Synthesis, characterization, and electrochemical studies of Co(II, III) dithiocarbamate complexes

Article abstract of DOI:10.1080/00958972.2019.1596263

Cobalt(II) complexes of N-methyl phenyl, 1-phenylpiperazyl, and morpholinyl dithiocarbamates have been synthesized and characterized by UV–Visible, FTIR, ¹H-, ¹³C-NMR, and mass spectrometry. The spectroscopic data indicated that two ligands coordinated in bidentate chelating to the metal ion to form four-coordinate cobalt(II) complexes (1–3), which was confirmed by mass analysis (TOF MS ES⁺) of the complexes with m/z [M]⁺ = 450.98, 382.94, and 382.94 for 1, 2, and 3, respectively. Single crystal analysis of 2A and 3A show centrosymmetric mononuclear cobalt(III) bonded to three dithiocarbamate ligands forming a distorted octahedral geometry, indicating the cobalt(II) undergoes aerial oxidation to cobalt(III) during recrystallization. In addition, 2A crystallized with one solvated molecule of toluene. The redox behaviors of the complexes were studied by cyclic and square wave voltammetry in dichloromethane; the result revealed a metal centered redox process consisting of a one-electron quasi-reversible process assigned to Co(III)/Co(IV) oxidation and a corresponding Co(IV)/Co(III) reduction. Randles–Sevcik plots (anodic peak current versus the square root of the scan rate (I_p,a versus ν^1/2)) for the redox couples revealed diffusion-controlled behavior.

Full text of DOI:10.1080/00958972.2019.1596263

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: https://www.tandfonline.com/loi/gcoo20
Synthesis, characterization and electrochemical
studies of Co(II, III) dithiocarbamate complexes
Fartisincha P. Andrew & Peter A. Ajibade
To cite this article: Fartisincha P. Andrew & Peter A. Ajibade (2019): Synthesis, characterization
and electrochemical studies of Co(II, III) dithiocarbamate complexes, Journal of Coordination
Chemistry, DOI: 10.1080/00958972.2019.1596263
To link to this article: https://doi.org/10.1080/00958972.2019.1596263
View supplementary material
Accepted author version posted online: 18
Mar 2019.
Submit your article to this journal
View Crossmark data
Full Terms & Conditions of access and use can be found at
https://www.tandfonline.com/action/journalInformation?journalCode=gcoo20

Synthesis, characterization and electrochemical studies of Co(II, III)
dithiocarbamate complexes
FARTISINCHA P. ANDREW and PETER A. AJIBADE*
School of Chemistry and Physics, University of KwaZulu-Natal, Private Bag X01, Scottsville, Pietermaritzburg,
3209 South Africa
Cobalt(II) complexes of N-methyl phenyl, 1-phenylpiperazyl and morpholinyl dithiocarbamates
1
have been synthesized and characterized by UV-Visible, FTIR, H-, 13C-NMR and mass
spectrometry. The spectroscopic data indicated that two ligands coordinated bidentate chelating
to the metal ion to form four-coordinate cobalt(II) complexes (1-3), which was confirmed by
mass analysis (TOF MS ES+) of the complexes with m/z [M]+ = 450.98, 382.94 and 382.94 for 1,
2 and 3, respectively. Single crystal analysis of 2A and 3A show centrosymmetric mononuclear
cobalt(III) bonded to three dithiocarbamate ligands forming a distorted octahedral geometry,
indicating the cobalt(II) undergoes aerial oxidation to cobalt(III) during recrystallization. In
addition, 2A crystallized with one solvated molecule of toluene. The redox behaviors of the
complexes were studied by cyclic and square wave voltammetry in dichloromethane; the result
revealed a metal centered redox process consisting of a one-electron quasi-reversible process
assigned to Co(III)/Co(IV) oxidation and a corresponding Co(IV)/Co(III) reduction. Randles-
Sevcik plots (anodic peak current versus the square root of the scan rate (Ip,a vs. ν1/2)) for the
redox couples revealed diffusion-controlled behavior.
*Corresponding author. Email: ajibadep@ukzn.ac.za
1

Graphical abstract
Keywords: Synthesis; Cobalt(II); Dithiocarbamates; Crystal structure; Cyclic voltammetry
1. Introduction
The chemistry of metal dithiocarbamates has been subject of several biological and material
studies [1-9]. Due to the stable bonding configuration of metal dithiocarbamates and various
structural motifs in solid state, they have found applications in medicine, agriculture, industry,
analytical and organic chemistry [10-13]. They have been extensively used as pesticides,
fungicides, vulcanization accelerators in rubber industry, heavy metal scavengers, floating agents
in metal metallurgy and as photosensitized solar cells [14, 15]. They are also characterized by a
broad spectrum of biological activity against both plants and animal pathogens. Metal
dithiocarbamates have rich and interesting electrochemical and optical properties due to their
redox behavior and ability to stabilize transition metals in different oxidation states [16]. Hogarth
and Bond et al. [17, 18], in separate studies, have reported the electrochemistry of metal
2

