Synthesis and spectroscopic characterization of nickel(II) complexes of 1-benzotriazol-1-yl-[(p-X-phenyl)hydrazone]propan-2-one

Article abstract of DOI:10.1016/j.saa.2005.09.024

The reaction of NiCl₂·H₂O with 1-benzotriazol-1-yl-[(p-X-phenyl)hydrazone]propan-2-one, X = H (HL¹), X = Cl (HL²), X = Br (HL³) and X = Me (HL⁴), gave the complexes [(HL)NiCl₂]·nH₂O and [LNi(OH)]₂, where L is the monobasic anion of HL² or HL³. The nature of the products is solvent and ligand dependent. The complexes are characterized by elemental analyses, molar conductivity, magnetic moments and spectroscopic (IR and UV/vis) measurements. The IR showed that the ligands act as neutral bidentate coordinated to the nickel(II) through the azomethine nitrogen and carbonyl oxygen atoms in case of [(HL)NiCl₂]·nH₂O. In case of [LNi(OH)]₂, the ligands are monobasic bidentate bonded to the nickel(II) through the azomethine nitrogen and the enolato oxygen atoms. The room temperature magnetic moment values of 1.58-2.49 B.M. for [(HL)NiCl₂]·nH₂O and [LNi(OH)]₂ and their electronic spectral data indicate that these complexes have square planar-tetrahedral equilibrium. The values of 1.61 and 1.58 B.M. for the hydroxo-complexes support their dimeric nature. The electronic spectral of [(HL)NiCl₂]·nH₂O and [LNi(OH)]₂ in pyridine or α-picoline indicated the formation of six-coordinate adducts. The hydroxo-complexes reacted with different Lewis bases to give the complexes [L₂Ni(L_s)₂], where L_s = Py, 2-Pic, 3-Pic, 4-Pic or n-PrNH₂. The relationship between the pK_b of the Lewis base and the υ_Ni-O of the ligand and υ_Ni-N of the Lewis base was studied. The different ligand field parameters are calculated for the parent ligands in solutions and the solid mixed ligand complexes. The data showed that both are associated with a distorted octahedral ligand field around the nickel(II) and the ligand fields in solution are different from that in solid. The extent of distortion for the parent complexes is more than that in the solid adducts. Furthermore, the data showed that the nickel-ligand bonding in [LNi(OH)]₂ is more covalent than in [L₂Ni(L_s)₂].

Full text of DOI:10.1016/j.saa.2005.09.024

Spectrochimica Acta Part A 65 (2006) 36–43
Synthesis and spectroscopic characterization of nickel(II) complexes
of 1-benzotriazol-1-yl-[(p-X-phenyl)hydrazone]propan-2-one
Nouria Al-Awadi, Nadia M. Shuaib, Ali El-Dissouky∗
Chemistry Department, Faculty of Science, Kuwait University, P.O. Box 5969, Safat 13060, Kuwait
Received 14 July 2005; accepted 12 September 2005
Abstract
The reaction of NiCl2·H2O with 1-benzotriazol-1-yl-[(p-X-phenyl)hydrazone]propan-2-one, X = H (HL1), X = Cl (HL2), X = Br (HL3) and
X = Me (HL4), gave the complexes [(HL)NiCl2]·nH2O and [LNi(OH)]2, where L is the monobasic anion of HL2 or HL3. The nature of the products
is solvent and ligand dependent. The complexes are characterized by elemental analyses, molar conductivity, magnetic moments and spectroscopic
(IR and UV/vis) measurements. The IR showed that the ligands act as neutral bidentate coordinated to the nickel(II) through the azomethine
nitrogen and carbonyl oxygen atoms in case of [(HL)NiCl2]·nH2O. In case of [LNi(OH)]2, the ligands are monobasic bidentate bonded to the
nickel(II) through the azomethine nitrogen and the enolato oxygen atoms. The room temperature magnetic moment values of 1.58–2.49 B.M. for
[(HL)NiCl2]·nH2O and [LNi(OH)]2 and their electronic spectral data indicate that these complexes have square planar–tetrahedral equilibrium.
The values of 1.61 and 1.58 B.M. for the hydroxo-complexes support their dimeric nature. The electronic spectral of [(HL)NiCl2]·nH2O and
[LNi(OH)]2 in pyridine or ␣-picoline indicated the formation of six-coordinate adducts. The hydroxo-complexes reacted with different Lewis
bases to give the complexes [L2Ni(Ls)2], where Ls = Py, 2-Pic, 3-Pic, 4-Pic or n-PrNH2. The relationship between the pKb of the Lewis base and the
υNi–O of the ligand and υNi–N of the Lewis base was studied. The different ligand field parameters are calculated for the parent ligands in solutions
and the solid mixed ligand complexes. The data showed that both are associated with a distorted octahedral ligand field around the nickel(II) and
the ligand fields in solution are different from that in solid. The extent of distortion for the parent complexes is more than that in the solid adducts.
