Synthesis and characterization of new NNO ligands and some metal(II) complexes: Crystal structures of (BBH)2Co and (BIH)2Ni

Article abstract of DOI:10.1080/00958972.2012.709627

The ligands 2-acetylbenzimidazole benzoylhydrazone (HBBH) and 2-acetylbenzimidazole isonicotinoylhydrazone (HBIH) were prepared and characterized by elemental analysis, IR, NMR, and mass spectra. The complexes of these ligands with Co(II), Ni(II), Cu(II), and Zn(II) were prepared by the reaction of methanolic acetate salts with the ligands in methanol in a 1:2 metal:ligand mole ratio. M(II)L₂ were characterized based on elemental analysis, IR, NMR, MS, conductance, and electronic spectral measurements. Co(BBH)₂ and Ni(BIH)₂ were crystallographically characterized. They consist of two ligands that give six coordinate bonding to Co(II) and Ni(II) on a meridional plane through benzimidazole ring nitrogen, azomethine nitrogen, and benzoyl or isonicotinoyl oxygen, respectively. Co(BBH)₂ crystallizes in the triclinic space group P and Z=2 at 150K with a=9.9010(3), b=9.9705(4), c=15.8141(6), =96.424(2), =94.1580(10), and =92.153(2). Ni(BBH)₂ crystallizes in the monoclinic space group P₂₁/n and Z=4 at 100K with a=14.3156(2), b=24.7402(4), c=19.8215(3), =90, =98.7761(7), and =90. The metal centers in these complexes have two ligands in a meridional, slightly distorted octahedron.

Full text of DOI:10.1080/00958972.2012.709627

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Synthesis and characterization of
new NNO ligands and some metal(II)
complexes: crystal structures of
(BBH)2Co and (BIH)2Ni
Salman M. Saadeh a
a Chemistry Department, Faculty of Science , Islamic University of
Gaza , PO Box 108, Gaza , Palestine
Accepted author version posted online: 06 Jul 2012.Published
online: 24 Jul 2012.
To cite this article: Salman M. Saadeh (2012) Synthesis and characterization of new NNO ligands
and some metal(II) complexes: crystal structures of (BBH)2Co and (BIH)2Ni, Journal of Coordination
Chemistry, 65:17, 3075-3085, DOI: 10.1080/00958972.2012.709627
To link to this article: http://dx.doi.org/10.1080/00958972.2012.709627
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Journal of Coordination Chemistry
Vol. 65, No. 17, 10 September 2012, 3075–3085
Synthesis and characterization of new NNO ligands
and some metal(II) complexes: crystal structures
of (BBH)2Co and (BIH)2Ni
SALMAN M. SAADEH*
Chemistry Department, Faculty of Science, Islamic University of Gaza,
PO Box 108, Gaza, Palestine
(Received 13 March 2012; in final form 30 May 2012)
The ligands 2-acetylbenzimidazole benzoylhydrazone (HBBH) and 2-acetylbenzimidazole
isonicotinoylhydrazone (HBIH) were prepared and characterized by elemental analysis, IR,
NMR, and mass spectra. The complexes of these ligands with Co(II), Ni(II), Cu(II), and Zn(II)
were prepared by the reaction of methanolic acetate salts with the ligands in methanol in a 1 : 2
metal : ligand mole ratio. M(II)L2 were characterized based on elemental analysis, IR, NMR,
MS, conductance, and electronic spectral measurements. Co(BBH)2 and Ni(BIH)2 were
crystallographically characterized. They consist of two ligands that give six coordinate
bonding to Co(II) and Ni(II) on a meridional plane through benzimidazole ring nitrogen,
azomethine nitrogen, and benzoyl or isonicotinoyl oxygen, respectively. Co(BBH)2 crystallizes
ꢀ
˚
˚
in the triclinic space group P1 and Z ¼ 2 at 150 K with a ¼ 9.9010(3) A, b ¼ 9.9705(4) A,
ꢀ
ꢀ
ꢀ
˚
c ¼ 15.8141(6) A, ꢀ ¼ 96.424(2) , ꢁ ¼ 94.1580(10) , and ꢂ ¼ 92.153(2) . Ni(BBH)2 crystallizes in
˚
˚
the monoclinic space group P21/n and Z ¼ 4 at 100 K with a ¼ 14.3156(2) A, b ¼ 24.7402(4) A,
ꢀ
ꢀ
ꢀ
˚
c ¼ 19.8215(3) A, ꢀ ¼ 90 , ꢁ ¼ 98.7761(7) , and ꢂ ¼ 90 . The metal centers in these complexes
have two ligands in a meridional, slightly distorted octahedron.
