Synthesis, spectroscopic and structural characterization of Co(II), Ni(II) and Cu(II) complexes of substituted 2-pyridyl amine based [N,N] chelating ligand

Article abstract of DOI:10.1016/j.poly.2012.08.019

The reaction of N-benzylaminopyridine with the imidoylchloride of N-(2,6-iPr₂C₆H₃)acetamide in the presence of Et₃N affords a new neutral [N,N] chelating ligand, (PhCH ₂)N(2-pyridyl)C{(Me)(N-2,6-iPr₂C₆H ₃)} (L). The reaction of equimolar quantities of L with Cu(NO ₃)₂, CuCl₂ and NiBr₂, respectively, in DCM, acetonitrile and DME yields the corresponding mononuclear complexes L·Cu(NO₃)₂ (1), L·CuCl₂ (2) and L·NiBr₂ (3). Whereas, the reaction of L with CoCl ₂·6H₂O leads to the formation of [HL·CoCl₃] (4) with pyridine nitrogen coordinated to cobalt. Solid state structure of L and compounds 1-4 have been investigated by single crystal X-ray structural analysis. The ligand L shows the E-anti arrangement in the solid state and its mononuclear complex 1 shows six coordinated Cu in a quasi square planar geometry with two long distanced donors; complexes 2 and 3 show distorted tetrahedral arrangement of the substituents around metal ions. Interestingly, the solid state structure of complex 4 reveals C-H?Cl intra-molecular hydrogen bonding and N-H?Cl and C-H?Cl inter-molecular hydrogen bonds. These hydrogen bonding interactions in complex 4 facilitate the formation of an extended 2D network structure.

Full text of DOI:10.1016/j.poly.2012.08.019

Polyhedron 47 (2012) 112–117
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Polyhedron
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Synthesis, spectroscopic and structural characterization of Co(II), Ni(II) and
Cu(II) complexes of substituted 2-pyridyl amine based [N,N] chelating ligand
⇑
Billa Prashanth, Maheswararao Karanam, A.R. Choudhury, Sanjay Singh
Department of Chemical Sciences, Indian Institute of Science Education and Research Mohali, Knowledge City, Sector 81, SAS Nagar, Mohali 140306, Punjab, India
a r t i c l e i n f o
a b s t r a c t
Article history:
The reaction of N-benzylaminopyridine with the imidoylchloride of N-(2,6-iPr2C6H3)acetamide in the
presence of Et3N affords a new neutral [N,N] chelating ligand, (PhCH2)N(2-pyridyl)C{(Me)(@N-2,6-iPr2C6-
H3)} (L). The reaction of equimolar quantities of L with Cu(NO3)2, CuCl2 and NiBr2, respectively, in DCM,
acetonitrile and DME yields the corresponding mononuclear complexes LÁCu(NO3)2 (1), LÁCuCl2 (2) and
LÁNiBr2 (3). Whereas, the reaction of L with CoCl2Á6H2O leads to the formation of [HLÁCoCl3] (4) with pyr-
idine nitrogen coordinated to cobalt. Solid state structure of L and compounds 1–4 have been investigated
by single crystal X-ray structural analysis. The ligand L shows the E-anti arrangement in the solid state
and its mononuclear complex 1 shows six coordinated Cu in a quasi square planar geometry with two
long distanced donors; complexes 2 and 3 show distorted tetrahedral arrangement of the substituents
around metal ions. Interestingly, the solid state structure of complex 4 reveals C–HÁ Á ÁCl intra-molecular
hydrogen bonding and N–HÁ Á ÁCl and C–HÁ Á ÁCl inter-molecular hydrogen bonds. These hydrogen bonding
interactions in complex 4 facilitate the formation of an extended 2D network structure.
Received 28 May 2012
Accepted 8 August 2012
Available online 17 August 2012
Keywords:
Pyridyl amine
Cobalt complex
Tetrahedral nickel complex
Copper complex
Hydrogen bonding
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
(III) are comparatively rare and a few of these have been useful in
the preparation of metal complexes containing metal–metal bonds
Anionic versus neutral ligands and sterically encumbered ver-
sus sterically less demanding ligands have provided the chemists
with a synthetic tool to control the nuclearity of the metal com-
plexes. This subtle control can further be enhanced by incorporat-
ing the chelate character in the ligand. These elegant features can
easily be incorporated in the ligand design by using various syn-
thetic methodologies available at hand. It is due to proper design
of the ligand that has made possible the syntheses of several inter-
esting molecules [1–5]. In recent years, the bis(2-pyridyl) amine
based ligands with C2N3 backbone have emerged as potential spec-
tator ligands in view of their strong [N,N] chelation to metals and
tuneable steric and electronic factors [6]. Additionally, unlike the
mono- or di-anionic ligands these ancillary neutral bis(2-pyridyl)
amines do not engage covalent valence on the metal center and
have proved to be very useful in controlling the coordination num-
ber and nuclearity in the metal complexes.