Furthermore, the data showed that the nickel–ligand bonding in [LNi(OH)]2 is more covalent than in [L2Ni(Ls)2].
© 2005 Elsevier B.V. All rights reserved.
Keywords: Benzotriazole; Hydrazone; Nickel(II); Mixed ligand complexes; Spectra; Structure
1. Introduction
lular homeostasis [8]. Therefore, if there are polyfunctional
ligands that can react with nickel(II) before bonding to pro-
teins or DNA, it will prevent the nickel carcinogenesis. There-
fore, it is important to study the bonding of nickel(II) with
different polyfunctional ligands with different donors. Further-
more, mixed ligand complexes have a key role in biological
chemistry [9] because the mixed chelation occurs commonly
in biological fluids as millions of potential ligands are likely
to compete for metal ions in vivo [10]. These create spe-
cific structures [9–11] and have been implicated in the storage
and transport of active substances through membranes. Among
these ligands are the triazole and its derivatives where they act
as polyfunctional having different donors. Triazole-containing
complexes are very important due to their uses in different
fields [12–16]. Recently, the triazole derivatives as 4-alkyl-
3,5-di(pyridyl)-4H-1,2-triazole [17], 3-phenyl-5-(2-pyridyl)-4-
(4-pyridyl)-4H-1,2,4-triazole [18], 4,4ꢀ-(1,4-phenylene)bis[3-
phenyl-5-(2-pyridyl)-4H-1,2,4-triazole] [18] and other related
In our previous work, we reported the synthesis and spec-
troscopic characterization of nickel(II) complexes with dif-
ferent polyfunctional ligands having different donors [1–5].
Nickel(II) complexes are used in different fields of chemistry
and industry. (1-Me-indyl)(PPh3)Ni-CCPh was used as a cata-
lyst for the synthesis of cis-poly(1-ethylenepyrene) [6]. (1-Me-
indyl)Ni(PR3) was used for dehydrogenative oligomerization
of PhSiH3 [7]. Furthermore, nickel(II) compounds are known
to cause respiratory cancer in human and induce tumors in
the experimental animals. This is because of its bonding to
the proteins and DNA leading to generate reactive oxygen
species and other reactive intermediate and changing the cel-
∗
Corresponding author. Tel.: +965 6014156; fax: +965 4816482.
E-mail address: adissouky@yahoo.com (A. El-Dissouky).
1386-1425/$ – see front matter © 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2005.09.024

N. Al-Awadi et al. / Spectrochimica Acta Part A 65 (2006) 36–43
37
compounds [19–21] are used as chelating agents for different
metal ions, among them is the nickel(II). Furthermore, Haas-
noot has reported a review on the coordination chemistry of
many triazole derivatives with different metal ions [22]. We
have reported the copper(II) complexes of the new chelating
agents 1-benzotriazol-1-yl-[(p-X-phenyl)hydrazone]propan-2-
one, I [23]. The ligands give copper(II) complexes with unique
stereochemical, magnetic and spectral properties. It is found that
the nature of copper–ligand bonding in the complexes of HL1,
HL4 and HL5 is covalent in nature while for the complexes
of HL2 and HL3 is ionic. This is due to the different electronic
effects of the p-substituent. Due to the importance of these types
of ligands, the mixed ligand complexes, the absence of their
nickel(II) complexes in literature and our interest in the ligat-
ing behavior of the triazole-containing organic compounds, we
aim to synthesize and characterize nickel(II) complexes of 1-
benzotriazol-1-yl-[(p-X-phenyl)hydrazone]propan-2-one, I, as
well as the products of the reaction of these complexes with
different nitrogen-containing Lewis bases.
They were synthesized according to the method (a) but
using CH3CN as a solvent. Only HL2 and HL3 gave the
hydroxo-complexes.
(c) [L2Ni(Ls)2]; Ls = Py, 2-Pic, 3-Pic, 4-Pic or n-PrNH2.
The adduct complexes were prepared by dissolving
[LNi(OH)] in the least amount of the corresponding Ls. The
resulting solution was filtered off to remove any undissolved
solid and the filtrate was refluxed for 1–2 h. After cooling to
room temperature, H2O was added dropwise until the first
turbidity. The mixture was left overnight at room tempera-
ture and the isolated solid was filtered off, washed several
times with EtOH H2O mixture (30:70, v/v), followed by
Et2O until the filtrate become uncolored and dried.