Keywords: Cobalt(II) complex; Nickel(II) complex; Schiff bases; NNO Tridentate ligands;
Crystal structures
1. Introduction
Schiff bases have been used as pigments and dyes, catalysts, intermediates in organic
synthesis, and polymer stabilizers. Coordination chemistry of these ligands through
the selection of suitable amine and aldehyde substituents with different steric and
electronic properties may bring about subtle structural and functional variations [1].
A large number of Schiff bases and their metal complexes have been synthesized
for their properties [2], e.g., light emission diode (LED) [3], corrosion inhibitor [4],
potentiometric sensors [5, 6], intermediates to obtain heterocyclic compounds [7],
conjugate polymers containing azomethine [8], and their wide-spectrum biological
activities [9–11].
*Email: ssaadeh2003@yahoo.com
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2012 Taylor & Francis
http://dx.doi.org/10.1080/00958972.2012.709627

3076
S.M. Saadeh
Acylhydrazones are capable of exhibiting keto-enol tautomerism and have interesting
coordination properties to transition metals [12]. A class of hydrazones can be obtained
by condensation of a functionalized aldehyde or ketone with properly substituted
hydrazine to produce tridentate ligands containing donors such as NNO and SNO.
Tridentate monoanionic NNO ligands have been employed for the preparation of
complexes with many metals [13–18]. For example, transition metal(II) complexes of
2-acetylpyridine benzoylhydrazone [19] and a few 2-pyridinecarbaldehyde hydrazone
[20] ligands containing the trifunctional N, N, O-donor system have been synthesized,
and a few were crystallographically characterized.
The interesting properties of transition metal hydrazone complexes promoted us
to synthesize two new hydrazones from the reaction of 1-(1-H-benz[d]imidazol-2-yl-1-
ethanone) [21] with benzoylhydrazine and isonicotinoyl hydrazine. The resulting
ligands were complexed with M(II) (M ¼ Co, Ni, Cu, and Zn). The new ligands,
2-acetylbenzimidazole benzoylhydrazone (BBH) and 2-acetylbenzimidazole isonicoti-
noylhydrazone (BIH), and their complexes were characterized by elemental analysis and
IR, 1H, and 13C NMR and mass spectral data. The structures of Co(BBH)2 and
Ni(BIH)2 were determined by single-crystal X-ray diffraction. The ligands formed bis
complexes and coordinated meridionally through their benzimidazole-N, imine-N, and
carbonyl-O, forming distorted octahedral cis-CoN4O2 complexes.
2. Experimental
2.1. Materials and methods
2-Acetyl benzimidazole was prepared as described in [21]. Phenylenediamine, lactic
acid, potassium permanganate, benzoylhydrazine, and isonicotinoyl hydrazine were
obtained from Merck (Darmstadt, Germany). Reagent grade salts of all cations were
purchased from Aldrich (St. Louis, MO, USA) and used as received. Commercially
available solvents were used as received. FTIR spectra were recorded with a
Thermoscientific FTIR spectrometer using KBr pellets. Melting points were recorded
on a Gallenkamp apparatus and are uncorrected. UV-Vis spectra of dimethylforma-
mide (DMF) solutions of the complexes were recorded on a SHIMADZU UV-Vis
spectrophotometer (UV-1601). Conductivity measurements were made on a PHYWE
conductivity meter. C, H, N, and S microanalyses were performed at the
Microanalytical Center, University of Montreal, Canada, using the ‘‘dynamic flash
combustion method.’’ Accurate mass measurements were performed on an LC-MSD-
TOF instrument from Agilent Technologies (Englewood, CO, USA) in a positive
electrospray mode. Protonated molecular ions (M þ H)þ were used for empirical
formula confirmation. NMR spectra were obtained using a Varian/Agilent VNMRS-
500 spectrometer. 1H- and 13C-NMR spectra were acquired at 500 MHz for solutions in
DMSO-d6 at 21ꢀC. Chemical shifts are in given in ppm relative to TMS.