[7]. Only one report illustrating the [N,N] chelating 2-pyridylbenz-
amidine ligand and its Ni complex for ethylene oligomerization
appeared in 2009 [8]. This ligand (III) possesses a sterically
congested 2,6-iPr2C6H3 group on the benzamidine moiety while
the amine N contains H atom. The steric demand of the substituent
on the benzamidine N atom and the electronic factors of the
Chart 1 depicts well characterized skeletal arrangement in the li-
gands with C2N3 skeleton as reported in the literature, [7–12]. The
ligands are mostly either aryl substituted bis(2-pyridyl) amine
(with the substituents located at different positions of the pyridyl
ring) and/or on the amine nitrogen connecting the two pyridyl rings
(I) or based on quinolylimine (II). However, the pyridylamidines
⇑
Corresponding author.
E-mail address: sanjaysingh@iisermohali.ac.in (S. Singh).
Chart 1. Common [N,N] chelate ligands based on C2N3 skeleton.
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.08.019

B. Prashanth et al. / Polyhedron 47 (2012) 112–117
113
substituents on pyridyl ring can influence the structure and reactiv-
ity of the metal complex. A report on the copper complexes with
bis(2-pyridyl) amine ligands (type I) show that the steric effect of
the substituents on the remote amine N can also play an important
role on the reactivity of the metal complexes [9,10]. These copper
complexes were used for the separation of olefins. Only one ligand
(IV) contains the sterically demanding substituents on amidine
nitrogen as well as on the remote amine nitrogen. The catalyst pre-
pared in-situ from PdCl2 and IV has been used in Suzuki–Miyaura
reaction however, no attempt was made to characterize the metal
complex [12].
We were interested in designing a neutral pyridylamidine li-
gand based on the C2N3 backbone that will offer a [N,N] bidentate
chelate to the metal ions and with the aim to incorporate sterically
demanding substituents on the amidine as well as on the remote
amine nitrogen atom. Consequently, we report here on the synthe-
sis, characterization and structure of the [N,N] donor neutral che-
late ligand (PhCH2)N(2-pyridyl)C{(Me)(@N-2,6-iPr2C6H3)} (L) and
its mononuclear complexes with Co(II), Ni(II) and Cu(II). The steric
effect of the substituents on acetamidine N as well as that of the
amine N have also been explored.
Mohali. The UV–Vis spectra of the complexes were recorded with
LABINDIAÒ UV3000+ UV–Vis spectrophotometer.
2.2. X-ray crystallography: compounds L and 1–4
Single crystal X-ray diffraction data were collected on a Bruker
AXS KAPPA APEX-II CCD diffractometer (monochromatic MoK
a
radiation) equipped with Oxford cryosystem 700 plus at 100 K (ex-
cept L). Data collection and unit cell refinement for the data sets
were done using the Bruker APPEX-II suite, data reduction and
integration were performed by SAINTV 7.685A (Bruker AXS, 2009)
and absorption corrections and scaling were done using SAD-
ABSV2008/1 (Bruker AXS, 2009). The crystal structures were solved
by using either OLEX2 or WINGX package using SHELXS-97 and the
structure were refined using SHELXL-97 [14]. Single crystal data
and refinement results are listed in Table 1. All non hydrogen
atoms were refined anisotropically. Hydrogen atoms were fixed
at geometrically calculated positions and were refined using riding
model except H3a of complex 4. The H(3a) in 4 was located from
difference Fourier map and refined isotropically. DIAMOND version
2.1d was used to generate graphics for the X-ray structures.
2.2.1. Synthesis of (PhCH2)N(2-pyridyl)C{(Me)(@N-2,6-iPr2C6H3)} (L)
To a solution of NEt3 (35 g, excess) and N-benzylaminopyridine
(7.50 g, 40 mmol) in 150 mL dry toluene was added 2,6-iPr2C6H3-
N@C(Me)Cl, (10.20 g, 43 mmol) dropwise at 0 °C. The mixture
was refluxed for 6 h. After removal of all volatiles under vacuo the
residue was taken in 200 mL dichloromethane (DCM) and washed
with H2O (3 Â 100 mL), the organic layer was dried over MgSO4, fil-
tered and all volatiles were removed to afford light brown solid.