2.3. Physical measurements and analysis
CHN analysis was obtained from LECO-CHNS 932 Ana-
lyzer. FT-IR spectra were recorded as KBR discs with Schi-
madzu 2000 FT-IR spectrophotometer. Electronic spectra were
accomplished by Carry Varian 5 UV/vis/NIR spectrophotome-
ter. The room temperature magnetic susceptibility measure-
ments for the complexes were determined by a Gouy balance
using Hg[Co(CN)4] as the calibrant. Molar conductance of the
complexes was measured for 1.00 × 10−3 M DMF solutions at
room temperature using a systronic conductivity bridge type
305.
3. Results and discussion
3.1. General
The interaction of HL1–HL4 with NiCl2·H2O (Scheme 1)
in EtOH in a mole ratio 1:1 or 1:2 (Ni2+:HL) all gave only
complexes [(HL)NiCl2]·nH2O, HL = HL1–HL4 and n = 1–3. In
CH3CN as solvent HL2 and HL3 gave [LNi(OH)]2 while HL1
and HL4 gave [(HL)NiCl2]·nH2O. All complexes are air stable,
partially soluble in EtOH but freely soluble in Lewis bases such
as pyridine (Py) or 2-picoline (2-Pic) with color change. The
color change could be taken as an evidence for the interaction
of these complexes with Py or ␣-Pic. The molar conductivity
values of the complexes as 1.00 × 10−3 M DMF solutions at
298 K (Table 1) indicate their non-electrolytic nature [25]. Only
[LNi(OH)] gave solid base adducts complexes [L2Ni(Ls)2],
Ls = Py, 2-Pic, 3-Pic, 4-Pic or n-PrNH2 (Scheme 2), which are
decomposed within 3–4 days to give [L2Ni], where L is the
monobasic anion of HL2 and HL3.
2. Experimental
All chemicals were reagent grade quality obtained from BDH
or Aldrich and used without further purification.
2.1. Synthesis of the ligands
The ligands were synthesized according to the method
reported by Al-Awadi and co-workers [24].
2.2. Synthesis of the nickel(II) complexes
(a) [(HL)NiCl2]·nH2O; HL = HL1, HL2, HL3 and HL4; n = 1–3.
These complexes were synthesized by the addition of a
hot ethanolic solution (20 cm3) of NiCl2·H2O (0.001 mol)
to a hot ethanolic solution (20 cm3) of the corresponding
ligand (0.0022 or 0.001 mol) in the same solvent (30 cm3).
The reaction mixture was then refluxed for 2–3 h and cooled
to room temperature. The solid formed in each case was
filtered off, washed several times with EtOH, Et2O and dried
in vacuum over P4O10 (yield 52–63%).
3.2. Electronic spectral and magnetic data
3.2.1. [(HL)NiCl2]·nH2O, n = 1–3, and HL = HL1, HL2,
HL3 or HL4
The room temperature magnetic moment values of these
complexes (Table 3) are in the 1.59–2.57 cm−1 range. These
values are lower than these of octahedral, tetrahedral or high
spin five-coordinate nickel(II) complexes. Therefore, the com-
plexes may be low spin five-coordinate nickel(II) complexes.
According to the molar conductivity values, elemental analy-
(b) [LNi(OH)]2; L = anion of HL2 or HL3.

38
N. Al-Awadi et al. / Spectrochimica Acta Part A 65 (2006) 36–43
Scheme 1.
sis, IR and the nature of the ligands, these complexes could
be assigned to be four-coordinate nickel(II) complexes. Fur-
thermore, these magnetic values are similar to that reported for
[NiX2PR3], bis(salicylaldiminato)nickel(II) and [NiCl(H2O)L],
L = azo-nitrosoresorcinol derivatives complexes which exist in
a square planar–tetrahedral mixture in the solid state [1–5,26].
The nujol mull electronic spectra of all complexes are
recorded in the range of 5000–30,000 cm−1. The spectra of
[(HL)NiCl2]·nH2O and [LNi(OH)] are similar and exhibit two
bands at 6700–6900 and 18,300–18,900 cm−1 (Table 2), char-
acteristic of square planar–tetrahedral nickel(II) complexes
[2–5]. The band at 6700–6900 cm−1 could be assigned to
where µobsd is the measured room temperature magnetic
moment and 3.3 is the magnetic moment for ideal tetrahedral
nickel(II) complexes. The values of Nt of [(HL)NiCl2]·nH2O
are in the order of: Ph (HL1) > p-Cl (HL2) > p-Br (HL3) > p-Me
(HL4), which is the reverse of the bulkiness effect of the p-
substituted phenyl moiety. This sequence means that the large
steric requirement enhances the planar form and therefore low
Nt value. The lower Nt values for [LNi(OH)]2 relative to those of
[(HL)NiCl2]·nH2O can be referred to the increased planarity of
the hydroxo-containing complexes due to their dimeric forms.