Crystal structures were determined using a Bruker AXS (Madison, WI, USA),
consisting of a Microsource MX copper source from Incoatec (Geesthacht, Germany)
using a Quasar mirror and mounted on a Platform 3 circles goniometer with a fixed CHI.
The detector is a small area APEX II kept at 4 cm distance from the crystal along the
data collection. It is usually done at 2ꢃ positions using an omega scan mode, by fixing
the detector at ꢃ and omega scanning of 0.3ꢀ for each frame. That arrangement allows

NNO ligands with Ni and Co
3077
the scanning of 600 images for each phi orientations of the crystal. The crystal is kept at
100 K during data collection using a Kryoflex low-temperature system, also from
Bruker. The structures were solved by SHELEXS and refined [22–24] with SHELXL
by full-matrix least-squares on F2. Graphics were drawn with Mercury and Platon
for windows, the final look was performed with the assistance of POV-Ray program.
2.2. Synthesis of ligands
2.2.1. Preparation of 2-acetylbenzimidazole benzoylhydrazone (HBBH, 3a). 2-Acetyl
benzimidazole (1) was condensed with benzoylhydrazine (2a) in a 1 : 1 mole ratio in
ethanol and some drops of acetic acid were used as a catalyst. The reaction mixture was
refluxed for 2 h. Cooling the solution precipitated the corresponding hydrazone in good
yield (78%) (scheme 1). m.p. ¼ 285ꢀC. Its elemental analysis calculated for C16H14N4O
is C, 69.04; H, 5.07; N, 20.14. Found: C, 69.06; H, 5.04; N, 20.14. The IR spectrum
contains prominent peaks (in cmꢁ1) at 3400, 3100, 1670, 1570, corresponding to the two
1
N–H, C ¼ O, and C¼N, respectively. The H-NMR spectrum (in DMSO-d6) contains
peaks at 2.53 (s, 3H), 7.380–8.043 (multiplet, 9H), 13.131 (s, 1H, NH of benzimidazole),
and 15.292 (s, 1H, NH of hydrazone). The mass spectrum contains the peak at 279
corresponding to (M þ 1)þ and at 301 corresponding to (M þ Na)þ. UV-Vis spectrum:
325 nm (log " ¼ 4.27).
2.2.2. Preparation of 2-acetylbenzimidazole isonicotinoylhydrazone (HBIH, 3b).
2-Acetylbenzimidazole isonicotinoylhydrazone was prepared similarly by the conden-
sation of 2-acetyl benzimidazole (1) and isonicotinoylhydrazine (2b). m.p. ¼ 282ꢀC. Its
elemental analysis calculated for C15H13N5O is C, 64.50; H, 4.69; N, 25.08. Found:
C, 64.52; H, 4.66; N, 25.09. The IR spectrum contains prominent peaks (in cmꢁ1) at
3400, 3100, 1670, 1560, corresponding to the two N–H, C¼O, and C¼N, respectively.
1
The H-NMR spectrum (in DMSO-d6) contains peaks at 2.553 (s, 3H), 7.163–8.780
(multiplet, 9H), 11.210 (s, 1H), and 12.732 (s, 1H). The 13C-NMR spectrum (in DMSO-
d6) contains peaks at 163.312, 150.603, 150.229, 149.607, 143.634, 141.325, 135.548,
124.204, 122.494, 122.217, 119.867, 112.606, and 14.209. The mass spectrum contains
the peak at 280 corresponding to (M þ 1)þ. UV-Vis spectrum: 325 nm (log " ¼ 4.19).
Scheme 1. Synthesis of the ligands: 2-acetylbenzimidazole benzoylhydrazone and 2-acetylbenzimidazole
isonicotinoylhydrazone.

3078
S.M. Saadeh
2.3. Preparation of metal complexes
To a well-stirred suspension of the ligand (1.0 mmol) in methanol (25 mL), the metal
acetate, Co(OAc)2 ꢂ 4H2O, Ni(OAc)2 ꢂ 4H2O, Cu(OAc)2 ꢂ H2O, or Zn(OAc)2 ꢂ 2H2O,
(0.5 mmol) solid was added. The resulting solution was stirred for 24 h during which
a solid appeared. The solid was collected by filtration, washed with methanol, diethyl
ether, and dried.
