Palladium(II) complexes of terdentate azo ligands with an O,N,S donor set: Synthesis, spectroscopic characterization, X-ray structure and TD-DFT calculations

Article abstract of DOI:10.1016/j.poly.2012.02.021

The reaction of 2-hydroxy-1-(2′-alkylthiophenylazo)naphthalenes (HL¹-HL⁵) and 1-hydroxy-2-(2′-alkylthiophenylazo) naphthalenes (HL⁶-HL¹⁰) with sodium tetrachloropalladate in ethanol medium at room temperature leads to the formation of a new series of complexes of the type [Pd(L)Cl]. All the palladium compounds have been isolated in their pure form and characterized by spectral and elemental analysis data. The crystal structures of [PdL³Cl] (3) and [PdL⁶Cl] (6) have been determined by single crystal X-ray diffraction as representative cases. The crystal structures show that both complexes have distorted square-planar structures in which he palladium(II) centers are bonded to O1 of the naphtholato function, N2 of the diazene group and S1 at the 2′ position of the phenyl fragment. Therefore, the ligands bind palladium(II) in a tridentate monoanionic [O, N, S] fashion, which give rise to five- and six-membered chelate rings in each case. The fourth coordination site is occupied by a chloride ion. These complexes show intense absorption bands in the visible and UV region. The nature of the electronic transitions has been examined using (TD-DFT) formalism.

Full text of DOI:10.1016/j.poly.2012.02.021

Polyhedron 38 (2012) 50–57
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Palladium(II) complexes of terdentate azo ligands with an O,N,S donor set:
Synthesis, spectroscopic characterization, X-ray structure and TD-DFT calculations
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
The reaction of 2-hydroxy-1-(20-alkylthiophenylazo)naphthalenes (HL1–HL5) and 1-hydroxy-2-(20-alkyl-
thiophenylazo)naphthalenes (HL6–HL10) with sodium tetrachloropalladate in ethanol medium at room
temperature leads to the formation of a new series of complexes of the type [Pd(L)Cl]. All the palladium
compounds have been isolated in their pure form and characterized by spectral and elemental analysis
data. The crystal structures of [PdL3Cl] (3) and [PdL6Cl] (6) have been determined by single crystal X-
ray diffraction as representative cases. The crystal structures show that both complexes have distorted
square–planar structures in which he palladium(II) centers are bonded to O1 of the naphtholato function,
N2 of the diazene group and S1 at the 20 position of the phenyl fragment. Therefore, the ligands bind pal-
ladium(II) in a tridentate monoanionic [O, N, S] fashion, which give rise to five- and six-membered che-
late rings in each case. The fourth coordination site is occupied by a chloride ion. These complexes show
intense absorption bands in the visible and UV region. The nature of the electronic transitions has been
examined using (TD-DFT) formalism.
Article history:
Received 13 December 2011
Accepted 5 February 2012
Available online 3 March 2012
Keywords:
Palladium
Diazene
ONS donors
TD-DFT
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
compounds via an O,N-donor set towards divalent metal ions of
the first transition series was established. The bidentate behavior
Metal complexes with an ONS ligand framework have engen-
dered much research in the past few decades because of their po-
tential applications in fundamental and applied sciences and their
importance in the area of coordination chemistry [1–7]. However,
most of the studies reported so far involve complexes of tridentate
chelating ONS ligands with the metals of the first transition series
[8–15]. Copper(II) complexes with ONS donor atoms have been
shown to possess interesting magnetic properties [8–11]. An
antimony(V) complex of the salicylaldehyde Schiff base of
S-benzyldithicarbazate (an ONS ligand) has been shown to display
marked activity against leukemia [12]. Nickel(II) complexes of
some bivalent ONS thiosemicarbazone ligands have also been
found to catalyze important reactions related to CO-dehydrogenase
[13] and silane alcoholysis [14]. Nickel(II) complexes of Schiff bases
derived from S-alkyl esters of dithiocarbazic acid have also been
shown to have fungitoxicities [15].
of azophenols with palladium(II) is also well known [20].
In continuation of our interest in the synthesis and reactivity of
new palladium compounds [21], the present report deals with pal-
ladium complexes with a terdentate ligand system having an
O,N,S-donor set. The diazene group is well known to bind to soft
metal centers in their different oxidation states. In addition to
the diazene group two other donor groups, viz. a soft thioether
and relatively harder naphtholato functions have been incorpo-
rated in the ligand framework. In all the ligands mentioned above,
the presence of both ‘hard’ (–OH) as well as soft (–SR) donors to-
gether with the excellent metal binding diazene functionality de-
serves mention. This paper describes the synthesis and structural
characterization of square–planar palladium(II) complexes of tri-
dentate diazene ligands (HL). Moreover, the electronic structure
of the palladium(II) complexes have been calculated using time
dependent density functional theory (TD-DFT).
On the other hand, transition metal complexes incorporating
azo ligands have displayed several interesting properties related
to electron-transfer reactions [16], liquid crystals [17], photochro-
mism [18] and organic transformations via metal carbon bond for-
mation [19]. Thus the bidentate behavior of ortho-hydroxylarylazo
2. Experimental
2.1. Materials
Palladium dichloride was purchased from Arora Mathey,
Kolkata. All other chemicals and solvents were reagent-grade
commercial materials and were used as received.
⇑
Corresponding author. Tel.: +91 353 2776381; fax: +91 353 2699001.
E-mail address: pbchem@rediffmail.com (P. Bandyopadhyay).
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2012.02.021

S. Acharya et al. / Polyhedron 38 (2012) 50–57
51
2.2. Synthesis of the ligands
line) and 1-naphthol. The coupling provided the major product
with the diazene moiety introduced at the 4-position of 1-naphthol
together with a minor amount of the ortho substituted isomer.
Both isomers were isolated by preparative thin layer chromatogra-
phy on silica gel plates using petroleum ether as the eluant. The
faster moving pink band was isolated, extracted with methanol.