The values of Nt are used to calculate the molar extinc-
tion coefficient (εmax) of the tetrahedral in the 6700–6900 cm−1
region, where the planar forms do not absorb, using Eq. (2)
3
3T1 → T1(P) transition for the tetrahedral nickel(II) complexes
1
while that at 18,300–18,900 cm−1 due to 1A1g → B1g transi-
42Nt
tion in the square planar nickel(II) complexes [27]. This assign-
ment of the electronic transitional bands is made evident by
comparing with the spectra of similar complexes [1–3].
The percentage of tetrahedral (Nt) in these complexes could
be obtained by applying Eq. (1)
εmax
=
(2)
100
where 42 is the molar extinction coefficient of the band at
6700–69,500 cm−1 for pure tetrahedral nickel(II) complexes.
The values of ε (Table 2) are shown to be in the same order
of Nt. The spectral data for the solid complexes showed the sig-
nificant property of the ligand field in the existence of a clear
trend between the energies of the bands at 6700–6900 cm−1
2
100(µobsd
(3.3)2
)
Nt =
(1)

N. Al-Awadi et al. / Spectrochimica Acta Part A 65 (2006) 36–43
39
Table 1
Elemental analysis, % found (% calcd.), color, molar conductivity of the ligands and their nickel(II) complexes
Compounda
Mediumb
Color
ΛM (S cm2 mol−1
)
C
H
N
Ni
c
HL1
64.85 (64.52)
58.00 (57.74)
50.49 (50.28)
65.12 (65.52)
38.66 (38.89)
39.50 (39.11)
46.07 (46.37)
56.93 (57.03)
57.68 (57.95)
57.66 (57.95)
58.19 (57.95)
53.59 (53.88)
37.20 (3691)
41.49 (41.61)
47.10 (46.91)
47.68 (47.94)
48.1 (47.94)
47.66 (47.94)
44.19 (43.94)
43.29 (43.56)
4.63 (4.66)
4.02 (3.83)
3.43 (3.35)
4.97 (5.12)
3.93 (4.11)
2.99 (2.80)
3.18 (3.09)
4.00 (3.80)
4.02 (4.14)
3.92 (4.14)
4.21 (4.14)
4.85 (4.99)
2.61 (2.46)
2.86 (2.77)
3.09 (3.32)
3.78 (3.61)
3.66 (3.61)
3.72 (3.61)
4.08 (4.27)
3.63 (3.86)
25.21 (25.09)
22.53 (22.33)
19.76 (19.55)
24.05 (23.89)
15.06 (15.13)
15.39 (15.20)
18.21 (18.03)
19.81 (19.96)
19.51 (19.32)
19.29 (19.32)
19.23 (19.32)
21.02 (20.95)
14.08 (14.35)
15.98 (18.18)
16.26 (16.42)
16.15 (15.98)
15.76 (15.98)
16.21 (15.98)
17.33 (17.09)
15.76 (15.88)
HL2
HL3
HL4
[(HL1)NiCl2]·3H2O
[(HL2)NiCl2]·H2O
[L2Ni(OH)]
EtOH or CH3CN
EtOH
CH3CN
Py
2-Pic
3-Pic
4-Pic
PrNH2
EtOH
CH3CN
Py
2-Pic
Green-brown
Green
Brown
13.0
16.0
8.0
3.2
2.8
3.0
2.0
2.7
14.0
6.0
2.8
3.0
2.3
2.4
2.1
9.0
15.10 (15.12)
7.09 (6.98)
7.00 (6.76)
6.88 (6.76)
6.58 (6.76)
13.01 (13.13)
[L22Ni(Py)2]
[L22Ni(2-Pic)2]
[L22Ni(3-Pic)2]
[L22Ni(4-Pic)2]
[L22Ni(PrNH2)2]
[(HL3)NiCl2]·H2O
[L3Ni(OH)]
Red
Red-brown
Red-brown
Red-brown
Brown-yellow
Green
Brown
Red
Red
Red-brown
Brown
13.97 (13.71)
[L32Ni(Py)2]
[L32Ni(2-Pic)2]
[L32Ni(3-Pic)2]
[L32Ni(4-Pic)2]
[L32Ni(PrNH2)2]
[(HL4)NiCl2]·H2O
11.58 (11.70)
11.80 (11.70)
11.58 (11.70)
12.01 (11.94)
3-Pic
4-Pic
PrNH2
EtOH or CH3CN
Brown-yellow
Green
a
Py: pyridine; 2-Pic: 2-picoline; 3-Pic: 3-picoline; 4-Pic: 4-picoline; n-PrNH2: n-propylamine.
Medium of the synthesis.