Cis-bis[2-acetylbenzimidazole benzoylhydrazone]cobalt(II) [Co(BBH)2] (4a) tan
solid. Yield: 0.216 g (67%). The m.p. decomposes at 238–240ꢀC, ESI MS: m/z 613.15
(Mþ). Anal. Calcd for (C16H13N4O)2Co ꢂ CH3OH: C, 59.54; H, 4.65; N, 17.36. Found:
C, 61.63; H, 4.91; N, 17.73. ÃM (mMho cm2 molꢁ1): 26.23, and for DMSO solvent 8.46.
UV-Vis (nm, log "): 710 (1.94), 380 (3.71), and 265 (3.57). Significant infrared bands
(cmꢁ1): 3400, 3100, 1570, 1480, 1430, 1360, 1280, 1190, 1140, 1080, 970, 760, 720.
Crystals of Co(BBH)2 deposited in the undisturbed filtrate by slow evaporation at room
temperature for a few days.
Cis-bis[2-acetylbenzimidazole benzoylhydrazone]nickel(II) [Ni(BBH)2] (5a) tan solid.
Yield: 0.159 g (52%). The m.p. decomposes at about 250ꢀC. ESI MS: m/z 613.16 (Mþ).
Anal. Calcd for (C16H13N4O)2Ni: C, 62.66; H, 4.24; N, 18.27. Found: C, 62.15; H, 4.49;
N, 18.07. ÃM (Mho cm2 molꢁ1): 28.64. UV-Vis (nm, log "): 250 (3.74), 275 (4.19), 325
(4.18), 395 (4.55), and 896 (1.38). Significant infrared bands (cmꢁ1): 3400, 3100, 1570,
1470, 1430, 1360, 1290, 1220, 1160, 1070, 980, 760, 690.
Cis-bis[2-acetylbenzimidazole benzoylhydrazone]copper(II) [Cu(BBH)2] (6a) olive
green solid. Yield: 0.176 g (57%). The m.p. decomposes at 243–245ꢀC. ESI MS: m/z
618.16 (Mþ). Anal. Calcd for (C16H13N4O)2Cu: C, 62.18; H, 4.21; N, 18.13. Found:
C, 61.96; H, 4.22; N, 17.93. ÃM (mMho cm2 molꢁ1): 6.47. UV-Vis (nm, log "): 650
(2.14), 400 (3.636), 330 (3.78), 265 (3.60). Significant infrared bands (cmꢁ1): 3400, 3100,
1570, 1520, 1460, 1420, 1360, 1310, 1280, 1160, 1060, 970, 750, 720.
Cis-bis[2-acetylbenzimidazole benzoylhydrazone]zinc(II) [Zn(BBH)2] (7a) yellow
solid. Yield: 0.195 g (63%). The m.p. decomposes at 303ꢀC. ESI MS: m/z 619.15
(Mþ). Anal. Calcd for (C16H13N4O)2Zn: C, 61.99; H, 4.55; N, 18.08. Found: C, 61.34;
H, 4.20; N, 17.94. ÃM (Mho cm2 molꢁ1): 5.83. UV-Vis (nm, log "): 330 (3.95) and 265
1
(3.64). H-NMR (ppm): 13.42 (s, NH of benzimidazole), 7.09–8.14 (br, ArH), 2.75
(s, 3H, CH3). 13C-NMR: 173.679, 151.088, 140.307, 139.633, 137.032, 135.344,
130.921, 128.557, 128.260, 123.960, 123.549, 117.013, 113.009. Significant infrared
bands (cmꢁ1): 3400, 3100, 1570, 1490, 1460, 1430, 1355, 1290, 1190, 1060, 960, 820,
750, 710.
Cis-bis[2-acetylbenzimidazole isonicotinoylhydrazone]cobalt(II) [Co(BIH)2] (4b) tan
solid. Yield: 0.187 g (61%). The m.p. decomposes above 260ꢀC. ESI MS: m/z 615.14
(Mþ). Anal. Calcd for (C15H12N5O)2Co: C, 58.56; H, 3.90, N, 22.77. Found: C, 58.14;
H, 4.28; N, 22.46. ÃM (mMho cm2 molꢁ1): 5.54. UV-Vis (nm, log "): 906 (1.45), 270
(4.37), 315 (4.13), 375 (4.35). Significant infrared bands (cmꢁ1): 3400, 3100, 1570, 1540,
1470, 1370, 1330, 1210, 1150, 1070, 980, 850, 760, 700.
