Diastereoselectivity in dinuclear complexes of chiral tridentate ligands

Article abstract of DOI:10.1016/j.ica.2012.04.017

Using a racemic mixture of two chiral tridentate ligands 2-((1-(2-pyridyl)ethylimino)methyl)phenolate ion (L1) and 2-((phenyl(2-pyridyl) methylimino)methyl)phenolate ion (L2) and Cu(II) or Ni(II) salts, complexes having formulae [Cu(L2)(μ-1,1-NO₃)]₂ (1), [Cu(L2)(μ-Cl)]₂ (2), [Cu₂(L2)₂(μ-1,2- SO₄)] (3), [Cu₂(L1)₂(μ-1,2-SO₄)] (4) and [Ni₂(L2)₂(OAc)(N(CN)₂)(MeOH)] (5) were synthesized and characterized. Determination of molecular structures of all the five complexes confirmed the presence of a dimetallic core constructed by monochelates of the ligands. Compound 1, 2 have NO₃^- and Cl^- bridge between two copper centers and 3-5 have phenoxo as well as SO42- (3,4) and OAc^- (5) bridges. Compounds 1 and 2 have center of inversion in the dicopper core and are heterochiral. Whereas, in 3-5 center of inversion do not lie in the dimetallic core and are homochiral. Compound 1 has a rare feature of μ-1,1-NO₃^- bridge between two copper centers.

Full text of DOI:10.1016/j.ica.2012.04.017

Inorganica Chimica Acta 390 (2012) 154–162
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Inorganica Chimica Acta
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Diastereoselectivity in dinuclear complexes of chiral tridentate ligands
⇑
Himanshu Sekhar Jena, Vadivelu Manivannan
Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781 039, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Using a racemic mixture of two chiral tridentate ligands 2-((1-(2-pyridyl)ethylimino)methyl)phenolate
ion (L1) and 2-((phenyl(2-pyridyl)methylimino)methyl)phenolate ion (L2) and Cu(II) or Ni(II) salts, com-
Received 12 January 2012
Received in revised form 22 March 2012
Accepted 10 April 2012
plexes having formulae [Cu(L2)(l-1,1-NO3)]2 (1), [Cu(L2)(l-Cl)]2 (2), [Cu2(L2)2(l-1,2-SO4)] (3),
[Cu2(L1)2( -1,2-SO4)] (4) and [Ni2(L2)2(OAc)(N(CN)2)(MeOH)] (5) were synthesized and characterized.
l
Available online 27 April 2012
Determination of molecular structures of all the five complexes confirmed the presence of a dimetallic
core constructed by monochelates of the ligands. Compound 1, 2 have NO3 and Clꢀ bridge between
ꢀ
Keywords:
Schiff base
Racemic mixture
Diastereoselectivity
Dimetallic core
two copper centers and 3–5 have phenoxo as well as SO24ꢀ (3,4) and OAcꢀ (5) bridges. Compounds 1
and 2 have center of inversion in the dicopper core and are heterochiral. Whereas, in 3–5 center of inverꢀ-
sion do not lie in the dimetallic core and are homochiral. Compound 1 has a rare feature of l-1,1-NO3
bridge between two copper centers.
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
without further purification. (R,S)-1-(2-pyridyl)ethylamine [25]
and L1H [13] were prepared using the reported procedures.
A Perkin–Elmer Spectrum One spectrometer (4000–250 cmꢀ1),
Perkin–Elmer Lambda 25 spectrometer, Perkin–Elmer Series II
CHNS/O Analyzer 2400, Bruker 400 MHz spectrophotometer, JEOL
JES FA-200 X-band EPR spectrometer and a Lakshore VSM Setup
were used for performing the relevant measurements. Thermo-
Chirality has been the core theme of research for many investi-
gators because of its fundamental importance in biology and
chemistry. Chiral recognition in particular is crucial in many bio-
logical processes [1] as well as in synthetic chemistry [2,3]. Factors
that contribute to the mechanisms of such recognitions include
steric, electronic, intermolecular forces and rotational symmetry
[4–6]. The mode by which a tridentate ligand having a chiral center
[7–13] as well as multidentate ligands having one or more chiral
centers [14–24] bind to a metal ion have been reported. An end
capped monochelated metal complex formed from racemic mix-
tures of a chiral tridentate ligand, in the presence of suitable bridg-
ing ligands can dimerize to form a dimetallic core in three ways
having RS or RR or SS combinations of the ligands. Herein we report
a bridging ligand dependent chiral preference (Scheme 1) based on
its ability/inability to accommodate the center of symmetry at the
dimetallic core.
