cu2(µꢀBr)2(LꢀNPh)2(PPh3)] (11)
[Cu2(µꢀI)2(LꢀNPh)2(PPh3)2] (12)
LꢀNEt
3176 s
3217 s
3142 w
3222 s
3210 s
3200 s
3226 s
3194 s
3218 s
3239 s
3210 m
3241 s
3191 s
3207 s
3196 s
3203 s
1093 s
1093 s
1099 m
1084 s
1095 m
1094 s
1093 m
1094 s
1093 m
1092 m
1095 m
1095 s
ꢀ
1512 s
1514 s
1483 m
1496 s
1510 s
1515 s
1515 s
1514 s
1513 s
1510 s
1502 s
1506 s
1513 s
1514 s
1514 s
1518 s
1281 s
1283 m
1314 s
1300 w
1288 m
1291 s
1283 m
1282 m
1283 m
1281 m
1239 s
1305 w
1279 m
1280 s
1284 s
1288 m
1027 m
1029 w
1024 m
1037 m
1028 m
1027 m
1028 w
1029 w
1028 w
1027 w
1029 w
950 w
747 s
751 m
740 s
771 w
750 s
744 s
752 m
751 s
751 m
747 s
750 s
750 s
792 m
806 w
803 w
757 s
1037 m
1037 w
1041 w
1040 m
LꢀNPrn
ꢀ
LꢀNBun
ꢀ
LꢀNPh
ꢀ
s = strong, m = medium, w = weak
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The1H NMR spectral data of coordination compounds 1ꢀ12 are given in Table 3. The NꢀH
protons of the uncoordinated thioꢀligands showed a single peak in each case in the range 5.91ꢀ
6.38 ppm, which after coordination to the metal centre shifted to the low field in the range, 7.83ꢀ
9.43 ppm in compounds 1ꢀ12. These changes suggest coordination through S donor atoms of the
thioꢀligands. The C4H2 ring protons showed NMR signals at low magnetic field as compared to
the C5H2 ring protons. Both types of these ring protons showed multiplets. The NꢀCH2 protons of
the NꢀR moiety have shown low field shifts and in some cases merge with the C4H2 /C5H2 ring
protons in the coordination compounds. The oꢀH, mꢀH and pꢀH protons of the coordinated PPh3
phenyl rings appear as multiplets and showed a low field shift as compared to the protons of the
uncoordinated PPh3.
13
In C NMR spectroscopy, the C2 signal of a coordinated thioꢀligand showed a significant
upfield shift and thus these 13C NMR signals in complexes occurred in the range, 179.64ꢀ181.74
ppm relative to the free ligands (cf. LꢀNR, range 182.92ꢀ183.70 ppm) (Table 4). The C4, C5 and
NꢀR carbon NMR signals of the thioꢀligands showed minor variations. The upfield shift of the C2
NMR signal showed coordination of a thioꢀligand to Cu(I) metal centre through S donor atom.
13
As regards the coordinated PPh3, the C NMR signals undergo variations of ipso, ortho, meta
and para carbons as follows: (i) ipsoꢀcarbons of PꢀPh moiety have shown upfield shifts, (ii)
orthoꢀ and metaꢀcarbons of PꢀPh have displayed irregular trend (upꢀfield or lowꢀfield shifts) and
1