Cis-bis[2-acetylbenzimidazole isonicotinoylhydrazone]nickel(II) [Ni(BIH)2] (5b) tan
solid. Yield: 0.160 g (52%). The m.p. 224ꢀC. ESI MS: m/z 615.15 (Mþ). Anal. Calcd
for (C15H12N5O)2Ni: C, 58.56; H, 3.90; N, 22.77. Found: C, 58.29; H, 4.31; N, 22.14.
ÃM (mMho cm2 molꢁ1): 6.44. UV-Vis (nm, log "): 250 (3.74), 280 (4.14), 395 (4.42), 918
(1.92). Significant infrared bands (cmꢁ1): 3400, 3100, 1570, 1470, 1350, 1240, 1180,
1060, 970, 840, 750, 690. Single crystals of Ni(BIH)2 suitable for X-ray diffraction study

NNO ligands with Ni and Co
3079
were obtained by slow evaporation of the filtrate of reaction at room temperature
for about a week.
Cis-bis[2-acetylbenzimidazole isonicotinoylhydrazone]copperl(II) [Cu(BIH)2] (6b)
olive green solid. Yield: 0.173 g (56%). The m.p. decomposes at 290ꢀC. ESI MS: m/z
620.14 (Mþ). Anal. Calcd for (C15H12N5O)2Cu: C, 58.13; H, 3.87; N, 22.60. Found:
C, 57.89; H, 4.19; N, 22.31. ÃM (mMho cm2 molꢁ1): 9.68. UV-Vis (nm, log "): 275
(4.39), 340 (4.53), 395 (4.65), 686 (2.00). Significant infrared bands (cmꢁ1): 3400, 3100,
1570, 1500, 1460, 1360, 1300, 1170, 1130, 1040, 960, 820, 750, 680.
Cis-bis[2-acetylbenzimidazole isonicotinoylhydrazone]zinc(II) [Zn(BIH)2] (7b) tan
solid. Yield: 0.183 g (59%). The m.p. decomposes at 295ꢀC. ESI MS: m/z 621.15 (Mþ)
Anal. Calcd for (C15H12N5O)2Zn: C, 57.96; H, 3.86; N, 22.54. Found: C, 57.54; H, 4.11;
N, 22.25. ÃM (mMho cm2 molꢁ1): 14.50. UV-Vis (nm, log "): 275 (4.65), 385 (4.49).
1H-NMR (ppm): 11.121 (s, NH of benzimidazole), 7.063–8.598 (br, ArH), 2.776 (s, 3H,
CH3). 13C-NMR: 172.013, 150.762, 150.248, 144.234, 142.220, 140.152, 135.507,
124.208, 123.838, 122.394, 116.995, 113.283, 13.124. Significant infrared bands (cmꢁ1):
3400, 3100, 1570, 1510, 1480, 1420, 1360, 1310, 1240, 1190, 1140, 1070, 1020, 970, 860,
830, 750, 700, 670.
3. Results and discussion
The Schiff base ligands (3a, b) used in this work were synthesized by the condensation
of acid hydrazides (2a–b) with 2-acetylbenzimidazole (1) in a 1 : 1 mole ratio in ethanol
(scheme 1). They were characterized based on physicochemical measurements. Results
1
of elemental analysis, infrared, and H-NMR as well as 13C-NMR and mass spectral
data are in accord with the expected structures. Metallation of these ligands with
metal(II) acetate [metal(II) ¼ Co(II), Ni(II), Cu(II), and Zn(II)] in a 2 : 1 ligand : metal
mole ratio yielded six coordinate complexes 4–7, in which the Schiff bases are N, N,
O-tridentate ligands forming stable five-membered rings by binding with 2-acetylben-
zimidazole-N, the imine-N, and the amide-O atoms (scheme 2).
Scheme 2. Synthesis of some metal(II) complexes of the present ligands.

3080
S.M. Saadeh
3.1. Conductivity measurements
Molar conductance of the complexes in DMSO are almost negligible, indicating
that the complexes are electrically non-conductive. This suggests that each of these
complexes is neutral with two uninegative ligands coordinated to metal(II).
3.2. IR spectra
The IR spectra of the ligands have prominent bands at 3400 and 1670 cmꢁ1 due to N–H
and C¼O stretching modes, respectively. The band due to C¼O disappears on
complexation and a new C–O band at 1040–1080 cmꢁ1 appeared. Bands due to C¼N
and NH of benzimidazole are observed in all spectra of ligands and complexes.
