Synthesis, characterization, X-ray structure and spectroscopic study of platinum(II) complexes with tridentate diazene ligands having O,N,S donor set

Article abstract of DOI:10.1016/j.ica.2012.09.041

At room temperature, 2-hydroxy-1-(2′-alkylthiophenylazo)naphthalenes and 1-hydroxy-2-(2′-alkylthiophenylazo)napthalenes (HL) slowly react with di-μ-chloro-bis(η³-2-methylallyl)platinum(II) in chloroform and afford complexes of the type [Pt

Full text of DOI:10.1016/j.ica.2012.09.041

Inorganica Chimica Acta 394 (2013) 757–764
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Synthesis, characterization, X-ray structure and spectroscopic study
of platinum(II) complexes with tridentate diazene ligands having O,N,S donor set
Suvra Acharya a, Ambica Kejriwal a, Achintesh Narayan Biswas b, Purak Das a, Debatra Narayan Neogi a,
Pinaki Bandyopadhyay a,
⇑
a Department of Chemistry, University of North Bengal, Raja Rammohunpur, Siliguri 734013, India
b Department of Chemistry, Siliguri College, Siliguri 734001, India
a r t i c l e i n f o
a b s t r a c t
At room temperature, 2-hydroxy-1-(20-alkylthiophenylazo)naphthalenes and 1-hydroxy-2-(20-alkylthi-
Article history:
ophenylazo)napthalenes (HL) slowly react with di-l-chloro-bis(g
3-2-methylallyl)platinum(II) in chloro-
Received 25 May 2012
Received in revised form 28 September
2012
Accepted 28 September 2012
Available online 9 October 2012
form and afford complexes of the type [PtII(L)Cl]. Potassium tetrachloroplatinate also reacts with the HL
group of ligands in acetonitrile medium under reflux condition and produces complexes of the type [PtII
(L)Cl]. All the platinum complexes [PtII(L)Cl] have been successfully isolated in pure form and character-
ized by spectroscopic techniques. The solid state structures of [PtII(L3)Cl] (3) and [PtII(L9)Cl] (9) have been
determined by single crystal X-ray diffraction. The crystal structures have revealed that diazene ligands
bind to the metal ion as monoanionic terdentate O,N,S donors and the fourth coordination position is
occupied by a halide ion. All the platinum(II) complexes absorb strongly in the ultraviolet and visible
region. The TD-DFT (time-dependent density functional theory) calculation has been carried out for bet-
ter understanding of the electronic structure of platinum(II) complexes and the nature of spectral tran-
sitions. The low energy absorptions are attributed to intraligand charge transfer transitions having
admixtures of metal-to-ligand charge-transfer transitions whereas the high energy absorptions are due
to ILCT and LLCT transitions. The reactivity of [PtII(L)Cl] with iodine and methyl iodide has been studied.
Ó 2012 Elsevier B.V. All rights reserved.
Keywords:
Platinum
Diazene
O,N,S donors
TD-DFT
1. Introduction
On the other hand, the reactivity of platinum(II) with aryldiaz-
enes [21–25] added a new dimension to metal mediated intramo-
The serendipitous discovery of the antiproliferative and cyto-
toxic activities of cisplatin [1–3] has generated tremendous
amount of interest on the coordination chemistry of platinum(II)
[4–11]. However, due to the toxic side effects of cisplatin [12], ef-
forts have been devoted to the development of alternative antican-
cer agents based on platinum(II) [13–17]. An improved strategy
developed in this regard relies on the design of complexes contain-
ing a Pt(II)–S bond [13]. This strategy is initiated primarily because
of the detoxicant properties of sulfur containing ligands and the
lability of Pt–S bond in presence of other nucleophiles [18]. A num-
ber of platinum(II) complexes with bidentate N,S ligands have been
shown to be potential anticancer drugs [19]. However, the use of
tridentate ligands in generation of antiproliferative metal com-
plexes is relatively sparse. A new Au(III) complex derived from tri-
dentate 2-(phenylazo)pyridine in 2007, has been tested in vitro in
a number of tumor cell lines and showed promising cytotoxic
activity [20].
lecular C(aryl)–H bond activation [26]. Since then, platinum
complexes with diazene ligands having N,S [27], N,N [23,24,28],
C,N,O [25] and C,N,S [21,22] coordination spheres have been re-
ported in the literature.
Here, we have examined the reactivity of platinum(II) towards
tridentate ligands (HL1–HL10
)
with O(naphtholato),N(dia-
zene),S(thioether) donor set. The isolation and structural charac-
terization of the resulting platinum(II) complexes have been
described. The reactivity of platinum(II) complexes with iodine
and methyl iodide has been studied. The isolation and character-
ization of the products have been done.
2. Experimental
2.1. Materials
Commercial potassium tetrachloroplatinate K2[PtCl4] was pur-
chased from Arora Matthey Ltd., Kolkata, India. 1-Chloro-2-methyl
prop-2-ene (Merck, Germany), 2-aminothiophenol (Merck,
Germany), 1-naphthol, 2-naphthol (R. Merck, India), sodium acetate,
silica gel, methyl iodide, ethyl bromide, n-propyl bromide, butyl
⇑
Corresponding author. Tel.: +91 353 2776381; fax: +91 353 2699001.
E-mail address: pbchem@rediffmail.com (P. Bandyopadhyay).
0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2012.09.041

758
S. Acharya et al. / Inorganica Chimica Acta 394 (2013) 757–764
bromide and benzyl chloride (SD Fine Chemicals, India) were used
without further purification. All solvents were purified according
to standard procedures. Solid iodine (SM, India) was purified
7.39–7.49 (m, 5H), 7.69–7.80 (m, 2H), 8.07 (d, 1H, J = 9.6 Hz), 8.63
(d, 1H, J = 7.6 Hz). MS: m/z 551 [M]+.
by sublimation. Complex di-
l
-chloro-bis(
g
3-2-methylallyl)plati-
2.3.4. Isolation of [Pt(L4)Cl] (4)
num(II), [Pt(allyl)Cl]2, was synthesized following reported method
[29].