(iii) the paraꢀcarbons showed low field shifts. It is found that J(13C–31P) coupling of pꢀcarbon is
observed in all complexes which was absent in free PPh3 ligand (Table 4). The 13C–31P coupling
constants (JCꢀP) pertaining to oꢀ, mꢀ, and pꢀcarbons of PꢀPh moiety are found to increase in the
complexes. These variations in JCꢀP coupling constants are attributed to a dative bond formation
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between PPh3 and Cu metal centre (See Supporting Information, Fig.S52 ꢀ Fig.S83 for NMR
(1H/13C) spectra of complexes/ligands)
1
Table 3 H NMR spectral data (δ in ppm) of complexes 1-12
Free thioꢀligand (LꢀNR)e/ ꢀNH / (C4H2) / (C5H2)
ꢀNR , R =Et, Pr, Bu, Ph
P(C6H5)3
5
Complex
4
1
3
RꢀN
NꢀH
2
S
LꢀNEtb
6.09 (s; 1H) / 3.68(m; 3.68(m; NꢀCH2; 4H)a, 1.20 (t;
ꢀ
ꢀ
ꢀ
4H)a/ 3.58 (m; 2H)
5.91 (s; 1H) / 3.71(t;
2H) / 3.46 (t; 2H)
CH3; 3H)
3.58 (m; NꢀCH2; 2H)a, 1.65 (m;
CH2;2H), 0.97 (t; CH3;3H)
n,
b
LꢀNPr
6.02 (s; 1H) / 3.69 (m; 3.59 (m; NꢀCH2; 2H)a, 1.59 (m;
n,
b
LꢀNBu
2H) / 3.59 (m; 2H)a
CH2; 2H), 1.32 (m; CH2; 2H),
0.97 (t; CH3; 3H)
LꢀNPhb
6.38 (s; 1H)/ 4.20 (t;
7.60 (m; oꢀH, 2H), 7.42 ( m;
mꢀH, 2H), 7.27 (m; pꢀH, 2H)
ꢀ
ꢀ
2H)/ 3.76 (t; 2H)
ꢀ
b
PPh3
7.32 (m; oꢀH, mꢀH, pꢀH)
1b (Cl, LꢀNPrn)
9.22 (s; 1H)/ 3.72 (m; 3.72 (m; NꢀCH2; 2H)a, 1.65 (m; 7.69 (m; oꢀH, 12H), 7.42
2H)a/ 3.49 (t; 2H)
8.34 (s; 1H)/ 3.61 (dt; 3.61 (dt; NꢀCH2; 2H)a, 1.61
CH2; 2H), 0.96 (t; CH3; 3H)
(m; mꢀH, pꢀH, 18H)
2b (Br, LꢀNPrn)
7.43 (m; oꢀH, 12H), 7.36 (
2H)a/ 3.46 (t; 2H)
(sx; CH2;2H), 0.93 (t; CH3;3H) m; mꢀH, 12H), 7.30 (m; pꢀ
H, 6H)
3b (Cl, LꢀNBun)
4b (I, LꢀNBun)
8.96 (s; 1H)/ 3.71 (m; 3.71 (m; NꢀCH2; 2H)a, 1.59 (m; 7.40 (m; oꢀH, 12H), 7.25 (
2H)a/ 3.50 (t; 2H)
CH2; 2H), 1.33 (m; CH2; 2H),
0.93 (t; CH3; 3H)
m; mꢀH, 12H), 7.16 (m; pꢀ
H, 6H)
7.83 (s; 1H)/ 3.62(dt; 3.62 (dt; NꢀCH2; 2H)a, 1.54 7.70 (m; oꢀH, 12H), 7.43
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2H)a/ 3.50 (t; 2H)
(quint; CH2; 2H), 1.35 (m; CH2; (m; mꢀH, pꢀH, 18H)
2H), 0.95 (t; CH3;3H)
d
5b (Br, LꢀNPh)
6b (I, LꢀNPh)
8.20 (s; 2H)/ 4.16 (t;
4H)/ 3.80 (t; 4H)
7.40 (m; oꢀH, mꢀH, pꢀH,
25H)
d
8.43 (s; 1H)/ 4.07 (m;
2H)/ 3.70 (t; 2H)
7.37 (m; oꢀH, mꢀH, pꢀH,
35H)
7b (Br, LꢀNEt)
8b (Cl, LꢀNPrn)
9b (Br, LꢀNPrn)
10c (I, LꢀNPrn)
11b (Br, LꢀNPh)
12b (I, LꢀNPh)
8.92 (s; 1H)/ 3.74 (m; 3.74 (m; NꢀCH2;4H)a, 1.21 (t; 7.52 (m; oꢀH, 12H), 7.39
4H)a/ 3.59 (m; 4H)
9.26 (s; 1H)/ 3.71 (m; 3.71 (m; NꢀCH2; 4H)a, 1.65 (m; 7.69 (m; oꢀH, 12H), 7.46
4H)a/ 3.48 (t; 4H)