gravimetry was studied by
a computer controlled METTLER
TOLEDO STARe system of module TGA/SDTA851e under static
nitrogen atmosphere using platinum pan at a heating rate of
10 °C/min in the noted temperature ranges. The instrument was
calibrated using RTypSDTA sensor.
X-ray crystallographic data were collected using Bruker SMART
APEX-CCD diffractometer with Mo K
a radiation (k = 0.71073 Å).
The intensity data were corrected for Lorentz and polarization ef-
fects and empirical absorption corrections was applied using SAINT
program [26,27]. All the structures were solved by direct methods
using SHELXS-97 [28]. Non-hydrogen atoms located from the differ-
ence Fourier maps were refined anisotropically by full-matrix
least-squares on F2, using SHELXL-97 [28]. All hydrogen atoms were
included in the calculated positions (except for the water mole-
cules of crystallization for which hydrogen atoms could neither
be added at calculated positions and nor be located from FMAP)
and refined isotropically using a riding model.
2. Experimental
2.1. Materials and methods
2-Acetyl pyridine, 2-benzoyl pyridine, NaN(CN)2, (Aldrich,
USA); 2-hydroxybenzaldehyde, Cu(NO3)2ꢁ3H2O, CuCl2ꢁ2H2O,
CuSO4ꢁ5H2O, Ni(OAc)2ꢁ4H2O, hydroxylamine hydrochloride and
Zn dust (Merck India Ltd.) and solvents were used as received
2.2. Synthesis
2.2.1. Phenyl(2-pyridyl)ketoxime
To a mixture of phenyl(2-pyridyl)ketone (10.0 g, 55 mmol) and
NH2OHꢁHCl (6.0 g, 86 mmol) in methanol (50 mL), an aqueous
solution (50 mL) of NaOH (11.0 g, 275 mmol) was added and
⇑
Corresponding author. Tel.: +91 361 258 2306; fax: +91 361 258 2349.
E-mail address: mani@iitg.ernet.in (V. Manivannan).
0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2012.04.017

H.S. Jena, V. Manivannan / Inorganica Chimica Acta 390 (2012) 154–162
155
Scheme 1. Chirality selective dimetallic core (B = bridging ligand).
stirred at 100 °C for 24 h. The reaction mixture was cooled first to
room temperature and then kept in refrigerator (at 0–4 °C). After
standing for overnight, the pale pink crystals deposited was
filtered, washed with water and dried in desiccators. Yield: 9.51 g
(87%). IR (KBr, cmꢀ1): 3152(b), 3009(s), 2852(s), 1627(w),
1591(s), 1560(w), 1475(s), 1435(s), 1411(w), 1325(s), 1241(w),
1179(s), 1156(s), 1052(w), 995(s), 947(s), 913(w), 790(s), 778(s),
748(s), 699(s), 623(s). 400 MHz 1H NMR (d (J, Hz), CDCl3): 9.42
(OH, s), 8.62 (1H, d, 8.0), 7.69 (1H, t, 7.6), 7.58 (1H, d, 7.6),
7.50–7.41 (3H, m), 7.26 (1H, t, 5.2). 100 MHz 13C NMR (d, CDCl3):
158.8, 154.7, 149.5, 136.7, 129.6, 129.2, 128.7, 128.5, 128.2, 123.1.
