Synthesis, characterization, molecular structure and self-assembly of some cobalt(III) complexes derived from diacetyl- and benzil bisaroylhydrazones

Article abstract of DOI:10.1016/j.poly.2013.10.009

Cobalt(III) complexes of the general formula [Co(HL¹-R)(L ¹-R)], [Co(HL²-R)(L²-R)] and [Co(HL ¹-R)₂]Cl, where H₂L¹-R and H ₂L²-R referred respectively to diacetyl and benzil bis(aroylhydrazone), have been prepared and characterized by IR, electronic, ESI and ¹H NMR spectral measurements. The bisaroylhydrazone ligand in these complexes acts either as mononegative N₂O tridentate, [HL ^1,2-R]^-, or dinegative N₂O tridentate, [L ^1,2-R]^2-. Coordination occurs via the two diimine nitrogens and the deprotonated enolimine oxygen of one aroylhydrazone moiety, leaving the other one uncoordinated. The X-ray crystal structures of [Co(HL ²-CH₃)(L²-CH₃)] and [Co(HL ¹-R)₂]Cl (R = H, CH₃) show that the molecular units are assembled into dimers through π-π stacking and hydrogen-bonded interactions respectively in the neutral and cationic complexes. Both types of dimers are linked together giving linear chains which in turn are interconnected to produce layers. These layers are further assembled with each other in [Co(HL²-CH₃)(L²-CH₃)] and [Co(HL¹-H)₂]Cl to generate three-dimensional frameworks, while in the cationic complex [Co(HL¹-CH₃)₂]Cl, the molecular units form chains of dimers with a one-dimensional tubular structure.

Full text of DOI:10.1016/j.poly.2013.10.009

Polyhedron 68 (2014) 164–171
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis, characterization, molecular structure and self-assembly
of some cobalt(III) complexes derived from diacetyl- and benzil
bisaroylhydrazones
Nahed M.H. Salem a, Amal R. Rashad a, Laila El Sayed a, Wolfgang Haase b, Magdi F. Iskander a,
⇑
a Chemistry Department, Faculty of Science, Alexandria University, PO Box 426, Ibrahimia, Alexandria 21321, Egypt
b Institut fur Physikalische Chemie, AG Kondensierte Materie, Fachbereich Chemie, Technische Universitat Darmstadt, Petersenstrasse 20, D-64287 Darmstadt, Germany
a r t i c l e i n f o
a b s t r a c t
Cobalt(III) complexes of the general formula [Co(HL1–R)(L1–R)], [Co(HL2–R)(L2–R)] and [Co(HL1–R)2]Cl,
where H2L1–R and H2L2–R referred respectively to diacetyl and benzil bis(aroylhydrazone), have been
prepared and characterized by IR, electronic, ESI and 1H NMR spectral measurements. The bisaroylhyd-
razone ligand in these complexes acts either as mononegative N2O tridentate, [HL1,2–R]À, or dinegative
N2O tridentate, [L1,2–R]2À. Coordination occurs via the two diimine nitrogens and the deprotonated
enolimine oxygen of one aroylhydrazone moiety, leaving the other one uncoordinated. The X-ray crystal
structures of [Co(HL2–CH3)(L2–CH3)] and [Co(HL1–R)2]Cl (R = H, CH3) show that the molecular units are
Article history:
Received 11 May 2013
Accepted 1 October 2013
Available online 23 October 2013
Keywords:
Diacetyl bis(aroylhydrazones)
Benzil bis(aroylhydrazones)
Co(III) complexes
assembled into dimers through
p–p stacking and hydrogen-bonded interactions respectively in the
neutral and cationic complexes. Both types of dimers are linked together giving linear chains which in
turn are interconnected to produce layers. These layers are further assembled with each other in
[Co(HL2–CH3)(L2–CH3)] and [Co(HL1–H)2]Cl to generate three-dimensional frameworks, while in the
cationic complex [Co(HL1–CH3)2]Cl, the molecular units form chains of dimers with a one-dimensional
tubular structure.
X-ray crystal structure
Self-assembly
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
diacetylbis(aroylhydrazonato)cobalt(III) cation [8] indicates a dis-
torted octahedral geometry with the bisaroylhydrazone in the
Condensation of
a
-dicarbonyl compounds with aroylhydrazines
equatorial plane and the two bases in the axial positions. More-
over, X-ray diffraction studies of a series of organotin complexes
with benzil bis(benzoylhydrazone) revealed that in the distorted
octahedral arrangement the ligand behaves as a tetradentate
N2O2 dianion in the equatorial plane and the organic groups are
positioned in the axial sites [9]. In the case of a 5-coordinate mono-
nuclear Cu(II) complex with diacetyl bis(benzoylhydrazone),
CuLMeOH, the X-ray crystal structure indicated that the Cu(II)
ion is in a square pyramidal environment where the dianionic
N2O2 tetradentate ligand occupies the basal plane, while the
methanol oxygen atom lies at the apex [10]. Another mode of coor-
dination is exhibited by the base adduct of nickel diacetyl bis
(benzoylhydrazone) with 1,10-phenanthroline, where the X-ray
crystal structure revealed that the bishydrazone ligand acts as an
anionic N2O tridentate ligand, leaving one enolimide oxygen atom
uncoordinated [11]. This is different from the monobase adduct of
nickel phenylglyoxal bisaroylhydrazone with imidazole in which
the ligand functions as a dinegative ligand with N2O donor atoms,
namely the imine nitrogen, enolimine oxygen and hydrazine nitro-
gen, forming two 5- and 6-membered rings [3]. In a more peculiar
affords the corresponding bisaroylhydrazones (Scheme 1). The
ligating properties of these bisaroylhydrazones have attracted
considerable research interest due to their versatility in binding
to metal ions in different ways. They can function as dinegative tet-
radentate N2O2 ligands, coordinating via the diimine nitrogens and
the two enolimine oxygens, forming neutral complexes with diva-
lent metal ions. The increased electron delocalization in the dian-
ion produces a square planar N2O2 environment, well designed
for Ni(II) and Cu(II) ions which have a strong tendency to form
square planar complexes [1–3]. In fact, neutral [Ni(L)] complexes
have been synthesized with diacetyl- and benzil bis(benzoylhyd-
razone) and their X-ray crystal structures [2,3] have shown that
the bishydrazone ligand acts as a dinegative tetradentate N2O2
ligand, forming three 5-membered chelating rings. Using the same
argument for mononuclear octahedral complexes, the doubly
deprotonated N2O2 bishydrazone would lie in the equatorial plane
[3,4–7]. The X-ray structure analysis of a nickel diacetyl bis
(aroylhydrazone) bisimidazole adduct [3] and a trans diammine
way, the X-ray crystal structure of dimeric [Cu2(
diacetyl bis(benzoylhydrazone) acts as bridging ligand. Each Cu(II)
l-L)2] reveals that
⇑
Corresponding author. Tel.: +20 3 3911794.