8.70 (s; 1H)/ 3.71 (m; 3.71 (m; NꢀCH2; 4H)a, 1.66 (m; 7.69 (m; oꢀH, 12H), 7.48
CH3;6H)
(m; mꢀH, pꢀH, 18H)
CH2 4H), 0.96 (t; CH3; 6H)
(m; mꢀH, pꢀH, 18H)
4H)a/ 3.49 (t; 4H)
8.12 (s; 1H)/ 3.67 (t; 3.49(t; NꢀCH2 ; 4H)a, 1.50 (m;
CH2; 4H), 0.96 (t; CH3;6H)
7.46 (m; mꢀH, pꢀH, 18H)
7.56 (m; oꢀH, mꢀH, pꢀH,
30H)
2H)c/ 3.49 (t; 4H) a
9.43 (s; 1H)/ 4.18 (t;
4H)/ 3.86 (t; 4H)
CH2;2H), 0.81 (t; CH3;3H)
d
7.69 (m; oꢀH, 16H), 7.43
(m; mꢀH, pꢀH, 24H)
7.45 (m; oꢀH, mꢀH, pꢀH,
40H)
d
8.80 (s; 1H)/ 4.17 (t;
4H)/ 3.86 (t; 4H)
a (NꢀCH2) and (ring proton of CH2) got merged; b CDCl3; c DMSO, d NꢀPh protons obscured by
phenyl ring of PPh3
Table 4 C13 NMR spectral data (δ in ppm) of complexes 1-12
Free thioꢀligand (LꢀNR)e/
Complex
ꢀNꢀR
P(C6H5)3
C2/(C4H2)/(C5H2)
LꢀNEtb
182.92/ 41.39/ 47.97
41.67 (NꢀCH2), 12.21
(CH3)
ꢀ
ꢀ
183.70/ 41.39/ 48.62a
48.62 (NꢀCH2)a, 20.44
n,
b
LꢀNPr
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(CH2), 11.16 (CH3)
n,
b
183.42/ 41.44/ 48.61
46.77 (NꢀCH2), 29.26
(CH2), 19.99 (CH2),
13.89 (CH3)
ꢀ
ꢀ
LꢀNBu
LꢀNPhb
182.99/ 41.65/ 52.13
139.95 (NꢀC), 124.47
(oꢀC), 128.82 (mꢀC),
126.44 (pꢀC)
b
PPh3
ꢀ
ꢀ
137.14 (iꢀC), (40 Hz); 133.83 (oꢀ
C), (76 Hz); 128.60 (mꢀC), (28 Hz)
128.85 (pꢀC)
1b (Cl, LꢀNPrn)
2b (Br, LꢀNPrn)
3b (Cl, LꢀNBun)
4b (I, LꢀNBun)
5b (Br, LꢀNPh)
6b (I, LꢀNPh)
180.77/ 41.94/ 48.64
180.49/ 41.71/ 48.59
180.89/ 41.82/ 48.49
179.99/ 41.57/ 48.68
181.18/ 42.02/ 52.43
181.02/ 42.22/ 52.49
47.82 (NꢀCH2),
20.54(CH2), 11.23
(CH3)
134.45 (iꢀC), (100 Hz); 134.13 (oꢀ
C), (56 Hz); 128.30 (mꢀC), (36 Hz)
129.29 (pꢀC), (8 Hz)
47.76 (NꢀCH2), 20.49
(CH2), 11.21 (CH3)
134.26 (iꢀC), (96 Hz); 134.17 (oꢀ
C), (60 Hz); 128.29 (mꢀC), (32 Hz)
129.29 (pꢀC), (4 Hz)
45.93 (NꢀCH2), 29.27
(CH2), 19.86 (CH2),
13.94 (CH3)
134.56 (iꢀC), (88 Hz); 134.13 (oꢀ
C), (56 Hz); 128.27 (mꢀC), (36 Hz)
129.19 (pꢀC), (8 Hz)
45.82 (NꢀCH2), 29.20
(CH2), 19.87 (CH2),
13.94 (CH3)
134.11 (iꢀC), (160 Hz); 134.16 (oꢀ
C), 128.30 (mꢀC), (36 Hz);
129.38 (pꢀC), (4 Hz)
139.23 (NꢀC), 124.43
(oꢀC), 128.93 (mꢀC),
126.79 (pꢀC)
133.97 (iꢀC), (60 Hz); 133.19 (oꢀ
C), (125 Hz); 128.50 (mꢀC), (40
Hz); 129.64 (pꢀC), (5 Hz)
139.13 (NꢀC), 124.96
(oꢀC), 128.96 (mꢀC),
126.88 (pꢀC)
133.91 (iꢀC), (60 Hz); 133.28 (oꢀ
C), (110 Hz); 128.55 (mꢀC), (40
Hz); 129.65 (pꢀC), (5 Hz)
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7b (Br, LꢀNEt)
8b (Cl, LꢀNPrn)
9b (Br, LꢀNPrn)
10c (I, LꢀNPrn)
11b (Br, LꢀNPh)
12b (I, LꢀNPh)
179.64/ 41.01/ 48.32
41.94 (NꢀCH2), 12.21