Solvent evaporation and recrystallization by methanol provided
the dark pink coloured 1-hydroxy-2-(20-alkylthiophenylazo)
naphthalenes.
2.2.1. Synthesis of 2-hydroxy-1-(20-methylthiophenylazo)naphthalene
(HL1)
The ligand HL1 was prepared following a reported procedure by
coupling alkaline 2-naphthol with the diazonium salts of 2-(alkyl-
thio) aniline [22].
Yield: 40%. Anal. Calc. for C17H14N2OS: C, 69.4; H, 4.8; N, 9.5.
Found: C, 69.3; H, 4.8; N, 9.4%. UV–Vis. (CH2Cl2), k (nm)
(dm3 molꢀ1 cmꢀ1): 234 (27500), 310sh (5600), 487 (10800). IR
(KBr;
cmꢀ1): 1448 (–N@N–), 3433 (–OH). 1H NMR (300 MHz;
e
m
2.2.7. 1-Hydroxy-2-(20-methylthiophenylazo)naphthalene (HL6)
Yield: 8%. Anal. Calc. for C17H14N2OS: C, 69.4; H, 4.8; N, 9.5.
CDCl3; standard SiMe4) d: 3.41 (s, 3H, –SCH3), 6.90 (d, 1H, J =
9.6 Hz), 7.41–7.63 (m, 6H), 7.72 (d, 1H, J = 9.6 Hz), 8.07 (d, 1H, J =
8.1 Hz), 8.60 (d, 1H, J = 8.1 Hz), 16.12 (s, 1H, –OH).
Found: C, 69.4; H, 4.7; N, 9.3%. UV–Vis. (CH2Cl2), k (nm)
e
(dm3 molꢀ1 cmꢀ1): 296sh (9900), 500 (4800) IR (KBr;
m
cmꢀ1):
1450(–N@N–), 3420 (–OH). 1H NMR (300 MHz; CDCl3; standard
SiMe4) d: 3.41 (s, 3H, –SCH3), 6.90 (d, 1H, J = 9.6 Hz), 7.41–7.63
(m, 6H), 7.72 (d, 1H, J = 9.6 Hz), 8.07 (d, 1H, J = 8.1 Hz), 8.60 (d,
1H, J = 8.1 Hz), 16.20 (s, 1H, –OH).
2.2.2. Synthesis of 2-hydroxy-1-(20-ethylthiophenylazo)naphthalene
(HL2)
The synthesis of the compound (HL2) was made using ethyl bro-
mide (4.4 g, 3 ml, 0.04 mol) following the method described for
compound (HL1).
2.2.8. 1-Hydroxy-2-(20-ethylthiophenylazo)naphthalene (HL7)
Yield: 308 mg, 001 mol, 6%. M.p. 140–145 °C; Anal. Calc. for
Yield: 35%. Anal. Calc. for C18H16N2OS: C, 70; H, 5.2; N, 9. Found:
C, 69.6; H, 5.0; N, 8.8%. UV–Vis. (CH2Cl2), k (nm)
e
(dm3 molꢀ1
C
18H16N2OS: C, 70; H, 5.2; N, 9. Found: C, 69.7; H, 5.1; N, 8.8%.
UV–Vis. (CH2Cl2), k (nm)
(dm3 molꢀ1 cmꢀ1): 295sh (5300), 501
(5500). IR (KBr;
cmꢀ1): 1442 (–N@N–), 3432 (–OH). 1H NMR
cmꢀ1): 234 (28800), 307sh (7200), 488 (14500). IR (KBr;
m
cmꢀ1):
e
1449 (–N@N–), 3422 (–OH). 1H NMR (300 MHz; CDCl3; standard
SiMe4) d: 1.32 (t, 3H, –CH3), 3.00 (m, 2H, –SCH2–), 6.83 (d, 1H, J =
9.6 Hz), 7.39–7.42 (m, 3H), 7.53–7.59 (m, 3H), 7.69 (d, 1H, J =
9.6 Hz), 8.09 (d, 1H, J = 8.4 Hz), 8.54 (d, 1H, J = 8.4 Hz), 16.36 (s,
1H, –OH).
m
(300 MHz; CDCl3; standard SiMe4) d: 1.31 (t, 3H, –CH3), 2.97 (m,
2H, –SCH2–), 6.83 (d,1H, J = 9.6 Hz), 7.39–7.42 (m, 3H), 7.53–7.59
(m, 3H), 7.69 (d, 1H, J = 9.6 Hz), 8.09 (d, 1H, J = 8.4 Hz), 8.54 (d,
1H, J = 8.4 Hz), 16.18 (s, 1H, –OH).
2.2.3. Synthesis of 2-hydroxy-1-(20-propylthiophenylazo)naphthalene
(HL3)
2.2.9. 1-Hydroxy-2-(20-propylthiophenylazo)naphthalene (HL8)
Yield: 6%. Anal. Calc. for C19H18N2OS: C, 70.8; H, 5.6; N, 8.7.
Yield: 38%. Anal. Calc. for C19H18N2OS: C, 70.8; H, 5.6; N, 8.7.
