Synthesis and characterization of O,O'-(o-, m-, p-Ditolyl/dibenzyl/ diphenyldithiophosphate) complexes with cobalt

Article abstract of DOI:10.1080/15533174.2011.591298

Tris(O,O'-ditolyl/dibenzyl/diphenyldithiophosphato)cobalt(III) complexes (1-5) were synthesized by the reaction of CoCl₂·6H ₂O and NH₄S₂P(OR)₂. Initially, the bis(O,O'-ditolyl/dibenzyl/diphenyldithiophosphato)cobalt(II) complexes were formed, oxidized to their analogous tris complexes. In this study, oxidation rate of individual dithiophosphate ligand were investigated on the basis of physical changes. Cobalt(III) complexes (1-5) were characterized by elemental analyses, conductivity measurement, TGA/DSC, and spectroscopic techniques (infrared [IR], ultraviolet [UV]-visible, ¹H-, ¹³C-, and ³¹P-NMR, mass). The experimental results suggest that these complexes have distorted octahedral geometry with bidentate chelation dithiophosphate moieties. Molecular weight determinations of these complexes indicate their monomeric nature. Copyright Taylor &Francis Group, LLC.

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Synthesis and Characterization of O,O’-(o-, m-,
p-Ditolyl/dibenzyl/diphenyldithiophosphate)
Complexes with Cobalt
Subhash C. Bajia a
a Department of Pure and Applied Chemistry , Maharshi Dayanand Saraswati University ,
Ajmer, India
Published online: 11 Aug 2011.
To cite this article: Subhash C. Bajia (2011) Synthesis and Characterization of O,O’-(o-, m-, p-Ditolyl/dibenzyl/
diphenyldithiophosphate) Complexes with Cobalt, Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal
Chemistry, 41:7, 746-749, DOI: 10.1080/15533174.2011.591298
To link to this article: http://dx.doi.org/10.1080/15533174.2011.591298
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 41:746–749, 2011
Copyright ꢀ Taylor & Francis Group, LLC
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ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2011.591298
Synthesis and Characterization of
O,O’-(o-, m-, p-Ditolyl/dibenzyl/diphenyldithiophosphate)
Complexes with Cobalt
Subhash C. Bajia
Department of Pure and Applied Chemistry, Maharshi Dayanand Saraswati University, Ajmer, India
Bis(O,Oꢁ-dialkyl/dibenzyldithiophosphato)cobalt(II) com-
Tris(O,Oꢀ-ditolyl/dibenzyl/diphenyldithiophosphato)cobalt(III)
complexes (1–5) were synthesized by the reaction of
CoCl2·6H2O and NH4S2P(OR)2. Initially, the bis(O,Oꢀ-
plexes are extremely air sensitive and oxidize to their analo-
gous tris complexes. Attempts made to synthesize bis(O,Oꢁ-
ditolyl/diphenyl dithiophosphato)cobalt(II) complexes were un-
successful, giving oxidized products. We have tried to avoid
the oxidation by doing the reaction at low temperature, with
moisture-free reaction medium, and in the presence of nitrogen.
Recently, O,Oꢁ-ditolyl/dibenzyl dithiophosphates have been
used to examine the influence of bulkier groups on phospho-
rus and have reported the syntheses, spectroscopic studies,
and single-crystal x-ray structures of Ni[S2P(OC6H4CH3-
o)2]2,[10] Ni[S2P(OC6H4CH3-m)2]2,[10] Ni[S2P(OCH2Ph)2]2,[10]
[Ni{S2P(OC6H4Me-p)2}2(N2C10H8)],[11] [Ni{S2P(OC6H4Me-
o)2}2(N2C14H12)].C6H6,[11] Me2Sn[S2P(OC6H4Me-o)2]2,[12]
ditolyl/dibenzyl/diphenyldithiophosphato)cobalt(II)
complexes
were formed, oxidized to their analogous tris complexes. In this
study, oxidation rate of individual dithiophosphate ligand were in-
vestigated on the basis of physical changes. Cobalt(III) complexes
(1–5) were characterized by elemental analyses, conductivity
measurement, TGA/DSC, and spectroscopic techniques (infrared
[IR], ultraviolet [UV]-visible, 1H-, 13C-, and 31P-NMR, mass). The
experimental results suggest that these complexes have distorted
octahedral geometry with bidentate chelation dithiophosphate
moieties. Molecular weight determinations of these complexes
indicate their monomeric nature.