(CH3)
133.94 (iꢀC), (60 Hz); 132.49 (oꢀ
C), (130 Hz); 128.66 (mꢀC), (40
Hz); 129.94 (pꢀC), (5 Hz)
180.49/ 42.09/48.90
180.25/ 41.97/ 49.00
180.52/ 41.82/ 49.01
180.74/ 42.12/ 52.28
181.02/ 42.22/ 52.49
47.93 (NꢀCH2), 20.49
(CH2), 11.10 (CH3)
133.91 (iꢀC), (60 Hz); 132.54 (oꢀ
C), (135 Hz); 128.68 (mꢀC), (40
Hz); 129.95 (pꢀC)
47.94 (NꢀCH2), 20.46
(CH2), 11.13 (CH3)
133.94 (iꢀC), (60 Hz); 132.51 (oꢀ
C), (130 Hz); 128.67 (mꢀC), (40
Hz); 129.96 (pꢀC), (5 Hz)
48.07 (NꢀCH2), 20.49
(CH2), 11.26 (CH3)
134.13 (iꢀC), (60 Hz); 132.13 (oꢀ
C), (40 Hz); 128.44 (mꢀC), (36 Hz)
129.62 (pꢀC), (8 Hz)
139.28 (NꢀC), 124.87
(oꢀC), 128.88 (mꢀC),
126.65 (pꢀC)
134.15 (iꢀC), (80 Hz); 133.94 (oꢀ
C), (65 Hz); 128.39 (mꢀC), (35 Hz)
129.33 (pꢀC)
138.58 (NꢀC), 125.15
(oꢀC), 129.03 (mꢀC),
127.17 (pꢀC)
134.06 (iꢀC), (60 Hz); 132.10 (oꢀ
C), (40 Hz); 128.54 (mꢀC), (35 Hz)
129.84 (pꢀC)
a (NꢀCH2) and (ring carbon CH2) got merged; b CDCl3
3.3 . Molecular structures
The analytical data of these coordination compounds are supported by their stoichiometry as
follows: [CuX(PPh3)2(LꢀNR)] (1ꢀ4, 6), [CuX(PPh3)(LꢀNR)2] (5) and {CuX(LꢀNR)(PPh3)}(7ꢀ12).
The single crystal xꢀray crystallography has supported 1ꢀ6 as mononuclear complexes and 7ꢀ12
as dinuclear complexes. Complexes 5ꢀ10 each crystallized in the triclinic crystal system in space
group Pī, whereas complexes 1ꢀ4, 11, 12 crystallized in monoclinic crystal system in space
groups P21/n (1ꢀ4) or P21/c (11, 12) (Table 1).
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Mononuclear coordination compounds. The crystal structure of coordination compound 1
shows that the Cu metal centre is coordinated to one S atom of the LꢀNPrn thioꢀligand, the P
donor atom of two PPh3 ligands and one Cl anion at bond distances of 2.3735 (6); 2.2779 (5),
2.2634 (5), and 2.3531 (5) Å, respectively (Table 5). These distances are comparable to the sum
of covalent radii of metal and the donor group (CuꢀS, 2.35; CuꢀP, 2.43; CuꢀCl, 2.32 Å)53 (Fig. 1).
The CuꢀS and CuꢀP bond distances in coordination compounds 2ꢀ4 lie in the range, 2.3673ꢀ
2.4391 (S) Å, and 2.2634ꢀ2.291(P) Å, and are similar to those found in compound 1 (Fig. 2ꢀ4).
The copperꢀhalogen bond distances vary in the order: CuꢀCl < CuꢀBr < CuꢀI, as expected. In
compound 5, with two thioꢀligands (LꢀNPh) and one PPh3 bonded to the copper metal centre,
CuꢀS, CuꢀP distances are shorter than those found in analogous compounds (Table 5) (Fig. 5).