This was recrystallized from acetone in 77% yield (11.87 g,
30.8 mmol). X-ray quality crystals were grown by slow evaporation
from acetone. Mp: 120 °C. Anal. Calc. for C26H31N3: C, 81.00; H, 8.10;
N, 10.90. Found: C, 80.27; H, 8.02; N, 10.82%. 1H NMR (400 MHz,
CDCl3, d ppm): 0.94 (d, J = 6.8 Hz, 6H, Me2CH), 1.04 (d, J = 7.2 Hz,
6H, Me2CH), 1.72 (s, 3H, C@NMe), 2.71 (sept, J = 7.2 and 6.8 Hz,
2H, Me2CH), 5.30 (s, 2H, CH2Ph), 6.87–6.90 (m, 2H, Ar), 6.95–6.97
2. Experimental
2.1. General procedures
All chemicals were purchased from Sigma–Aldrich and used
without further purification. Solvents were distilled by standard
methods prior to use. The imidoylchloride, 2,6-iPr2C6H3N@C(Me)Cl
was prepared following the reported procedure [13]. IR spectra of
the complexes were recorded in the range 4500–400 cmÀ1 using a
Perkin Elmer Lambda 35-spectrophotometer. 1H and 13C NMR
spectra were recorded with Brucker 400 MHz spectrometer with
TMS as an external reference. Elemental analyses were recorded
with Thermo Scientific Flash 2000 Series and mass spectrometry
was performed with Thermo Scientific LTQ XL instrument at NIPER
Table 1
Crystallographic data for L and 1–4.
Compound
L
1ÁHNO3
2ÁCH3CN
3Á0.5DME
4
Empirical formula
Formula mass
T (K)
C
26H31N3
C26H32N6CuO9
636.12
100(2)
C26H31N3CuCl2ÁCH3CN
C26H31N3NiBr2Á0.5(DME)
C26H32N3Cl3Co
551.83
100(2)
385.54
298(2)
561.03
649.13
100(2)
100(2)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
monoclinic
P21/c
9.962(5)
18.377(10)
15.640(9)
90.00
126.87(4)
90.00
2291.0(2)
4
monoclinic
C2/c
36.666(3)
8.467(6)
19.4913(14)
90.00
96.154(4)
90.00
6016.0(7)
8
triclinic
monoclinic
C2/c
37.849(5)
8.435(1)
19.621(3)
90.00
114.099(1)
90.00
5718.52(2)
8
monoclinic
P21/c
7.691(2)
22.879(4)
16.761(3)
90.00
112.566(2)
90.00
2723.57(2)
4
ꢀ
P1
9.485(1)
10.584(1)
14.067(1)
79.222(2)
87.074(1)
80.665(1)
1368.65(1)
2
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dcalc (g cmÀ3
)
1.118
0.066
1.405
0.786
1.36
1.017
1.51
3.498
1.346
0.943
l(MoK
a
) (mmÀ1
)
F(000)
832
2648
586
2648
1148
h range (°)
Index range
1.97–25.03
À11 6 h 6 10
À21 6 k 6 21
À18 6 l 6 18
15821
2.1–25.02
À43 6 h 6 43
À10 6 k 6 9
À23 6 l 6 22
29231
2.2–25.0
À9 6 h 6 11
À12 6 k 6 12
À16 6 l 6 15
13981
1.2–29.6
À52 6 h 6 51
À11 6 k 6 11
À26 6 l 6 27
35239
1.8–25.0
À7 6 h 6 9
À25 6 k 6 27
À19 6 l 6 19
14000
Reflections collected
Independent reflections
Data/restraints/parameters
4030
5311
4827
8012
4751
4030/0/267
0.060, 0.163
0.117, 0.215
1.046
5311/0/473
0.055, 0.134
0.070, 0.134
1.044
4827/0/322
0.028, 0.066
0.036, 0.069
1.045
8012/0/441
0.032, 0.072
0.051, 0.086
1.064
4751/0/295
0.055, 0.120
0.104, 0.140
0.996
R1, wR2 [I > 2r
(I)]a
R1, wR2 (all data)a
GOF
D
qmax
,
D
qmin (e Å3)
0.241, À0.404
1.336, À0.903
0.365, À0.292
0.556, À0.510
0.964, À0.758
a
R1
=
R
||Fo| À |Fc||/
R
|Fo|. wR2 = [
R
w(|Fo2| À |Fc2|)2/
R .