[Pt(L4)Cl] (4) was made following the same procedure of com-
plex 1. The following yield is based on HL4 (0.024 g, 0.07 mmol)
and [Pt(allyl)Cl]2 complex (0.02 g, 0.035 mmol) (Yield: 0.031 g,
0.054 mmol, 77%). Anal. Calc. for C20H19N2OSClPt: C, 42.4; H, 3.4;
2.2. Synthesis of the ligands
N, 5. Found: C, 41.9; H, 3.0; N, 4.7%. IR (KBr;
(–N@N–). UV–Vis (CH2Cl2), k/nm (
m
/cmꢀ1): 1437
e
/dm3 molꢀ1 cmꢀ1): 305 (4600),
2-Hydroxy-1-(20-alkylthiophenylazo)naphthalenes (HL1–HL5)
and 1-hydroxy-2-(20-alkylthiophenylazo)naphthalenes (HL6–HL10
)
401 (6700), 523 (6800), 554 (9600). 1H NMR in CDCl3 (ppm): 3.50
(m, 2H, –SCH2), 1.63 (m, 2H, –CH2), 1.24 (m, 2H, –CH2), 0.88 (m,
3H, –CH3), 7.18 (br, 1H), 7.32–7.49 (m, 3H), 7.57–7.61 (m, 2H),
7.68–7.75 (m, 2H), 8.06 (d, 1H, J = 9.2 Hz), 8.60 (d, 1H, J = 8.8 Hz).
MS: m/z 565 [M]+.
were prepared following reported procedure using 2-naphthol
and 1-naphthol, respectively [30].
2.3. Synthesis of platinum(II) complexes
2.3.1. Isolation of [Pt(L1)Cl] (1)
2.3.5. Isolation of [Pt(L5)Cl] (5)
2.3.1.1. Procedure (1). HL1 (0.02 g, 0.07 mmol) was dissolved in
chloroform (10 mL). Then the orange yellow ligand solution was
added dropwise to a solution of [Pt(allyl)Cl]2 complex (0.02 g,
0.035 mmol) in chloroform (10 mL) and stirred at room tempera-
ture. The yellow color of mixture turned into pink very slowly
and the stirring of the mixture was continued for 24 h at room
temperature. The solvent was then evaporated to give a solid mass.
The solid mass was dissolved in dichloromethane and subjected to
purification by thin layer chromatography using ethyl acetate as
eluant. A pink band was separated and extracted with methanol
(yield: 0.026 g, 0.05 mmol, 74%).
[Pt(L5)Cl] (5) was made following the same procedure of com-
plex 1. The following yield is based on HL5 (0.026 g, 0.07 mmol)
and [Pt(allyl)Cl]2 complex (0.02 g, 0.035 mmol) (Yield: 0.03 g,
0.05 mmol, 70%). Anal. Calc. for C23H17N2OSClPt: C, 46; H, 2.8; N,
4.7. Found: C, 45.8; H, 2.71; N, 4.2%. IR (KBr;
(–N@N–). UV–Vis (CH2Cl2), k/nm
m
/cmꢀ1): 1436
e
/dm3 molꢀ1 cmꢀ1): 310
(
(5600), 402 (7400), 523(7500), 555 (10400). 1H NMR in CDCl3
(ppm): 3.48 (m, 2H, –SCH2), 7.18–7.34 (m, 6H), 7.39–7.46
(m, 4H), 7.73–7.75 (br, 2H), 8.06 (d, 1H, 9.2 Hz), 8.57 (d, 1H,
8.4 Hz). MS: m/z 599 [M]+, 564 [MꢀCl]+.
2.3.6. Isolation of [Pt(L6)Cl] (6)
2.3.1.2. Procedure (2). The ligand HL1 (0.07 g, 0.24 mmol) was dis-
solved in 100 mL acetonitrile. To this was added an aqueous solu-
tion of K2[PtCl4] (0.1 g, 0.24 mmol) and the mixture was refluxed
on a steam bath for 3 h. During the period the orange color of
the mixture slowly became reddish-orange. The reaction mixture
was then cooled and filtered. It was left undisturbed for slow evap-
oration. After three days dark crystalline products, deposited in the
reaction vessel, were collected by filtration and washed thoroughly
with diethyl ether and finally air-dried in a vaccum dessicator
(Yield: 85%). Anal. Calc. for C17H13N2OSClPt: C, 39; H, 2.5; N, 5.3.
A pink colored solution of HL6 (0.009 g, 0.03 mmol) in chloro-
form (10 mL) was slowly added dropwise to
a solution of
[Pt(allyl)Cl]2 (0.009 g, 0.015 mmol) in chloroform (10 mL) and stir-
red at room temperature. The pink color of the reaction mixture
immediately turned into violet and stirring of the mixture was con-
tinued for 3 h. The solvent was then evaporated to give a solid
mass. The solid mass was then dissolved in dichloromethane and
subjected to purification by TLC, using ethyl acetate as eluant. A
violet band separated, which was extracted with methanol (Yield:
0.013 g, 0.024 mmol, 80%).
Found: C, 38.3; H, 2.0; N, 4.9%. IR (KBr;
m
/cmꢀ1): 1437 (–N@N–).
/dm3 molꢀ1 cmꢀ1): 401 (4900), 522
UV–Vis (CH2Cl2), k/nm
(e
2.3.6.1. Procedure (2). The ligand HL6 (0.071 g, 0.24 mmol) was re-
acted with the salt K2[PtCl4] (0.1 g, 0.24 mmol) in boiling aqueous
acetonitrile (CH3CN: H2O, 9: 1) to produce Complex [PdL6Cl] in
excellent yields (89%). Procedure was same as described earlier.
Anal. Calc. for C17H13N2OSClPt: C, 39; H, 2.5; N, 5.3. Found: C,
(5000), 553 (7000). 1H NMR in CDCl3 (ppm): 3.01 (s, 3H, –SCH3),
7.21–7.84 (8H), 8.48 (d, 1H, J = 8.4 Hz), 8.86 (d, 1H, J = 8.2 Hz).