Molar conductivity of 1.00 × 10−3 M DMF solution at 25 1 ◦C.
b
c
Table 2
Electronic spectral data and room temperature magnetic moments for the complexes
’
Complex
µeff
State
Nt
εmax
v (cm−1
)
[(HL1)NiCl2]·3H2O
2.49
Solid
Py
2-Pic
56.9
23.9
6900, 18050
9800, 9980, 11800, 15410, 15620, 23250
9500, 9700, 1200, 15100, 15380, 23000
[(HL2)NiCl2]·H2O
2.35
1.61
Solid
Py
2-Pic
50.7
23.8
21.3
10.0
6830, 18300
9830, 11920, 1430, 15900, 23800
9480, 11950, 15020, 15680, 23700
[L2Ni(OH)]
Solid
Py
2-Pic
6850, 19150
10500, 12500, 15240, 15890, 24990
9300, 9400, 12800, 15250, 15550, 23120
[L22Ni(Py)2]
3.20
3.22
3.21
3.30
3.26
Solid
Solid
Solid
Solid
Solid
9820, 12700, 16100, 17050, 24060
9420, 10300, 12790, 152800, 16600, 23600
9800, 12000, 12890, 15900, 23800
10100, 12200, 12700, 16300, 24080
10400, 10900, 13000, 16700, 17350, 25000
[L22Ni(2-Pic)2]
[L22Ni(3-Pic)2]
[L22Ni(4-Pic)2]
[L22Ni(PrNH2)2]
[(HL3)NiCl2]·H2O
2.26
Solid
Py
2-Pic
46.9
22.9
19.7
9.6
6800, 18780
9640, 11700, 15000, 15500, 23670
9200, 12000, 15000, 23420
[L3Ni(OH)]
1.58
Solid
Py
2-Pic
6850, 19200
10100, 12460, 15280, 14800, 23790
9900, 12900, 15310, 15530, 23700
[L32Ni(Py)2]
3.19
3.24
3.28
3.30
3.30
Solid
Solid
Solid
Solid
Solid
9800, 11500, 13000, 16100, 24200
9400, 10600, 12900, 15300, 23600
9770, 10400, 12980, 15900, 16080, 23800
9900, 10800, 13600, 16200, 24000
10350, 11600, 13000, 16850, 24900
[L32Ni(2-Pic)2]
[L32Ni(3-Pic)2]
[L32Ni(4-Pic)2]
[L32Ni(PrNH2)2]
[(HL4)NiCl2]·H2O
2.19
Solid
Py
2-Pic
44.0
18.5
6760, 18900
10125, 13000, 15700, 24000
9660, 13000, 15380, 23140

40
N. Al-Awadi et al. / Spectrochimica Acta Part A 65 (2006) 36–43
Scheme 2.
and the planar component band at 18,300–19,000 cm−1. The
data showed a direct proportionality between Nt and the energy
of the band at 6700–6900 cm−1 but inverse relation with the
higher energy band (18,300–19,000 cm−1). The higher energy
band (combination band) provides a measure of the frequency
trend of the planar d–d transition due to: (i) the intensity increase
with decreasing Nt and (ii) the trend of the higher energy band
is opposite to that in the lower energy band.
The electronic spectra of the complex in a Lewis base
as Py or ␣-Pic (Table 2) are quite different from the nujol
mull. The color change with the new spectral features are
taken as evidences for the interaction of the Lewis base lead-
ing to ligand field change around the nickel(II). The spectra
of all complexes display bands with maxima at 9300–10,100,
11,000–13,000, 15,000–16,000 and 22,400–24,400 cm−1 which
are characteristic of tetragonally distorted octahedral nickel(II)
complexes [13,14]. The bands at 9300–10,100, 15,000–15,700
and 23,000–24,400 cm−1 are assigned to ν1[4A2g → T2g],
4
ν2[4A2g → T1g(F)] and ν3[4A2g → T1g(P)] transition, respec-
4
4
tively. The bands at 11,000–13,000 cm−1 can be attributed to the
3
1
3
1
forbidden A2g → Eg(D) and A2g → Eg(G) transition [27].
Furthermore, the splitting of ν2 could be taken as an evidence
for the distortion from the ideal symmetry. The interaction of
these bases with the complexes to form six-coordinate nickel(II)
complexes is presented in Scheme 1.