Found: C, 70.5; H, 5.4; N, 8.7%. UV–Vis. (CH2Cl2), k (nm) e
Found: C, 70.5; H, 5.2; N, 8.4%. UV–Vis. (CH2Cl2), k (nm)
e
(dm3
(dm3 molꢀ1 cmꢀ1): 296 (10000), 501 (6200). IR (KBr; cmꢀ1):
m
molꢀ1 cmꢀ1): 234 (29700), 306sh (8000), 488 (18400) IR (KBr;
m
1452 (–N@N–), 3433 (–OH). 1H NMR (300 MHz; CDCl3; standard
SiMe4) d: 1.02 (t, 3H, –CH3), 1.67 (m, 2H, –CH2–), 2.99 (t, 2H,
–SCH2–), 6.85 (d, 1H, J = 9.6 Hz), 7.2 (m, 1H), 7.40 (m, 2H), 7.52–
7.59 (m, 3H),7.70 (d, 1H, J = 9.6 Hz), 8.10 (d, 1H, J = 8.4 Hz), 8.55
(d, 1H, J = 8.4 Hz), 16.35 (s, 1H, –OH).
cmꢀ1): 1457(–N@N–), 3431 (–OH). 1H NMR (300 MHz; CDCl3;
standard SiMe4) d: 1.02 (t, 3H, –CH3), 1.67 (m, 2H, –CH2–), 2.99
(t, 2H, –SCH2–), 6.85 (d, 1H, J = 9.6 Hz), 7.2 (m, 1H), 7.40 (m, 2H),
7.52–7.59 (m, 3H), 7.70 (d, 1H, J = 9.6 Hz), 8.10 (d, 1H, J = 8.4 Hz),
8.55 (d, 1H, J = 8.4 Hz), 16.35 (s, 1H, –OH).
2.2.10. 1-Hydroxy-2-(20-butylthiophenylazo)naphthalene (HL9)
Yield: 10%. Anal. Calc. for C20H20N2OS: C, 71.4; H, 6; N, 8.3.
2.2.4. Synthesis of 2-hydroxy-1-(20-butylthiophenylazo)naphthalene
(HL4)
Found: C, 71.3; H, 5.8; N, 8.2%. UV–Vis. (CH2Cl2), k (nm)
e
Yield: 40%. Anal. Calc. for C20H20N2OS: C, 71.4; H, 6; N, 8.3. Found:
(dm3 molꢀ1 cmꢀ1): 300sh (11500), 502 (6800). IR (KBr; cmꢀ1):
m
C, 71.1; H, 5.8; N, 8.2%. UV–Vis. (CH2Cl2), k (nm)
e
(dm3 molꢀ1 cmꢀ1):
1449 (–N@N–), 3433 (–OH). 1H NMR (300 MHz; CDCl3; standard
SiMe4) d: 0.90 (t, 3H, –CH3), 1.25 (m, 2H, –CH2–), 1.46 (m, 2H,
–CH2–), 2.94 (m, 2H, –SCH2–), 6.85 (d,1H, J = 9.6 Hz), 7.23 (m,
1H), 7.40 (m, 2H), 7.52–7.59 (m, 3H), 7.69 (d, 1H, J = 9.6 Hz), 8.10
(d, 1H, J = 8.1 Hz), 8.55 (d, 1H, J = 8.1 Hz), 16.18 (s, 1H, –OH).
234 (30900), 306sh (8400), 489 (18600) IR (KBr;
m
cmꢀ1): 1448
(–N@N–), 3434 (–OH). 1H NMR (300 MHz; CDCl3; standard SiMe4)
d: 0.90 (t, 3H, –CH3), 1.46 (m, 2H, –CH2–), 1.62 (m, 2H, –CH2–),
2.94 (m, 2H, –SCH2–), 6.85 (d, 1H, J = 9.6 Hz), 7.23 (m, 1H), 7.40
(m, 2H), 7.52–7.59 (m, 3H),7.69 (d, 1H, J = 9.6 Hz), 8.10 (d, 1H,
J = 8.1 Hz), 8.55 (d, 1H, J = 8.1 Hz), 16.32 (s, 1H, –OH).
2.2.11. 1-Hydroxy-2-(20-benzylthiophenylazo)naphthalene (HL10
Yield: 10%. Anal. Calc. for C23H18N2OS: C, 74.6; H, 4.9; N, 7.6.
Found: C, 74.3; H, 4.8; N, 7.5%. UV–Vis. (CH2Cl2), k (nm)
)
2.2.5. Synthesis of 2-hydroxy-1-(20-benzylthiophenylazo)naphthalene
(HL5)
e
(dm3 molꢀ1 cmꢀ1): 296 (11100), 503 (7200). IR (KBr;
m
cmꢀ1):
Yield: 33%. Anal. Calc. for C23H18N2OS: C, 74.6: H, 4.9; N, 7.6.
1454 (–N@N–), 3433 (–OH). 1H NMR (300 MHz; CDCl3; standard
SiMe4) d: 4.0 (s, 2H, –SCH2–), 6.82 (d, 1H, J = 9.6 Hz), 7.11–7.19
(m, 5H), 7.25 (s, 1H), 7.38 (m, 3H), 7.50–7.57 (m, 2H), 7.68 (d,
1H, J = 9.6 Hz), 8.02 (d, 1H, J = 7.8 Hz), 8.48 (d, 1H, J = 8.1 Hz),
16.32 (s, 1H, –OH).
Found: C, 74.3; H, 4.8; N, 7.2%. UV–Vis. (CH2Cl2), k (nm)
(dm3 molꢀ1 cmꢀ1): 234 (34500), 306sh (9400), 488 (19400) IR
(KBr;
cmꢀ1): 1456 (–N@N–), 3434 (–OH). 1H NMR (300 MHz;
e
m
CDCl3; standard SiMe4) d: 4.07 (s, 2H, –SCH2–), 6.82 (d, 1H, J =
9.6 Hz), 7.11–7.19 (m, 5H), 7.25 (s, 1H), 7.38 (m, 3H), 7.50–7.57
(m, 2H), 7.68 (d, 1H, J = 9.6 Hz), 8.02 (d, 1H, J = 7.8 Hz), 8.48 (d,
1H, J = 8.1 Hz), 16.32 (s, 1H, –OH).