MS: m/z 523 [M]+.
2.3.2. Isolation of [Pt(L2)Cl] (2)
38.6; H, 2.2; N, 5.0%. IR (KBr;
Cl2), k/nm (e
m
/cmꢀ1): 1438 (–N@N–). UV–Vis (CH2-
[Pt(L2)Cl] was made following the same procedure of complex 1.
The following yield is based on HL2 (0.025 g, 0.07 mmol) and
[Pt(allyl)Cl]2 (0.02 g, 0.035 mmol) (Yield: 0.029 g, 0.054 mmol,
77%). Anal. Calc. for C18H15N2OSClPt: C, 40.0; H, 2.8; N, 5.2. Found:
/dm3 molꢀ1 cmꢀ1): 306 (7700), 376 (4100), 528 (4000),
566 (5300). 1H NMR in CDCl3 (ppm): 3.02 (s, 3H, –SCH3), 7.26 (m,
2H), 7.47–7.49 (m, 4H), 7.71–7.74 (m, 2H), 8.46 (d, 1H, J = 8.2 Hz),
8.82 (d, 1H, J = 8.4 Hz). MS: m/z 523 [M]+.
C, 39.4; H, 2.71; N, 4.9%. IR (KBr;
(CH2Cl2), k/nm (
m
/cmꢀ1): 1436 (–N@N–). UV–Vis
/dm3 molꢀ1 cmꢀ1): 401 (5900), 522 (5400), 554
e
2.3.7. Isolation of [Pt(L7)Cl] (7)
(7300). 1H NMR in CDCl3 (ppm): 3.51 (m, 2H, –SCH2), 1.24 (t, 3H,
–CH3), 7.18 (d, 1H, J = 9.2 Hz), 7.42–7.55 (m, 3H), 7.61 (d, 1H,
J = 8.0 Hz), 7.68–7.77 (m, 3H), 8.50 (d, 1H, J = 8.4 Hz), 8.86 (d, 1H,
J = 8.0 Hz). MS: m/z 537 [M]+.
[Pt(L7)Cl] (7) was made following the same procedure of com-
plex 6. The following yield is based on HL7 (0.009 g, 0.03 mmol)
and [Pt(allyl)Cl]2 (0.009 g, 0.015 mmol) (Yield: 0.013 g,
0.024 mmol, 79%). Anal. Calc. for C18H15N2OSClPt: C, 40; H, 2.8;
N, 5.2. Found: C, 38.6; H, 2.6; N, 4.8%. IR (KBr;
m
/cmꢀ1): 1436 (–
N@N–). UV–Vis (CH2Cl2), k/nm (e
/dm3 molꢀ1 cmꢀ1): 307 (8300),
2.3.3. Isolation of [Pt(L3)Cl] (3)
[Pt(L3)Cl] (3) was made following the same procedure of com-
plex 1. The amount of HL3 and [Pt(allyl)Cl]2 used were (0.023 g,
0.07 mmol) and (0.020 g, 0.035 mmol), respectively (Yield:
0.018 g, 0.055 mmol, 79%). Anal. Calc. for C19H17N2OSClPt: C,
374 (4500), 528 (4300), 564 (5500). 1H NMR in CDCl3 (ppm):
3.47 (m, 2H, –SCH2), 1.21 (t, 3H, –CH3), 7.18–7.78 (m, 8H, complex
pattern), 8.56 (d, 1H), 8.78 (d, 1H). MS: m/z 537 [M]+.
41.3; H, 3.1; N, 5.1. Found: C, 40.9; H, 2.71; N, 4.9%. IR (KBr;
m/
2.3.8. Isolation of [Pt(L8)Cl] (8)
cmꢀ1): 1438 (–N@N–). UV–Vis (CH2Cl2), k/nm (
e
/dm3 molꢀ1 cmꢀ1):
[Pt(L8)Cl] (8) was made following the same procedure of com-
plex 6. The amount of HL8 and [Pt(allyl)Cl]2 complex used were
(0.01 g, 0.03 mmol) and (0.01 g, 0.015 mmol) respectively.
400 (6300), 522 (6500), 554 (9200). 1H NMR in CDCl3 (ppm): 3.49
(m, 2H, –SCH2), 1.26 (m, 2H, –CH2), 1.08 (t, 3H, –CH3), 7.16 (m, 1H),

S. Acharya et al. / Inorganica Chimica Acta 394 (2013) 757–764
759
(Yield: 0.012 g, 0.023 mmol, 75%). Anal. Calc. for C19H17N2-
2.4.4. Isolation of [Pt(L4)I] (14)
OSClPt: C, 41.3; H, 3.1; N, 5.1. Found: C, 40.8; H, 2.8; N, 4.8%. IR
This compound was sysnthesized following method described
above. The following yield is based on [Pt(L4)Cl] (0.023 g,
0.04 mmol). (Yield: 78%). Anal. Calc. for C20H19N2OSIPt: C, 36.5;
(KBr;
m e
/cmꢀ1): 1439 (–N@N–). UV–Vis (CH2Cl2), k/nm ( /dm3 -
molꢀ1 cmꢀ1): 301 (9700)(9(9700),700), 369 (5300), 531 (4400),
564 (5600). 1H NMR in CDCl3 (ppm): 3.46 (m, 2H, –SCH2), 1.24
(m, 2H, –CH2), 1.04 (t, 3H, –CH3), 7.18 (t, 1H), 7.40–7.53 (m, 5H),
7.75–7.85 (m, 2H), 8.11 (d, 1H, J = 8.2 Hz), 8.78 (d, 1H, J = 8.4 Hz).
MS: m/z 551 [M]+.