2.2.4. [Cu2(L2)2(l-1,1-NO3)2] (1)
To L2H (0.29 g, 1.0 mmol) dissolved in methanol (30 mL), solid
Cu(NO3)2ꢁ3H2O (0.24 g, 1.0 mmol) was added and the resulting
green solution was stirred at room temperature for 1 h. The solvent
was removed and the green residue was washed with ice-cold
methanol. Yield: 0.55 g (66%). Single crystals of 1 suitable for X-
ray diffraction study were obtained slow evaporation of methanol
solution. Anal. Calc. for C38H30Cu2N6O8: C, 55.27; H, 3.66; N, 10.18.
Found: C, 54.97; H, 3.58; N, 9.87%. IR (KBr, cmꢀ1): 3458(b), 3308(s),
3238(b), 1610(s), 1599(s), 1570(s), 1487(s), 1446(w), 1398(b),
1384(b), 1315(w), 1258(s), 1151(s), 1098(s), 1071(w), 1009(s),
999(w), 824(s), 771(s), 701(s), 666(s), 621(w), 542(s). UV–Vis
[kmax, nm (
382(5442); 289(6861). EPR (CH3OH solution, 298 K): g = 2.233,
A = 72 G. eff/Cu (298 K), 1.91 B.M.
e
, Mꢀ1 cmꢀ1), CH3OH solution]: 635(173); 405(268);
2.2.2. (R,S) Phenyl(2-pyridyl)methaneamine
l
To an ice-cold mixture of phenyl(2-pyridyl)ketoxime (5.0 g,
25.2 mmol), acetic acid (50 mL) and ethanol (100 mL), zinc dust
(50 g) was added in 2 g increments over a period of 2 h and then
the heterogeneous mixture was stirred at ambient temperature
for 24 h. The mixture was filtered to remove undissolved zinc
and washed with sufficient quantity of ethanol. The combined fil-
trate and washings was concentrated in vacuo, several 10 mL por-
tions of H2O were added to it and evaporated to remove acetic acid.
The pH of the mixture was adjusted to ꢂ12 using aqueous KOH
solution and then extracted with 3 ꢃ 50 mL of diethyl ether. The
combined ether portions were dried over Na2SO4 and the solvent
was removed in vacuo. Yield: 4.5 g (96.8%). IR (KBr, cmꢀ1):
3445(b), 3307(b), 3255(s), 3180(s), 3101(w), 1630(s), 1604(s),
1549(w), 1519(s), 1477(s), 1466(s), 1441(s), 1363(s), 1282(s),
1252(s), 1211(w), 1161(w), 1097(s), 1038(s), 766(s), 658(w),
640(w), 543(s). 400 MHz 1H NMR (d (J, Hz), CDCl3): 8.53 (1H, d,
4.8), 7.56 (1H, t, 7.6), 7.39 (1H, d, 8), 7.30 (1H, t, 7.6), 7.24 (1H, t,
6.4), 7.19 (1H, d, 6.4), 7.10 (1H, t, 6.2), 5.21 (1H, s), 2.75 (NH2, s).
100 MHz 13C NMR (d, CDCl3): 158.6, 154.2, 149.6, 136.7, 131.0,
129.2, 128.7, 128.5, 123.1, 56.2.
2.2.5. [Cu2(L2)2(
l
-Cl)2]ꢁ2CH3OH (2)
To L2H (0.29 g, 1.0 mmol) dissolved in methanol (30 mL), solid
CuCl2ꢁ2H2O (0.17 g, 1.0 mmol) was added and stirred at room tem-
perature for 1 h. The green solution was kept in room temperature
and after a week green crystals of 2 suitable for X-ray diffraction
study were obtained and washed with cold methanol. Yield:
0.53 g (63%). Anal. Calc. for C40H38Cl2Cu2N4O4: C, 57.42; H, 4.58;
N, 6.70. Found: C, 56.87; H, 4.28; N, 6.54%. IR (KBr, cmꢀ1):