Bu2Sn[S2P(OC6H4Me-o)2]2,[12]
Mo2O3[S2P(OC6H4Me-
Keywords bidentate complexes, dithiophosphate, Lewis bases, spec-
o)2]4,[13] Mo2O3[S2P(OC6H4Me-m)2]4,[13] and MoO2[S2P-
troscopic techniques
(OC6H4Me-p)2]2.[13]
In continuation of this interest, herein we report
the syntheses and characterization of tris(O,Oꢁ-ditolyl/
dibenzyl/diphenyldithiophosphato)cobalt(III) complexes (1-5).
The oxidation rate for the individual dithiophosphate ligands
with CoCl2·6H2O were observed on the basis of color changes,
magnetic susceptibility measurement, and ultraviolet (UV)-
visible absorption spectra. Attempts have been made to grow
crystals, in different solvents and mixtures of the solvent, but
did not yield crystals.
INTRODUCTION
O,Oꢁ-Dialkyl dithiophosphate complexes of transition
metals have received increasing attention in recent owing
to their extensive applications in lubrication engineering[1]
and plastic industries.[2] Dialkyl/alkylene dithiophosphate
complexes with cobalt were synthesized in moisture free
reaction condition. Cobalt(II) dithiophosphate complexes can
stabilized by Lewis bases such as Co{S2P(OMe)2}2·PPh3,[3]
[NMe4][CoCl{S2P(OMe)2}2],[4] Co{S2P(OEt)2}2(C5H5N)2,[5]
Co{S2P(OCy)2}2(C5H5N)2,[6]
Co{S2P(OC6H4Me-p)2}2
EXPERIMENTAL
C5H5N)2,[7]
Co(S2POCMe2CH2CHMeO)2(NC5H4Me-2),[8]
All chemicals (Emerk) were used after purification and sol-
vents were dried by standard methods.[20] Ammonium salt of
O,Oꢁ-ditolyl/dibenzyl/diphenyl dithiophosphoric acid was pre-
pared by the reaction of P2S5 with o-, m-, p-cresol/benzyl
alcohol/phenol.[14] Cobalt and sulfur were estimated by pyri-
dine thiocyanate[21] and Messenger’s methods,[21] respectively.
Co(S2POCMe2CH2CHMeO)2(NC5H4Me-3),[8] and Co{S2P
(OC6H4Me-p)2}2(NC5H4Me-3)2.[9]
Received 4 October 2010; accepted 21 February 2011.
Subhash C. Bajia is grateful to UGC, New Delhi for financial sup- Micro-elemental (C and H) analysis was carried out on a
port, and to Prof. K. G. Ojha for spectroscopic discussion. The author
Vario EL elemental analyzer. Molecular weights were deter-
thanks the reviewers for their valuable suggestions, and the Central
mined cryoscopically in benzene. The conductivity measure-
Drug and Research Institute, Lucknow, for spectroscopic facilities.
ments were carried out with a CM-821 Elico conductivity
Address correspondence to Subhash C. Bajia, Department of Pure
dredge in dichloromethane. Magnetic susceptibility measure-
ments were done with a Sherwood Scientific MSB auto at room
and Applied Chemistry, Maharshi Dayanand Saraswati University,
Ajmer 305 009, India. E-mail: subhashbajia@gmail.com
746

BIDENTATE DITHIOPHOSPHATE COBALT COMPLEXES
747
24H, -C6H4); 31P-NMR (CDCl3, δ ppm): 80.80 (s). Mass spec-
tra fragment m/z (%) [Co{S2P(OC6H4Me-p)2}3]+ 987 (100),
[Co{S2P(OC6H4Me-p)2}2]+, 677 (75.2), [Co{S2P(OC6H4Me-
p)2]+, 368 (40.3), [CoS2PO2]+, 186 (13.4), [CoS2PO]+, 170
(7.6), [CoS2P]+, 154 (13), [CoS2]+, 123 (9.8), [C6H4Me-p]+,
91 (21.4), [PO2]+, 62.9 (10.3), [CoS]+ 91 (13).