dithiocarbamates and established that they easily undergo sequential one-electron transfer
reactions, associated with interesting structural and spectral changes that have important
applications in both materials and biological sciences.
Understanding the redox properties of these compounds helps to tailor their applications
in electrocatalysis, electro-active and opto-active materials [19] in pharmaceutical or biological
processes [20]. Reports on the electrochemical properties of Co(II) dithiocarbamate complexes
[21-23] show they undergo spontaneous oxidation into Co(III). Bond et al., in a review about
oxidation-reduction of Co(III) dithiocarbamates, concluded that their electrochemical reduction
depends on the nature of the R substituent, solvent and nature of the electrodes [24]. Therefore,
in continuation of our studies on metal dithiocarbamate complexes [16, 25-28], we report the
synthesis, characterization and electrochemistry of Co(II) complexes of N-methylphenyl,
1-phenylpiperazyl and morpholinyl dithiocarbamates. The crystal structures of
tris(1-phenylpiperazyl and morpholinyldithiocarbamato S,S′)Co(III) (2A and 3A) are also
reported, showing that the Co(II) complexes (2 and 3) undergo aerial oxidation to Co(III).
2. Experimental
2.1. Materials and methods
Cobalt(II) acetate tetrahydrate, N-methylbenzylamine, 1-phenylpiperazine, morpholine and all
1
13
the solvents were used as obtained. H and C NMR spectra of the ligands were recorded on a
Bruker Avance III 400 MHz spectrometer at room temperature using (TMS) as internal standard.
The proton and carbon NMR shifts are quoted in ppm relative to water signal. FTIR spectra were
recorded from 4000-650 cm-1 using a Cary 630 FTIR spectrophotometer from Agilent
Technologies. The UV-Visible spectra were recorded using a Cary 100-UV-Vis
spectrophotometer from Agilent Technologies. The molar conductivity was recorded using a
Jenway 4510 conductivity meter. Single mass analysis (TOF MS ES+) was done using a Waters
Micromass LCT Premier TOF-MS.
Electrochemical measurements were performed with an Autolab potentiostat (with Nova
1.7 software) equipped with a three electrode system, a glassy carbon working electrode
(GCWE), Ag/AgCl reference electrode and an auxiliary platinum counter electrode. Fresh 2 mM
solution of the complexes and 0.1 M tetrabutylammonium hexafluorophosphate (TBAPF6)
supporting electrolyte was prepared in dichloromethane (DCM). The solutions of the complexes
3

were purged with a nitrogen steam for about 15 min before every experiment. The glassy carbon-
working electrode is polished between each run with a slurry of alumina and ultra-pure water on
a Buehler felt pad and rinsed thoroughly with ultra-pure water.
2.2. Synthesis of ligands (L1-L3)
The sodium salt of N-methylphenyldithiocarbamate (L1), 1-phenylpiperazine dithiocarbamate
(L2) and morpholine dithiocarbamate (L3) were synthesized by a reported method [18, 19].
Equimolar N-methylbenzylamine (6.0224 g, 50 mmol), 1-phenylpiperazine (8.0712 g, 50 mmol)
and morpholine (4.4440 g, 50 mmol) were dissolved in 20 mL methanol and NaOH (2.0 g, 50
mmol) and minimum amount of water was added, followed by the addition of cold carbon
disulfide (3.798 g, 50 mmol). The reaction mixtures were stirred for 4 h at 0-4 C; the resulting
white precipitates were filtered, washed with diethyl ether and dried under vacuum over silica.
2.3. Synthesis of cobalt complexes 1-3
The cobalt complexes were synthesized according to the general procedure. Aqueous solution of
cobalt(II) acetate tetrahydrate (0.5 mmol, 0.1245 g) was added dropwise into an aqueous solution
of the ligands N-methylphenyldithiocarbamate (L1: 1 mmol, 0.2174 g), 1-phenylpiperazine
dithiocarbamate (L2: 1 mmol, 0.2600 g) and morpholine dithiocarbamate (L3: 1 mmol, 0.2600 g).
The reaction mixtures were stirred for 4 h, resulting in a green precipitate, which was filtered and
washed with distilled water and methanol, and dried over silica.
2.4. Characterization of the ligands (L1-L3) and complexes (1-3)
2.4.1. N-Methylphenyldithiocarbamate (L1). Yield 98%, m.p 129 C, molar conductivity
(Ω-1cm2mol-1, DMSO ): 44.60. Anal. calc. for Na(S2CNCH3CH2C6H5)·2H2O: C, 42.34; H, 5.53;
N, 5.49; S, 25.12. Found: C, 42.20; H, 5.60; N, 5.46; S, 25.54. 1H NMR (400 MHz, D2O, δ, ppm)
13
(t, 2H), 7.50 (t, 2H), 7.42 (t, 1H), 7.36 (d, 2H), 5.50 (s, 2H), 3.50 (s, 3H). C NMR (400 MHz,
D2O, δ, ppm), 210.14 (CS), 42.69 (N-CH3), 59.63 (N-CH2-(C6H5)), 136.79, 126.83, 127.40,
128.87 (-C6H5). UV-Vis (H2O, λmax, nm) 258, 285. Selected IR (solid state, cm-1) 1625 ν(C-N) cm-
1, 949 ν(C-S) cm-1. N-methylphenyldithiocarbamato-S,S’ cobalt(II) [Co(L1)2] 1 : Yield (0.362
g, 80%), m.p 192 °C, molar conductivity (Ω-1cm2mol-1, DMSO): 1.08. Anal calc. for
[Co(S2CNCH3CH2C6H5)2]·½H2O: C, 46.94; H, 4.60; N, 6.08. Found: C, 46.56; H, 4.80; N, 5.86.
4