3363(b), 3115(w), 3021(w), 2909(w), 1625(s), 1600(w), 1569(w),
1537(s), 1469(s), 1446(s), 1438(w), 1395(s), 1348(w), 1323(s),
1283(s), 1211(w), 1152(s), 1129(w), 1078(w), 1045(s), 1030(s),
979(w), 935(w), 913(w), 878(w), 852(w), 765(s), 755(s), 707(s),
625(s), 552(s) 454(w). UV–Vis [kmax, nm (
solution]: 635(144); 382(2735); 288(4331). EPR (CH3OH solution,
298 K): g = 2.101, A = 70 G, eff/ Cu (298 K), 1.94 B.M.
e
, Mꢀ1 cmꢀ1), CH3OH
l
2.2.6. [Cu2(L2)2(
l
-1,2-SO4)]ꢁ7H2O (3)
To L2H (0.29 g, 1.0 mmol) dissolved in methanol (30 mL), solid
CuSO4ꢁ5H2O (0.25 g, 1.0 mmol) was added and stirred at room
temperature for 1 h. The green solution was kept in room temper-
ature and after a week green crystals of 3 suitable for X-ray diffrac-
tion study were isolated and washed with cold methanol. Yield:
0.652 g (71%). Anal. Calc. for C38H30Cu2N4O13S: C, 50.16; H, 3.32;
N, 6.16. Found: C, 49.97; H, 3.01; N, 5.94%. IR (KBr, cmꢀ1):
3426(b), 3054(w), 3038(w), 2925(s), 1618(s), 1570(w), 1548(s),
1483(w), 1457(s), 1441(w), 1420(s), 1392(w), 1336(s), 1301(s),
1286(w), 1243(s), 1192(w), 1147(s), 1165(w), 1147(w), 1100(w),
1022(b), 963(s), 875(s), 818(s), 759(s), 736(w), 704(s), 686(w),
2.2.3. (R,S) 2-((Phenyl(2-pyridyl)methylimino)methyl)phenol (L2H)
A
mixture
of
phenyl(2-pyridyl)methaneamine
(4.5 g,
26.3 mmol) and 2-hydroxybenzaldehyde (3.2 g, 26.3 mmol) in
methanol (100 mL) was stirred for 3 h. Yellow precipitate of L2H
deposited were collected by suction filtration, washed with cold
methanol and dried over CaCl2. Yield: 7.2 g (95%). IR (KBr, cmꢀ1):
3081(s), 3009(s), 2897(s), 1622(s), 1586(s), 1464(s), 1430(s),
1383(w), 1313(s), 1279(s), 1215(w), 1200(s), 1151(s), 1053(s),
1028(s), 988(s), 938(w), 914(s), 859(s), 780(w), 757(s), 695(s),
621(s), 611(s), 539(s), 480(w), 463(s). 400 MHz 1H NMR (d (J,
Hz), CDCl3): 13.50 (OH, s), 8.55 (1H, s), 8.54 (1H, d, 6.8), 7.65
(1H, t, 4.6), 7.42 (1H, d, 8.0), 7.40 (1H, d, 8.4), 7.36 (1H, t, 8.4),
7.32 (1H, t, 7.6), 7.30 (1H, t, 8.4), 7.28 (1H, d, 7.6), 7.15 (1H, t,
6.0), 6.99 (1H, d, 8.0), 6.89 (1H, t, 7.6), 5.75 (1H, s). 100 MHz 13C
NMR (d, CDCl3): 166.1, 161.7, 161.1, 149.4, 141.5, 137.2, 132.9,
132.0, 128.9, 127.8, 127.5, 122.6, 122.0, 119.0, 117.2, 116.4, 78.9.
632(w), 589(b), 568(s), 516(w), 484(s). UV–Vis [kmax, nm (
e,
Mꢀ1 cmꢀ1), CH3OH solution]: 638(165); 381(1793); 287(2449).
EPR (CH3OH solution, 298 K): g = 2.117, A = 71 G.