E-mail address: m.iskander@link.net (M.F. Iskander).
0277-5387/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2013.10.009

N.M.H. Salem et al. / Polyhedron 68 (2014) 164–171
165
methanol (50 ml). The reaction mixture was heated under reflux
with constant stirring for 2 h, during which time a stream of air
was bubbled through the mixture to ensure the complete oxidation
of any Co(II) intermediates that may have been formed in solution.
The resulting brown solution was filtered to separate any insoluble
impurities, and then evaporated to half its volume. The brown
Co(III) complex, which separated on cooling to room temperature,
was isolated by filtration, washed with diethyl ether, then dried in
air.
2.2.1. [Co(HL1–H)2]Cl (1)
Yield 42%. Anal. Calc. for C36H34N8O4ClCo: C, 58.66; H, 4.65; N,
Scheme 1.
15.20. Found: C, 58.45; H, 4.51; N, 14.92%. IR (KBr, cmÀ1): 3080
m(N–H), 1675 amide I
m
(C@O), 1595
m
(C@N–N@C), 1550,
m(N@C–
C@N), 1533 amide II [d(N–H) +
m
(C–N)], 1322 amide III
m(C–N);
is in a distorted square planar N2O2 environment formed by two
halves of two different ligand molecules, giving rise to a double
helical structure [12]. An unusual mode of chelation of diacetyl
bis(benzoylhydrazone) is shown in a dinuclear dimeric neutral
Pd(II) complex, where the ligand behaves as dianionic N3O
tetradentate [13]. Each metal center is coordinated in a square
planar structure to two imine nitrogens and one deprotonated
enolic oxygen belonging to one ligand and the deprotonated amide
nitrogen of the other ligand. The versatility of benzil bis(ben-
zoylhydrazone) has also been demonstrated in the various molec-
ular architectures adopted by the binuclear [Pb(L)]2 and [Cd(L)]2
complexes as well as the trinuclear [Zn(L)]3 and [Cu(L)]3 helicates
[2]. In the binuclear complexes, each metal center is in a 5-coordi-
nate environment formed from one tetradentate N2O2 dianion and
the oxygen of another ligand acting as bridge in a strongly TBP
structure. However in the trinuclear complexes, each bishydrazone
is pentadentate N3O2, where it acts as tridentate N2O towards one
metal center via the imine nitrogen, the oxygen of one arm and the
deprotonated amide nitrogen of the other arm, and also functions
as bidentate NO, being bound to another metal center via the
remaining imine nitrogen and oxygen of the bishydrazone ligand
[2].
The various modes of chelation and the flexibility of diacetyl-
and benzil bis(aroylhydrazone) stimulated our attention to investi-
gate the ligating behavior and the coordination sites of these
ligands with regard to the octahedral geometry of cobalt(III) ions.
In this context, cationic [Co(HL1–R)2]Cl (R = H and CH3) as well as
neutral [Co(HL1–R)(L1–R)] (R = H, CH3, CH3O, Cl) and [Co(HL2–
R)(L2–R)] (R = CH3 and Cl) bisligand Co(III) complexes have been
synthesized and characterized. The X-ray molecular and supramo-
lecular structures of [Co(HL1–H)2]Cl, [Co(HL1–CH3)2]Cl and [Co
(HL2–CH3)(L2–CH3)] will be discussed.
UV–Vis. (methanol, saturated solution, kmax/nm): 290, 350sh,
403, 520. ESI (+) MS (DMF/CH3OH) m/z Calcd. (RA): 380.1
(379.2832) (75.6), [Co(L1–H)]1+; 452.0 (452.3683) (6.0), [Co(L1–
H)(DMF)]1+; 525.0 (525.4721) (5.2) [Co(L1–H)(DMF)2]1+; 647.2
(645.6025) (70.0) [{Co2(L1–H)3}(DMF)2(MeOH)2 + 2H]2+
;
701.2
(701.6490) (70.4) [Co(HL1–H)2]1+; 759.0 (759.5744) (5.0) [{Co(L1–
H)}2 + H]1+ 1H NMR (CDCl3, ppm): 2.63 (s, 6H, 2CH3–C@N), 2.67
.
(s, 6H, 2CH3–C@N), 7.35 (m, 4H, aromatic), 7.45 (m, 6H, aromatic),
7.57 (s, 2H, aromatic), 8.00 (m, 4H, aromatic), 8.13 (m, 4H, aro-
matic), 11.90 (s, 2H, N–H).
2.2.2. [Co(HL1–CH3)2]Cl (2)
Yield 40%. Anal. Calc. for C40H42N8O4ClCo: C, 60.57; H, 5.34; N,
14.13. Found: C, 60.34; H, 5.04; N, 13.85%. IR (KBr, cmÀ1): 3080
m
(N–H), 1670 amide I
C@N), 1533 amide II [d(N–H) +
(C–N); UV–Vis. (methanol, saturated solution, kmax/nm): 300,
m
(C@O), 1560
m(C@N–N@C), 1555 m(N@C–
(C–N)], 1375s, 1325s amide III
m
m
355sh, 400, 525. ESI (+) MS (DMF/CH3OH) m/z Calcd. (RA): 407.0
(407.3369) (90) [Co(L1–CH3)]1+; 480.2 (480.4312) (5.50) [Co(L1–
CH3)(DMF)]1+
;
553.0 (553.5256) (4.20) [Co(L1–CH3)(DMF)2]1+
;
;
686.2 (687.6829) (55.63) [{Co2(L1–CH3)3}(DMF)2(MeOH)2 + 2H]2+
757.2 (757.7563) (80.5) [Co(HL1–CH3)2]1+; 814.0 (815.6815) (6.2)
[{Co(HL1–CH3)}2]1+ 1H NMR (CDCl3, ppm): 2.17 (s, 6H, 2CH3–
.
C@N), 2.45 (s, 6H, 2CH3–C@N), 2.30 (s, 12H, 4 p-CH3), 7.26 (8H, aro-
matic), 7.78 (4H, aromatic), 8.10 (4H, aromatic), 11.80 (s, 2H, NH).
2.3. Preparation of neutral [Co(HL1–R)(L1–R)]ÁnH2O (R = H, CH3, CH3O,
Cl) and [Co(HL2–R)(L2–R)]ÁnH2O (R = CH3, Cl) complexes
The neutral cobalt(III) complexes [Co(HL1–R)(L1–R)]ÁnH2O
(R = C6H5, p-CH3C6H4, p-CH3OC6H4, p-ClC6H4) and [Co(HL2–R)
(L2–R)]ÁnH2O (p-CH3C6H4, p-ClC6H4) were prepared using the same
procedure described for the preparation of the cationic complexes
(Section 2.2), but using cobalt(II) acetate tetrahydrate instead of
cobalt(II) chloride hexahydrate.