2.3. Synthesis of the palladium(II) complexes
2.3.1. Synthesis of [Pd(L1)Cl] (1)
2.2.6. Synthesis of 1-hydroxy-2-(20-alkylthiophenylazo)naphthalene
An orange-yellow ethanolic solution (10 ml) of HL1 (0.05 g,
0.17 mmol) was slowly added to a brown solution of Na2[PdCl4]
(0.05 g, 0.18 mmol) in ethanol (10 ml). Immediately the colour of
the mixture changed to pink violet. The mixture was stirred for
(HL6–HL10
)
The ligands (HL6–HL10) were obtained as minor products from
the coupling reactions between the appropriate 2-(alkylthioani-

52
S. Acharya et al. / Polyhedron 38 (2012) 50–57
1 h, then the volume was reduced to about 10 ml and the reaction
mixture was kept undisturbed for 24 h at room temperature. It was
then filtered and the residue was washed thoroughly with a mix-
ture of ethanol and water (1:1 v/v), then with diethyl ether and
dried in a vacuum over P2O5.
2.3.8. Synthesis of [Pd(L8)Cl] (8)
Yield: 88%. Anal. Calc for C19H17N2OSClPd: C, 49.25; H, 3.67; N,
6.05. Found: C, 49.12; H, 3.76; N, 5.85%. IR (KBr;
m
cmꢀ1): 1439
(–N@N–), UV–Vis (CH2Cl2),
k (nm) e
(dm3 molꢀ1 cmꢀ1): 304
(22000), 352 (10700), 524 (10300), 560 (13200). 1H NMR
(300 MHz; CDCl3; standard SiMe4) d: 3.48 (m, 2H, –SCH2), 1.20
(m, 2H, –CH2), 1.08 (t, 3H, –CH3), 6.7–8.8 (other aromatic protons).
Yield: 79%. Anal. Calc for C17H13N2OSClPd: C, 46.9; H, 2.99; N,
6.44. Found: C, 46.0; H, 2.71; N, 6.32%. IR (KBr;
m
cmꢀ1): 1436
(–N@N–), UV–Vis (CH2Cl2),
k (nm) e
(dm3 molꢀ1 cmꢀ1): 242
(30200), 302 (8800), 394 (6300), 543 (10300). 1H NMR (300
MHz; CDCl3; standard SiMe4) d: 3.01 (s, 3H, –SCH3), 6.7–8.8 (other
aromatic protons).
2.3.9. Synthesis of [Pd(L9)Cl] (9)
Yield: 85%. Anal. Calc for C20H19N2OSClPd: C, 50.3; H, 3.98; N,
5.87. Found: C, 50; H, 3.82; N, 5.71%. IR (KBr;
m
cmꢀ1): 1440
(–N@N–), UV–Vis (CH2Cl2), (nm) e
k
(dm3 molꢀ1 cmꢀ1): 304
(23500), 352 (11100), 525 (10500), 560 (13500). 1H NMR
(300 MHz; CDCl3; standard SiMe4) d: 3.49 (m, 2H, –SCH2), 1.58
(m, 2H, –CH2), 1.21 (m, 2H, –CH2), 0.88 (m, 3H, –CH3), 6.7–8.8
(other aromatic protons).
2.3.2. Synthesis of [Pd(L2)Cl] (2)
Compound 2 was synthesized following the same above proce-
dure using the ligand HL2 instead of HL1.
Yield: 82%. Anal. Calc for C18H15N2OSClPd: C, 48.1; H, 3.34; N,
6.24. Found: C, 47.7; H, 3.21; N, 6.32%. IR (KBr;
m
cmꢀ1): 1437
2.3.10. Synthesis of [Pd(L10)Cl] (10)
Yield: 76%. Anal. Calc for C23H17N2OSClPd: C, 54; H, 3.33; N,
5.48. Found: C, 53.8; H, 3.30; N, 5.35%. IR (KBr;
(–N@N–), UV–Vis (CH2cl2),
k (nm) e
(dm3 molꢀ1 cmꢀ1): 242
(36000), 303 (10200), 394 (6700), 543 (10300). 1H NMR (300
MHz; CDCl3; standard SiMe4) d: 3.48 (m, 2H, –SCH2) 1.20 (t, 3H,
–CH3), 6.7–8.8 (other aromatic protons).
m
cmꢀ1): 1435
(–N@N–), UV–Vis (CH2Cl2),
k (nm) e
(dm3 molꢀ1 cmꢀ1): 304
(25200), 352 (12800), 525 (12500), 560 (15000). 1H NMR
(300 MHz; CDCl3; standard SiMe4) d: 3.46 (m, 2H, –SCH2) 6.7–8.8
(other aromatic protons).
2.3.3. Synthesis of [Pd(L3)Cl] (3)
Yield: 85%. Anal. Calc for C19H17N2OSClPd: C, 49.25; H, 3.67; N,
6.05. Found: C, 49.08; H, 3.76; N, 5.90%. IR (KBr;
m
cmꢀ1): 1440
2.4. Physical measurements
(–N@N–), UV–Vis (CH2Cl2),
k (nm) e
(dm3 molꢀ1 cmꢀ1): 242
(37200), 303 (9400), 394 (7200), 543 (14600). 1H NMR (300
MHz; CDCl3; standard SiMe4) d: 3.49 (m, 2H, –SCH2), 1.21 (m,
2H, –CH2), 1.05 (t, 3H, –CH3), 6.7–8.8 (other aromatic protons).
Microanalyses (C, H, N) were done using a Heraeus Carlo Erba
1108 elemental analyzer. NMR spectra in CDCl3 solutions were
2.3.4. Synthesis of [Pd(L4)Cl] (4)
Yield: 84%. Anal. Calc for C20H19N2OSClPd: C, 50.3; H, 3.98; N,
5.87. Found: C, 49.8; H, 3.84; N, 5.62%. IR (KBr;
Table 1
Crystal data and structure refinement details for 3 and 6.