w|Fo2|2]1/2

114
B. Prashanth et al. / Polyhedron 47 (2012) 112–117
(m, 3H, Ar), 7.08–7.09 (m, 1H, Ar), 7.15–7.18 (m, 2H, Ar), 7.23 (m,
2H, Ar), 7.45–7.49 (m, 1H, Ar), 8.31–8.33 (m, 1H, Ar). 13C NMR
(100 MHz, CDCl3, d ppm): 18.42, 23.07, 23.57, 28.08, 29.77, 30.96,
52.57, 119.23, 119.61, 122.45, 122.83, 126.64, 126.86, 127.38,
128.02, 128.24, 137.65, 137.95, 139.57, 145.80, 148.67, 155.05,
[MÀCH3]+; 519 [MÀ2CH3ÀH]+; 503 [MÀCH3ÀCl]+; 386 [MÀCoCl3-
ÀH]+. UV–Vis [CHCl3, kmax, nm]: 637, 567.
3. Results and discussion
157.46. IR (
m
cmÀ1, KBr): 2953, 2922, 2862, 1632, 1582, 1474,
3.1. Ligand synthesis and molecular structure
1438, 1374, 1321, 1275, 1227, 1197. EI-MS (m/z): 386 [M]+.
The ligand (PhCH2)N(2-pyridyl)C{(Me)(@N-2,6-iPr2C6H3)} (L)
was synthesized in a single step by the reaction of N-benzylamino-
pyridine with the imidoyl chloride, 2,6-iPr2C6H3N@C(Me)Cl in the
presence of Et3N (Scheme 1). Compound L is a white crystalline so-
lid soluble in common organic solvent. It was characterized by IR,
1H and 13C NMR spectroscopy, EI mass spectrometry, elemental
analysis, and X-ray structural analysis. Sharp absorption bands
around 1632 and 1582 cmÀ1 in the IR spectrum of L can be attrib-
uted to the imine stretching frequency. The 1H NMR spectrum of L
exhibits resonances in accordance with the expected chemical
shifts and pattern. The benzylic CH2 appears as singlet at
5.30 ppm whereas the methyl groups of iso-propyl moiety appear
as two doublets (0.94 and 1.04 ppm) and CH of the same is seen
as a septet at 2.71 ppm. The backbone methyl group appears as a
singlet at 1.72 ppm. The base peak in the EI mass spectrum of L
at m/z 386 corresponds to the molecular ion peak [M]+. The molec-
ular structure of L has been determined by single crystal X-ray dif-
fraction (Fig. 1). Single crystals of L suitable for X-ray structural
analysis were obtained by slow evaporation from acetone. Com-
pound L crystallizes in the monoclinic system with space group
P21/c (Fig. 1 and Table 1).
2.2.2. Synthesis of LÁCu(NO3)2 (1)
To a solution of L (0.19 g, 0.50 mmol) in DCM (30 mL) was
added Cu(NO3)2Á3H2O (0.12 g, 0.50 mmol) in portions. An immedi-
ate green color developed which was stirred for 15 h. This was fol-
lowed by filtration through celite and slow evaporation of the
solvent to afford green crystals suitable for X-ray analysis. The
crystals were isolated from the mother liquor and washed with
hexane. This gave analytically pure compound as green solid in
74% yield (0.21 g, 0.37 mmol). Drying the crystals under vacuum
for longer duration leads to the evaporation of HNO3 molecules
present in the crystal lattice. The data reported below corresponds
to this material. Mp: 220 °C. Anal. Calc. for C26H31N5CuO6: C, 54.49;
H, 5.45; N, 12.22. Found: C, 53.92; H, 5.42; N, 11.45%. IR (m ,
cmÀ1
KBr): 2966, 2927, 2868, 1601, 1559, 1483, 1441, 1398, 1286,
1136, 1088, 1005. EI-MS (m/z): 510 [MÀNO3]+; 386
[MÀCu(NO3)2]+. UV–Vis [CHCl3, kmax, nm]: 716, 384.