The ligand field parameters ∆o (splitting parameter),
Bꢀ (Racah parameter of interelectronic repulsion) and β
(nephelauxetic ratio) for these nickel(II) complexes are calcu-

N. Al-Awadi et al. / Spectrochimica Acta Part A 65 (2006) 36–43
41
Table 3
Electronic spectral parameters for the octahedral nickel(II) complexes
Complex
Mediuma
ν1
ν2
ν3
ν2/ν1
Dq
980
Bꢀ
β
Dq/Bꢀ
[(HL1)NiCl2]·3H2O
Py
2-Pic
9800
9500
15515
15240
23250
23000
1.58
1.60
624
649
0.60
0.62
1.57
1.46
950
[(HL2)NiCl2]·H2O
Py
2-Pic
9830
9480
15665
15350
23800
23200
1.59
1.62
983
948
665
674
0.64
0.65
1.48
1.41
[L2Ni(OH)]
Py
2-Pic
10500
9900
15565
15400
23900
23120
1.48
1.56
1050
990
531
588
0.51
0.56
1.98
1.68
[L22Ni(Py)2]
Solid
Solid
Solid
Solid
Solid
9820
9420
9800
10100
10400
16100
15280
15900
16300
16700
24060
23600
23800
24180
25000
1.64
1.62
1.62
1.61
1.61
982
942
980
1010
1040
713
708
686
678
700
0.68
0.68
0.66
0.65
0.67
1.38
1.33
1.43
1.49
1.49
[L22Ni(2-Pic)2]
[L22Ni(3-Pic)2]
[L22Ni(4-Pic)2]
[L22Ni(PrNH2)2]
[(HL3)NiCl2]·H2O
Py
2-Pic
9640
9200
15250
15000
23670
23420
1.58
1.63
964
920
666
721
0.64
0.69
1.45
1.28
[L3Ni(OH)]
Py
2-Pic
10100
9900
15540
15420
23790
23700
1.53
1.55
1010
990
615
628
0.59
0.60
1.64
1.58
[L32Ni(Py)2]
Solid
Solid
Solid
Solid
Solid
9800
9400
9770
9900
10350
16100
15300
15900
16200
16850
24200
23600
23800
24000
24900
1.64
1.65
1.64
1.64
1.63
980
930
967
990
1035
726
713
692
700
713
0.70
0.68
0.66
0.67
0.68
1.35
1.32
1.41
1.41
1.45
[L32Ni(2-Pic)2]
[L32Ni(3-Pic)2]
[L32Ni(4-Pic)2]
[L32Ni(PrNH2)2]
[(HL4)NiCl2]·H2O
Py
2-Pic
10125
9660
15700
15680
24000
23140
1.55
1.62
1012
966
621
656
0.60
0.63
1.63
1.47
3
lated following Eqs. (3)–(5):
values are further evidences for octahedral with A2g ground
state.
∆o = ν1
(3)
(4)
ν2 + ν3 − 3ν1
3.2.2. [L2Ni(Ls)2], Ls = Py, 2-Pic, 3-Pic, 4-Pic or PrNH2
The formation of the solid complexes [L2Ni(Ls)2], Ls = Py,
2-Pic, 3-Pic, 4-Pic or n-PrNH2, as a result of interaction of the
Lewis base (Ls) with [LNi(OH)]2 was proved from the elemental
analysis (Table 1) and can be interpreted on the basis of Eq. (6):
Bꢀ =
15
Bꢀ
β =
(5)
Bo
where Bo = 1041 cm−1 for the free Ni2+ ion.
[LNi(OH)]2 + Ls → [L2Ni(Ls)2] + Ni(OH)2
(6)
The values of Dq for the nickel(II) complexes (Table 3) are
found to be in the 920–1010 cm−1 range, indicating the inter-
mediate ligand field position of the ligands in the nephelauxetic
series, Dq for octahedral nickel(II) complexes vary between
6400 and 12,700 cm−1. The interelectronic repulsion param-
eter Bꢀ was calculated and found to be in the 531–666 and
588–721 cm−1 for the pyridine and ␣-picoline-containing com-
plexes, respectively. These values are lower than that for the free
Ni2+ ion (1041 cm−1) which attributed to the delocalization of
the electrons over the molecular orbitals that encompass both
the metal and the ligands. Furthermore, the values of Bꢀ showed
that the eg-electrons are ␴-antibonding and spend some of their
time on the ligand. The t2g-electrons may become ␲-bonding or
antibonding and spend some of their time on the ligand. Such
delocalization leads to increase in the mean distance between
the d-electrons and therefore reduces the interelectronic repul-
sion parameter Bo. The nephelauxetic ratio β = Bꢀ/Bo for the
complexes (Table 3) indicates the presence of electron delocal-
ization over all the molecular orbitals and therefore a covalent
characterofnickel(II)–ligandbonding. Theratioν2/ν1 andDq/Bꢀ
The room temperature magnetic moments of the solid adducts
(Table 2) are in the range of 3.19–3.30 B.M. characteristic of
either octahedral or five-coordinate high spin nickel(II) com-
plexes [26]. On the basis of the analytical data, the bidentate
and monodentate nature of the anions L1–L4 and Ls, respec-
tively, octahedral structure could be assumed for [L2Ni(Ls)2].