H, 2.9; N, 4.3%. Found: C, 36.2; H, 2.5; N, 4.1%. IR (KBr;
m
/cmꢀ1):
e
/dm3 molꢀ1 cmꢀ1): 310
1436 (–N@N–). UV–Vis (CH2Cl2), k/nm (
(8000), 410 (10300), 527 (7100), 564 (10300). 1H NMR in CDCl3
(ppm): 3.48 (m, 2H, –SCH2), 1.59 (m, 2H, –CH2), 1.21 (m, 2H, –
CH2), 0.90 (m, 3H, –CH3), 7.37–7.45 (m, 5H), 7.58 (br, 2H), 7.71
(br, 2H), 8.64 (m, 1H). MS: m/z 657 [M]+.
2.3.9. Isolation of [Pt(L9)Cl] (9)
[Pt(L9)Cl] (9) was made following the same procedure of com-
plex 6. The amount of HL9 and [Pt(allyl)Cl]2 used were (0.01 g,
0.03 mmol) and (0.009 g, 0.015 mmol) respectively. (Yield:
0.014 g, 0.024 mmol, 80%). Anal. Calc. for C20H19N2OSClPt: C,
2.4.5. Isolation of [Pt(L5)I] (15)
The preparation of [Pt(L5)I] (15) was made following the above
procedure. Amount of [PtL5Cl] used was (0.023 g, 0.038 mmol).
(Yield: 79%). Anal. Calc. for C23H17N2OSIPt: C, 40; H, 2.5; N, 4.1.
42.4; H, 3.4; N, 5. Found: C, 41.9; H, 3.0; N, 4.7%. IR (KBr;
m/
cmꢀ1): 1437 (–N@N–). UV–Vis (CH2Cl2), k/nm (
e
/dm3 molꢀ1 cmꢀ1):
Found: C, 39.8; H, 2.1; N, 3.8%. IR (KBr;
UV–Vis (CH2Cl2), k/nm
m
/cmꢀ1): 1438 (–N@N–).
(e
/dm3 molꢀ1 cmꢀ1): 310 (9100), 410
307 (9000), 374 (5000), 528 (4500), 565 (5800); 1H NMR in CDCl3
(ppm): 3.47 (m, 2H, –SCH2), 1.61 (m, 2H, –CH2), 1.21 (m, 2H, –CH2),
0.86 (m, 3H, –CH3), 7.15–7.80 (m, 8H, complex pattern), 8.56 (d,
1H), 8.86 (d, 1H). MS: m/z 565 [M]+.
(11000), 527 (7400), 562 (10800). 1H NMR in CDCl3 (ppm): 3.45
(m, 2H, –SCH2), 7.14–7.26 (m, 6H), 7.29–7.54 (m, 4H), 7.70 (m,
1H), 8.02 (d, 1H, J = 9.3 Hz), 8.49 (d, 1H, J = 8.4 Hz), 8.60 (d, 1H,
8.4 Hz). MS: m/z 691 [M]+.
2.3.10. Isolation of [Pt(L10)Cl] (10)
The preparation of [Pt(L10)Cl] (10) was made following the above
procedure. The following yield is based on HL10 (0.011 g, 0.03 mmol)
and [Pt(allyl)Cl]2 (0.009 g, 0.015 mmol). (Yield: 0.012 g, 0.02 mmol,
65%). Anal. Calc. for C23H17N2OSClPt: C, 46; H, 2.8; N, 4.7. Found: C,
2.4.6. Isolation of [PtL6I] (16)
A dichloromethane solution containing iodine (1%) was added
dropwise to
a
violet colored solution (10 mL) of [Pt(L6)Cl]
(0.008 g, 0.015 mmol) in CH2Cl2 with stirring. Stirring was contin-
ued for 2 h till the violet color of the reaction mixture changed to
deep violet. The solvent was then evaporated to give a solid mass,
which was then chromatographed by TLC using ethyl acetate as
eluant. A deep violet band separated, which was then extracted
with methanol. (Yield: 82%). Anal. Calc. for C17H13N2OSIPt: C,
45.6; H, 2.68; N, 4.1%. IR (KBr;
m
/cmꢀ1): 1436 (N@N). UV–Vis (CH2-
307(10200), 375(6400),
Cl2), k/nm
(e
/dm3 molꢀ1 cmꢀ1):
533(5300), 565(6500); 1H NMR in CDCl3 (ppm): 3.48 (m, 2H, –
SCH2), 6.82 (d, 1H, J = 8.2 Hz), 7.12–7.56 (m, 6H), 7.41–7.59 (m,
4H), 8.20 (br, 2H), 8.87 (d, 1H, J = 7.8 Hz). MS: m/z 599 [M]+.
33.2; H, 2.1; N, 4.6. Found: C, 33.1; H, 1.9; N, 4.2%. IR (KBr; m/
2.4. Preparation of the iodo-compounds
cmꢀ1): 1436 (–N@N–). UV–Vis (CH2Cl2), k/nm ( /dm3 molꢀ1 cmꢀ1):
e
314 (12600), 390 (6500), 538 (4600), 576 (5800). 1H NMR in CDCl3
(ppm): 3.01 (s, 3H, –SCH3), 7.19–7.77 (8H), 8.53 (d, 1H, J = 8.1 Hz),
8.81 (d, 1H, J = 8.4 Hz). MS: m/z 615 [M]+.
2.4.1. Isolation of [Pt(L1)I] (11)
A dichloromethane solution containing iodine (1%) was added
drop wise to a pink colored dichloromethane solution (10 mL) of
[Pt(L1)Cl] (1) (0.018 g, 0.035 mmol) with stirring till the pink color
of the reaction mixture changed to pinkish violet. The mixture was
chromatographed on TLC and a violet band containing [Pt(L1)I] was
eluted by benzene. Shining crystals of (11) were collected by evap-
oration of the solvent. (Yield: 80%). Anal. Calc. for C17H13N2OSIPt: C,
2.4.7. Isolation of [Pt(L7)I] (17)
This compound was synthesized following method described
above. The following yield is based on [Pt(L7)Cl] (0.008 g,
0.015 mmol).
(Yield: 80%). Anal. Calc. for C18H15N2OSIPt: C, 34.3; H, 2.4; N, 4.5.