Selected IR (solid state, cm-1) (νC-N), 1493, (ν(C-S2 ), 962, UV-Vis (DCM, λmax, nm (cm-1)), 275
(36363), 329 (30395), 642 (15576), TOF-MS ES+: m/z [M]+ = 450.98 (100%).
2.4.2. 1-Phenylpiperazine dithiocarbamate (L2). Yield 78%, m.p 159 C, molar conductivity
(Ω-1cm2mol-1, DMSO): 68.20, white solid. Anal. calc. for Na(S2CNC4H8NC6H5)·2H2O: C, 44.58;
1
H, 5.78; N, 9.45; S, 21.64. Found: C, 44.28; H, 5.82; N, 9.35; S, 21.92. H NMR (400 MHz,
13
D2O, δ, ppm) 7.41 (t, 2H), 7.17 (d, 2H), 7.08 (t, 1H), 4.50 (t, 4H), 3.23 (t, 4H). C NMR (400
MHz, D2O, δ, ppm); 209.01 (CS), 49.70, 50.45 (N-CH4CH4N-) 117.98, 122.16, 129.59, 150.34 (-
C6H5). UV-Vis (H2O, λmax, nm) 261, 286(shoulder). Selected IR (solid state, cm-1) 1494 ν(C-N)
cm-1, 994 ν(C-S) cm-1. 1-phenylpiperazinedithiocarbamato-S,S’ cobalt(II) [Co(L2)2] 2: Yield
(0.218 g, 82%), m.p 187 °C, molar conductivity (Ω-1cm2mol-1, DMSO): 1.45. Anal. calc. for
Co(S2CNC4H8NC6H5)2]·2H2O: C, 46.38; H, 5.31; N, 9.83. Found: C, 46.27; H, 5.90; N, 9.79.
Selected IR (solid state, cm-1) (νC-N), 1479, (ν(C-S2 ), 1004, UV-Vis (DCM, λmax, nm (cm-1)), 254
(39370), 330 (30303), 644 (15527), TOF-MS ES+: m/z [M]+ = 533.04 (100%).
2.4.3. Morpholine dithiocarbamate (L3). Yield 65%, m.p 185 C, molar conductivity
(Ω-1cm2mol-1, DMSO): 66.30. Anal. calc. for Na(S2CNC4H8O)·H2O: C, 29.55; H, 4.96; N, 6.89;
S, 31.55. Found: C, 29.18; H, 5.04; N, 6.92; S, 32.08. 1H NMR (400 MHz, D2O, δ, ppm) 4.45 (t,
4H), 3.84 (t, 4H). 13C NMR (400 MHz, D2O, δ, ppm); 209.37 (CS), 51.40, 66.13 (OCH4CH4N-).
UV-Vis (H2O, λmax, nm) 264, 286(shoulder). Selected IR (solid state, cm-1) 1418 ν(C-N) cm-1, 979
ν(C-S) cm-1. Morpholinedithiocarbamato-S,S’ cobalt(II) [Co(L3)2] 3: Yield; (0.292 g, 76%),
m.p 196 °C, molar conductivity (Ω-1cm2mol-1, DMSO): 2.9. Anal. calc. for
[Co(S2CNC4H8O)2]·1.5H2O: C, 29.26; H, 4.67; N, 6.82. Found: C, 29.24; H, 4.71; N, 6.84.
Selected IR (solid state, cm-1) (νC-N), 1477, (ν(C-S2 ), 1008, (DCM, λmax, nm (cm-1), 279 (35842),
331 (30211), 647 (15455), TOF-MS ES+: m/z [M]+ = 382.94 (100%).
2.5. Single crystal X-ray crystallography
Single crystals of 2A and 3A were obtained by layering dichloromethane solutions of the
complexes with toluene. Suitable crystals (0.32×0.27×0.15 mm3 and 0.39×0.24×0.14 mm3 of 2A
and 3A, respectively) were selected and mounted on a MITIGEN holder in paratone oil on a
Bruker SMART APEX2 area detector diffractometer. The crystal was kept at a steady T =
5

100(2) K during data collection. The structure was solved with the ShelXS-2013 [29] structure
solution program using the Intrinsic Phasing solution method and by using Olex2 [30] as the
graphical interface. The model was refined with version 2016/6 of ShelXL [31] using least
squares minimization. Crystal data are in table 1; distances and angles are in tables 2-5.
3. Results and discussion
3.1. Synthesis and characterization
Three cobalt complexes (scheme 1) of N-methylphenyldithiocarbamate (L1), 1-phenylpiperazine
dithiocarbamate (L2) and morpholine dithiocarbamate (L3) were synthesized by reaction of each
ligand with cobalt(II) acetate tetrahydrate in 2:1 ratio at room temperature (scheme 1). The
complexes were obtained in good yields ranging from 76 – 82%. The complexes are air stable
and melt at 187 – 196 °C. They were soluble in dichloromethane, chloroform, DMSO and
acetonitrile. The single mass analyses (TOF MS ES+) were determined and the spectra are
presented in figures S13-S15. The m/z ion peaks are 450.98, 382.94 and 382.94 for 1, 2 and 3,
respectively, agreeing with the theoretical molecular weight of the respective complexes.
3.2. Single crystal structures of 2A and 3A
The complexes are formulated as four-coordinate Co(II), consistent with the results obtained
from elemental analysis, spectroscopic and mass spectrometry. However, single crystal
structures of 2A and 3A (figures 1 and 2) revealed six-coordinate octahedral cobalt(III), which
indicates the compounds were oxidized to cobalt(III) during recrystallization. Complex 2A
crystallized in the triclinic crystal system and P-1 space group. The structure consists of a
centrosymmetric monomeric entity where the cobalt(III) is six coordinate by six sulfur (S1, S2,
S3, S4, S5 and S6) donors from three dithiocarbamate ligands forming a distorted octahedral
geometry with retained toluene within the crystal structure. The S—Co—S bite angles averaged
76.55°, in the range of related cobalt dithiocarbamate complexes [32, 33].
Complex 3A crystallized in the monoclinic crystal system and C2/c space group. The
molecular structure has been described previously, however, unlike the reported structures, 3A
crystallized in the C2/c space group, different from P21/c and Pī space groups previously
reported [34, 35]. Furthermore, one morpholine is clearly superimposed in the crystal state. The
6