2.2.3. Synthesis of LÁCuCl2 (2)
A solution of L (0.38 g, 1.0 mmol) in dry acetonitrile (10 mL) was
added drop wise to a solution of CuCl2 (0.13 g, 1.0 mmol) in dry
acetonitrile (25 mL) at room temperature. The color of the solution
immediately turned to dark brown. Stirring was continued for 12 h
followed by removal of the solvent under vacuum to 10 mL. Stor-
age at À30 °C afforded brown crystals of 2 in 1 week. Drying the
crystals under vacuum eliminates the solvated acetonitrile and
the following data reported is for this material. Crystalline 60%
yield (0.31 g, 0.6 mmol). Mp: 158 °C. Anal. Calc. for C26H31N3CuCl2:
In the solid state L exists as a monomer with E-anti geometry
similar to [N,N]-phenylpyridylbenzamidine [7] that exists as a di-
mer due to intermolecular hydrogen bonding but contrary to
[N,N] 2-pyridylbenzamidine ligand [8] which exist as a monomer
with E-syn configuration. The N(2)–C(6) and C(6)–N(3) bond length
of 1.396(3) and 1.277(3) Å, respectively, correspond to the amino
and imino nature of the bonds which is in good agreement with
the similar moieties reported earlier [7,8]. The C(1)–N(1) distance
C, 60.05; H, 6.01; N, 8.08. Found: C, 60.04; H, 5.99; N 8.09%. IR (
m
cmÀ1, KBr): 2960, 2926, 1597, 1554, 1476, 1436, 1396, 1363,
1258, 1223, 1027. EI-MS (m/z): 483 [MÀCl]+. UV–Vis [CHCl3, kmax
,
nm]: 775, 428.
2.2.4. Synthesis of LÁNiBr2 (3)
A solution of NiBr2 (0.43 g, 2.0 mmol) in dry DME (20 mL) was
prepared at room temperature. To it was added drop wise a solu-
tion of L in 20 mL dry DME (0.77 g, 2.0 mmol) at room temperature.
Color of the solution slowly changed from yellow-brown to deep
purple. The solution was stirred overnight followed by concentra-
tion of the solution under vacuum and storage at À30 °C afforded
purple colored X-ray quality crystals. Drying the crystals under
vacuum leads to the loss of DME molecules present in the crystal
lattice. The following data pertains to this material. Crystalline
88% yield (1.06 g, 1.76 mmol). Mp: 255 °C. Anal. Calc. for C26H31N3-
NiBr2: C, 51.70; H, 5.17; N, 6.96. Found: C, 52.56; H, 5.18; N, 6.95%.
Scheme 1. Synthesis of the [N,N] chelating ligand L.
IR (m
cmÀ1, KBr): 2962, 2922, 1601, 1560, 1475, 1458, 1436, 1349,
1261, 1107. EI-MS (m/z): 605 [M]+; 526 [MÀBr]+; 386 [MÀNiBr2]+.
UV–Vis [CHCl3, kmax, nm]: 983, 503.
2.2.5. Synthesis of [HLÁCoCl3] (4)
To a solution of L (0.19 g, 0.5 mmol) in DME (30 mL) was added
CoCl2Á6H2O (0.12 g, 0.5 mmol). Color of the solution gradually
turned to blue and stirring was continued for 20 h. The blue solu-
tion was filtered through celite and removal of DME under reduced
pressure afforded blue solid which was washed with hexane and
dried under vacuo. Crystalline 56% yield (0.15 g, 0.28 mmol). Mp:
235 °C. Anal. Calc. for C26H32N3CoCl3: C, 56.59; H, 5.84; N, 7.61.
Found: C, 58.74; H, 6.03; N, 7.35%. IR (
m
cmÀ1, KBr): 3428, 2963,
Fig. 1. Molecular crystal structure of L. All hydrogen atoms have been omitted for
2923, 1599, 1435, 1390, 1260, 1095, 1025. EI-MS (m/z): 538
clarity. Thermal ellipsoids have been drawn at 50% probability.

B. Prashanth et al. / Polyhedron 47 (2012) 112–117
115
within the pyridine ring is 1.330(3) Å. The N(2)–C(6)–N(3) of the
ligand is arranged in a non linear fashion with an angle of
116.30(2)°. The angles C(1)–N(2)–C(6) and N(1)–C(1)–N(2) are
122.8(2)° and 117.4(2)°, respectively, which are similar to the re-
ported values [7,8].
3.2. Copper(II) complexes (1 and 2) and their crystal structure
Reaction of L with 1 equiv of Cu(NO3)2Á3H2O in DCM affords
LÁCu(NO3)2 (1). Compound LÁCu(NO3)2 is a green crystalline solid
that melts at 220 °C. The IR spectral analysis gave the preliminary
indication of formation of the metal complexes with L in addition
to the color change and improved solubility of the metal salts.