33.2; H, 2.1; N, 4.6. Found: C, 33; H, 1.8; N, 4.1%. IR (KBr;
m
/cmꢀ1):
/dm3 molꢀ1 cmꢀ1): 308
Found: C, 34.1; H, 2; N, 4.1%. IR (KBr;
m
/cmꢀ1): 1437 (–N@N–). UV–
1436 (–N@N–). UV–Vis (CH2Cl2), k/nm (
e
Vis (CH2Cl2), k/nm (e
/dm3 molꢀ1 cmꢀ1): 312 (10400), 390 (5800),
(6000), 408 (7200), 526 (5400), 560 (7500). 1H NMR in CDCl3
(ppm): 3.0 (s, 3H, –SCH3), 7.35–7.46 (m, 4H), 7.56 (br, 2H), 7.72
(m, 2H), 8.62-8.67 (m, 2H). MS: m/z 615 [M]+.
538 (4800), 574 (6200). 1H NMR in CDCl3 (ppm): 3.46 (m, 2H, –
SCH2), 1.19 (t, 3H, –CH3), 7.19–8.68 (aromatic protons). MS: m/z
629 [M]+.
2.4.2. Isolation of [Pt(L2)I] (12)
2.4.8. Isolation of [Pt(L8)I] (18)
This compound was synthesized following method described
above. Amount of [Pt(L2)Cl] used was (0.019 g, 0.035 mmol). (Yield:
76%). Anal. Calc. for C18H15N2OSIPt: C, 34.3; H, 2.4; N, 4.5. Found: C,
The preparation of [Pt(L8)I] (18) was made following the above
procedure. The amount of [Pt(L8)Cl] (8) used was (0.008 g,
0.015 mmol). (Yield: 84%). Anal. Calc. for C19H17N2OSIPt: C, 35.5;
34; H, 2.1; N, 4.2%. IR (KBr;
m
/cmꢀ1): 1438 (–N@N–). UV–Vis (CH2-
H, 2.6; N, 4.4. Found: C, 35.2; H, 2.2; N, 4%. IR (KBr;
m
/cmꢀ1):
1438 (–N@N–). UV–Vis (CH2Cl2), k/nm (e
/dm3 molꢀ1 cmꢀ1): 312
Cl2), k/nm
(e
/dm3 molꢀ1 cmꢀ1): 309 (7400), 409 (7900), 527
(5700), 562 (7900). 1H NMR in CDCl3 (ppm): 3.48 (m, 2H, –SCH2),
(11200), 369 (5700), 538 (5100), 575 (6700). 1H NMR in CDCl3
(ppm): 3.46 (m, 2H, –SCH2), 1.21 (m, 2H, –CH2), 1.0 (t, 3H, –CH3),
7.18–7.80 (8H), 8.51 (d, 1H, J = 8.2 Hz), 8.84 (d, 1H, J = 8.2 Hz).
MS: m/z 643 [M]+.
1.21 (t, 3H, –CH3), 7.36–8.66 (aromatic protons). MS: m/z 629 [M]+.
2.4.3. Isolation of [Pt(L3)I] (13)
This complex was prepared in the same process as mentioned
above. The following yield is based on [Pt(L3)Cl] (0.011 g,
0.02 mmol). (Yield: 76%). Anal. Calc. for C19H17N2OSIPt: C, 35.5;
2.4.9. Isolation of [Pt(L9)I] (19)
The preparation of [Pt(L9)I] (19) was made following the above
procedure. The amount of [Pt(L9)Cl] (9) used was (0.009 g,
0.015 mmol). (Yield: 80%). Anal. Calc. for C20H19N2OSIPt: C, 36.5;
H, 2.6; N, 4.4. Found: C, 35.1; H, 2.2; N, 4.1%. IR (KBr;
m
/cmꢀ1):
e
/dm3 molꢀ1 cmꢀ1): 310
1437 (–N@N–). UV–Vis (CH2Cl2), k/nm (
(7400), 410 (9800), 528 (6900), 564 (10000). 1H NMR in CDCl3
(ppm): 3.47 (m, 2H, –SCH2), 1.24 (m, 2H, –CH2), 1.01 (t, 3H,
–CH3), 7.30-8.90 (aromatic protons). MS: m/z 643 [M]+.
H, 2.9; N, 4.3. Found: C, 36.1; H, 2.6; N, 4%. IR (KBr;
1436 (–N@N–). UV–Vis (CH2Cl2), k/nm (
/dm3 molꢀ1 cmꢀ1): 312
(12300), 368 (6400), 538 (5500), 575 (7000). 1H NMR in CDCl3
m
/cmꢀ1):
e

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S. Acharya et al. / Inorganica Chimica Acta 394 (2013) 757–764
(ppm): 3.45 (m, 2H,–SCH2), 1.51 (m, 2H,–CH2), 1.18 (m, 2H,–CH2),
0.90 (m, 3H, –CH3), 7.19–7.70 (8H), 8.54 (m, 1H), 8.81 (d, 1H,
J = 8.4 Hz). MS: m/z 657 [M]+.
microscope and glued to a thin glass fiber with cynaoacrylate
adhesive. Selected crystal data and data collection parameters are
given in Table 1. Crystallographic data collections were performed
on a Bruker SMART 1000 CCD area-detector diffractometer using
2.4.10. Isolation of [Pt(L10) I] (20)
graphite monochromated Mo K
a (k = 0.71073 Å) radiation by x
The compound [Pt(L10)I] (20) was synthesized following the de-
scribed method. The following yield is based on [Pt(L10)Cl] (10)
(0.009 g, 0.015 mmol). (Yield: 85%). Anal. Calc. for C23H17N2OSIPt:
scan. The structure was solved by direct methods using SHELXS-97
[31] and difference Fourier syntheses and refined with SHELXL97
package incorporated in WINGX 1.64 crystallographic collective
package [32]. All the hydrogen positions for the compound were
initially located in the difference Fourier map, and for the final
refinement, the hydrogen atoms were placed geometrically and
held in the riding mode. The last cycles of refinement included
atomic positions for all the atoms, anisotropic thermal parameters
for all non-hydrogen atoms and isotropic thermal parameters for
all the hydrogen atoms. Full-matrix-least-squares structure refine-
ment against |F2|. Molecular geometry calculations were per-
formed with PLATON [33], and molecular graphics were prepared
using ORTEP-3 [34].