2. Experimental
2.1. Materials
2.3.1. [Co(HL1–H)(L1–H)] (3)
Diacetyl and benzil were purchased from Aldrich and were used
as received. Hydrazine hydrate (99%), cobalt(II) acetate tetrahy-
drate and cobalt(II) chloride hexahydrate (BDH) were used without
further purification. The aroylhydrazines were prepared as previ-
ously described [14] by the hydrazinolysis of carboxylic methyl es-
ters in methanol. The diacetyl and benzil bis(aroylhydrazone) were
prepared using the same procedure previously described [1–3].
Yield 42%. Anal. Calc. for C36H33N8O4Co: C, 61.71; H, 4.75; N,
15.99. Found: C, 61.10; H, 4.744; N, 15.64%. IR (KBr, cmÀ1):
3430m
1298m amide III
(log )): 310(4.64), 404(4.41), 645(sh). ESI (+) MS (DMF/CH3OH)
m/z Calcd. (RA): 380.1 (379.2832) (100) [Co(L1–H)]1+
452.0
(452.3683) (7.41) [Co(L1–H)(DMF)]1+
525.0 (525.4721) (6.21)
[Co(L1–H)(DMF)2]1+ 647.2 (645.6025) (60.45) [{Co2(L1–H)3}
(DMF)2(MeOH)2 + 2H]2+ 701.2 (701.6490) (45.19) [Co(HL1–H)
(L1–H) + H]1+ 760.0 (759.5744) (5.20) [{Co(L1–H)}2 + H]1+ 1H
m
(O–H), 1595s
m
(C@N–N@C), 1549s
m(N@C–C@N), 1376vs,
(N–N). UV–Vis. (DMF, kmax/nm
m(C–N), 967m
m
e
;
;
2.2. Preparation of the Co(III) cationic complexes [Co(HL1–R)2]Cl
(R = H, CH3)
;
;
;
.
A hot solution of cobalt(II) chloride hexahydrate (1.0 mmol) in
methanol (50 ml) was added dropwise to a stirred suspension of
the bis(aroylhydrazone), H2L1–R (R = H, CH3), (2.2 mmol) in
NMR (CDCl3, ppm): 2.22 (s, 6H, 2CH3–C@N), 2.52 (s, 6H, 2CH3–
C@N), 7.37 (m, 12H, aromatic), 7.90 (s, 4H, aromatic), 8.17 (s, 4H,
aromatic), 11.89 (s, 1H, OH).

166
N.M.H. Salem et al. / Polyhedron 68 (2014) 164–171
2.3.2. [Co(HL1–CH3)(L1–CH3)]ÁH2O (4)
2.4. Physical measurements
Yield 38%. Anal. Calc. for C40H43N8O5Co: C, 62.01; H, 5.59; N,
14.46. Found: C, 62.18; H, 5.492; N, 14.31%. IR (KBr, cmÀ1):
The infrared spectra were recorded on a Perkin-Elmer 1430
Data system and/or a Perkin-Elmer (FT-IR) Paragon 1000 PC spec-
trophotometer. Solid samples were examined as KBr discs. The
UV–Vis absorption spectra were recorded on a V-530 Jasco, UV–
Vis recording spectrophotometer, using 10 mm quartz cells and/
or a double beam ratio recording Lambda 4B Perkin-Elmer spectro-
photometer. 1H NMR spectra were recorded on a Bruker WM 300
using tetramethylsilane (TMS) as an internal standard. ESI mass
spectra were recorded on an Esquire-LC from Bruker Daltonic Neb-
ulizer 10 psi (dry gas 8 L minÀ1, dry temperature 250 °C). The the-
oretical isotopic distribution patterns for ionic species were
generated using the ISOFORM program and/or Sheffield University
Chemputer software [15]. Elemental analyses (C, H, N) were per-
formed at the Micro analytical Laboratory, at the Institut für
Organische Chemie Technische Universität, Darmstadt, Germany.
X-ray diffraction data for complexes 1 and 2 were collected on a
Nonius CADY diffractometer, while diffraction data for 7 were col-
lected on an XCalibur diffractometer. Graphite monochromated Mo
3438m
1301m amide III
(log )): 313(4.58), 401(sh), 500(sh), 634(sh). ESI (+) MS (DMF/
m
(O–H), 1605s
m
(C@N–N@C), 1535s
m(N@C–C@N), 1375vs,
m
(C–N), 969m
m(N–N). UV–Vis. (DMF, kmax/nm
e
CH3OH) m/z Calcd. (RA): 407.0 (407.3369) (100) [Co(L1–CH3)]1+
;
480.2 (480.4312) (8.50) [Co(L1–CH3)(DMF)]1+; 553.0 (553.5256)
(5.40) [Co(L1–CH3)(DMF)2]1+; 686.2 (687.6829) (55.63) [{Co2(L1–
CH3)3}(DMF)2(MeOH)2 + 2H]2+; 757.2 (757.7563) (60.20) [Co(HL1–
CH3)(L1–CH3) + H]1+; 815 (815.6815) (5.10) [{Co(L1–CH3)}2 + H]1+
.
1H NMR (CDCl3, ppm): 2.18 (s, 6H, 2CH3–C@N), 2.49 (s, 6H,
2CH3–C@N), 2.38 (s, 12H, 4 p-CH3), 7.26 (8H, aromatic), 7.78 (4H,
aromatic), 8.05 (4H, aromatic); 11.88 (s, 1H, OH).
2.3.3. [Co(HL1–OCH3)(L1–OCH3)] (5)
Yield 38%. Anal. Calc. for C40H41N8O8Co: C, 58.54; H, 5.04; N,
13.65. Found: C, 57.98; H, 5.019; N, 13.35%. IR (KBr, cmÀ1):
3432m
1307s amide III
(log )): 340(4.59), 493(sh), 639(sh). ESI (+) MS (DMF/CH3OH) m/z
Calcd. (RA): 439.2 (439.3356) (100) [Co(L1–OCH3)]1+
512.0
(512.4299) (7.8) [Co(L1–OCH3)(DMF)]1+; 584.2 (585.5244) (6.5)
m(O–H), 1603s
m
(C@N–N@C), 1558
m(N@C–C@N), 1373vs,
m(C–N), 967m
m(N–N). UV–Vis. (DMF, kmax/nm
e
Ka radiation (k = 0.71013 Å) was used in all cases. The structures
;
were solved by direct methods with SHELXS-97 [16] and refined with
full-matrix least squares on F2 using SHELXL-97 [16]. Drawings of the
molecules were produced with ORTEP3 [17] or PLATON [18]. Crystal
data and details concerning data collection and structure refine-
ment for [Co(HL1–H)2]Cl (1), [Co(HL1–CH3)2]Cl (2) and [Co(HL2–
CH3)(L2–CH3)] (7) are collected in Table 1. Selected bond distances
and bond angles for both (1) and (2) are listed in Table 2, while
those of (7) are given in Table 3.