1.84 B.M.
leff/Cu (298 K),
2.2.7. [Cu2(L1)2(
l
-1,2-SO4)]ꢁ2H2OꢁCH3OH (4)
To a methanolic solution (30 mL) of L1H (0.23 g, 1 mmol), solid
CuSO4ꢁ5H2O (0.250 g, 1.0 mmol) was added and stirred for 4 h.

156
H.S. Jena, V. Manivannan / Inorganica Chimica Acta 390 (2012) 154–162
From the green solution dark green crystals of 4 were formed on
standing for few days. Yield: 0.450 g (60%). Anal. Calc. for
rationalized to the ability or inability of the bridging ligand in
allowing a center of symmetry at dimetallic core.
C
29H30Cu2N4O9S: C, 47.21; H, 4.10; N, 7.59. Found: C, 47.04; H,
The IR spectra of 1–5, show a strong peak in the range 1610–
3.89; N, 7.44%. IR (KBr, cmꢀ1): 3420(b), 3277(s), 3138(w),
3068(w), 2970(w), 1626(w), 1605(s), 1567(s), 1480(s). 1442(s),
1292(s), 1401(w), 1379(w), 1362(w), 1292(s), 1247(s), 1117(b),
1039(b), 979(s), 905(w), 791(s), 764(s), 743(w), 701(w), 649(w),
1640 cmꢀ1 assignable to azomethine group. In addition the charac-
teristic peaks for NO3ꢀ in 1 at 1384 cmꢀ1, SO42ꢀ in 3, 4 at 1441 cmꢀ1
,
OAcꢀ in 5 at 1467 cmꢀ1 and m(Cu–Cl) in 2 at 454 cmꢀ1 are notewor-
thy. In methanol the electronic spectra of compounds 1–4 display a
d–d transition at around 635 nm, and 5 exhibits the same at 841
and 576 nm as a broad band as well as at 746 nm as a sharp band.
The allowed transitions in 1–5 were observed at around 380 and
287 nm. The room-temperature magnetic moment values of poly-
crystalline samples are consistent with the presence of one un-
paired electron in 1–4 and two unpaired electrons per nickel
atom in 5. In methanol medium, the EPR spectra of 1–4 at 298 K
are isotropic in nature with the hyperfine splitting. The thermo-
gravimetric analyses of 3–4 were carried out after keeping the
freshly prepared samples in desiccators, overnight. In 3, a weight
loss of 14.0% (Calcd. 13.8%, Fig. S1) was observed in the tempera-
ture range 37–196 °C that corresponds to the loss of all seven
water molecules. Sample of 4 shows a weight loss of 9.0% (Calcd.
9.2%) for loss of one methanol and two water molecules in the tem-
perature range 78–113 °C.
618(s), 477(w). UV–Vis [kmax, nm (
636(208); 377(4323); 284(3028). EPR (CH3OH solution, 298 K):
g = 2.114, A = 76 G, eff/Cu (298 K), 1.86 B.M.
e
, Mꢀ1 cmꢀ1), CH3OH solution]:
l
2.2.8. [Ni2(L2)2(OAc)(DCA)(CH3OH)]ꢁCH3OH (5)
To Ni(OAc)2ꢁ4H2O (0.990 g, 4.0 mmol) dissolved in methanol
(60 mL), L2H (1.14 g, 4.0 mmol) and sodium dicyanamide
(0.352 g, 4.0 mmol) were added and the solution was stirred at
room temperature for 24 h. The solvent was removed and the
green residue was washed with ice-cold methanol. Yield: 1.04 g
(69%). Single crystals of 5 suitable for X-ray diffraction study were
obtained by slow diffusion of methanolic solution of the crude 5
into dichloromethane. Anal. Calc. for C44H40N7O6Ni2: C, 60.04; H,
4.58; N, 11.14. Found: C, 59.87; H, 4.48; N, 10.87%. IR (KBr,
cmꢀ1): 3431(b), 3408(b), 3050(b), 3007(w), 2891(b), 2297(s),
2243(s), 2185(s) (dicyanamide), 1641(s), 1598(s), 1568(w),
1543(w), 1493(w), 1467(s), 1443(s), 1394(s), 1349(s), 1288,(s),
1244(w), 1196(s), 1147(s), 1120(w), 1081(w), 1047(w), 933(w),
898(w), 849(s), 784(s), 756(s), 703(s), 623(s), 553(w). UV–Vis
3.2. Molecular structures
The molecular structures of 1–5 were determined and the crys-
tallographic and refinement parameters are listed in Table 1. Both
L1 and L2 bind to the metal ion, in tridentate meridional fashion
with NPNIOP donor set {NP = pyridyl-N; NI = imine-N; OP = pheno-
late-O}. The chelate ring formed by NPNI atoms is five-membered
and that by NIOP atoms is six-membered. During synthesis of 1–
5, a racemic mixture of L1H/L2H has been used and all the five
compounds have a monochelated dimetallic unit. Compounds 1,
2 have center of inversion in the dicopper core and are heterochi-
ral. Whereas, in 3–5 center of inversion do not lie in the dimetallic
core and are homochiral.