geometric measurements are within the range of similar six-coordinate Co(III) dithiocarbamate
complexes [32, 33]. The six Co—S interatomic distance are 2.2926(4) - 2.2433(4) Å for 2A,
whereas for 3A, the interatomic Co—S3, Co—S1 = Co—S11 and Co—S2 = Co—S21 distances
are 2.2684(10), 2.2629(9) and 2.2758(9) Å, respectively. The thioureide C—N bond lengths for
2A and 3A are 1.3228(16) - 1.388(10) Å, shorter than a perfect C—N single bond of 1.465 Å and
longer than the normal C═N of 1.279 Å; this is indicative of partial double bond character as a
result of the delocalized π-electron density over thioureide (NCS2) moiety [36, 37]. Similarly, the
thioureide C—S bond lengths in 2A and 3A of 1.707 – 1.721 Å are shorter than normal C—S
single bond lengths of 1.81 Å and longer than C═S bond lengths of 1.69 Å, suggesting resonance
or partial double bond formation from the delocalized electron between the C—S upon
complexation [38]. S1, S2, S4 and S5 in 2A are in the same equatorial plane with a small
distortion from the perfect 180° trans coordination angle, with trans S1—Co1—S4 and S5—
Co1—S2 angles of 165.487(14) and 166.138(14), respectively, and the axial S3—Co—S6 is
166.478(15)°. In 3 S2, S21, S3 and S31 are distorted in the same equatorial plane with trans
coordination angles S3—Co2—S2 and S31—Co2—S21 of 166.64(4)°, less than the perfect 180°
trans coordination angle. Similarly axial S1—Co2—S11 coordination angle is 168.50(6), also
slightly distorted from the perfect 180° [39]. These data are consistent with tris(dithiocarbamato-
S,S′) cobalt(III) compounds previously reported [40-44].
3.3. Electronic spectra
Electronic spectra of the ligands and the complexes recorded in water and dichloromethane are
presented in figures S7-S9 of the Supplementary Material. All three ligands exhibit absorption at
258 – 286 nm assigned to intraligand π-π* transition corresponding to S-C=S and N-C=S of the
dithiocarbamate moiety [26]. These absorptions shift to higher wavelength of 254 – 331 nm upon
complexation, but were still assigned to intraligand π-π* transitions. An additional broad band
observed in the visible region at 642, 644 and 647 nm for CoL1, CoL2 and CoL3, respectively,
2
2
were attributed to d-d transition assigned as B1g←2Ag (d 2→dxy) and B3g←2Ag (dxz→dxy)
2
x -y
[21, 45].
7

3.4. FTIR spectra studies
The overlay FTIR spectra of the ligand and the complexes are presented in figures S10-S12.
Dithiocarbamate complexes are normally characterized by some diagnostic regions of stretching
vibrations; thus 1580-1450 cm-1 associated to ν(C-N), 1060–940 cm-1 due to ν(C-S) and 420-250
cm-1 associated to ν(M-S) [46, 47]. In the present study, bands at 1493, 1479 and 1477 cm-1 for
1, 2 and 3, respectively, were assigned to ν(C-N) stretching vibration with an intermediate bond
order between a single C-N and C=N bonds [25]. The single bands observed at 962, 1004 and
1008 cm-1 for 1, 2 and 3 were assigned to ν(C-S) implying that the ligands coordinate in a
bidentate coordination mode to the metal ion [48-50].
3.5. Electrochemistry
The electrochemical behaviors of the complexes were studied using cyclic and square wave
voltammetry in dichloromethane at room temperature. The cyclic voltammetric data of 1-3 and
ferrocene standard at 100 mV/s scan rate are listed in table 6. The cyclic voltammogram of
ferrocene standard is shown in figure 3. The electrochemistry of cobalt(II) dithiocarbamate
complexes (figures 4-12) revealed that Co(II) dithiocarbamate complexes undergo quasi-
reversible oxidation to Co(III), because Co(II) complexes are easily oxidized to more stable
Co(III) oxidation state in addition to the strongly antibonding M—S σ* HOMO [51].
The overlay cyclic voltammograms of 1, 2 and 3 at increasing scan rate are shown in
figures 4, 7 and 10, respectively, and the data are collected in tables 7-9. All the complexes
display one redox couple at positive potential range of 0.72 – 1.32 V vs. Ag/AgCl comprising
Co(II)/(III) oxidation and Co(III)/(II) reduction [24, 52-54]. The Co(II)/(III) oxidation (Eq. I)
was observed at Ep,a = 0.99 V vs. Ag/AgCl for 1, 0.95 V vs. Ag/AgCl for 2, 0.99 V vs. Ag/AgCl
for 3 and Co(III)/(II) reduction (Eq. II) was observed at Ep,c = 0.90 V vs. Ag/AgCl for 1, 0.74 V
vs. Ag/AgCl for 2 and 0.9 V vs. Ag/AgCl for 3.
8