[Co(L1–OCH3)(DMF)2]1+
;
735.0 (735.6810) (60.0) [{Co2(L1–O
CH3)3}(DMF)2(MeOH)2 + 2H]2+; 821.0 (821.7539) (35.3) [Co(HL1–
OCH3)(L1–OCH3) + H]1+; 878.9 (879.6790) (8.9) [{Co(L1–OCH3)}2 +
H]1+ 1H NMR (CDCl3, ppm): 2.20 (s, 6H, 2CH3C@N), 2.49 (s, 6H,
.
2CH3C@N), 3.91 (s, 12H, 4p-OCH3), 6.89 (s, 8H, aromatic), 7.86 (s,
4H, aromatic), 8.14 (s, 4H, aromatic), 11.75 (s, 1H, OH).
2.3.4. [Co(HL1–Cl)(L1–Cl)]ÁH2O (6)
Yield 48%. Anal. Calc. for C36H31N8O5Cl4Co: C, 50.49; H, 3.65; N,
13.08. Found: C, 50.55; H, 3.613; N, 12.87%. IR (KBr, cmÀ1): 3428m
3. Results and discussion
m(O–H), 1593s
m(C@N–N@C), 1545
m(N@C–C@N), 1377vs, 1293m
3.1. Synthesis and characterization
amide III (C–N), 970m
m
m
(N–N). UV–Vis. (DMF, kmax/nm (loge
)):
316(4.55), 434(sh). ESI (+) MS (DMF/CH3OH) m/z Calcd. (RA):
The reaction of cobalt(II) acetate tetrahydrate with two equiva-
lents of diacetyl bis(aroylhydrazone), H2L1–R (R = H, CH3, CH3O, Cl),
and benzil bis(aroylhydrazone), H2L2–R (R = CH3, Cl), in methanol
followed by air oxidation afforded the neutral bisligand Co(III)
complexes [Co(HL1–R)(L1–R)]ÁnH2O (R = H, CH3, CH3O, Cl) and
[Co(HL2–R)(L2–R)] (R = CH3, Cl) respectively. On using Co(II) chlo-
ride, the reaction proceeded with the formation of the cationic
bisligand complexes, [Co(HL1–R)2]Cl (R = H and CH3). Both the neu-
tral and cationic Co(III) complexes are diamagnetic and display d–d
spectra diagnostic of distorted octahedral Co(III) complexes. The
solution spectra of both the neutral [Co(HL1–R)(L1–R)]ÁnH2O
(R = H, CH3, CH3O, Cl) and [Co(HL2–R)(L2–R)] (R = CH3, Cl) and cat-
ionic [Co(HL1–R)2]Cl (R = H and CH3) complexes in DMF are more
or less similar and display absorptions at 350–400, 480–500 and
630–650 nm due to different transitions from singlet 1A1g to higher
448.1 (448.1728) (100) [Co(L1–Cl)]1+; 521.2 (521.2579) (11.85)
[Co(L1–Cl)(DMF)]1+
;
751.2 (750.4388) (93.28) [{Co2(L1–Cl)3}
;
(DMF)2(MeOH)2 + 2H]2+
837.1 (839.4282) (11.00) [Co(HL1–
Cl)(L1–Cl) + H]1+; 897.0 (897.3548) (6.10) [{Co(L1–Cl)}2 + H]1+
.
2.3.5. [Co(HL2–CH3)(L2–CH3)] (7)
Yield 53%. Anal. Calc. for C60H49N8O4Co: C, 71.71; H, 4.91; N,
11.15. Found: C, 71.37; H, 4.862; N, 11.02%. IR (KBr, cmÀ1):
3431m
III (C–N), 1020m
ESI (+) MS (DMF/CH3OH) m/z Calcd. (RA): 531.5 (531.4784)
(100) [Co(L2–CH3)]1+ 605.4 (604.5635) (28.57) [Co(L2–CH3)
(DMF)]1+; 677.5 (677.6486) (44.36) [Co(L2–CH3)(DMF)2]1+; 873.5
(873.8428) (44.78)
[{Co2(L2–CH3)3}(DMF)2(MeOH)2 + 2H]2+
1005.5 (1006.041) (67.67) [Co(HL2–CH3)(L2–CH3) + H]1+ 1H NMR
m
(O–H), 1583m
m(C@N–N@C), 1442s, 1375vs, 1269m amide
m
m
(N–N). UV–Vis. (DMF, kmax/nm (log
e
)): 351(sh).
;
;
1
.
1T1g and T2g states [19].
(CDCl3, ppm): 2.38 (d, 12H, 4p-CH3), 7.17 (m, 28H, aromatic),
7.26 (s, 3H, aromatic), 8.08 (s, 5H, aromatic), 12.61 (s, 1H, OH).
The IR spectra of the neutral complexes [Co(HL1–R)(L1–R)]ÁnH2O
(R = H, CH3, CH3O, Cl and [Co(HL2–R)(L2–R)] (R = CH3, Cl) lack
absorptions which could be attributed to
(C@O)] and amide II [d(NH) + (C–N)], but show a series of absorp-
tion bands at 3430–3440, 1610–1590 and 1550–1540 cmÀ1 respec-
tively due to hydrogen bonded (OH), oxazine (C@N–N@CO) and
diimine (N@C–C@N) stretching vibrations of the protonated enoli-
mine aroylhydrazone residue. Different from the spectra of the neu-
tral complexes, the IR spectra of the cationic complexes show
absorption bands at 3060, 1673 and 1533 cmÀ1 respectively due
m(N–H), amide I
2.3.6. [Co(HL2–Cl)(L2–Cl)]Á1.5H2O (8)
[m
m
Yield 55%. Anal. Calc. for C56H37N8O4Cl4CoÁ1.5H2O: C, 60.39; H,
3.62; N, 10.06. Found: C, 59.95; H, 3.390; N, 10.05. IR (KBr,
m
m
cmÀ1): 3440w
1326s amide III
m
m
(O–H), 1582m, 1526vs
m(C@N–N@C), 1380vs,
m
(C–N), 940m (N–N). UV–Vis. (DMF, kmax/nm
m
(log
OH) m/z Calcd. (RA): 572.0 (572.3144) (100) [Co(L2–Cl)]1+; 645.3
(645.3995) (3.70) [Co(L2–Cl)(DMF)]1+
934.0 (934.1423) (5.0)
[Co2(L2–Cl)3(DMF)2(MeOH)2 + 2H]2+; 1087.0 (1087.7114) (53.38)
[Co(HL2–Cl)(L2–Cl) + H]1+ 1145.2 (1146.6459) (5.0) [{Co(L2–
Cl)}2 + H]1+ 1H NMR (CDCl3, ppm): 7.31 (d, 28H, aromatic), 7.71
(s, 4H, aromatic), 8.15 (s, 4H, aromatic), 12.75 (s, 1H, OH).
e)): 341(4.61), 399(sh), 443(sh), 465(sh). ESI (+) MS (DMF/CH3-
;
to m(N–H), amide I [m(C@O)] and amide II [d(NH) + m(C–N)] of the
ketoamide aroylhydrazone residue (Scheme 2-i). The spectra also
;
show intense absorptions at 1595 and 1550 cmÀ1 respectively due
.
to
m(C@N–N@CO) and diimine m(N@C–C@N) stretching vibrations
of the deprotonated enolimine aroylhydrazone residue.