The bond angles around Cu metal centre fall in the range, 102.62–123.50o, with P1ꢀCuꢀP2 being
the largest, and P1ꢀCuꢀS1, the shortest. The bonding patterns of the other coordination
compounds (2ꢀ4, 6) are similar to that observed in complex 1 (Fig. 6), except for the differences
in the halogen anion (Br, 2; Cl, 3; I, 4, 6) and thioꢀligand, which alter the bond parameters
around Cu(I). The largest PꢀCuꢀP bond angle lies within a range of 123.46–123.973o. Another
type of mononuclear complex reported here is [CuBr(PPh3)(LꢀNPh)2] (5), where Cu(I) is bonded
to two sulfur atoms of two thioꢀligands, a P donor atom of PPh3 and a bromide anion with the
bond lengths of 2.3484, 2.3247 (S), 2.2408 (P), and 2.5183 (Br) Å, respectively (Table 5). Bond
angles around the central Cu atom lie within the range 99.74–112.84o, and where the PꢀCuꢀX is
the largest angle (112.84o).
Dinuclear complexes. The single crystal xꢀray crystallography showed that coordination
compound 7 existed as a dinuclear complex (Fig. 7). In this dinuclear complex, [Cu2(µꢀ
Br)2(κ1:SꢀLꢀNEt)2(PPh3)2], bromine atoms form bridges and each copper metal is further bonded
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to one P donor atom of a PPh3 ligand and one S donor atom of a thioꢀligand. The CuꢀS and CuꢀP
bond distances of 2.3021(6) Å and 2.2421(5) Å respectively are less than the sum of covalent
radii of Cu/S (2.35 Å) and Cu/P (2.43Å).53 The unequal CuꢀBr bond distances of 2.5063(3) Å
and 2.6124(4) Å of Cu2Br2 core are longer than the sum of covalent radii of Cu/Br (2.44 Å) due
to bridging and it reveals that the Cu2Br2 core forms a parallelogram. The angles around each
metal centre in the range, 97.73–115.31º are typical of a distorted tetrahedral geometry.18 The
Cu2Br2 core angles for Cu/Br are 97.73 and 82.26º respectively. The bonding parameters of the
other dinuclear compounds 8ꢀ12 are similar to those of compound 7 (Table 5) (Fig. 8ꢀ12). The
Cu2Br2 core angles of bromoꢀbridged dinuclear compound 9 are similar to those of compound 7.
Interestingly, in compound 11, the Cu2Br2 core angles for Cu/Br are 102.87and 77.12º,
respectively, and are different from the corresponding angles found in the 7/9 compounds. The
difference may be attributed to the presence of a bulky group at an N atom of the imidazolidine
ring of the LꢀNPh thioꢀligand in compound 11. The choroꢀbridged dinuclear compound 8 has
shown Cu2Cl2 core angles comparable to those of compound 9 having the same thioꢀligand, Lꢀ
NPrn. The bulky bridging iodine atoms in dinuclear compounds 10 and 12 make angles of 102ꢀ
106/73ꢀ78º at Cu/I, respectively, which are similar to those in compound 11.
The C–S bond lengths in compounds 1ꢀ12 fall in the range, 1.68–1.70 Å, which are less than
the C–S single bond length (1.81 Å) but longer than the C=S double bond length (1.62 Å),
suggesting a partial double bond character in the C–S bond.53,54 Finally, the CuꢀCu separations
of 3.157–3.410 Å in all the dimeric compounds are more than twice the sum of van der Waals
radius of Cu atom, 2.80 Å.53 It shows that there are no metalꢀmetal interactions in dinuclear
compounds.