[Pd(L3)Cl] (3)
[Pd(L6)Cl] (6)
m
cmꢀ1): 1439
(–N@N–), UV–Vis (CH2Cl2), (nm) e
k
(dm3 molꢀ1 cmꢀ1): 242
CCDC deposition number
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
CCDC-855797
CCDC-855798
C17H13N2OSClPd
435.20
293(2)
0.71073
(38200), 302 (13600), 391 (7400), 544 (11600). 1H NMR (300
MHz; CDCl3; standard SiMe4) d: 3.49 (m, 2H, –SCH2), 1.62 (m,
2H, –CH2), 1.21 (m, 2H, –CH2), 0.90 (m, 3H, –CH3), 6.7–8.8 (other
aromatic protons).
C
19H17ClN2OPdS
463.26
293(2)
0.71073
orthorhombic
Pbca
monoclinic
P2(1)/n
Unit cell dimensions
a (Å)
b (Å)
2.3.5. Synthesis of [Pd(L5)Cl] (5)
Yield: 80%. Anal. Calc for C23H17N2OSClPd: C, 54; H, 3.33; N,
5.48. Found: C, 53.6; H, 3.25; N, 5.24%. IR (KBr;
18.673(6)
9.637(3)
20.163(6)
90
90
90
3628.3(19)
8
1.696
1.294
7.3594(12)
10.3332(16)
21.240(3)
90
95.270(3)
90
1608.4(4)
4
1.797
m
cmꢀ1): 1439
c (Å)
(–N@N–), UV–Vis (CH2Cl2),
k (nm) e
(dm3 molꢀ1 cmꢀ1): 243
a
(°)
b (°)
(°)
(39100), 308 (10900), 438 (8600), 544 (15400). 1H NMR
(300 MHz; CDCl3; standard SiMe4) d: 3.48 (m, 2H, –SCH2), 6.7–
8.8 (other aromatic protons).
c
Volume (Å3)
Z
DCalc (mg mꢀ3
)
Absorption coefficient
(mmꢀ1
F(000)
1.453
2.3.6. Synthesis of [Pd(L6)Cl] (6)
The compound 6 was synthesized following the same above
procedure using the ligand HL6 instead of HL1.
Yield: 85%. Anal. Calc for C17H13N2OSClPd: C, 46.9; H, 2.99; N,
)
1856
864
Crystal size (mm)
h range for data collection
Limiting indices
0.35 ꢁ 0.26 ꢁ 0.12
2.02°–25.00°
ꢀ22 ꢂ h ꢂ 22
ꢀ11 ꢂ k ꢂ 11
ꢀ23 ꢂ l ꢂ 23
28947
3134 (0.0403)
multi-scan
Full-matrix least-
squares on F2
3134/0/227
1.046
R1 = 0.0271,
wR2 = 0.0653
R1 = 0.0340,
wR2 = 0.0690
0.594 and –0.254
0.25 ꢁ 0.17 ꢁ 0.10
1.93°–25.00°
ꢀ8 ꢂ h ꢂ 8
6.44. Found: C, 46.5; H, 2.80; N, 6.39%. IR (KBr;
m
cmꢀ1): 1438
k (nm) e
(dm3 molꢀ1 cmꢀ1): 304
ꢀ12 ꢂ k ꢂ 12
ꢀ25 ꢂ l ꢂ 25
14808
(–N@N–), UV–Vis (CH2Cl2),
(20700), 352 (9800), 523 (9500), 559 (11600). 1H NMR (300
MHz; CDCl3; standard SiMe4) d: 3.01 (s, 3H, –SCH3), 6.7–8.8 (other
aromatic protons).
Reflections collected
Independent reflections Rint
Absorption correction
Refinement method
2820 (0.0315)
multi-scan
Full-matrix least-
squares on F2
2820/0/209
1.294
R1 = 0.0546,
wR2 = 0.1068
R1 = 0.0564,
wR2 = 0.1076
0.752 and –0.896
2.3.7. Synthesis of [Pd(L7)Cl] (7)
Yield: 82%. Anal. Calc for C18H15N2OSClPd: C, 48.1; H, 3.34; N,
6.24. Found: C, 47.9; H, 3.29; N, 6.32%. IR (KBr;
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2
r
(I)]
m
cmꢀ1): 1435
(–N@N–), UV–Vis (CH2Cl2),
k (nm) e
(dm3 molꢀ1 cmꢀ1): 304
R indices (all data)
(21600), 559 (11900), 1H NMR (300 MHz; CDCl3; standard SiMe4)
d: 3.49 (m, 2H, –SCH2), 1.23 (t, 3H, –CH3), 6.7–8.8 (other aromatic
protons).
Largest differences in peak
and hole (eÅꢀ3
)

S. Acharya et al. / Polyhedron 38 (2012) 50–57
53
recorded on a Bruker Avance 300 spectrometer. IR spectra were
obtained on a Jasco 5300 FT-IR spectrophotometer with samples
prepared as KBr disks. Electronic spectra were recorded on a JASCO
V-570 spectrophotometer.
parameters for all the hydrogen atoms. Full-matrix-least-squares
structure refinement was against |F2|. Molecular geometry calcula-
tions were performed with PLATON [25] and molecular graphics
were prepared using ORTEP-3 [26].
2.6. Method and computational details
2.5. X-ray crystallographic analysis
The calculations have been performed within the TD-DFT for-
malism as implemented in ADF2007 [27]. 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 VWN parametrization [28] in the SCF
step, Becke [29] and Perdew–Wang [30] gradient corrections to
the exchange and correlation respectively and the Adiabatic Local
Density Approximation (ALDA) for the XC kernel in the post-SCF
step. TD-DFT calculations have been performed with the uncon-
tracted triple-STO basis set with a polarization function for all
atoms. In the calculation of the optical spectra, the 70 lowest
spin-allowed singlet–singlet transitions have been taken into ac-
count. Transition energies and oscillator strengths have been inter-
polated by a GAUSSIAN convolution with an s value of 0.2 eV. Solvent
effects were modelled by the ‘‘Conductor-like Screening Model’’
(COSMO) [31] of solvation as implemented in ADF.