The peak-to-peak separations (ΔEp) of 1 and 3 are similar, 90 mV vs. Ag/AgCl at 100 mVs-1, 2 is
210 mV vs. Ag/AgCl higher than 1 and 3; this shows that the ligands are able to influence the
redox potential probably from relative donor strength. The ring strain in addition to the hetero
piperazine moiety of L2 might favor dithiocarbamate resonance formation to thioureide in 2, as
such reducing electron density on the metal [51]. The higher peak-to-peak separations in 1-3 in
comparison with that of the ferrocene standard 70 mV vs. Ag/AgCl (table 6) suggest one-
electron quasi-reversible redox processes in all the complexes [55, 56]. The ratio of the peak
currents Ip,a/Ip,c ≈ 1 and the square wave of all the complexes confirmed a one-electron quasi-
reversible redox couple [57-59].
Randles-Sevcik equation (Eq. III) was used to study the diffusion-controlled behavior of
each redox couple. The overlay voltammograms of 1, 2 and 3 at increasing scan rate are shown
in figures 4, 7 and 10, respectively,
1
퐼푃,푎 = 0.4463푛퐹퐴퐶 (푛퐹휈퐷)2 ---------------------------------------- (III)
푅푇
where Ip,a = anodic peak current, n = number electron, F = Faraday’s constant (96485 Cmol-1-),
A = electrode area (cm-2), D = analyte diffusion coefficient cm2s-1, C = concentration of
complex.
The effect of scan rate on cathodic peak current was determined via the plot of Ip,a vs. ν1/2. All the
complexes displayed a linear relationship (figures 6, 9 and 12), indicating diffusion-controlled
behavior [60].
4. Conclusion
Tris(dithiocarbamate-S,S′) cobalt(II) complexes of N-methylphenyl (1), 1-phenylpiperazyl (2)
and morpholinyl (3) dithiocarbamates have been synthesized and characterized by mass
1
spectrometry, FTIR, UV-Visible, H and 13C NMR spectroscopy. The spectroscopic studies
indicated the bidentate coordination of the ligands to cobalt(II). The molecular structures of 2A
and 3A were confirmed by single crystal X-ray crystallography. Both structures formed six-
coordinate Co(III) distorted octahedral geometry different from the proposed four-coordinate
Co(II) complexes, showing that the Co(II) had undergone aerial oxidization to Co(III). The
electrochemical behavior of 1-3 revealed one redox couple corresponding to one-electron
9

transfer oxidation and reduction process of Co(II)/Co(III) oxidation and a corresponding
Co(III)/Co(II) reduction. Furthermore, the effect of scan rate on cathodic peak current was
determined via Randles-Sevcik plot, a linear relationship was observed in the plots of Ip,a vs. ν1/2
indicating diffusion-controlled behavior of 1-3.
Supplementary crystallographic data
CCDC 1877635 and 1877636 contain supplementary crystallographic data and can be obtained
from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif or
from the Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK (Fax: +44-1223-336-033;
E-mail: deposit@ccdc.cam.ac.uk).
Acknowledgements
The authors acknowledge the financial support of Sasol South Africa and FPA acknowledge
Tertiary Education Trust Fund (TETfund) and Modibbo Adama University of Technology,
Nigeria for the award of PhD scholarship.
References
[1]
M.K. Amir, S.Z. Khan, F. Hayat, A. Hassan, I.S. Butler. Inorg. Chim. Acta, 451, 31
(2016).
[2]
[3]
[4]
A.M. Paca, P.A. Ajibade. Mater. Chem. Phys., 202, 143 (2018).
A.S. Sonia, R. Bhaskaran. J. Mol. Struct., 1134, 416 (2017).
A.P. Balasubramaniam, A. Peuronen, M. Lahtinen, M. Manickavachagam, E.
Kolehmainen, E. Haapaniemi, M. Sillanpää. Polyhedron, 123, 453 (2017).
E. Sathiyaraj, K. Padmavathy, C.U. Kumar, K.G. Krishnan, C. Ramalingan. J. Mol.
Struct., 1147, 103 (2017).
[5]
[6]
A.Z. Halimehjani, K. Marjani, A. Ashouri, V. Amani. Inorg. Chim. Acta, 373, 282
(2011).
[7]
[8]
[9]
P.A. Ajibade, J.Z. Mbese, B. Omondi. Inorg. Nano-Met. Chem., 47, 202 (2017).
D.C. Onwudiwe, P.A. Ajibade. Polyhedron, 29, 1431 (2010).
S.Z. Khan, M.K. Amir, I. Ullah, A. Aamir, J.M. Pezzuto, T. Kondratyuk, S. Khan. Appl.
Organomet. Chem., 30, 392 (2016).
10