The IR spectrum of
1 shows C@N vibrations at 1600 and
1559 cmÀ1 which is around 30 cmÀ1 red shifted as compared to
the ligand. The nitrate absorption bands appear at 1483, 1286
and 1005 cmÀ1. The UV–Vis spectrum shows a broad absorption
centered at 13965 cmÀ1 = 291 L molÀ1 cmÀ1) assignable to the
(e
2Eg ? 2Tg2g transition for an octahedral geometry of the complex
[15]. Another high energy band at 26040 cmÀ1 = 1650 L molÀ1
cmÀ1) may be assigned to a charge transfer transition.
Fig. 3. Molecular structure of LÁCuCl2 complex 2. All hydrogen atoms and solvated
acetonitrile molecule have been deleted for clarity. Thermal ellipsoids are drawn at
50% probability.
(e
-
Compound LÁCu(NO3)2 crystallize in monoclinic system with
space group C2/c (Table 1). The molecular structure of this complex
reveals the nitrate coordination to copper in a bidentate mode
which was also initially envisaged by the IR spectrum of this com-
plex. The C2N3Cu six member ring is non planar in a boat confor-
mation with Cu(1) and N(2) forming the bow and stern of the
boat. The C(13)–N(1), C(22)–N(3) and C(13)–N(2) bond lengths of
1.304(5), 1.343(5) and 1.386(5) Å, respectively, are slightly longer
than that of the free ligand, vide-supra. The Cu atom in this com-
plex resides in a quasi square-planar geometry and two additional
long distanced oxygen ligands at axial positions making Cu as six
coordinated. The quasi square plane consists of two oxygen atoms
from two nitrate molecules [Cu(1)–O(1) 2.045(3) and Cu(1)–O(4)
1.994(3) Å] and two nitrogen atoms [Cu(1)–N(1) 1.965(3) and
Cu(1)–N(3) 1.950(5) Å] of the ligand. The oxygen atoms O(2) and
O(5) of two nitrate ions coordinate to Cu(1) as distant axial sites
with a distance of 2.457(4) and 2.433(3) Å, respectively (Fig. 2).
The N(1)–Cu(1)–N(3) and O(1)–Cu(1)–O(4) angles in the quasi
suare plane are 91.36(3)° and 86.61(1)°, respectively. The angle
around Cu(1) with the distanced oxygen atoms O(2)–Cu(1)–O(5)
is 130.32(1)°. Other metric parameters for 1 agree well with that
of similar moieties [16–19].
The reaction of L with one equivalent of anhydrous CuCl2 in dry
acetonitrile easily affords LÁCuCl2 (2). Compound 2 is a red-brown
solid that melts at 158 °C. The IR spectrum of 2 shows the ligand
C@N vibrations (1597 and 1554 cmÀ1) which show negative shift
as compared to the free ligand and also in consistence with the for-
mation of complex 1. Crystals of 2 suitable for X-ray structure anal-
ysis were grown from acetonitrile at À30 °C. Complex 2 crystallizes
ꢀ
in triclinic system with P1 space group. The UV–Vis spectrum
shows a broad absorption centered at 12900 cmÀ1
(
e
= 178 L
molÀ1 cmÀ1) due to d–d transition for tetrahedral geometry of
Cu(II) [15]. The other high energy band at 23360 ( = 1318
e
L molÀ1 cmÀ1) may be assigned to a charge transfer transition.
The molecular structure of 2 shows the expected chelate com-
plex with Cu residing in a distorted {ꢀ11%, considering the ob-
served sum of the bond angles around Cu and comparing this
value with that for an ideal Td (656.8°) and for D4h (720.0°)} tetra-
hedral arrangement of two N atoms of the ligand and two chloride
ions (Fig. 3 and Table 1). The C2N3Cu six member ring is puckered,
the Cu(1)–N(1) and Cu(1)–N(3) bond lengths of 1.970(2) and
1.965(2) Å are in good agreement with 1. The C(13)–N(3), C(13)–
N(2), C(5)–N(2) and C(5)–N(1) bonds in the C2N3Cu chelate ring,
respectively, are 1.297(3), 1.387(3), 1.414(3) and 1.343(3) Å, which
are slightly longer than the corresponding distances in free ligand.