In compound 1, the copper center is bound by NPNIOP donor set
of nearly-planar L2 and O2 of nitrate ion, which together form a
distorted square-planar arrangement. The O2 atom deviates from
the plane containing N1N2O1Cu1 atoms, by a distance of 0.33 Å
and an angle of 9.45°. The O2 atom of nitrate ion is further linked
[kmax, nm (e
, Mꢀ1 cmꢀ1), CH3OH solution]: 841(36); 746(23);
576(16); 377 (2510); 286 (2299). leff/Ni (298 K), 2.84 B.M.
3. Results and discussion
3.1. Synthesis and characterization
The nature of metal ion and its preferred coordination stereo-
chemistry, electronic and steric requirements of multidentate li-
gands as well as coordination mode of bridging ligands are
crucial factors in synthesis of coordination complexes. During the
formation of a dinuclear core self-assembly of monochelated chiral
tridentate ligand could occur and the role of bridging ligand on
binucleation is scanty [29,30]. To make an illuminating investiga-
tion on this effect, it is necessary to synthesize a variety of com-
pounds with variety of bridging ligand by keeping the other
parameters to a near constant. From this perspective, we have syn-
thesized a set of five complexes 1–5, having a dimetallic core using
two racemic tridentate end-capped Schiff bases (L1H and L2H,
Scheme 2) and different copper salts and a nickel salt. Determina-
tion of their molecular structures (vide infra) reveal a bridging li-
gand dependant preference of RS combination of two L2 ligands
coordinated to dicopper core of 1, 2 and RR(SS) combination of
L1 and L2 (Scheme 3) in 3–5. Such chiral combinations can be
to another copper center in a l-1,1 bridging fashion, leading a di-
mer having the Cu2O2 unit. To the best of our knowledge this is the
second example where such bridging by nitrate ion has been ob-
served [31]. The Cu2O2 unit has diamond shape having the param-
eters, Cu1ꢁ ꢁ ꢁCu1A, 3.844(1) Å; Cu1–O2, 2.045(2) Å; Cu1–O2A,
2.559(2) Å; O2–Cu1–O2A, 67.32(8)°; Cu1–O2–Cu1A, 112.68(9)°.
The dimer contains RS pair of asymmetric carbon C6 and a center
of symmetry is present at the center of Cu2O2 unit. The distance be-
tween two N1N2O1Cu1 planes in the dimer is 1.84 Å. A perspective
view of 1 is shown in Fig. 1. The d9 copper(II) ion is usually severely
Jahn–Teller distorted and as a result has a long axial bond. The
Cu1–O2A bond having a distance 2.561(2) Å is quite longer than
the usual range and deviate by an angle of 31.86° from the axial po-
sition, hence orienting along dxz/dyz orbital than the d2. Among the
z
bond distances within the nitrate ion, N3–O2, 1.264(4) Å is longer
than other two N3–O3, 1.193(5) Å; N3–O4, 1.204(4) Å which is due
to involvement of O2 atom in bridging.