temperature. TGA/DSC was performed with a universal V3.5B
TA SDT Q600 V3.8 built 51 thermal analyzer. The experiment
was done under nitrogen atmosphere using alumina powder as
the reference material. The weight of the sample was taken in
between 6 to 16 mg, and the heating rate was maintained at
10◦C/min. Electronic spectra were recorded on a Perkin Elmer
UV/visible/near-infrared spectrometer in the range 200–1100
nm. IR spectra (4000–350 cm−1) were recorded on an AB-
Bomen FTLA-2000 spectrophotometer using KBr discs. The
Tris(O,Oꢁ-dibenzyldithiophosphato)cobalt(III) Complex (4)
Same as for 1, purple solid; yield: 1.20 g, (90%); mol. wt.
found (calcd.), 980 (987.04); calc. for C42H42O6P3S6Co: C,
51.11; H, 4.29; S, 19.49; Co, 5.97. Found: C, 51.10; H, 4.22;
S, 19.42; Co, 5.94; UV-vis spectral data [λmax, nm(A); ε(L
mol−1cm−1)] in 0.004 M benzene solution, 710 (282), 526 (109),
433 (312); IR KBr νmax/cm−1, 992s (P)-O-C, 835s P-O-(C),
645s (P=S) or (P-S)asym, 562m (P-S) or (P-S)sym, 419m (Co-
S); 1H-NMR (CDCl3, δ ppm); 5.24 (s, 12H, CH2), 7.0–7.35 (s,
30H, Ph); 31P-NMR (CDCl3, δ ppm): 81.49 (s).
1
1H-, 13C-, and 31P{ H}-NMR spectra were recorded in CDCl3
on a Bruker AV300 (300 MHz) spectrometer. Electron impact
mass spectra (EIMS) were recorded on a Finnigan MAT-312
connected to a DPD 11/34 (DEC) computer system.
Syntheses of Tris(O,Oꢀ-ditolyl/dibenzyl/
diphenyldithiophosphato)cobalt(III) Complexes (1-5)
Tris(O,Oꢁ-(ditolyl-o)dithiophosphato)cobalt(III) Complex (1)
To an aqueous solution (10 mL) of CoCl2·6H2O (0.237g, 1.0
mmol), an aqueous solution (10 mL) of NH4S2P(OC6H4Me-o)2
(0.978 g, 2.99 mmol) was added with constant stirring. A green-
colored solution was obtained. Benzene (50 mL) was added to
extract the complex from the aqueous reaction mixture. After
some hours green-colored benzene solution changes into purple.
Benzene was pumped off under vacuum, yielded a purple solid.
Yield: 1.19 g, (89%); mol. wt. found (calcd.), 983 (987.04); calc.
for C42H42O6P3S6Co; C, 51.11; H, 4.29; S, 19.49; Co, 5.97.
Found: C, 51.03; H, 4.20; S, 19.50; Co, 5.99; UV-vis spectral
data [λmax, nm(A); ε(L mol−1cm−1)] in 0.005 M benzene solu-
tion, 752 (254), 545 (178), 482 (298); IR KBr νmax/cm−1, 1050m
(P)-O-C, 806s P-O-(C), 650s (P=S) or (P-S)asym, 555m (P-S)
or (P-S)sym, 420m (Co-S); 1H-NMR (CDCl3, δ ppm); 2.27 (s,
18H, CH3); 6.90–7.25 (m, 24H, -C6H4); 31P-NMR (CDCl3, δ
ppm): 81.21 (s).