Table 5 Bond lengths (Ǻ) and bond angles (o) of complexes 1 − 12
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Mononuclear complexes
1(Cl)
2(Br)
3(Cl)
4(I)
6(I)
5(Br)
Cu1–S1
Cu1–X1
Cu1–P1
Cu1–P2
S–C
2.3735(6)
2.3531(5)
2.2779(5)
2.2634(5)
1.695(2)
2.3721(7) 2.3791(5)
2.4817(5) 2.3554(5)
2.2766(7) 2.2655(5)
2.2706(7) 2.2810(5)
2.3673(9)
2.6548(5)
2.2853(9)
2.4390(8) Cu1–S1
2.6065(4) Cu1–S2
2.2773(8) Cu1–X1
2.3484(7)
2.3247(6)
2.5183(4)
2.2408(6)
1.684(2)
1.691(2)
2.2800(10) 2.2908(8) Cu1–P1
1.704(4) 1.691(3) S1–C1
102.64(3) 108.828(18) 103.67(4) 104.08(3) S2–C10
109.06(3) 104.972(18) 108.64(4)
1.703(3)
1.698(2)
P1–Cu1–S1
P2–Cu1–S1
102.62(2)
109.12(2)
106.63(3) P1–Cu1–S1
103.18(2) P1–Cu1–S2
112.69(3)
112.16(2)
P1–Cu1–X1 109.90(2)
P2–Cu1–X1 102.66(2)
X1–Cu1–S1 108.55(2)
108.67(2) 100.735(18) 106.85(3)
102.46(2) 108.627(19) 102.22(3)
108.96(2) P1–Cu1–X1 112.849(19)
107.41(2) X1–Cu1–S1 108.79(2)
125.46(3) X1–Cu1–S2 109.83(2)
109.98(2) 109.18(2)
112.12(3)
P2–Cu1–P1
123.50(2)
123.78(3) 123.973(18) 123.44(4)
S1–Cu1–S2
99.74(2)
Halogenꢀbridged dinuclear complexes
7(Br)
8 (Cl)
7(Br)
8 (Cl)
Cu1–S1
Cu1–X1
Cu1–X1*
Cu1–P1
S1–C1
2.3021(6)
2.5063(3)
2.6124(4)
2.2421(5)
1.707(2)
3.368
2.3055(6)
2.3806(5)
2.5020(6)
2.2238(5)
1.6960(19)
3.221
P1–Cu1–S1
P1–Cu1–X1
P1–Cu1–X1*
S1–Cu1–X1
S1–Cu1–X1*
X1–Cu1–X1
Cu1–X1–Cu1
115.31(2)
112.933(17)
108.956(17)
104.618(16)
115.173(16)
97.738(11)
82.263(11)
9 (Br)
113.82(2)
111.041(19)
114.281(18)
103.640(19)
114.687(19)
97.500(17)
82.499(17)
10 (I)
Cu···Cu
9 (Br)
10 (I)
Cu1–S1
Cu1–X1
Cu1–X1*
Cu1–P1
2.3027(7)
2.5061(4)
2.6206(4)
2.2370(6)
2.3070(8)
2.6642(4)
2.6642(4)
2.2567(7)
P1–Cu1–S1
P1–Cu1–X1
P1–Cu1–X1*
S1–Cu1–X1
114.48(3)
112.49(2)
110.014(19)
102.78(2)
113.92(3)
109.87(2)
111.43(2)
101.97(2)
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S1–C1
1.709(2)
3.300
1.701(2)
S1–Cu1–X1*
X1–Cu1–X1
Cu1–X1–Cu1
115.487(19)
99.910(14)
80.090(14)
11(Br)
116.16(2)
102.179(14)
77.821(14)
12 (I)
Cu···Cu
3.410
11(Br)
12 (I)
Cu1–S1
Cu1–X1
Cu1–X1*
Cu1–P1
S1–C1
2.3210(6)
2.5233(3)
2.5233(3)
2.2387(6)
1.689(2)
3.157
2.3302(9)
2.6866(6)
2.6867(6)
2.2584(9)
1.693(4)
3.222
P1–Cu1–S1
P1–Cu1–X1
P1–Cu1–X1*
S1–Cu1–X1
S1–Cu1–X1*
X1–Cu1–X1
Cu1–X1–Cu1
116.21(3)
115.83(4)
107.16(3)
111.16(3)
102.28(3)
112.94(3)
106.462(19)
73.540(19)
109.164(19)
113.290(18)
102.617(18)
111.215(18)
102.874(12)
77.12(12)
Cu···Cu
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Fig. 1 Molecular structure of complex [CuCl(LꢀNPrn)(PPh3)2] (1). Displacement ellipsoids are
drawn at the 40% probability level.
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Fig. 2 Molecular structure of complex [CuBr(LꢀNPrn)(PPh3)2] (2). Displacement ellipsoids are
drawn at the 40% probability level.
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Fig. 3 Molecular structure of complex [CuCl(LꢀNBun)(PPh3)2] (3). Displacement ellipsoids are
drawn at the 40% probability level.
29