The electronic spectra of the solid adducts (Table 3) are con-
sistent with that reported for a distorted octahedral nickel(II)
complexes [27]. The different ligand field parameters are cal-
culated according to Eqs. (3)–(5) and the results are given in
Table 3. The data showed that: (i) the values of Dq are in the
order PrNH2 > 4-Pic > Py > 2-Pic > 3-Pic. The lower values for
the pyridines than PrNH2 could be attributed to the steric effects
of the pyridine derivatives and suggest that PrNH2 behaves as a
stronger ␴-donor than the pyridine derivatives. (ii) The Dq val-
ues for the solid adducts are different from those obtained for the
solution spectra of the parent complexes in the corresponding
Lewis base. This could be attributed to the formation of differ-
ent species in solution but both have the octahedral structure.

42
N. Al-Awadi et al. / Spectrochimica Acta Part A 65 (2006) 36–43
Table 4
’
The main IR spectral bands (v , cm−1) for the ligands and their nickel(II) complexesa
b
b
b
c
b
c
b
d
Compound
νNH; OH
νC
νC
νN
νC
νNi
νNi
νNi
O(Chel)
pKb
O;C O(Chel)
N(Chel)
N(Chel)
N(Base)
N(Chel)
N(Base)
HL1
3270–3400 br,m
3456s, 3316 m
3220–3400 br,m
3432 s, 3320 m
3538 br,m
1698 vs
1663 s
1679 vs
1648 s
1600 s
1587 m
1602 s
1582 m
[(HL1)NiCl2]·3H2O
468 w
500 w
HL2
[(HL2)NiCl2]·H2O
[L2Ni(OH)]
470 w
487 w
492 w
488 w
490 w
490 w
486 w
498 w
508 w
526 w
515 w
519 w
508 w
500 w
1441 m
1438 m
1440 m
1446 m
1451 m
1449 m
1680 vs
1651 s
1440 m
1455 m
1449 m
1450 m
1450 m
1439 m
1674 vs
1649 s
1395 m
1390 m
1396 m
1395 m
1398 m
1392 m
[L22Ni(Py)2]
[L22Ni(2-Pic)2]
[L22Ni(3-Pic)2]
[L22Ni(4-Pic)2]
[L22Ni(PrNH2)2]
HL3
1558
1555
1558
1560
422 w
432 w
428 w
440 w
448 w
8.77
8.21
8.32
7.98
4.26
3488–3518 br,m
3245–418 br,m
3423 vs, 3266 m
3576 s
1602 s
1581 m
[(HL3)NiCl2]·H2O
466 w
475 w
478 w
480 w
481 w
484 w
478 w
486 w
499 w
530 w
520 w
517 w
508 w
502 w
[L3Ni(OH)]
1400 m
1398 m
1402 m
1396 m
1399 m
1390 m
[L32Ni(Py)2]
[L32Ni(2-Pic)2]
[L32Ni(3-Pic)2]
[L32Ni(4-Pic)2]
[L32Ni(PrNH2)2]
HL4
1550
1556
1553
1552
424
435
428
441
448
8.77
8.21
8.32
7.98
4.26
3496 br,m
3220 br,m
3438 s, 3357 m
1600 vs
1583 s
[(HL4)NiCl2]·H2O
466 w
494 w
a
br: broad; m: medium; s: strong; vs: very strong; w: weak.
Chel: chelate or ligand.
Lewis base.
b
c
d
Base constant for the Lewis base.
(iii) The values of β parameter in case of [L2Cu(Ls)2] are lower
than that of the free nickel(II) suggesting the covalency of the
nickel–ligand bonding. Furthermore, the values for [L2Cu(Ls)2]
are lower than those of [LNi(OH)]2 suggesting that the cova-
lency in the hydroxo-complexes is more than that in the adducts.
(iv) There is direct proportionality between the values of Kb of
the Ls and the values of Dq.
formation in most cases indicating its non-bonding nature
[17–19].
(iv) Thespectra ofthe free ligands displaybands at1674–1698
and 1600–1602 cm−1 due to ν(C O) and ν(C N), respec-
tively. The position of ν(C O) is found to be dependent
on the electronic nature of the p-substituents and can be
ordered as HL1 (H) > HL4 (p-Me) > HL2 (p-Cl) > HL3 (p-
Br), while that due to ν(C N) is not. This could be taken
as an evidence for the involvement of C O in hydrogen
bonding and the presence of the ligands in keto-hydrazo
form.
(v) The spectra of [(HL)NiCl2]·nH2O showed that these two
bands are shifted to lower wavenumbers relative to the
free ligands. Therefore, the ligands act as neutral bidentate
bonded to the nickel(II) through the azomethine nitrogen
and the keto-oxygen atoms.