[10] F. Shaheen, A. Badshah, M. Gielen, M. Dusek, K. Fejfarova, D. de Vos, B. Mirza. J.
Organomet. Chem., 692, 3019 (2007).
[11] K.V. Gopal, P.S. Jyothi, P.A.G. Raju, K. Rameshbabu, J. Sreeramulu. J. Chem. Pharm.
Res., 6, 50 (2013).
[12] R. Yadav, Y. Waghadkar, G. Kociok-Kohn, A. Kumar, S.B. Rane, R. Chauhan. Opt.
Mater., 62, 176 (2016).
[13] S. Farhadi, F. Siadatnasab. Chin. J. Catal., 37, 1487 (2016).
[14] I.P. Ferreira, G.M. de Lima, E.B. Paniago, J.A. Takahashi, C.B. Pinheiro. Inorg. Chim.
Acta, 423, 443 (2014).
[15] S. Kanchi, P. Singh, K. Bisetty. Arab. J. Chem., 7, 11 (2014).
[16] F.P. Andrew, P.A. Ajibade. J. Mol. Struct., 1155, 843 (2018).
[17] G. Hogarth. Mini Rev. Med. Chem., 12, 1202 (2012).
[18] A.M. Bond, R.L. Martin. Coord. Chem. Rev., 54, 23 (1984).
[19] L. Chen, C. Yang, J. Qin, J. Gao, H. You, D. Ma. J. Organomet. Chem., 691, 3519
(2006).
[20] S.S. David, E. Meggers. Curr. Opin. Chem. Biol., 12, 194 (2008).
[21] N.V. Khitrich, V.G. Vlasenko, I.I. Seifullina, Y.V. Zubavichus, S.I. Levchenkov, L.S.
Skorokhod. Russ. J. Gen. Chem., 84, 555 (2014).
[22] D.J. Harding, P. Harding, S. Dokmaisrijan, H. Adams. Dalton Trans., 40, 1313 (2011).
[23] A.C. Ekennia, D.C. Onwudiwe, A.A. Osowole. J. Sulfur Chem., 36, 96 (2015).
[24] A.M. Bond, A.R. Hendrickson, R.L. Martin, J.E. Moir, D.R. Page. Inorg. Chem., 22,
3440 (1983).
[25] F.P. Andrew, P.A. Ajibade. J. Mol. Struct., 1170, 24 (2018).
[26] F.P. Andrew, P.A. Ajibade. J. Coord. Chem., 71, 2776 (2018).
[27] P.A. Ajibade, N.L. Botha. Nanomaterials, 7, 32 (2017).
[28] A.M. Paca, P.A. Ajibade. Nanomaterials, 8, 187 (2018).
[29] G.M. Sheldrick. Acta Cryst., A64, 339 (2008).
[30] O.V. Dolomanov, L.J. Bourhis, R.J. Gildea, J.A.K. Howard, H. Puschmann. J. Appl.
Cryst., 42, 339 (2009).
[31] G.M. Sheldrick. Acta Cryst., C27, 3 (2015).
11

[32] L.T. Chan, H.W. Chen, J.P. Fackler Jr., A.F. Masters, W.H. Pan. Inorg Chem., 21, 4291
(1982).
[33] S. Merlino. Acta Cryst. B, 24, 1441 (1968).
[34] A. Kropidłowska, J. Chojnacki, J. Gołaszewska, D. Paliwoda, B. Becker. Acta
Cryst. E, 63, m2117 (2007).
[35] J. Zhang, F. Jian, L. Lu, X. Yang, X. Wang. J. Chem. Crystallogr., 31, 251 (2001).
[36] E. Kellö, J. Lokaj, V. Vrábel. Collect. Czech. Chem Commun., 57, 332 (1992).
[37] K. Ramalingam, G. Aravamudan, M. Seshasayee, C. Subramanyam. Acta Cryst. C, 40,
965 (1984).
[38] A.S. Sonia, R. Bhaskaran. J. Mol. Struct., 1134, 416 (2017).
[39] H.R. Jia, J. Li, Y.X. Sun, J.Q. Guo, B. Yu, N. Wen, L. Xu. Crystals, 7, 247 (2017).
[40] T. Brennan, I. Bernal. J. Phys. Chem., 73, 443 (1969).
[41] W. Dietzsch, N.V. Duffy, E. Gelerinter, E. Sinn. Inorg. Chem., 28, 3079 (1989).
[42] P.C. Healy, E. Sinn. Inorg. Chem., 14, 109 (1975).
[43] S. Petriček. Croat. Chem. Acta, 84, 515 (2011).
[44] A.R. Hendrickson, R.L. Martin, D. Taylor. J. Chem. Soc., Dalton Trans., 21, 2182
(1975).
[45] B.S. Manhas, B.C. Verma, S.B. Kalia. Polyhedron, 14, 3549 (1995).
[46] D.C. Bradley, M.H. Gitlitz. J. Chem. Soc. A, 1152 (1969).
[47] F. Bonati, R Ugo. J. Organomet. Chem., 10, 257 (1967).
[48] F. Bobinihi, D.C. Onwudiwe, E.C. Hosten. J. Mol. Struct., 1164, 475 (2018).
[49] K. Ramalingam, S. Srinivasan. J. Mol. Struct., 1100, 290 (2015).
[50] H. Mansouri-Torshizi, M. Saeidifar, A. Divsalar, A.A. Saboury. Spectrochim. Acta,
Part A, 77, 312 (2010).
[51] D.J. Harding, P. Harding, S. Dokmaisrijan, H. Adams. Dalton Trans., 40, 1313 (2011).
[52] D. Banerjee, U.S. Ray, J. S. Wu, T.H. Lu, C. Sinha. Polyhedron, 25, 3077 (2006).
[53] V. Rosa, S. Realista, A. Mourato, L.M. Abrantes, J. Henriques, M.J. Calhorda, V. Félix.
J, Organomet. Chem., 712, 52 (2012).
[54] K. Anbalagan, A.S. Ganeshraja. Inorg. Chem. Commun., 37, 59 (2013).
[55] E. Tas, M. Aslanoglu, A. Kilic, Z. Kara. J. Coord. Chem., 59, 861 (2006).
[56] I.N. Booysen, A. Adebisi, M.P. Akerman. Inorg. Chim. Acta, 433, 13 (2015).
12