The Cu–Cl distances are 2.249(5) and 2.224(6) Å similar to the re-
ported values [7]. The N(3)–Cu(1)–N(1) angle of 89.92(7)° in 2 is
narrower than that in 1. The other bond angles Cl(1)–Cu(1)–Cl(2)
99.20(2)°,
N(3)–Cu(1)–Cl(1)
139.25(5)°,
N(3)–Cu(1)–Cl(2)
103.81(5)°, N(1)–Cu(1)–Cl(1) 97.71(5)°, and N(1)–Cu(1)–Cl(2)
134.08(5)° also show significant deviation from the regular tetra-
hedral bond angle.
3.3. Nickel complex (3) and its molecular structure
Reaction of L with 1 equiv of NiBr2 in dimethoxyethane (DME)
affords LÁNiBr2 (3). Compound 3 is a purple crystalline solid that
melts at 255 °C. It has been characterized by IR, elemental analysis
and its structure elucidated by single crystal X-ray technique. IR
spectrum of 3 shows C@N vibrations at 1601 and 1560 cmÀ1 which
Fig. 2. Molecular structure of copper nitrate complex (1) with the ligand L. The
HNO3 molecule present in lattice has been deleted. All hydrogen atoms have been
deleted for clarity. Thermal ellipsoids are drawn at 50% probability.

116
B. Prashanth et al. / Polyhedron 47 (2012) 112–117
by-product of the reaction is a yellow solid which has been
investigated by IR spectroscopy; a sharp band at 3552 cmÀ1 as-
signed to OH functionality of cobalt hydroxo species. The powder
X-ray diffraction pattern of this material (see Supplementary data)
is identical to that reported for ClCo(OH) in a similar study [27].
The IR spectrum of 4 shows the NH stretching frequency at
3428 cmÀ1 and the C@N stretch is observed at 1599 and
1559 cmÀ1
.
The complex shows two bands at 15700 cmÀ1
(e ) (e )
= 284 L molÀ1 cmÀ1 and 17635 cmÀ1 = 201 L molÀ1 cmÀ1
which are the split components of 4A2 ? 4T1(P) (
m3) transition in
a tetrahedral geometry of the complex [15].
Blue block like crystals of 4 were obtained by slow diffusion of
pentane into a DME solution of 4. Compound 4 crystallizes in the
monoclinic system with space group P21/c (Fig. 5 and Table 1).
The C(1)–N(1) and C(13)–N(3) bond length of 1.338(6) and
1.320(6) Å are slightly longer than the corresponding bonds in free
ligand [1.330(3) and 1.277(3) Å], indicative of the coordination of
N(1) to cobalt and protonation of the imine, respectively. The aver-
age Co–Cl bond length is 2.249(1) Å, which is comparable to the
Co–Cl bond length found in the related compound (C9H8N)[CoCl3
(C9H7N)] (2.2541(8) Å) [20]. The Co(1)–N(1) bond length of
2.071(4) Å is also similar to that in (C9H8N)[CoCl3(C9H7N)]
(2.0643(19) Å) [20]. The tetrahedral arrangement around Co(1)
comprising of N(1)–Co(1)–Cl angles lie in the range 101.23(10)–
114.91(11)°. It has been well documented in the literature that
metal bound halide ions can act as good hydrogen bond acceptors
with O–H and N–H donors [21] in the form of M–ClÁ Á ÁH
interaction and this hydrogen bonding interaction leading to
extended 2D or 3D structure is more common in halide rich
complexes [22–24].
In chlorine rich complex 4 three chlorine atoms on cobalt par-
ticipate in hydrogen bonding (Fig. 6). The iminium cation links
the neighboring Co(II) anion via N(3)–H(3a)Á Á ÁCl(1) hydrogen bond
to form 1D network. The H(3a)Á Á ÁCl(1) contact range is 2.37(2) Å
and the N(3)–H(3a)Á Á ÁCl(1) angle is 154(1)°, this is in the normal
accepted range of strong N–HÁ Á ÁCl hydrogen bonding interaction
in such complexes [25–27]. In addition, the weak C–HÁ Á ÁCl
interactions along with N(3)–H(3a)Á Á ÁCl(1) interactions lead to
the formation of 2D network in the solid state structure of 4
(supplementary information includes distances and angles of these
interactions).
Fig. 4. Molecular crystal structure of LÁNiBr2 (3). DME molecule and all hydrogen
atoms have been deleted for clarity. Thermal ellipsoids are drawn at 50%
probability.
is around 30 cmÀ1 red shifted as compared to the free ligand and
consistent with that of the LÁCu(NO3)2 complex. The electronic
spectrum of the complex 3 shows absorption bands at 10170
(e
= 81.5 L molÀ1 cmÀ1) and 19880 cmÀ1
(e
= 224.5 L molÀ1 cmÀ1
)
attributable to the 3T1(F) ? 3A2(m2
)
and ? 3T1(P) transitions,
respectively, for the tetrahedral geometry of the complex.