N.M.H. Salem et al. / Polyhedron 68 (2014) 164–171
167
Table 1
Crystal data and structure refinement for [Co(HL1–H)2]Cl (1), [Co(HL1–CH3)2]Cl (2) and [Co(HL2–CH3)(L2–CH3] (7).
(1)
(2)
(7)
Empirical formula
Formula weight
T (K)
C
36H34ClCoN8O4
C40H42ClCoN8O4
793.20
303(2)
1.54180
monoclinic
C2/c
C60H49CoN8O4
1005.00
293(2)
735.11
299(2)
0.71093
monoclinic
P21/n
k (Å)
0.71073
Crystal system
Space group
Unit cell dimensions
a (Å)
b (Å)
c (Å)
triclinic
ꢀ
P1
11.358(4)
12.837(5)
24.392(9)
90
94.99(4)
90
3543(2)
4
24.167
14.082(2)
11.373(2)
90
90.54(1)
90
3870.3(11)
4
1.361
12.4715(8)
12.7650(8)
18.533(1)
71.988(6)
88.919(6)
69.843(5)
2621.2(3)
2
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dcalc (Mg mÀ3
)
1.378
0.609
1528
1.273
0.383
1048
Absorption coefficient (mmÀ1
F(000)
)
4.533
1656
Crystal size (mm)
h (°)
Limiting indices
0.52 Â 0.45 Â 0.25
1.68–25.98
13 6 h 6 4,
À15 6 k 6 0,
À30 6 l 6 30
9603
0.18 Â 0.13 Â 0.05
3.63–66.92
À28 6 h 6 28,
À16 6 k 6 3,
0 6 l 6 13
0.40 Â 0.24 Â 0.08
2.75–26.37
À12 6 h 6 15,
À14 6 k 6 15,
22 6 l 6 23
18668
Reflections collected
4420
Independent reflections (Rint
Completeness to h
Absorption correction
Maximum and minimum transmission
Refinement method
)
6913 (0.0540)
25.98 99.8%
none
0.8626 and 0.7404
Full-matrix least-squares on F2
6913/0/451
1.040
3444 (0.0582)
66.92 100.0%
psi-scan
0.7322 and 0.5025
Full-matrix least-squares on F2
3444/1/252
0.991
10544 (0.0264)
26.37 98.5%
semi-empirical from equivalents
0.9700 and 0.8619
Full-matrix least-squares on F2
10544/0/665
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
1.063
Final R indices (I > 2
r
(I))
R1 = 0.0677, wR2 = 0.1787
R1 = 0.1024, wR2 = 0.2005
1.110 and À1.502
R1 = 0.0565, wR2 = 0.1112
R1 = 0.1744, wR2 = 0.1412
0.272 and À0.320
R1 = 0.0644, wR2 = 0.1251
R1 = 0.1085, wR2 = 0.1430
0.533 and À0.353
R indices (all data)
Largest difference in peak and hole (e ÅÀ3
)
Table 2
Selected bond distances (Å) and bond angles (°) for [Co(HL1–H)2]Cl (1) and [Co(HL1–CH3)2]Cl (2).
[Co(HL1–H)2]Cl (1)
[Co(HL1–CH3)2]Cl (2)
Co1–O1
Co1–N1
Co1–N3
Co1–O2
Co1–N5
Co1–N7
1.900(2)
1.842(3)
1.919(3)
1.896(2)
1.839(3)
1.907(3)
N1–Co1–N7
O2–Co1–N5
N5–Co1–N7
N1–Co1–O2
O1–Co1–N3
O2–Co1–N7
N1–Co1–N5
O1–C3–N2
C1–N1–N2
C2–C1–N1
C1–C2–N3
C2–N3–N4
N3–N4–C28
N4–C28–O4
99.88(11)
81.69(10)
82.03(11)
96.47(10)
163.65(10)
163.61(10)
176.71(12)
123.1(3)
123.6(3)
111.4(3
Co1–O1
Co1–N1
Co1–N3
Co1–O1–
Co1–N1–
Co1–N3–
1.909(3)
1.851(3)
1.927(4)
1.909(3)
1.851(3)
1.927(4)
N1–Co1–O1
82.16(4)
100.80(16)
95.50(14)
81.58(16)
178.83(12)
163.68(13)
163.68(13)
124.2(4)
106.6(3)
124.2(3)
112.2(4)
113.0(4)
118.8(4)
117.9(4)
121.7(5)
N1–Co1–N3–
N1–– Co1–O1
N1–Co1–N3
N1–Co1–N1
O1––Co1–N3–
O1–Co–N3
O1–C1–N2
C1–N2–N1
C8–N1–N2
N1–C8–C9
C3 - O1
C3–N2
N2–N1
C1–N1
1.296(4)
1.331(4)
1.367(4)
1.294(4)
1.302(4)
1.398(4)
1.367(4)
1.214(4)
1.285(3)
1.334(4)
1.362(4)
1.304(4)
1.306(4)
1.402(4)
1.329(5)
1.218(5)
C1–O1
C1–N2
N1–N2
C8–N1
C9–N3
N3–N4
C10–N4
C10–O2
1.292(4)
1.342(5)
1.363(5)
1.295(5)
1.299(5)
1.413(5)
1.356(6)
1.219(6)
113.1(3)
118.9(3)
117.7(3)
121.2(3)
C2–N3
N3–C9–C8
C9–N3–N4
C10–N4–N3
O2–C10–N4
N3–N4
C28–N4
C28–O4
C21–O2
C21–N6
N5–N6
C19–N5
C20–N7
N7–N8
C10–N8
C10–O3
O2–C21–N6
N6–N5–C19
N5–C19–C20
C19–C20–N7
C20–N7–N8
N7–N8–C10
N8–C10 O3
123.8(3)
123.5(3)
111.6(3)
113.0(3)
118.9(3)
119.8(3)
122.0(4)
– (1 À x, y, Àz + 1/2), Symmetry transformation used to generate equivalent atoms.