(vi) The spectra of [LNi(OH)]2 display only a medium band
at 3538–3576 cm−1 which could be assigned to ν(OH)
with the disappearance of the bands characteristic of
ν(NH) and ν(C O). Furthermore, the spectra of these
complexes display another new bands at 1440–1441
and 1395–1400 cm−1 assignable to ν(C O) and ν(N N),
respectively, suggesting the formation of the azo-enol
form with the deprotonation of the enol-OH upon bond-
ing. The appearance of the ν(N N) at lower wavenumbers
relative to the free azo-group in most azo compounds
could be taken as an evidence for the bonding of one of the
nitrogen atoms to the nickel(II). Accordingly, the ligands
act as monobasic bidentate coordinated to the nickel(II)
via one of the azo-nitrogen and the enolato-oxygen atoms
[19–22].
3.3. Infrared spectra
The main IR spectra bands with their tentative assign-
ments for the free ligands and their nickel(II) complexes are
given in Table 4. The following points arise from the data in
Table 4:
(i) The spectra of all ligands display broad medium band
in the 3220–3418 cm−1 range due to the different vibra-
tional modes of NH of the hydrazo moiety. The broad
band at ca. 3400 cm−1 could be taken as an evidence for
the involvement of the NH proton in the formation of
hydrogen bonding of the NH···O type [28].
(ii) The bands at 3220–3245 cm−1 are not greatly affected
in case of [(HL)NiCl2]·nH2O indicating the unchanged
nature of the NH group in these complexes, whereas
the higher wavenumber band (3400 cm−1) appeared at
different positions with different intensities and shapes.
Thisbandcouldbeattributedtothewaterofcrystallization
or hydrogen bonded water molecules.
(iii) The triazole moiety displays a medium–strong band at
1554–1592 cm−1 in the spectrum of the free organic com-
pounds. This band is not greatly affected by complex

N. Al-Awadi et al. / Spectrochimica Acta Part A 65 (2006) 36–43
43
(vii) The spectra of [(HL)NiCl2]·nH2O and [LNi(OH)]2
Acknowledgements
exhibit new bands at 486–530 and 466–487 cm−1 char-
acteristic of ν(Ni O) and ν(Ni N)chel, respectively, sup-
porting our suggestion for the monobasic bidentate nature
of HL2 and HL3 in the hydroxo-complexes.
The authors acknowledge Kuwait University, for the provi-
sion grant SC04/03 and the general facility projects grant nos.
GS01/01 and GS03/01. Also, we would like to thank the under-
graduate student Abrar (Chem 499) and Dr. Alaa Basuony for
their participation in the experimental and library works.
(viii) The spectra of [L2Ni(Ls)2] display additional bands
to those observed in the parent hydroxo-complexes at
1550–1560 and 422–448 cm−1 due to ν(C N) of the hete-
rocyclic nitrogen ring of pyridine derivatives and ν(Ni N)
of Ls, respectively, supporting the bonding of the Ls via
its nitrogen atom. The observation of only one band due
to ν(Ni N) of Ls suggests that the two Ls molecules (as
supported from the elemental analysis) are identical in
their environments.
(ix) It is noted that the ν(Ni O)forthe[L2Ni(Ls)2] appearedat
higher wavenumbers relative to that of [LNi(OH)]2. Fur-
thermore, apparent shifts accompanying the variation of
Ls are observed in the ν(Ni N) of the Ls and ν(Ni O) of
the parent ligands (Table 4). The ν(Ni N) of Ls decreases
in the order: PrNH2 > 4-Pic > 2-Pic > 3-Pic > Py, while the
ν(Ni O) of the parent ligands increases in the order:
PrNH2 > 4-Pic > 2-Pic > 3-Pic > Py, corresponding to the
decrease in the basicity of the coordinated Ls molecules.
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A new nickel(II) complex is prepared by the reaction of
nickel(II) chloride with the benzotriazole hydrazone derivatives.
The products were found to be dependent on the solvent and the
nature of the ligand. All complexes are found to possess a square
planar–tetrahedral in the solid phase based on the electronic
spectra and magnetic moment values, in coordinating solvents
as Py or ␣-picoline to give the corresponding tetragonally dis-
torted octahedral complexes. The electronic spectra and the
calculated parameters confirmed the formation of the octahedral
adducts. Only solid mixed ligand complexes [L2Ni(Ls)2] were
obtained as a result of the reaction of [LNi(OH)]2 with Ls = Py,
2-Pic, 3-Pic, 4-Pic and n-PrNH2. Their electronic spectral and IR
parameters are dependent on the pKb of the Lewis base molecule
(Ls). Furthermore, the electronic transitional energies for the
solid adducts were different from that obtained for the solutions
of the parent complexes in the different Lewis bases but all were
consistent with distorted octahedral nickel(II) complexes. This
means the presence of different ligand fields in solutions from
those in solids.
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