C, 40; H, 2.5; N, 4.1. Found: C, 39.8; H, 2.2; N, 3.9%. IR (KBr; m/
cmꢀ1): 1438 (–N@N–). UV–Vis (CH2Cl2), k/nm ( /dm3 molꢀ1 cmꢀ1):
e
312 (14500), 369 (7100), 538 (6200), 575 (8100). 1H NMR in CDCl3
(ppm): 3.41 (m, 2H, –SCH2), 7.18–7.77 (8H), 8.51 (d, 1H, J = 8.0 Hz),
8.82 (d, 1H, J = 8.3 Hz). MS: m/z 691 [M]+.
2.5. Physical measurements
C, H and N elemental analyses were done by either Perkin-El-
mer (Model 240C) or Heraeus Carlo Ebra 1108 elemental analyzer.
The IR spectra were obtained on Jasco 5300 FT-IR. Visible and ultra-
violet spectra were recorded on a Jasco V-530 spectrophotometer.
1H NMR spectra were measured in CDCl3 with a Bruker Avance
DPX 300 spectrophotometer with SiMe4 as an internal standard.
The FAB mass spectra were recorded on a JEOL SX 102/DA-6000
Mass Spectrometer/Data System using Argon/Xenon (6 jV,
10 mA) as the FAB gas. ESI mass spectra were recorded on a Micro-
mass Quattro II triple quadrupole mass spectrometer.
2.7. Method and computational details
The calculations have been performed within the TD-DFT for-
malism as implemented in ADF2007 [35]. Two approximations
are generally made: one for the XC potential, and one for the XC
kernel, which is the functional derivative of the time-dependent
XC potential with respect to density. We used LDA (local density
approximation) including the VWN parametrization [36] in the
SCF step and Becke [37] and Perdew–Wang [38] gradient correc-
tions to the exchange and correlation respectively and Adiabatic
local Density Approximation (ALDA) for the XC kernel, in the
post-SCF step. TD-DFT calculations have been performed with the
uncontracted triple-STO basis set with a polarization function for
2.6. Crystallography
Single crystals of (3), (9) and (13) were grown by slow diffusion
of n-hexane into the dichloromethane solution of the complexes. A
suitable single crystal was carefully selected under a polarizing
Table 1
Crystal data and structure refinement table for the platinum(II) complexes.
[Pt(L3)Cl] (3)
[Pt(L9)Cl] (9)
[Pd(L3)I] (13)
CCDC Deposition Number
Empirical formula
Formula weight
T (K)
869984
19H17ClN2OPtS
551.95
876267
C20H19ClN2OPtS
565.97
869985
C19H17IN2OPtS
643.40
C
293(2)
293(2)
293(2)
k (Å)
Crystal system
Space group
0.71073
monoclinic
P21/n
0.71073
monoclinic
P21/n
0.71073
monoclinic
P21/n
Unit cell dimensions
a (Å)
b (Å)
c (Å)
12.2720(4)
8.9594(3)
8.976(4)
11.478(4)
8.913(3)
18.736(6)
13.531(3)
9.007(18)
16.564(3)
a
(°)
90
90
90
b (°)
108.213(2)
90
1836.61(11)
4
1.996
7.908
100.916(4)
90
1836.61(11)
4
1.997
7.720
108.50(3)
90
1914.4(7)
4
2.232
9.060
1200
c
(°)
V (Å3)
Z
Dcalc (Mg/m3)
Absorption coefficient (mmꢀ1
F(000)
)
1056
1088
Crystal size (mm)
h Range for data collection
Limiting indices
0.35 ꢁ 0.17 ꢁ 0.13
1.79–25.00°
ꢀ13 6 h 6 14
ꢀ10 6 k 6 10
ꢀ20 6 l 6 19
22771
0.37 ꢁ 0.21 ꢁ 0.11
1.93–25.00°
ꢀ13 6 h 6 13
ꢀ10 6 k 6 10
ꢀ22 6 l 6 22
14037
0.28 ꢁ 0.19 ꢁ 0.09
3.18–24.99°
ꢀ7 6 h 6 16
ꢀ10 6 k 6 10
ꢀ19 6 l 6 11
4151
Reflections collected
Independent reflections
Data/restraints/parameters
Goodness-of-fit on F2
3224 [Rint = 0.0359]
3224/0/227
1.064
3319 [Rint = 0.0426]
3319/0/236
1.049
2918 [Rint = 0.0970]
2918/0/227
0.866
Final R indices [I > 2
R indices (all data)a,b
Largest difference in peak and hole (e Åꢀ3
r
(I)]
R1 = 0.0184, wR2 = 0.0472
R1 = 0.0222, wR2 = 0.0489
0.635 and ꢀ0.659
R1 = 0.0279, wR2 = 0.0668
R1 = 0.0341, wR2 = 0.0701
2.056 and ꢀ0.565
R1 = 0.0385, wR2 = 0.0713
R1 = 0.0541, wR2 = 0.0751
1.381 and ꢀ0.708
)
a
R =
Rw = [
R
||Fo| ꢀ |Fc||/
R|Fo|.
b
R
w(|Fo|2 ꢀ |Fc|2)/
R .
w(Fo2)2]1/2

S. Acharya et al. / Inorganica Chimica Acta 394 (2013) 757–764
761
Scheme 1. Reactions of [(g l
3-C4H7)Pt( -Cl)]2 with the azo-ligands (HL1–HL5).
all atoms. In the calculation of the optical spectra, 70 lowest spin-
allowed singlet–singlet transitions have been taken into account.
Transition energies and oscillator strengths have been interpolated
by a Gaussian convolution with a s of 0.2 eV. Solvent effects were
modelled by the ‘‘Conductor-like Screening Model’’ (COSMO) [39]
of solvation as implemented in ADF.