Single crystals of [Pd(L3)Cl] (3) and [Pd(L6)Cl] (6) suitable for X-
ray crystallographic analysis were obtained by slow diffusion of
dichloromethane solutions of the compounds into n-hexane. Se-
lected crystal data and data collection parameters are given in
Table 1. Crystallographic data collections were performed on a Bru-
ker SMART 1000 CCD area-detector diffractometer using graphite
monochromated Mo Ka (k = 0.71073 Å) radiation by the x scan
method. The structures were solved by direct methods using SHEL-
XS-97 [23] and difference Fourier syntheses and refined with the
SHELXL97 package incorporated in the WinGX 1.64 crystallographic
collective package [24]. All the hydrogen positions for the com-
pounds were initially located in the difference Fourier map, and
for the final refinement, the hydrogen atoms were placed geomet-
rically 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
3. Results and discussion
3.1. The ligands and their metal-binding sites
Two sets of potentially tridentate diazene ligands (HL1–HL5 and
HL6–HL10) have been prepared by coupling 2-(alkylthio)anilines
with either 1-naphthol (HL1–HL5) or 2-naphthol (HL6–HL10
)
(Scheme 1). The ligands have been characterized by 1H NMR and
IR spectra. The –OH signals for HL1–HL10 are observed in the region
d 16.0–16.4 ppm, indicating the possibility of the existence of azo-
hydrazo tautomers in solution [32]. The methyl group attached to
the phenyl ring as –SCH3 (HL1 and HL6) appears as a singlet in the
range d 2.18–2.4 ppm. For all the other ligands, the alkyl groups
have been identified from their respective 1H NMR spectra. The
aromatic protons appear as a complex pattern in the region d
5.9–9.2 ppm, with the correct integration ratio. Infrared scanning
of free HL1–10 in the solid state revealed
m(O–H) vibrations in the
range 3000–3400 cmꢀ1
.
The compounds HL1–HL10 show an
absorption band in the region 1320–1400 cmꢀ1 which is attributed
to the presence of the –N@N– (diazene) moiety [33].
3.2. Synthesis of the palladium(II) complexes having SNO coordination
Scheme 1. Synthetic route to the tridentate ONS ligands. (i) Sodium ethoxide, CH3I,
reflux, 3 h; (ii) nitrososulfuric acid, 2-naphthol; (iii) nitrososulfuric acid, 1-
naphthol.
Na2[PdCl4] smoothly reacts with the ligands (HL1–HL10) in
aqueous ethanol medium at room temperature affording the dark
Scheme 2. Synthesis of the palladium(II) complexes.

54
S. Acharya et al. / Polyhedron 38 (2012) 50–57
purple coloured palladium(II) complexes [Pd(L)Cl] in decent yields
(Scheme 2). The observed elemental analytical data of the com-
plexes (1–10) are found to be consistent with their respective
formulation.
mode of the ligands in these complexes, the structures of two
representative palladium complexes (3 and 6) from the two
sets of ligands have been determined by single crystal X-ray
The formulation of the palladium(II) complexes indicates that
the ligands are probably coordinated to the metal center as a
monoionic tridentate O,N,S-donor. In order to verify the binding
Table 2
Selected bond lengths (Å) and bond angles (°) for complex 3.
Bond lengths (Å)
Bond angles (°)
Pd(1)–N(2)
Pd(1)–Cl(1)
Pd(1)–O(1)
Pd(1)–S(1)
N(1)–N(2)
N(1)–C(1)
N(2)–C(11)
1.975(2)
2.3250(10)
1.992(2)
2.2413(9)
1.274(3)
1.347(3)
1.435(3)
N(2)–Pd(1)–O(1)
N(2)–Pd(1)–S(1)
O(1)–Pd(1)–S(1)
N(2)–Pd(1)–Cl(1)
O(1)–Pd(1)–Cl(1)
S(1)–Pd(1)–Cl(1)
91.74(7)
87.53(6)
178.35(6)
177.08(6)
91.18(5)
89.55(2)
Fig. 1. ORTEP diagram of complex 3. Thermal ellipsoids are drawn at the 50%
probability level.
Fig. 3. Ortep diagram of complex 6. Thermal ellipsoids are drawn at the 50%
probability level.
Table 3
Selected bond lengths (Å) and bond angles (°) for complex 6.
Bond lengths (Å)
Bond angles (°)
Pd(1)–N(2)
Pd(1)–Cl(1)
Pd(1)–O(1)
Pd(1)–S(1)
N(1)–N(2)
N(1)–C(2)
N(2)–C(11)
1.977(5)
2.3109(16)
1.990(4)
2.2300(15)
1.258(6)
1.363(8)
1.434(7)
N(2)–Pd(1)–O(1)
N(2)–Pd(1)–S(1)
O(1)–Pd(1)–S(1)
N(2)–Pd(1)–Cl(1)
O(1)–Pd(1)–Cl(1)
S(1)–Pd(1)–Cl(1)
92.75(18)
86.97(14)
176.56(13)
175.22(14)
91.13(13)
89.33(6)
Fig. 2. Crystal packing diagram in 3 viewed along the normal of the [100] plane.
Fig. 4. Electronic spectrum of complex 6 in dichloromethane.

S. Acharya et al. / Polyhedron 38 (2012) 50–57
55
crystallography. The molecular structure of complex 3, along with
the atomic numbering scheme, is shown in Fig. 1 and the crystal
packing arrangement is shown in Fig. 2. Relevant bond parameters
for 3 are compiled in Table 2. The structure shows that the crystal
lattice of this complex contains discrete molecules. The palla-
dium(II) center is bonded to O1 of the naphtholato function, N2
of the diazo group and S1 at the 20 position of the phenyl fragment.