In compound 2, the L2 and Cl1 are attached to copper(II) center
forming a distorted square planar arrangements of donor atoms
around it and Cl1 atom deviate by 0.44 Å from the plane containing
N1N2O1Cu1 atoms. The Cl1 atom from each of [Cu(L2)Cl] unit
bridge each other having a distance of 2.881(2)Å, leading to a
[Cu(L2)Cl]2 dimeric unit, as shown in Fig. 2. Selected bond dis-
tances observed in 1 and 2 are listed in Table 2. A center of symme-
try is present at the center of Cu2Cl2 unit, as a result asymmetric
Scheme 2. Structure of L1H and synthesis of L2H.

H.S. Jena, V. Manivannan / Inorganica Chimica Acta 390 (2012) 154–162
157
Scheme 3. Schematic representation of bridging ligand dependant chirality selectivity in dimetallic core.
Table 1
Crystallographic and refinement parameters.
1
2
3
4
5
Formula
CCDC number
Formula weight
T (K)
C
38H32Cu2N6O8
C40H38Cl2Cu2N4O4
831680
836.74
C38H30Cu2N4O13
831681
909.83
S
C29H30Cu2N4O9S
831682
737.74
C44H41N7Ni2O6
831683
881.22
831679
827.80
296(2)
296(2)
296(2)
296(2)
296(2)
k (Å)
0.71073
monoclinic
P21/n
11.8705(3)
13.3174(3)
12.4683(3)
0.71073
monoclinic
P21/n
9.0248(5)
12.1801(6)
16.9307(9)
0.71073
triclinic
P1
0.71073
triclinic
P1
0.71073
monoclinic
P21/n
15.7499(12)
17.4273(13)
16.2398(12)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
ꢀ
ꢀ
10.8903(8)
13.0500(9)
16.1451(11)
69.523(4)
70.652(4)
86.379(4)
2024.5(2)
2
9.7891(15)
13.069(2)
13.390(2)
109.986(11)
104.239(12)
91.103(11)
1550.4(4)
2
a
(°)
b (°)
113.5240(10)
101.676(3)
114.261(3)
c
(°)
V (Å3)
1807.23(8)
2
1.521
1822.56(17)
2
1.525
4063.8(5)
4
1.440
Z
Dcalc (g mꢀ3
)
1.492
1.171
1.580
1.498
l
(mm–1
)
1.239
1.362
0.985
F(000)
848.0
3231
2379
1.87, 25.15
1.004
860.0
4692
2513
2.07, 28.66
1.045
928.0
7903
6217
1.67, 25.93
1.002
756.0
7797
5767
1.68, 28.43
1.001
1832.0
9735
7578
1.52, 27.89
1.002
Reflection collected
Unique reflections
hmin, hmax (°)
Goodness-of-fit (GOF)a on
F2
R [I > 2
r
(I)]
R1b = 0.0428,
wR2c = 0.1213
R1b = 0.0994,
wR2c = 0.1491
0.693/ꢀ0.519
R1b = 0.0349,
wR2c = 0.0965
R1b = 0.0456,
wR2c = 0.1041
0.358/ꢀ0.268
R1b = 0.0444,
wR2c = 0.1164
R1b = 0.0710,
wR2c = 0.1329
0.757/ꢀ0.518
R1b = 0.0874,
wR2c = 0.1898
R1b = 0.1914,
wR2c = 0.2408
0.862/ꢀ0.570
R1b = 0.0452,
wR2c = 0.1148
R1b = 0.0778,
wR2c = 0.1384
1.136/ꢀ0.707
R indices (all data)
Largest peak/hole (e Åꢀ3
)
ꢂ
ꢂ
ꢃ
ꢃ
1=2
ꢀ
ꢁ
2
P
F20 ꢀ F2c
=M ꢀ N
(M = number of reflections, N = number of parameters refined).
a
b
c
GOF ¼
w
P
P
R1 ¼ jjF0j ꢀ jFcjj= jF0j.