Crystals of 3 suitable for X-ray structural analysis were grown
from DME at À30 °C. Compound LÁNiBr2 crystallizes in monoclinic
system with space group C2/c. Asymmetric unit of 3 contains a
molecule of LÁNiBr2 and half a molecule of DME. The molecular
structure of 3 shows distorted tetrahedral geometry around nickel
(Fig. 4 and Table 1).
The C2N3Ni six-member ring is non planar in a boat conforma-
tion with Ni(1) and N(2) forming the bow and stern of the boat, this
is very similar to that of [2,6-iPr2C6H3–N@C(Ph)–NH–Py]NiBr2. The
N(1)–C(5), C(5)–N(2), N(2)–C(13), and C(13)–N(3) bond distances
1.347(3), 1.408(3), 1.390(3), and 1.299(3) Å, respectively, within
the C2N3Ni ring are slightly longer than the free ligand, and compa-
rable with [2,6-iPr2C6H3–N@C(Ph)–NH–Py]NiBr2. The Ni(1)–N(1)
and Ni(1)–N(3) of the C2N3Ni ring are 1.980(2) and 1.972(2) Å.
The Ni(1)–Br(1) 2.375(4) and Ni(1)–Br(2) 2.347(4) Å bond dis-
tances agree well with that reported for [2,6-iPr2C6H3–N@C(Ph)–
NH–Py]NiBr2 [8]. The N(1)–Ni(1)–N(3) angle of 90.14(7)° in 3 is
comparable to the same angle reported for [2,6-iPr2C6H3–
N@C(Ph)–NH–Py]NiBr2 [92.6(1)°] but the Br(1)–Ni(1)–Br(2) angle
In conclusion, we have reported on the synthesis and structure
of 2-pyridyl amine based [N,N] chelating ligand and its complexes
with Co(II), Ni(II) and Cu(II).
of 114.20(1)° in
3 is narrower than that in [2,6-iPr2C6H3–
N@C(Ph)–NH–Py]NiBr2 [123.94(3)°] [8].
3.4. Cobalt complex (4) and its crystal structure
The reaction of CoCl2Á6H2O with the ligand L affords the com-
plex [HLÁCoCl3] (4) featuring a tetrahedral Co(II) ion. Contrary to
the Cu or Ni complexes it does not form the usual chelate and
the cobalt is seen to coordinate with the pyridine nitrogen only
in addition to three chloride ions leaving cobalt ion in a tetrahedral
arrangement and the imine nitrogen of the 2,6-iPr2C6H3 bears a
proton to maintain the electrical neutrality. It is presumed that
hydrolysis of cobalt(II) chloride occurs followed by generation of
HCl which protonates the ligand to produce [HLÁCoCl3] (4). The
Fig. 5. Crystal structure of [LHÁCoCl3] (4). All hydrogen atoms except H(3a) have
been deleted for clarity. Thermal ellipsoids are drawn at 50% probability.

B. Prashanth et al. / Polyhedron 47 (2012) 112–117
117
Fig. 6. The 2D network structure of 4 arising due to the inter-molecular hydrogen bonds [N(3)ÀH(3a)Á Á ÁCl(1) along a axis] and [C(2)ÀH(2)Á Á ÁCl(2) along b axis].
[5] (a) T. Nguyen, A.D. Sutton, M. Brynda, J.C. Fettinger, G.J. Long, P.P. Power,
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Acknowledgments
(b) Y.-C. Tsai, H.-Z. Chen, C.-C. Chang, J.-S.K. Yu, G.-H. Lee, Y. Wang, T.-S. Kuo, J.
Am. Chem. Soc. 131 (2009) 12534;
B.P. and S.S. acknowledge the financial support, Grant No. SR/
FT/CS-009/2009, from Department of Science and Technology
(DST), India. M.K. thanks DST for a fellowship. The authors thank
IISER Mohali for NMR and X-ray facility and for all other infrastruc-
tural support.
(c) A. Sekiguchi, R. Kinjo, M. Ichinohe, Science 305 (2004) 1755.
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CCDC 882164, 882165, 882166, 882167, and 882168 contain
the supplementary crystallographic data for L, 1, 3, 2, and 4,
respectively. 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.
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