Tris(O,Oꢁ-diphenyldithiophosphato)cobalt(III) Complex (5)
Same as for 1, purple solid; yield: 0.788 g, (87%); mol.
wt. found (calcd.), 900 (902.88); calc. for C36H30O6P3S6Co:
C, 47.89; H, 3.35; S, 21.31; Co, 6.53. Found: C, 47.81;
H, 3.28; S, 21.20; Co, 6.51; UV-vis spectral data [λmax
,
nm(A); ε(Lmole−1cm−1)] in 0.002 M benzene solution, 704
(246), 514 (153), 440 (92); IR (KBr): νmax/cm−1, 1010m
(P)-O-C, 815s P-O-(C), 664s (P=S) or (P-S)asym, 563m (P-
S) or (P-S)sym, 425m (Co-S); 1H-NMR (CDCl3, δ ppm);
7.20–7.45 (m, 30H, Ph); 31P-NMR (CDCl3, δ ppm): 83.32 (s).
Mass spectra fragment m/z (%) [Co{S2P(OC6H5)2}3]+ 902.8
(100), [Co{S2P(OC6H5)2}2]+, 589 (75.2), [CoS2P(OC6H5)2]+,
340 (40.3), [CoS2PO2]+, 186 (11.9), [CoS2PO]+, 170 (8.3),
[CoS2P]+, 154 (14.2), [CoS2]+, 123 (9.2), [C6H5]+, 91 (18.9)
[PO2]+, 62.9 (12.3).
Tris(O,Oꢁ-(ditolyl-m)dithiophosphato)cobalt(III) Complex (2)
Same as for 1, purple solid; yield: 0.735 g, (88%); mol.
wt. found (calcd.), 985 (987.04); calc. for C42H42O6P3S6Co;
C, 51.11; H, 4.29; S, 19.49; Co, 5.97. Found: C, 51.06; H,
4.23; S, 19.43; Co, 5.91; UV-vis spectral data [λmax, nm(A); ε(L
mol−1cm−1)] in 0.004 M benzene solution, 724 (198), 545 (90),
422 (116); IR KBr νmax/cm−1, 1005m (P)-O-C, 852s P-O-(C),
642s (P=S) or (P-S)asym, 560m (P-S) or (P-S)sym, 410m (Co-
S); 1H-NMR (CDCl3, δ ppm); 2.41 (s, 18H, CH3; 7.20–7.34 (m,
24H, -C6H4); 31P-NMR (CDCl3, δ ppm): 81.52 (s).
RESULTS AND DISCUSSION
Tris(O,Oꢁ -ditolyl/dibenzyl/diphenyldithiophosphato)cobalt
(III) complexes (1-5) were synthesized by reaction of
CoCl2·6H2O and NH4S2P(OR)2 in aqueous medium by
refluxing the reaction mixture for 1 h and complexes were
extracted in benzene. Initially a green solution was obtained,
which turned to purple, indicating the formation of oxidized
cobalt(III) dithiophosphate complexes from cobalt(II) com-
plexes. Benzene was pumped off under vacuum, yielding a
purple solid. Attempts at recrystallization by mixture/dual
solvent system, layering, and freezing were unsuccessful.
Tris(O,Oꢁ-(ditolyl-p)dithiophosphato)cobalt(III) Complex (3)
Same as for 1, purple solid; yield: 1.11 g, (89%); mol. wt.
found (calcd.), 983 (987.04); calc. for C42H42O6P3S6Co; C,
51.11; H, 4.29; S, 19.49; Co, 5.97. Found: C, 51.04; H, 4.22;
S, 19.48; Co, 5.95; UV-vis spectral data [λmax, nm(A); ε(L
mol−1cm−1)] in 0.005 M benzene solution, 716 (305), 550 (130),
400 (146); IR KBr νmax/cm−1, 1015s (P)-O-C, 825s P-O-(C),
652s (P=S) or (P-S)asym, 550s (P-S) or (P-S)sym, 417m (Co-
CoCl2·6H2O + 3NH4S2P(OR)2 → Co{S2P(OR)2}2 + 2NH4Cl
Co{S2P(OR)2}2 → Co{S2P(OR)2}3
[R = o−C6H4Me (1), m − C6H4Me (2), p − C6H4Me (3),
−CH2Ph(4) and − Ph(5)]
The rapid oxidation was observed with tolyl dithiophosphate
S); 1H-NMR (CDCl3, δ ppm): 2.29 (s, 18H, CH3; 6.82–7.23 (m, rather than with benzyl and phenyl derivatives, probably due

748
S. C. BAJIA
to the electron-withdrawing effect of the tolyl moiety, which
makes the phosphorus have a lower electron density and in
turn withdraws electrons from the sulfur. The oxidation pro-
cess was monitored by color change (blue to purple), magnetic
susceptibility measurement, and UV-visible absorption spec-
tra. Cobalt(III) complexes (1-5) are soluble in common organic
solvents such as benzene and dichloromethane. The molecu-
lar weights are found near to those calculated, suggesting the
formation of tris cobalt(III) dithiophosphate complexes.