3.3. Mass spectra
Mass spectra of the ligands show a peak due to the molecular mass plus a proton,
(M þ H)þ, consistent with the molecular structure of the ligand. Mass spectra of
complexes show a peak due to ligand plus proton and the molecular ion peak of the
complex, consistent with the proposed structure, and it also indicates that each ligand
lost one proton upon complexation. The molecular ion peaks of the complexes contain
individual peaks for isotopes of the metals with the known relative abundance of each
metal as well as isotopic contributions for carbon and hydrogen which produce (M þ 1)
and (M þ 2) peaks. Here is an explanation of the mass spectrometric data of one sample
with this example being applicable for the other samples as well. In the case of sample
6b, the value of the molecular ion would be m/z ¼ 619. Nevertheless, ESI-MS in the
positive mode was used to measure these samples. Accordingly, the molecular ions
[M þ H]þ were obtained each time instead of [M]þ, and thus, the value 620 instead of
619 was measured. Regarding the isotopic profile, one needs to keep in mind that
the spectrum not only has the isotopic profile of Cu ions but also that of the ligand,
which is connected twice to the Cu ion. Consequently, this compound contains a Cu
atom, 30 C, 24 H, 10 N, and 2 O. Such a compound without Cu would have the isotopic
profile: [M þ H]þ, [M þ H þ 1]þ, and [M þ H þ 2]þ, respectively, with different inten-
sities of course; the profile and the corresponding intensities can be calculated
from automatic calculators in the website [25]. The addition of Cu to the ligands
will lead to the constellation: [M þ H]þ, [M þ H þ 1]þ and [M þ H þ 2]þ, [M þ H þ 3]þ,
[M þ H þ 4]þ. The first isotope of Cu would combine with the ligands resulting in the
molecular ions: [M þ H]þ, [M þ H þ 1]þ, and [M þ H þ 2]þ. The second isotope (which
differs by m/z ¼ 2 from the first) would result in the profile: [M þ H þ 2]þ,
[M þ H þ 3]þ, [M þ H þ 4]þ. As both profiles share the molecular ion [M þ H þ 2]þ,
one obtains five peaks in the spectrum, with the third peak (which corresponds to
[M þ H þ 2]þ) having more intensity than the second peak, [M þ H þ 1]þ. This reflects
that the intensities of both [M þ H þ 2]þ peaks add up.
3.4. NMR spectra
1H-NMR spectra for the ligands contain peaks corresponding to various protons.
13C-NMR spectra for the ligands contain peaks for various carbons in each ligand.
1H-NMR spectra for the complexes of Co(II), Ni(II), and Cu(II) were not helpful for

NNO ligands with Ni and Co
3081
1
identification due to their paramagnetism. H-NMR spectra of the zinc complexes
(7a, b) gave some information about these compounds. No peak was detected for NH
of the amide, evidence for the involvement of nitrogen in coordination to zinc. Some
changes in the aromatic region and its chemical shift can be observed, but the
complexity of the signals does not allow interpretation. The 13C-NMR spectra of 7a
and b show the correct number of signals, 14 signals from 7a and 13 signals from 7b, in
accord with the suggested structures.
3.5. Electronic spectra
Absorption spectra were obtained in DMF and the resulting data are given in Section 2.
A strong band at 375–400 nm and two or more moderately intense bands at 270–345 nm
are observed. The intense band near 395 nm may be associated with a charge transfer
(CT) transition. The bands below 345 nm are also observed in the free ligand (245–
355 nm), and hence can be attributed to intraligand transitions. Zinc complexes, with
d10 electronic configuration, have not allowed the d–d transition. The other complexes
exhibited one weak and broad peak at 710, 896, and 650 nm for 4a–6a and at 918, 906,
and 686 nm for 4b–6b, respectively. These observations are in line with common spectral
features of d-block metal complexes. CT gives intense absorptions, whereas ‘d–d’ bands
are much weaker. In some spectra, CT absorptions mask bands due to ‘d–d’ transitions,
although CT absorptions (as well as ligand-centered n–n* and n–n* bands) often occur
at higher energies than ‘d–d’ absorptions [26].