Therefore, 2-hydroxy-l-(20-alkyllthiophenylazo) naphthalene binds
palladium(II) as a monoanionic terdentate [O,N,S] ligand, forming a
five membered chelate ring and a six-membered chelate ring with
bite angles of 86.97(14) (N2–Pd1–S1) and 92.75(18)° (N2–Pd1–
O1). The O,N,S donor set, palladium(II) center and the chloride
ion constitute an almost planar geometry. The Pd–S and Pd–O bond
distances are normal [34]. The observed N1–N2 distance of the
coordinated azo (diazene) function is longer than that of the free
diazene group [35]. This may be attributed to back bonding from
the filled metal orbitals to the vacant p⁄ orbital localized on the
azo function. The tetra-coordination around palladium is essen-
tially planar, but in a distorted square–planar geometry.
Table 4
Energies and percentage composition of the lowest unoccupied and highest occupied
Kohn–Sham orbitals of 3 in terms of Pd and the ligand fragmenta.
MO
occ E (eV)
Pd
Ligand
The reaction of sodium tetrachloropalladate with 1-hydroxy-2-
122a
121a
120a
119a
118a
117a
116a
0
0
0
0
0
ꢀ1.394
ꢀ1.557
ꢀ2.216
ꢀ2.328
ꢀ3.279
93.39
98.13
92.89
91.08
51.77
85.26
71.64
(20-alkylthiophenylazo) naphthalenes (HL) follows
a similar
pattern, and the violet coloured compounds [PdLCl] (6–10) were
isolated. The molecular structure of the complex 6 was established
by single crystal X-ray crystallography. The ORTEP diagram, with
the atomic numbering scheme, of complex 6 is shown in Fig. 3.
The crystal data and selected bond parameters are compiled in
Table 3. The structure shows that the palladium(II) center is bonded
to O1 of the naphtholato function, N2 of the diazo group and S1 at
the 20 position of the phenyl fragment. Therefore, 1-hydroxy-2-(20-
alkyllthiophenylazo)naphthalene also binds palladium(II) as a
monoanionic terdentate [O,N,S] ligand. The tetra-coordination
around palladium is essentially planar, but in a distorted square–
planar geometry.
18.38 (dz2 ); 11.26 (dxy); 7.56 (dxz
)
ꢀ3.823 1.04 (dxz
ꢀ5.590
)
0
4.78 (dyz); 2.83 (dxy); 2.79 (dz2 ); 2.78
(dx2
)
ꢀy2
115a
114a
2
2
ꢀ6.213
ꢀ6.286
60.06
53.38
6.98 (dyz); 5.39 (dx2 ꢀy2 ); 5.08 (dxy); 2.08 (s)
12.81 (dyz); 4.76 (dxy); 3.83 (s); 2.25 (dz2 );
1.22 (dx2
)
ꢀy2
113a
2
ꢀ6.337
34.3
19.67 (dxz); 19.58 (dxy); 9.66 (dx2ꢀy2 ); 5.00
(s); 1.94 (dyz
10.78 (dz2 ); 7.46 (dxy); 5.37 (dyz); 1.24 (dxz
5.49 (dx2 ); 3.06 (dyz); 2.22 (dz2
)
112a
111a
2
2
ꢀ6.437
ꢀ6.739
52.21
67.06
)
)
ꢀy2
a
Bold characters are used for the HOMO (116a) and the LUMO (1171a).
Table 5
Energies and percentage composition of the lowest unoccupied and highest occupied Kohn–Sham orbitals 6 in terms of Pd and the ligand fragment.a
MO
occ
E (eV)
Pd
Ligand
66a
65a
64a
63a
62a
61a
0
0
0
0
0
ꢀ1.067
ꢀ1.565
ꢀ2.109
ꢀ2.199
ꢀ3.279
ꢀ3.689
ꢀ5.430
ꢀ6.247
ꢀ6.324
ꢀ6.403
ꢀ6.549
ꢀ6.695
1.05 (py)
93.43
96.12
90.55
93.15
50.39
87.98
26.46 (dz2 ); 7.54 (dxy); 2.09 (dx2ꢀy2 ); 1.07 (dz2 ); 1.07 (dyz
)
1.41 (dx2 ); 1.32 (dyz
)
ꢀy2
60a
59a
58a
57a
56a
55a
0
2
2
2
2
2
78.96
54.00
56.59
32.56
59.78
71.33
4.76 (dyz); 1.40 (dx2ꢀy2 ); 1.02 (dxz
16.11 (dyz); 5.92 (dxy); 2.61 (s); 5.883.27 (dz2 ); 3.04 (dxz); 1.27
13.84 (dxz); 6.13 (dxy); 2.06 (dz2 ); 1.70 (dyz); 1.38 (s); 1.08 (dxz
26.82 (dxy); 12.89 (dz2 ); 8.59 (s); 7.47 (dxz); 2.97 (dx2 ꢀy2
17.06 (dx2 ); 4.32 (dyz); 1.94 (s)
)
)
)
ꢀy2
ꢀy2
12.93 (dx2 ); 1.26 (dxz
)
a
Bold characters are used for the HOMO (60a) and the LUMO (61a).
Table 6
Selected list of vertical excitations computed at the TD-DFT/PW91/TZP level for 3.