[57] J. Hong, Y.X. Zhao, B.L. Xiao, A.A. Moosavi-Movahedi, H. Ghourchian, N. Sheibani.
Sensors, 13, 8595 (2013).
[58] I.N. Booysen, A. Adebisi, M.P. Akerman, O.Q. Munro, B. Xulu. J. Coord. Chem., 69,
1641 (2016).
[59] J. Hong, H. Ghourchian, S. Rezaei-Zarchi, A.A. Moosavi-Movahedi, S. Ahmadian, A.A
Saboury. Anal. Lett., 40, 483 (2007).
[60] M.B. Ismail, I.N. Booysen, M.P. Akerman. Inorg. Chem. Commun., 78, 78 (2017).
13

Scheme 1. Synthetic route for the synthesis of 1-3.
14

Table 1. Summary of crystal data and structure refinements for 2A and 3A.
Compound
2A
3A
Formula
Dcalc./g cm-3
μ/mm-1
C40H47CoN6S6
1.407
C29H48Co2N6O6S12
1.090
0.767
0.917
Formula weight
Size/mm3
T/K
863.12
0.32×0.27×0.15
100(2)
Triclinic
P-1
1079.31
0.39×0.24×0.14
100(2)
Monoclinic
C2/c
Crystal system
Space group
a/Å
12.5948(11)
13.2776(12)
14.7845(13)
113.527(3)
111.256(3)
94.689(3)
2037.1(3)
2
19.093(2)
17.6804(18)
12.2787(13)
90
b/Å
c/Å
α/
127.507(2)
90
β/
γ/
V/Å3
3288.0(6)
2
Z
Z’
1
0.25
Wavelength/Å
Radiation type
Θmin/
0.71073
MoKa
0.71073
MoKa
1.666
1.770
27.750
34985
25.999
17949
Θmax/
Measured reflns.
Independent reflns.
Reflections used
Rint
9532
3181
8812
2753
0.0229
479
0.0188
155
Parameters
Restraints
Largest peak
Deepest hole
GooF
0
108
0.400
2.426
-0.234
-0.508
1.027
1.084
wR2 (all data)
wR2
0.0627
0.0607
0.0272
0.0245
0.1315
0.1229
0.0588
0.0503
R1 (all data)
R1
15

Table 2. Selected bond lengths (Å) for 2A.
Bond
Length
Co1—S6
Co1—S2
Co1—S1
Co1—S5
Co1—S4
Co1—S3
S6—C23
S2—C1
2.2926(4)
2.2775(4)
2.2652(4)
2.2561(4)
2.2834(4)
2.2433(4)
1.7146(13)
1.7175(13)
1.7136(13)
1.7145(13)
1.7107(13)
1.7124(13)
1.3228(16)
1.3268(16)
1.3267(18)
S1—C1
S5—C23
S4—C12
S3—C12
N5—C23
N3—C12
N1—C1
16

Table 3. Selected bond lengths (Å) for 3A.
Bond
Length
S3—Co2
S3—C6
Co2—S11
Co2—S1
Co2—S21
Co2—S2
S1—C1
S2—C11
C3—O1
C3—C2
O1—C4
C5—N1
C5—C4
C1—N1
N1—C2
C6—N2
N2—C10
N2—C7
C10—C9
C9—O2
O2—C8
C8—C7
2.2684(10)
1.714(5)
2.2629(9)
2.2629(9)
2.2759(9)
2.2758(9)
1.707(3)
1.721(3)
1.425(5)
1.514(5)
1.429(4)
1.469(4)
1.517(5)
1.329(4)
1.473(4)
1.388(10)
1.484(7)
1.477(7)
1.498(9)
1.486(14)
1.477(14)
1.491(9)
17