The stoichiometry together with the IR and UV–visible spectral
data of the isolated neutral octahedral Co(III) complexes reveal that
only one aroylhydrazone residue of each of the two bisaroylhyd-
razone ligands is coordinated to the central Co(III) via two diimine
nitrogens and a deprotonated enolimine oxygen atom. The other
two aroylhydrazone residues remain uncoordinated, where one
of the aroylhydrazones exists in the deprotonated enolimine form
(Scheme 2-iii), while the other remains protonated (Scheme 2-ii).
This is evident from the absence of both
m(N–H) and m(C@O)
stretching vibrations from their IR spectra. In the cationic octahe-
dral Co(III) complexes, both of the two coordinated aroylhydrazone
residues are in the deprotonated enolimine form, similar to that

168
N.M.H. Salem et al. / Polyhedron 68 (2014) 164–171
Table 3
Selected bond lengths (Å) and bond angles (°) for [Co(HL2–CH3)(L2–CH3)] (7).
Co1–O2
Co1–N3
Co1–N5
Co1–O1
Co1–N1
Co1–N7
1.927(2)
1.851(2)
1.925(3)
1.904(2)
1.853(3)
1.917(3)
O2–Co1–N3
N1–Co1–N5
O2–Co1–N1
N3–Co1–N5
O2–Co1–N5
N3–C01–N1
O1–Co1–N7
81.92(10)
100.15(11)
95.72(10)
82.12(11)
164.00(10)
175.53(12)
164.46(10)
C5–O1
C5–N2
N2–N1
N1–C1
C2–N7
N7–N8
N8–C29
C29–O4
1.289(4)
1.338(5)
1.364(3)
1.305(5)
1.310(5)
1.390(3)
1.302(5)
1.287(4)
O1–C5–N2
C5–N2–N1
N2–N1–C1
N1–C1–C2
C1–C2–N7
C2–N7–N8
N7–N8–C29
123.9(9)
107.2(3)
124.8(3)
111.3(3)
113.8(3)
122.0(3)
114.8(3)
O2–C13
C13–N4
N4–N3
N3–C3
1.296(4)
1.325(5)
1.369(3)
1.297(5)
1.311(5)
1.388(4)
1.302(5)
1.296(4)
O2–C13–N4
C13–N4–N3
N4–N3–C3
N3–C3–C4
C3–C4–N5
C4–N5–N6
N5–N6–C21
124.4(3)
107.4(3)
124.0(3)
111.6(3)
114.1(3)
119.6(3)
115.3(3)
C4–N5
Fig. 1. Molecular structure of [Co(HL1-H)2]Cl (1).
N5–N6
N6–C21
C21–O3
cluster [Co2(L1–R)3(DMF)2(CH3OH)2 + 2H]+2. The spectra are also
characterized by the presence of the dimeric Co(II) species
[{Co(L1–R)}2 + H]1+, originating from the reduction of [Co(L1–R)]1+
followed by dimerization. The (+) ESI mass spectra of the neutral
[Co(HL2–R)(L2–R)] complexes (7 and 8) show similar spectral pat-
terns as recorded for 3–6.
O3–H30
O4–H30
1.16(3)
1.30(3)
C21–O3–H30
O3–H30–O4
H30–O4–C29
122.44(3)
167.64(3)
122.45(3)
proposed for the neutral complexes. The uncoordinated
aroylhydrazone residue remains in the neutral ketoamide form
(Scheme 2-i).
3.2. X-ray molecular structures and self-assembly of complexes 1 and 2
The 1H NMR spectra of the cationic complexes (1 and 2) derived
from diacetyl bis-aroylhydrazone) display two magnetically non-
equivalent methyl singlets at ca. 2.63 and 2.67 ppm, in addition
to a series of multiplets due to the hydrazide aromatic protons.
The spectra also show a sharp singlet at 11.90 ppm, attributed to
the N–H proton of the uncoordinated ketoamide residue. The 1H
NMR spectra of the neutral complexes (3–6) exhibit almost the
same spectral pattern. However, the broad singlet at ca.
11.88 ppm, which disappears on deuteration, can be attributed to
the hydrogen bonded OH proton of the uncoordinated enolimine
residue. The spectra of the neutral complexes (7 and 8) are domi-
nated by a series of aromatic multiplets due to the two phenyl
rings of the diimine moiety and the hydrazide aromatic protons.
The spectra also show the characteristic broad OH singlet of the
uncoordinated enolimine residue.
The X-ray crystal structures of both [Co(HL1–H)2]Cl (1), Fig. 1,
and [Co(HL1–CH3)2]Cl (2), Fig. 2, consist of the bisligand cationic
molecular unit [Co(HL1–R)2]1+ (R = H or CH3) and chloride ClÀ as
a counter ion. Different from Ni(II) and Cu(II) [3,10] complexes de-
rived from diacetyl bisaroylhydrazone ligands, where the bis-
aroylhydrazone behaves as a dianionic N2O2 tetradentate ligand,
each of (HL1–H)1À and (HL1–CH3)1À in 1 and 2, respectively, acts
as a monoanionic N2O tridentate ligand. The Co(III) centre in both
1 and 2 has a distorted octahedral geometry where the two bis-
aroylhydrazone ligands are bound to the Co(III) center via the
two imine nitrogens and one deprotonated enolimine oxygen,
forming two 5-membered chelate rings. The ketoamide oxygen in
each ligand remains uncoordinated. Taking the standard uncer-
tainties (su) into account, the bond distances between Co1 and
the donor atoms N1, N3 and O1 of one ligand in 1, Table 2, (Co1–
N1 = 1.842(3), Co–N3 = 1.919(3) and Co1–O1 = 1.900(2) Å) are
more or less equal to those between Co1 and the donor atoms
N5, N7 and O2 (Co–N5 = 1.839(3), Co1–N7 = 1.907(3) and Co1–
O2 = 1.896(2) Å) of the other ligand. In 2, however, the two
bisaroylhydrazone ligands are equivalent and the bond distances
between Co1 and the donor atoms N1, N3 and O1 (Co1–
N1 = 1.851(3), Co1–N3 = 1.927(4) and Co1–O1 = 1.909(3) Å) are
slightly longer than the corresponding bond distances recorded
The (+) ESI mass spectra of both the cationic [Co(HL1–R)2]Cl (1
and 2) and neutral [Co(HL1–R)(L1–R)] (3–6) complexes are more
or less similar and display peaks corresponding to the molecular
ion [Co(HL1–R)2]1+
. The spectra also show the monoligand
[Co(L1–R)]1+ cation which is generated from the molecular ion by
the expulsion of one of the bisaroylhydrazone ligands. Solvation
of [Co(L1–R)]1+ resulted in the formation of [Co(L1–R)(DMF)]1+
and [Co(L1–R)(DMF)2]1+ cations. Recombination of [Co(L1–R)]1+
with [Co(HL1–R)2]1+ followed by solvation gave rise to the cationic
Scheme 2.