3.6. Description o f the crystal structures
The crystal of Co(BBH)2 has one CH3OH in the asymmetric unit, but the crystal
of Ni(BIH)2 does not. The complexes display similar coordination geometry. ORTEP
representations of the complexes are shown in figures 1 and 2. Selected bond lengths
and angles are listed in table 1. The structure consists of two tridentate ligands
coordinating cobalt(II) such that the deprotonated ligands produce a neutral cobalt(II)
complex containing a CoN4O2 meridional coordination sphere (figure 1). Each of the
two ligands provides benzimidazole-N, imine-N, and amide-O for coordination,
forming two five-membered chelate rings upon chelation with cobalt(II).
The plane of the distorted octahedron is defined by two oxygen atoms and two
nitrogen atoms, while the two apical positions are occupied by nitrogen atoms.
Distortion of the coordination sphere is due to ligand rigidity, as observed in similar
complexes [19, 20]. The angles at Co show deviations (figure 1 and table 1), for example,
N2–Co–O1 angle: 81.57(5)ꢀ and N2–Co–N22: 82.77(5)ꢀ have deviation from 90ꢀ, while
N2–Co–N02: 178.23(5)ꢀ and O1–Co–N22: 164.31(5)ꢀ deviate from an ideal 180ꢀ. The two
ligands are almost equivalent in their bond angles and distances. Variations of the bond
˚
lengths are 0.004 A at most. Intraligand distances conform with the enolate form of
both ligands. The distances N1–C1, 1.330(2) and N01–C10 , 1.3026(2) are short compared to
0
˚
a typical single bond (1.52 A). C1–O1, 1.2955(19) and C1–O1, 1.2998(19) are lengthened
˚
compared with the normal ketonic bond length of 1.23 A.
Small deviations from planarity of the ligand in Co(BBH)2 are obvious by looking
at the torsion angles: N1–N2–C2–C21 has a dihedral angle of 1.732ꢀ, C2–N2–N1–C1 an
angle of 5.378ꢀ, N2–N1–C1–C11 an angle of 4.362ꢀ in one ligand coordinated to cobalt,

3082
S.M. Saadeh
Figure 1. Structure of Co(BBH)2 (ORTEP representation, 50% probability plot).
Figure 2. Structure of Ni(BIH)2 (ORTEP representation, 50% probability plot).
ꢀ
0
0
0
0
0
0
0
0
and N2 –C2 –C21 –N22 has a dihedral angle of 2.173 , N1 –N2 –C2 –C21 an angle of
3.446 , N2 –N1 –C1 –C11 an angle of 1.777ꢀ in the other.
ꢀ
0
0
0
0
The structure of Ni(BIH)2 has the same general description, the same mode of
bonding and the same pattern of distortion as Co(BBH)2. Angles at Ni are similar
to those in Co(BBH)2 (figure 2). In Ni(BIH)2 the two ligands are equivalent in binding

NNO ligands with Ni and Co
3083
ꢀ
˚
Table 1. Important bond lengths (A) and angles ( ) for Co(BBH)2 and Ni(BIH)2.
Co(BBH)2
Ni(BIH)2
Co–N(20)
Co–N(2)
1.8746(13)
1.8752(14)
1.9054(13)
1.9070(11)
1.9168(11)
1.9222(13)
1.2955(19)
1.330(2)
Ni(1)–N(16)
Ni–N(12)
Ni–N(17)
2.013(3)
2.016(3)
2.080(3)
2.084(3)
2.108(2)
2.129(3)
1.255(4)
1.342(4)
1.367(3)
1.285(4)
1.327(4)
1.463(5)
Co–N(220)
Co–O(10)
Co–O(1)
Ni(1)–N(13)
Ni(1)–O(11)
Ni(1)–O(12)
O(11)–C(11)
N(11)–C(11)
N(11)–N(12)
N(12)–C(12)
N(13)–C(127)
C(12)–C(127)
Co–N(22)
O(1)–C(1)
N(1)–C(1)
N(1)–N(2)
N(2)–C(2)
N(22)–C(21)
C(2)–C(21)
1.3721(18)
1.297(2)
1.336(2)
1.453(2)
N(20)–Co–N(2)
N(20)–Co–N(220)
N(2)–Co–N(220)
N(20)–Co–O(10)
N(2)–Co–O(10)
N(220)–Co–O(10)
N(20)–Co–O(1)
N(2)–Co–O(1)
N(220)–Co–O(1)
O(10)–Co–O(1)
N(20)–Co–N(22)
N(2)–Co–N(22)
N(220)–Co–N(22)
O(10)–Co–N(22)
O(1)–Co–N(22)
178.23(5)
N(16)–Ni1–N(12)
N(16)–Ni1–N(17)
N(12)–Ni1–N(17)
N(16)–Ni1–N(13)
N(12)–Ni1–N(13)
N(17)–Ni1–N(13)
N(16)–Ni1–O(11)
N(12)–Ni1–O(11)
N(17)–Ni1–O(11)
N(13)–Ni1–O(11)
N(16)–Ni1–O(12)
N(12)–Ni1–O(12)
N(17)–Ni1–O(12)
N(13)–Ni1–O(12)
O(11)–Ni1–O(12)
174.08(11)
78.48(13)
99.24(12)
95.98(11)
78.61(11)
92.80(11)
109.62(10)
75.90(10)
94.54(10)
154.29(11)
75.77(12)
106.83(11)
153.85(11)
94.32(10)
89.86(10)
82.98(6)
95.90(6)
81.78(5)
99.37(5)
164.69(5)
99.78(5)
81.57(5)
89.70(5)
91.45(5)
95.89(6)
82.77(5)
92.89(6)
90.12(5)
164.31(5)
Table 2. Crystal data and structure refinement for Co(BBH)2 and Ni(BIH)2.