OR
OR
P
S
S
S
S
RO
RO
Co
P
S
S
P
OR
OR
Infrared Spectra
Infrared (IR) bands were assigned by comparison with salts
of O,O-di(o-, m-, or p-tolyl) dithiophosphates[14] and nickel(II)
dithiophosphate complexes.[15,16] The bands in the regions
1050–992 and 852–806 cm−1 were assigned for ν[(P)-O-C]
and ν[P-O-(C)] stretching vibrations, respectively. Bands in the
regions 664–642 and 563–550 cm−1 may be assigned for ν(P =
S) or ν(P-S)asym and ν(P-S) or ν(P-S)sym stretching vibration.
The stretching vibrations for ν(Co-S)17 were found in the region
FIG. 1. Proposed octahedral geometry for Co{S2P(OR)2}3 complexes [where
R = o-C6H4Me (1), m-C6H4Me (2), p-C6H4Me (3), -CH2Ph (4), and -Ph (5)].
region δ 122.68–124.71 ppm, while one of the ortho-carbons
was observed with an upfield shift at δ 115.22 ppm. The tolyl
carbon atom attached to methyl group was found at δ 118.23
ppm. This abnormal shift value may be due to intramolecular
hydrogen bonding between the protons attached to the carbon
atom and oxygen atom. Intramolecular hydrogen bonding is also
suggested by the shifting of the chemical shift of C–O at δ 153.45
ppm, compared to its normal values δ 150–152 ppm. In the 13C-
NMR spectrum of complex 3, chemical shifts for the methyl
carbon of the tolyl rings were found at δ 17.40 and δ 17.43
ppm. The ortho-, meta-, and para-carbons were found in the
regions δ 122.64–124.70, δ 124.24–126.0, and δ 126.15–131.2
ppm, respectively, while one of the ortho-carbons was found
with an upfield shift at δ 115.14 ppm, which was due to the
intramolecular hydrogen bonding. The tolyl carbon attached to
the methyl group was found at δ 117.98 ppm.
425–410 cm−1
.
Electronic Absorption Spectra
Electronic spectra for the cobalt(III) complexes (1-5) was
recorded in benzene at room temperature. The absorption in the
regions 752–704, 575–514, and 482–400 nm were assigned for
1
1
1
the transitions 1A1g → T1g (P), 1A1g → T2g, and 1A1g → T1g,
respectively.18 The electronic absorption pattern suggests the
octahedral coordination (1–5).
1H-NMR Spectra
1
The H-NMR spectra of cobalt(III) complexes (1-5) were
recorded in CDCl3 at room temperature. A slightly deshielding
effect was observed on the coordination. The methyl protons
show a singlet in the range 2.23–2.39 ppm. The phenyl pro-
tons appear in the range 6.85–7.45 ppm, undergoing a slight
downfield shift of ∼0.07–0.31 ppm in comparison with the free
ligand, presumably as a consequence of coordination.
1
31P{ H}-NMR Spectra
31P NMR spectra of 1-5 were recorded in CDCl3. A rela-
tively sharp singlet in the region δ 80.8–83.32 ppm indicates the
bidentate chelation of dithiophosphate moieties with octahedral
coordination. Occurrence of a singlet for all complexes indi-
cated the equivalent nature of phosphorus in the molecule. The
31P-NMR chemical shifts are 25–29 ppm upfield from those
of the corresponding ammonium salt dithiophosphoric acids,
suggesting the coordination of dithiophosphate moieties.