State
S1
Energy (eV)
2.2177
kcal (nm)
kexp (nm)
f
Composition
560
543
0.105
HOMO ? LUMO (85.9%)
HOMOꢀ4 ? LUMO (6.5%)
S5
2.6724
462
–
0.102
HOMOꢀ2 ? LUMO (49.3%)
HOMOꢀ1 ? LUMO (42.5%)
HOMOꢀ4 ? LUMO (89.0%)
HOMOꢀ5 ? LUMO+1 (41.6%)
HOMOꢀ6 ? LUMO+1 (33.3%)
HOMOꢀ2 ? LUMO+2 (28.4%)
HOMOꢀ10 ? LUMO (14.7%)
HOMOꢀ6 ? LUMO+1 (11.1%)
HOMO ? LUMO+4 (20.8%)
HOMO-8 ? LUMO+1 (13.7%)
HOMOꢀ4 ? LUMO+3 (11.0%)
HOMOꢀ19 ? LUMO (15.1%)
HOMOꢀ8 ? LUMO+2 (14.6%)
HOMOꢀ7 ? LUMO+2 (13.3%)
HOMOꢀ4 ? LUMO+4 (12.7%)
HOMOꢀ12 ? LUMO+1 (16.2%)
HOMOꢀ4 ? LUMO+4 (9.8%)
HOMOꢀ13 ? LUMO+1 (7.0%)
HOMOꢀ19 ? LUMO (6.0%)
S6
S17
2.7897
3.6687
347
333
394
–
0.070
0.070
S22
S28
S57
4.0122
4.1849
5.0365
310
290
246
303
ꢀ
0.098
0.114
0.102
ꢀ
S59
5.0842
243
242
0.187

56
S. Acharya et al. / Polyhedron 38 (2012) 50–57
Table 7
Selected list of vertical excitations computed at the TD-DFT/PW91/TZP level for 6.
State
S2
Energy (eV)
2.2411
kcal (nm)
kexp (nm)
f
Composition
553
523, 559
0.066
HOMO ? LUMO (53.7%)
HOMOꢀLUMO+1 (39.3%)
HOMOꢀ4 ? LUMO (53.9%)
HOMOꢀ6 ? LUMO (18.4%)
HOMOꢀ5 ? LUMO (10.3)
HOMOꢀ2 ? LUMO+1 (26.6%)
HOMOꢀ1 ? LUMO+1 (19.5%)
HOMOꢀ7 ? LUMO (16.5%)
HOMO ? LUMO+3 (61.7%)
HOMOꢀ7 ? LUMO+1 (7.6%)
HOMOꢀ4 ? LUMO (6.2%)
HOMOꢀ9 ? LUMO (35.9%)
HOMOꢀ10 ? LUMO (15.7%)
HOMOꢀ6 ? LUMO+1 (14.2%)
S6
3.0667
3.3356
3.6846
4.0514
404
372
336
306
–
0.048
0.085
0.317
0.1033
S11
S16
S21
ꢀ
352
304
3.3. UV–Vis spectra and excited singlet state calculations
Each complex shows an intense absorption in the visible region
and a few very strong absorptions in the ultraviolet region. To
understand the origin of the absorptions, the electronic structures
of the two representative members (viz. 3 and 6) have been probed
with the help of DFT calculations. The coordinates of these com-
plexes are directly imported from their crystal data. It is well
known that an experimentally used model of an excited state cor-
responds to excitation of an electron from an occupied orbital to a
virtual orbital. Assignments of the character of each excited state
are based on the compositions of the occupied and virtual orbitals
of the dominant configurations for that excited state. The TD-DFT
results do not provide information on triplet-singlet absorption
intensities since spin–orbit coupling effects are not included in
the current TD-DFT methods. Thus we have only calculated the sin-
glet excited states, and only the singlet states with oscillator
strengths greater than 0.05 are listed. A detailed analysis of the
highest occupied and lowest unoccupied molecular orbitals of 3
and 6 are presented in Tables 4 and 5. Excitation energies and
oscillator strengths for the various absorption bands are reported
in Tables 6 and 7, together with the composition of the solution
vectors in terms of the most relevant transitions. Isodensity surface
plots of the relevant MO’s for 3 and 6 are shown in Fig. 5. Both the
HOMO and LUMO have been found to be distributed largely over
the diazene ligand frameworks. Hence the absorptions at 543 nm
(for 3) and 559 nm (for 6) involve transitions within the filled
(HOMO) and vacant (LUMO) orbitals of the monoanionic tridentate
The palladium(II) complexes 1–10 are found to be soluble in
dichloromethane producing either pink (1–5) or violet (6–10) solu-
tions. The electronic spectra of all the palladium(II) complexes
have been recorded in dichloromethane. The electronic spectrum
of complex 6 has been provided in Fig. 4 as a representative case.
diazene ligands, and can be assigned to intraligand
p–
p⁄ transi-
tions. The calculated electronic spectrum of complex 6 is shown
in Fig. 6. For both the complexes (3 and 6), transitions in the
Fig. 5. Partial molecular orbital diagram of the palladium(II) complexes 3 and 6.
Fig. 6. Electronic spectrum computed at the TD-DFT/PW91/TZP level for complex 6 in dichloromethane. The heights of the vertical lines on the abscissa correspond to the
oscillator strengths.

S. Acharya et al. / Polyhedron 38 (2012) 50–57
57
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transitions in some cases.
4. Conclusions
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Palladium(II) smoothly reacts with two groups of terdentate
ligands, viz. 2-hydroxy-1-(20-alkylthiophenylazo)naphthalenes
(HL1–HL5) and 1-hydroxy-2-(20-alkylthiopheny-lazo)naphthalenes
(HL6–HL10) and forms square planar palladium(II) complexes with
an ONS coordination sphere. The crystal structures of representa-
tive complexes reveal the square planar coordination of palla-
dium(II), with a six-membered Pd(1)–O(1)–C(1)–C(2)–N(1)–N(2)
chelate ring and a five-membered Pd(1)–N(2)–C(11)–C(12)–S(1)
chelate ring. The simulated electronic spectra of the palladium(II)
complexes, using time-dependent density functional theory (TD-
DFT), are in close agreement with the experimental spectra. The
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low energy absorptions are attributed to intraligand
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p–
p⁄ transi-
tions, whereas the high energy absorptions are primarily due to
intraligand p–
p⁄ transitions.
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Acknowledgements
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The financial support from the 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 fellowships to AK.
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[27] The ADF program system was obtained from Scientific Computing and
Appendix A. Supplementary Data
CCDC-855797 and 855798 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or
from the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44) 1223–336-033; or e-mail:
deposit@ccdc.cam.ac.uk.
Modelling, Amsterdam (http://www.scm.com/). For
a description of the
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