3. Results and discussion
2-Hydroxy-1-(20-alkylthiophenylazo)naphthalenes (HL1–HL5)
slowly react with [(g l-Cl)]2 in chloroform at room tem-
3-C4H7)Pt(
Fig. 1. ORTEP drawing of the compound (3). Thermal ellipsoids are drawn at 50%
perature (reaction time: 24 h) and the color of the reaction mixture
turns into pink (Scheme 1). Crystalline pink colored complexes
[PtIILCl] (1–5) were isolated using thin layer chromatography.
Higher yield of the complexes was achieved following an alter-
native route. Complexes (1–5) were obtained by refluxing K2[PtCl4]
with 2-hydroxy-1-(20-alkylthiophenylazo) naphthalenes (HL1–HL5)
in acetonitrile. The reaction time is 3 h and the yield is more than
85%. It is noteworthy that refluxing K2[PtCl4] with diazene based
ligands in acetonitrile often leads to the formation of platinum(IV)
complexes [40]. The formation of exclusive platinum(II) complexes
in the present case indicates the softness of the ligand frame.
The structure of complex (3) as a representative case has been
determined unambiguously by X-ray crystallography. The molecu-
lar structure is shown in Fig. 1. The crystal data for the complex 3
and its selected bond parameters are given in Tables 1 and 2,
respectively. The structure shows that the crystal lattice of this
complex contains discrete molecules. The structure shows that
the platinum(II) center is bonded to O1 of the naphtholato func-
tion, N2 of the diazene group and S1 at the 20 position of the phenyl
fragment and the fourth coordination position is occupied by a
chloride ion. Therefore, 2-hydroxy-1-(20-alkylthiophenylazo)naph-
thalene binds platinum(II) as a monoanionic tridentate O,N,S li-
gand forming a five membered chelate ring and a six-membered
chelate ring with bite angles 87.58(8)° (N2–Pt1–S1) and
92.99(10)° (N2–Pt1–O1), respectively. The tetra coordination
around platinum is essentially planner, but in a distorted square
planner geometry.
probability.
Table 2
Selected bond lengths (Å) and bond angles (°) for the complex (3).
Bond lengths (Å)
Bond angles (°)
Pt(1)–N(2)
Pt(1)–O(1)
Pt(1)–S(1)
Pt(1)–Cl(1)
N(1)–N(2)
N(1)–C(1)
N(2)–C(11)
1.954(3)
1.993(2)
2.2266(10)
2.3194(9)
1.293(4)
1.350(4)
1.441(4)
N(2)–Pt(1)–O(1)
N(2)–Pt(1)–S(1)
O(1)–Pt(1)–S(1)
N(2)–Pt(1)–Cl(1)
O(1)–Pt(1)–Cl(1)
S(1)–Pt(1)–Cl(1)
92.99(10)
87.58(8)
178.54(7)
177.95(8)
88.49(7)
90.98(4)
in refluxing acetonitrile medium affords platinum(II) complexes in
higher yield.
3.1. Reactivity of [PtLCl] complexes with halogens and alkyl halides
Platinum compounds [PtII(L)Cl] (1–10) readily undergo reaction
with iodine in dichloromethane medium at room temperature
(300 K) (Scheme 3). The product [PtII(L)I] was isolated by thin layer
chromatography on silica gel plate using 10% CH3COOEt in petro-
leum ether as eluant. The reaction of [PtII(L)Cl] with alkyl iodide
(RI) produces identical product.
X-ray crystallographic analysis of the representative complex
(13) has been done. The ORTEP diagram with the atom-numbering
scheme is shown in Fig. 3. The crystal data for the complex 13
and its selected bond parameters are given in Tables 1 and 4,
respectively. The Pt–N(diazene) distances in the square planar
complex (13) have been found to be slightly longer than that in
complex (3). The N–N distance in (13) (1.261 Å) is shorter than that
in complex (3) (1.293 Å). The Pt–I distance (2.6007 Å) is compara-
ble to the values reported in the literature [41].
The reactivity of another group of terdentate ligands (HL6–HL10
with O,N,S donor set with platinum(II) was examined. The di-
chloro-bis(
3-2-methylallyl)diplatinum(II) was found to react
)
l
-
g
with 1-hydroxy-2-(20-alkylthiophenylazo)naphthalenes in chloro-
form leading to the violet product [PtIILCl] (6–10) (Scheme 2).
The molecular structure of complex (9) has been determined by
X-ray crystallography. The molecular structure is shown in Fig. 2.
Thecrystal data for thecomplex (9) and its selected bond parameters
are given in Table 1 and 3, respectively. The structure shows that 1-
hydroxy-2-(20-alkylthiophenyl-azo)naphthalene binds platinum(II)
as a monoanionic tridentate (O,N,S) ligand and the fourth coordina-
tion position is occupied by a chloride ion. Here also, the reaction of
tridentate diazene ligands (HL6–HL10) with tetrachloroplatinate(II)
The reactivity pattern of [PtII(L)Cl] closely resembles the previ-
ously reported systems [41].
The following sequences seem reasonable: (a) initial formation of
an octahedral Pt (IV) intermediate with two iodine sitting trans to
each other, (b) conversion of the trans isomer to thermodynamically

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S. Acharya et al. / Inorganica Chimica Acta 394 (2013) 757–764
Scheme 3. Reactions of platinum(II) complexes (1–10) with iodine at room
temperature.
Scheme 2. Reactions of [(g l
3-C4H7)Pt( -Cl)]2 with the azo-ligands (HL6–HL10).
Fig. 3. ORTEP diagram of the platinum(II) compound (13). Thermal ellipsoids are
drawn at 50% probability.
Table 4
Selected bond lengths (Å) and bond angles (°) for the complex (13).
Bond lengths (Å)
Bond angles (°)
Fig. 2. ORTEP drawing of the compound (9). Thermal ellipsoids are drawn at 50%
probability.