Elemental analysis and spectroscopic studies (IR, UV-
13C-NMR Spectra
The 13C-NMR spectra were recorded in CDCl3 solution
at room temperature. In the 13C-NMR spectrum for complex
1, chemical shifts for the methyl carbon of the tolyl rings
were found at δ 17.38–17.41 ppm. Chemical shifts for para-
and meta-carbon were found in δ 125.92–130.21 ppm and
δ 124.14–125.72 ppm, respectively. The ortho-carbon (with
methyl group) was found at δ 120.98 ppm. The ortho-carbon
atom (unsubstituted one) was found in its normal region δ
122.54–124.62 ppm, suggesting that none of the proton atoms
was involved in the hydrogen atom. Absence of the hydro-
gen bending is also suggested by no significant shift in the
chemical shift of the C–O (151.12–151.30 ppm). The 13C-
NMR spectra of complex 2 showed the chemical shifts for
vis, and H-, 13C-, and 31P-NMR) are consistent with pur-
1
posed octahedral geometry of cobalt(III) complexes (1-5)
shown Figure 1. Rapid oxidation occurred for bis(O,Oꢁ-
ditolyldithiophosphato)cobalt(II) complexes rather than benzyl
and phenyl derivatives, probably due to the electron withdraw-
ing of the tolyl moiety, which makes the phosphorus have a
lower electron density.
Mass Spectrometry
Mass spectra of representative complexes (3 and 5) show
ortho-, meta-, and para-carbons were found in the regions δ the molecular ion peak with 100% intensity at m/z 987 and
122.68–124.71, δ 124.54–126.04, and δ 126.12–131.20 ppm, 902, respectively, suggesting monomeric complex formation.
respectively. The three ortho-carbons were found in the normal Fragments along with their m/z (percent abundance) values are

BIDENTATE DITHIOPHOSPHATE COBALT COMPLEXES
749
conductance of 10−3 mol L−1 solution of these cobalt(III) dithio-
given in the experimental section. The molar conductance values
of 10−3 mol L−1 solution of these cobalt(III) dithiophosphate
complexes are in the range 3.8–6.8 ohm−1cm2mol−1, suggesting
their nonionic nature.[19]
phosphate complexes are in the range 3.8–6.8 ohm−1 cm2 mol−1
suggesting their nonionic nature.
,
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TGA
Thermogravimetric analysis is a useful technique for the
determination of thermal stability and structural elucida-
tion. The thermal behavior of representative tris(O,Oꢁ-(ditolyl-
p)dithiophosphato)cobalt(III) complex (3) has been followed
up to 1000◦C. In our study, the first thermolytic cleavage (en-
dothermic) starts from 143 to 470◦C with 80.73% loss of weight,
corresponding to dithiophosphate moiety (found 80.70%). The
second stage ranges between 470 and 650◦C, corresponding to
the formation of intermediate Co(S2P)2, which decomposes at
higher temperatures to give CoS at 860◦C, after which a straight
line is observed, indicating no change above this temperature
range. The experimental mass losses of the compounds are in
very good agreement with the calculated values. The final de-
composition product CoS was identified by IR spectroscopy.
The DSC profile exhibits enthalpic changes from endother-
mal and exothermal bands and peaks. In the present case, the
DSC peaks correlate well with the TGA data. A broad exother-
mic peak is obtained between 270 and 450◦C due to the py-
rolysis of the whole dithiophosphate organic moiety. However,
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12. Drake, J.E.; Gurnani, C.; Hursthouse, M.B.; Light, M.E.; Nirman, M.;
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CONCLUSION
We have synthesized and characterized cobalt(III) dithio-
phosphate. The elemental analyses and spectroscopic studies
(IR, UV-visible, and H-, 13C-, and 31P NMR) data of these
1
complexes are consistent with proposed distorted octahedral
geometry. The molecular weight determinations and mass spec-
tra also suggested the distorted octahedral geometry. The molar