Empirical formula
Formula weight
Temperature (K)
C
644.57
150
1.54178
Triclinic
ꢀ
P1
33H29CoN8O3
C60H51N20Ni2O4
1233.63
100
1.54178
Monoclinic
P21/n
˚
Wavelength (A)
Crystal system
Space group
Unit cell dimensions (A, )
ꢀ
˚
a
b
c
ꢀ
ꢁ
ꢂ
9.9010(3)
9.9705(4)
15.8141(6)
96.424(2)
94.1580(10)
92.153(2)
1545.60(10), 2
1.385
4.747
668
2.82–69.68
74,747
5759 [R(int) ¼ 0.042]
0.7887 and 0.5554
410
1.048
R1 ¼ 0.0353, wR2 ¼ 0.0972
14.3156(2)
24.7402(4)
19.8215(3)
90
98.7761(7)
90
6938.01(18), 4
1.181
1.131
2556
2.88–71.04
116,846
13,314 [R(int) ¼ 0.058]
0.9558 and 0.8164
779
0.846
R1 ¼ 0.0593, wR2 ¼ 0.1510
3
˚
Volume (A ), Z
Calculated density (g cmꢁ3
)
Absorption coefficient (mmꢁ1
F(000)
)
ꢃ range for data collection (ꢀ)
Reflections collected
Independent reflection
Max. and min. transmission
Parameters
Goodness-of-fit (GOF)a on F2
Final R indices [I 4 2ꢄ(I)]bc
aGOF ¼ ½Æ½wðFo2 ꢁ Fc2Þ ꢃ=M ꢁ Nꢃ (M ¼ number of reflections, N ¼ number of parameters refined).
2
1=2
bR1 ¼ ÆjjFoj ꢁ jFcjj=ÆjFo
cwR2 ¼ ½Æ½wðFo2 ꢁ Fc2Þ ꢃ=ƽwðFo2Þ ꢃꢃ
.
2
2
1=2

3084
S.M. Saadeh
to nickel. Details of the structures of the two complexes are included in table 2 for
comparison.
4. Conclusion
Two tridenatate NNO-donor ligands, 2-acetylbenzimidazole benzoylhydrazone and
2-acetylbenzimidazole isonicotinoylbhydrazone, have been prepared and characterized.
M(II)L2 complexes (M ¼ Co, Ni, Cu, and Zn) have been synthesized and characterized
based on their analytical and spectral data. Crystal structure analyses of Co(BBH)2
and Ni(BIH)2 revealed that each metal is coordinated by two ligands, as monobasic
NNO tridentate, through the benzimidazole ring nitrogen, azomethine nitrogen, and
the carbonyl oxygen to form a distorted octahedral structure.
Supplementary material
Further details of the crystal structure determination can be obtained free of charge
from the Cambridge Crystallographic Data Centre (CCDC), 12 Union Road,
Cambridge CB2 1EZ, UK (Tel. þ44 (0) 1223 762911, Email: kamila@ccdc.cam.ac.uk),
by quoting the depository numbers CCDC 863-076 and CCDC 863-077.
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