Pt(1)–N(2)
Pt(1)–O(1)
Pt(1)–S(1)
Pt(1)–I(1)
N(1)–N(2)
N(1)–C(1)
N(2)–C(11)
1.980(6)
2.003(5)
2.222(2)
2.6007(8)
1.261(8)
1.369(9)
1.429(10)
N(2)–Pt(1)–O(1)
N(2)–Pt(1)–S(1)
O(1)–Pt(1)–S(1)
N(2)–Pt(1)–I(1)
O(1)–Pt(1)–I(1)
S(1)–Pt(1)–I(1)
92.4(2)
87.17(18)
177.76(16)
176.97(18)
89.03(15)
91.54(6)
Table 3
Selected bond lengths (Å) and bond angles (°) for the complex (9).
Bond lengths (Å)
Bond angles (°)
Pt(1)–N(2)
Pt(1)–O(1)
Pt(1)–S(1)
Pt(1)–Cl(1)
N(1)–N(2)
N(1)–C(2)
N(2)–C(11)
1.968(4)
2.003(3)
2.2241(13)
2.3200(15)
1.281(5)
1.355(6)
1.448(6)
N(2)–Pt(1)–O(1)
N(2)–Pt(1)–S(1)
O(1)–Pt(1)–S(1)
N(2)–Pt(1)–Cl(1)
O(1)–Pt(1)–Cl(1)
S(1)–Pt(1)–Cl(1)
92.94(15)
87.29(12)
176.50(10)
178.40(12)
88.55(10)
91.25(5)
more stable cis form, (c) dissociation of Clꢀ giving the five coordinate
intermediate and finally (d) reductive elimination of I–Cl leading to
the formation of [PtII(L)I].
3.2. UV–Vis spectra and excited singlet state calculations
All the platinum(II) complexes are soluble in common organic
solvents such as dichloromethane, acetonitrile, acetone, etc., pro-
ducing intense violet solutions. Spectral data are presented in the
Experimental Section. Electronic spectral patterns of the plati-
num(II) complexes have been shown in Fig. 4.
Fig. 4. Electronic spectra of (1) (pink), (3) (blue), (4) (red) and (5) (green). (For
interpretation of the references to color in this figure legend, the reader is referred
to the web version of this article.)

S. Acharya et al. / Inorganica Chimica Acta 394 (2013) 757–764
763
Fig. 5. Selected FMO’s of the complex (3).
TD-DFT calculation was carried out on the representative plati-
num(II) complexes (3, 9 and 13) to gain insight into the electronic
features of these complexes and also to understand the nature of
the low-lying excitation states.
features with a significant amount of metal to ligand charge trans-
fer and more or less
S4–S6).
p–
p⁄ intraligand density redistribution (Tables
All the platinum(II) complexes have been found to have similar
molecular orbitals. The relative contributions of each moiety to the
corresponding MOs are listed in the Supplementary information
(Table S1–S3). Selected FMOs for the complex 3 are shown in
Fig. 5. The calculations show that the HOMOs of all the three com-
plexes (3, 9 and 13) are mostly concentrated on the diazene ligand,
with very little contribution from the d(Pt) orbitals. For the com-
plex 3, HOMOꢀ1 and HOMOꢀ2 are also based primarily on the li-
gand framework. Whereas, in HOMOꢀ3 and HOMOꢀ4, substantial
amount of d(Pt) (22% and 44%, respectively) contribution has been
noted. Apart from LUMO+1, which has a contribution of 39% metal
character, all other unoccupied MOs are ligand based. On the other
hand, HOMOꢀ2, HOMOꢀ3 and HOMOꢀ4 contain sizeable contri-
bution from the d(Pt) orbitals (21%, 30% and 40% respectively).
For, the platinum(II) complex (13), in contrast the HOMO is largely
ligand based. However, HOMOꢀ1 is largely concentrated on the
terminal iodido ligand. Significant amount of contributions from
d(Pt) orbitals arise in HOMOꢀ4 and HOMOꢀ5 orbitals.
4. Conclusions
2-Hydroxy-1-(20-alkylthiophenylazo)naphthalenes (HL1–HL5)
and 1-hydroxy-2-(20-alkylthiopheny-lazo)naphthalenes (HL6–HL10
)
smoothly form planar platinum(II) complexes through O,N,S
donor set. Tetra coordination around platinum is essentially
planner, but in a distorted square planner geometry having
six-membered Pt(1)–O(1)–C(1)–C(2)–N(1)–N(2) chelate ring and
five-membered Pt(1)–N(2)–C(11)–C(12)–S(1) chelate rings. Com-
pounds [PtII(L)Cl] react with iodine and afford complexes [PtII(L)I].
The simulated electronic spectra of the platinum(II) complexes
using time-dependent density functional theory (TD-DFT) are in
close agreement with the experimental spectra. The low energy
absorptions are attributed to intraligand charge transfer transitions
having admixtures of metal-to-ligand charge-transfer transitions
whereas the high energy absorptions are due to ILCT and LLCT
transitions.
The excitation energies (eV), wavelengths (nm), oscillator
strengths (eV) and dominating contributing configurations ob-
tained at the TD-DFT/PW91/TZP level of theory for complexes (3,
9 and 13) are provided in Tables S4–S6. The calculations show that
electronic transition with dominant contributing configurations
involving the HOMO ? LUMO orbital pair occur at 551 nm (1st ex-
cited state for 3), 582 nm (1st excited state for 9) and 594 nm (1st
excited state for 13). The value obtained agrees well with the ob-
served bands, suggesting the suitability of the calculations for
these complexes. According to TD-DFT, these low-energy transi-
tions are indicative of intraligand charge transfer (ILCT) transition
having a small admixture of MLCT transitions. The other absorp-
tions in the visible region in have common density redistribution
Acknowledgments
The financial support from the SERB, Department of Science &
Technology (SR/S1/IC-53/2010) and CSIR (1/2498/11/EMR-II),
New Delhi are gratefully acknowledged. We also thank CSIR for
the award of fellowship to A.K.
Appendix A. Supplementary material
CCDC 869984, 869985 and 8762687 contains the supplemen-
tary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic Data

764
S. Acharya et al. / Inorganica Chimica Acta 394 (2013) 757–764
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