N.M.H. Salem et al. / Polyhedron 68 (2014) 164–171
169
and Cg1, Cg2 and Cg3 are respectively the corresponding centroids.
interactions, Table 4, are
The structure parameters of these CHÁ Á Á
p
within the range reported for this type of non-covalent bond
interactions [21,22]. The dimers are assembled together via pairs
of reciprocal hydrogen bonds (C24H24Á Á ÁO3, C24Á Á ÁO3 = 3.281 Å)
as well as reciprocal pairs of interactions (C17H17CÁ Á ÁC35,
C17Á Á ÁC35 = 3.377 Å), giving rise to a chain of dimers extended
along the a axis. The chains of dimers are connected together via
pairs of interactions (C18H18AÁ Á Á
well as pairs of reciprocal short contacts, between aromatic H31
and methyl H36B (H31Á Á ÁH36B = 2.151 Å), thus generating
p4, CH18AÁ Á ÁCg4 = 3.425 Å) as
a
two-dimensional layer extended parallel to the ab plane. The layers
are further interconnected through hydrogen bonds (C33H33Á Á ÁO3)
(C33Á Á ÁO3 = 3.520 Å) [23] to form a three-dimensional framework.
The two Cl1 counter anions are enclosed in the cavity between
the dimeric units and each Cl1 anion is involved in hydrogen bond
formation with the two hydrazinic protons N4H and N8H
(N4HÁ Á ÁCl1, N4Á Á ÁCl1 = 3.114 Å; N8HÁ Á ÁCl1, N8Á Á ÁCl1 = 3.149 Å) as
well as the two methyl protons H18A and H36A (CH18AÁ Á ÁCl1,
C18Á Á ÁCl1 = 3.729 Å; CH36AÁ Á ÁCl1, C36Á Á ÁCl1 = 3.636 Å) of one
molecular unit and with an adjacent molecular unit (CH36CÁ Á ÁCl1,
C36Á Á ÁCl1 = 3.797 Å).
Fig. 2. Molecular structure of [Co(HL1-CH3)2]Cl (2).
In 2, two cationic molecular units are linked together by pairs of
reciprocal hydrogen bonds (CH4Á Á ÁO2, C4Á Á ÁO2 = 3.508 Å) [23]
between the uncoordinated ketoamide O2 oxygen atom and the
CH4 proton of the aromatic ring in the coordinated p-meth-
ylbenzoylhydrazone residue, forming a hydrogen bonded dimer.
The dimers are linked to each other through two pairs of additional
hydrogen bonds (CH4Á Á ÁO2, C4Á Á ÁO2 = 3.508 Å), forming a chain of
dimers propagating along the c axis. The chain is further stabilized
by pairs of reciprocal interactions (C18H18AÁ Á ÁC18, C18Á Á ÁC18 =
3.308 Å). The self-assembly of the cationic molecular units
[Co(HL1–CH3)2]1+ resulted in the formation of a one-dimensional
tubular structure extending along the c axis. The Cl1 counter anion
is involved in a bifurcated hydrogen bond with the two N4H pro-
tons of the two uncoordinated ketoamide residues in each molec-
ular unit (N4HÁ Á ÁCl1, N4Á Á ÁCl1 = 3.184 Å). The two hydrogen bonds
(N4HÁ Á ÁCl1) generate an 8-membered ring of graph set R12 (8) [25].
The structural parameters of the non-covalent bonding interac-
tions for complex 2 are listed in Table 5.
for 1. The mean C–O (ca. 1.291 Å), C–N (ca. 1.347 Å) and N–N (ca.
1.364 Å) bond distances of the coordinated aroylhydrazone resi-
dues in both 1 and 2, Table 2, are in agreement with the deproto-
nated enolimine structure [2,3,8], while the corresponding mean
bond distances (C–O (ca. 1.217 Å), C–N (ca. 1.351 Å) and N–N (ca.
1.393 Å) of the uncoordinated residue suggest the neutral ketoa-
mide structure (Scheme 2-i) [2,3,20].
In the crystal lattice of 1, each two adjacent cationic molecular
units, [Co(HL1–H)2]1+, are linked together through pairs of recipro-
cal hydrogen bonds (C17H17AÁ Á ÁO2, C17Á Á ÁO2 = 3.472 Å) between
the methyl H17A proton and the coordinated enolimine oxygen
O2, forming a hydrogen bonded dimer. The dimeric structure is fur-
ther stabilized by three pairs of reciprocal (CHÁ Á Á
p) interactions,
namely (CH17AÁ Á Áp1
CH18BÁ Á ÁCg2 = 3.333 Å) and (CH17BÁ Á Á
where p1 2 and 3 are the delocalized
,
CH17AÁ Á ÁCg1 = 3.072 Å), (CH18BÁ Á Áp2
,
p
p
3, CH17BÁ Á ÁCg3 = 3.588 Å)
,
p
p
systems of the five-mem-
bered chelate ring (Co1,O1,C3,N3, N1) as well as (C4–C9) and (C22–
C27) phenyl rings of the coordinated benzoylhydrazone residues,
3.3. X-ray molecular structure and self-assembly of [Co(HL2–CH3)(L2–
CH3)] (7)
Table 4
Non-covalent bond interactions in [Co(L1–H)2]Cl (1).
D–HÁ Á ÁA
D–H
HÁ Á ÁA
DÁ Á ÁA
<D–HÁ Á ÁA
The X-ray crystal structure of 7, Fig. 3, reveals that the Co(III) cen-
tre is in a distorted octahedral environment where the two
bisaroylhydrazone ligands are meridionally coordinated around
the Co(III) centre. One of the bisaroylhydrazone ligands acts as a
mononegative N2O tridentate anion and is coordinated to Co(III)
via the two imine nitrogens (N3 and N5) (Co1–N3 = 1.851(2),
Co1–N5 = 1.925(3) Å) and deprotonated enolimine oxygen O2
(Co1–O2 = 1.927(2) Å). The protonated enolimine oxygen O3 (O3–
H = 1.166(3) Å) of the same ligandremains uncoordinated. Theother
bisaroylhydrazone acts as a dinegative N2O tridentate ligand and is
(i) Non-covalent bond interactions involved in dimer formation
C17H17AÁ Á ÁO2
C17H17AÁ Á ÁCg1
C18H18BÁ Á ÁCg2
C17H17BÁ Á ÁCg3
0.960
0.960
0.960
0.959
2.659
3.072
3.333
3.588
3.472(6)
3.980
3.860
142.72
158.40
117.13
133.46
4.304
(ii) Non-covalent bond interactions involved in the chain of dimers
C24H24Á Á ÁO3
0.931
0.960
2.454
2.841
3.281(7)
3.377
148.11
116.21
C17H17CÁ Á ÁC35
(iii) Non-covalent bond interactions between dimer chains
C18H18AÁ Á ÁCg4 0.961 3.425 3.817
(iv) Non-covalent bond interactions between 2D layers
C33H33Á Á ÁO3 0.930 2.661 3.520(6)
106.92
154.03
Table 5
(v) non-covalent bond interactions involving the Cl1 counter ion
Non-covalent bond interactions in [Co(HDabh–CH3)2]Cl (2).