Table 4. Selected bond angles (°) for 2A.
Atoms
Angle
S2—Co1—S6
S2—Co1—S4
S1—Co1—S6
S1—Co1—S2
S1—Co1—S4
S5—Co1—S6
S5—Co1—S2
S5—Co1—S1
S5—Co1—S4
S4—Co1—S6
S3—Co1—S6
S3—Co1—S2
S3—Co1—S1
S3—Co1—S5
S3—Co1—S4
C23—S6—Co1
C1—S2—Co1
C1—S1—Co1
C23—S5—Co1
C12—S4—Co1
C12—S3—Co1
C23—N5—C24
C23—N5—C27
C27—N5—C24
C12—N3—C16
C12—N3—C13
C13—N3—C16
C1—N1—C5
C1—N1—C2
C2—N1—C5
96.001(13)
94.590(13)
94.830(14)
76.545(14)
165.487(14)
76.366(13)
166.138(14)
92.400(15)
97.851(14)
97.544(13)
166.478(15)
96.662(14)
92.710(14)
92.134(13)
76.733(13)
85.93(4)
86.37(5)
86.85(5)
87.10(4)
85.84(4)
87.08(4)
122.92(11)
123.48(11)
113.56(10)
122.56(11)
120.93(11)
115.35(10)
123.70(11)
122.59(11)
112.13(11)
18

Table 5. Selected bond angles (°) for 3A.
Atoms
Angle
C6—S3—Co2
S31—Co2—S3
S3—Co2—S2
S31—Co2—S21
S31—Co2—S2
S3—Co2—S21
S1—Co2—S3
S11—Co2—S31
S11—Co2—S3
S1—Co2—S31
S1—Co2—S11
S1—Co2—S2
S11—Co2—S2
S1—Co2—S21
S11—Co2—S21
S2—Co2—S21
C1—S1—Co2
C11—S2—Co2
N1—C5—C4
S1—C1—S21
N1—C1—S1
N1—C1—S21
C5—N1—C2
C1—N1—C5
C1—N1—C2
N1—C2—C3
S31—C6—S3
N2—C6—S3
N2—C6—S31
C6—N2—C10
C6—N2—C7
C7—N2—C10
N2—C10—C9
N2—C7—C8
86.4(2)
76.73(5)
166.64(4)
166.64(4)
93.83(3)
93.83(3)
94.56(4)
94.56(4)
94.46(4)
94.46(4)
168.50(6)
95.60(3)
76.67(3)
76.67(3)
95.60(3)
96.93(5)
86.75(12)
86.02(11)
109.7(3)
110.44(18)
124.6(3)
125.0(2)
113.9(3)
123.2(3)
122.8(3)
108.7(3)
110.5(5)
120.1(3)
125.1(3)
126.8(4)
120.3(5)
112.0(5)
109.0(6)
109.6(5)
19

Table 6. Selected CV parameters of ferrocene standard and complexes
recorded at 100 mVs-1.
Compound
Ep,a (V)
Ep,c (V)
E1/2 (V)
ΔE (mV)
Ferrocene
[Co(L1)2]
[Co(L2)2]
[Co(L3)2]
0.45
0.99
0.95
0.99
0.38
0.90
0.74
0.90
0.42
0.95
0.85
0.95
70
90
210
90
20

Table 7. Cyclic voltammetry data for 1 at increasing scan rates.
Scan rate (ν) /mVs-1
ν1/2 (mVs-1)1/2
Ep,a/V
Ep,c/V E1/2/V ΔEp/mV Ip,a/10-5 (μA)
100
125
150
175
200
10.00
11.18
12.24
13.22
14.14
0.99
0.99
0.99
0.99
0.99
0.90
0.89
0.89
0.89
0.89
0.95
0.94
0.94
0.94
0.94
90
3.06
3.50
3.90
4.32
4.72
100
100
100
100
E1/2 = (Ep,a + Ep,c)/2, ΔEp = Ep,a - Ep,c
21

Table 8. Cyclic voltammetry data for 2 at increasing scan rates.
Scan rate (ν) /mVs-1 ν1/2 (mVs-1)1/2
Ep,a/V
Ep,c/V E1/2/V ΔEp/mV Ip,a/10-5 (μA)
100
125
150
175
200
10.00
11.18
12.24
13.22
14.14
0.95
0.97
1.00
1.01
1.03
0.74
0.72
0.71
0.71
0.70
0.85
0.85
0.86
0.86
0.87
210
250
290
300
330
9.45
12.8
15.1
17.4
19.0
E1/2 = (Ep,a + Ep,c)/2, ΔEp = (Ep,a - Ep,c), Ip,a is anodic peak current
22

Table 9. Cyclic voltammetry data for 3 at increasing scan rates.
Scan rate (ν) /mVs-1 ν1/2 (mVs-1)1/2
Ep,a/V
Ep,c/V E1/2/V ΔEp/mV Ip,a/10-5 (μA)
100
125
150
175
200
225
10.00
11.18
12.24
13.22
14.14
15.00
0.99
0.98
0.99
0.99
0.99
0.99
0.90
0.90
0.89
0.89
0.89
0.89
0.95
0.94
0.94
0.94
0.94
0.94
90
80
3.29
3.71
4.07
4.51
4.84
5.20
100
100
100
100
E1/2 = (Ep,a + Ep,c)/2, ΔEp = Ep,a - Ep,c
23

Figure 1. Thermal ellipsoids (50% probability) of 2A.
24

Figure 2. Thermal ellipsoids (50% probability) of 3A. Hydrogens were omitted for clarity.
25

Figure 3. Cyclic voltammogram of ferrocene standard at 100 mVs-1.
26

Figure 4. Overlay cyclic voltammogram of 1 at increasing scan rates.
27

Figure 5. Square wave voltammogram of 1.
28

Figure 6. Randles-Sevcik plot for 1 redox couple.
29