N4H4Á Á ÁCl1
0.860
0.859
0.961
0.959
0.960
2.349
2.446
2.928
2.841
2.908
3.114(3)
3.149(3)
3.728
3.636
3.797
148.32
139.41
141.47
140.87
154.43
N8H8Á Á ÁCl1
D–HÁ Á ÁA
D–H
HÁ Á ÁA
DÁ Á ÁA
<D–HÁ Á ÁA
C18H18AÁ Á ÁCl1
C36H36AÁ Á ÁCl1
C36H36CÁ Á ÁCl1
Intermolecular non-covalent bond interactions
C4H4Á Á ÁO2
0.930
0.959
2.663(4)
2.813
3.508(4)
3.308
151.4
113.1
Cg1 = five-membered chelate ring (Co1, N1, N2, C3, O1) centroid.
Cg2 = phenyl ring (C4–C9) centroid.
Cg3 = phenyl ring (C22–C27) centroid.
C18H18AÁ Á ÁC18
Intramolecular non-covalent bond interaction
N4H4Á Á ÁCl1 0.89(3) 2.34 (4)
3.164(4)
155.0(40)
Cg4 = phenyl ring (C11–C16) centroid.

170
N.M.H. Salem et al. / Polyhedron 68 (2014) 164–171
aromatic ring (C30–C35) and the
ring (CH32Á Á ÁCg1 = 3.220 Å) of the adjacent dimeric unit, giving
rise to a linear chain of stacked dimers propagating along
the b axis. The chains are assembled together by pairs of reciprocal
CHÁ Á Á interactions between the CH58 proton of the benzil phenyl
ring (C55–C60) and the -system of the aroylhydrazone aromatic
p-system of the other (C6–C11)
p–p
p
p
ring (C22–C27) (CH58Á Á ÁCg3 = 2.876 Å), forming a two-dimen-
sional layer of chains extended parallel to the ac plane. These 2D
layers are further interconnected along the a axis through pairs
of reciprocal interactions (CH38Á Á ÁCg2, CH38Á Á ÁCg2 = 3.986 Å), gen-
erating a three-dimensional framework.
4. Conclusions
In the present work, the octahedral cationic bisligand Co(III)
complexes [Co(HL1–R)2]Cl (R = H and CH3) as well as octahedral
neutral complexes [Co(HL1–R)(L1–R)] (R = H, CH3, OCH3, Cl) and
[Co(HL2–R)(L2–R)] (H and CH3) have been prepared and character-
ized. The X-ray crystal structures of [Co(HL1–R)2]Cl (R = H and CH3)
reveal that the two bis(aroylhydrazone) ligands in each of these
complexes are both coordinated to the Co(III) centre through the
two diimine nitrogens and the deprotonated enolimine oxygen,
while the keto amide oxygen remains uncoordinated (Scheme 2-
i). In the neutral Co(III) complexes [Co(HL1–R)(L1–R)] (R = H, CH3,
OCH3, Cl) and [Co(HL2–R)(L2–R)] (H and CH3), one of the two bis-
aroylhydrazones functions as a mononegative N2O tridentate an-
ion, while the other acts as a dinegative N2O tridentate anion.
Both the mono- and dinegative bisaroylhydrazone ligands are
coordinated to the Co(III) centre via the two dimine nitrogens
and the deprotonated enolimine oxygen. The uncoordinated resi-
due of the mononegative ligand exists as a protonated enolimine
oxygen (Scheme 2-ii), while the uncoordinated enolimine residue
of the of the dinegative ligand is deprotonated (Scheme 2-iii).
The X-ray crystal structure of [Co(HL2–CH3)(L2–CH3)] shows that
the free enolimine proton of the mononegative ligand is involved
in a very strong hydrogen bond with the uncoordinated deproto-
nated enol imine oxygen of the dinegative ligand.
Fig. 3. Molecular structure of [Co(HL2-CH3)(L2-CH3)] (7).
bound to the Co(III) centre through the two diimine nitrogens (N1
and N7) (Co1–N1 = 1.853(3), Co1–N7 = 1.917(3) Å) and the deproto-
nated enolimine oxygen O1 (Co1–O1 = 1.904(2) Å). The other depro-
tonated enolimine oxygen O4 remains uncoordinated, but is
involved in a strong intramolecular hydrogen bond (O3–HÁ Á ÁO4)
withtheuncoordinatedenolimineprotonoftheotherligand. Forma-
tion of such a chelated proton [24] gives rise to an R12 (10) macrocy-
clic ring [25]. The structural parameters of the intramolecular
hydrogen bond (O3HÁ Á ÁO4À), Table 6, suggest a strong interaction
between the O3H enolimine proton and the negatively charged
enolimine O4 oxygen and they are within the range expected for
[HOÁ Á ÁOÀ] hydrogen bonds [28].
Each molecular unit is linked to another neighboring molecular
Acknowledgment
unit by a pair of reciprocal
p–p stacking interactions [26,27]
between the aromatic ring (C6–C11) of the coordinated aroylhyd-
razone residue and the benzil phenyl ring (C49–C54) of the adja-
Thanks are due to DFG (1.8131e-2/09) for supporting this bilat-
eral project.
cent molecular unit (Cg1–Cg2 = 3.981 Å), forming a
p–p stacked
dimer. The dimeric structure is stabilized by a pair of reciprocal
H7Á Á ÁH19 (H7Á Á ÁH19 = 2.2906(1) Å) short contacts. The formed di-
Appendix A. Supplementary data
mers are connected to each other by two pairs of reciprocal CHÁ Á Á
p
interactions [21] between the CH32 proton of the aroylhydrazone
CCDC 929243, 929244 and 929276 contain the supplementary
crystallographic data for [Co(HL1-CH3)2]Cl, [Co(HL2-CH3)(L2–CH3)]
and [Co(HL1–H3)2]Cl, 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.
Table 6
Non-covalent bond interactions in [Co(HL2–CH3)(L2–CH3)].
D–HÁ Á ÁA
D–H
HÁ Á ÁA
DÁ Á ÁA <D–
HÁ Á ÁA
Intramolecular non-covalent bond interactions
O3–H3Á Á ÁO4 1.167 1.297
Intermolecular non-covalent bond interactions
2.448 167.64
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