ꢂ
ꢂ
ꢃ
ꢂ
ꢃꢃ
1=2
2
ꢀ
ꢁ
ꢀ
ꢁ
2
P
P
wR2
¼
w
F20 ꢀ F2c
=
w
F02
.
ꢀ
carbons (C6) have a RS combination. The Cu2Cl2 unit has a near
rectangular shape with the parameters: Cu1–Cl1, 2.300(1) Å;
Cu1–Cl1A, 2.881(2) Å; Cu1–Cl1–Cu1A, 90.92(4)°; Cl1–Cu1–Cl1A,
89.08(4)° and these values are comparable with reported ones
[32–36]. The distance between two N1N2O1Cu1 planes in a dimer
is 2.40 Å. The OP is hydrogen bonded to the methanol oxygen with
O1ꢁ ꢁ ꢁO2 distance of 2.911(6) Å.
Compounds 3 and 4 crystallized in space group P1, respectively
contain a non-centrosymmetric dimeric units of [Cu2(L2)2(
SO4)] and [Cu2(L1)2( -1,2-SO4)]. In both cases, each copper atom
is bound by the mono anionic ligand, one oxygen atom from the
sulfate ion which bridge in -1,2 fashion [37–45] and by bridging
OP. The ligand has a slight bowl shape and copper center has a dis-
torted square pyramidal geometry, with bridged-OP being in the
l-1,2-
l
l

158
H.S. Jena, V. Manivannan / Inorganica Chimica Acta 390 (2012) 154–162
Fig. 1. ORTEP diagram (30% probability ellipsoids) of 1 (symmetry code: ꢀx, ꢀy, ꢀz).
Fig. 2. ORTEP diagram (30% probability ellipsoids) of 2 (symmetry code: ꢀx, ꢀy, ꢀz).
Table 2
shorter (2.338(3) Å in 1; 2.308(4) Å in 2), than Cu2ꢁ ꢁ ꢁO1 distance
Selected bond distances (Å) in 1 and 2.
(2.519(3) Å in 1; 2.517(5) Å in 2). The OP bridge leads to a butterfly
shaped Cu2O2 unit with angle between two planes containing
atoms Cu1O2Cu2 and Cu1O1Cu2 planes being 155.98° in 1;
160.64° in 2, while between O2Cu1O1 and O2Cu2O1 planes being
157.79° in 1; 161.44° in 2. The non-bonded Cu1ꢁ ꢁ ꢁCu2 contact has a
distance of 3.1785(6) Å in 1 and 3.112(2) Å in 2. Within a dimer,
the asymmetric carbon atoms have a RR or SS enantiomeric combi-
nations and since inversion center do not lie within Cu2O2 unit,
such combination has occurred. Perspective views of RR-
1
2
Cu1–N1
Cu1–N2
Cu1–O1
Cu1–O2
Cu1–O2A
Cu1ꢁ ꢁ ꢁCu1A
1.968(2)
1.946(2)
1.874(2)
2.045(2)
2.559(2)
3.8445(3)
Cu1–N1
Cu1–N2
Cu1–O1
Cu1–Cl1
Cu1–Cl1A
Cu1ꢁ ꢁ ꢁCu1A
2.002(4)
1.953(4)
1.898(4)
2.300(1)
2.881(2)
3.715(9)
axial site. Out of two axial bridged-OP linkages, Cu1ꢁ ꢁ ꢁO2 contact is
[Cu2(L2)2(
l-1,2-SO4)] and SS-[Cu2(L1)2(l-1,2-SO4)] are displayed
in Figs. 3 and 4 and the selected bond distances are listed in Table 3.

H.S. Jena, V. Manivannan / Inorganica Chimica Acta 390 (2012) 154–162
159
Fig. 3. ORTEP diagram (30% probability ellipsoids) of [Cu2(L2)2(l-g
2-SO4)] in 3.
Fig. 4. ORTEP diagram (30% probability ellipsoids) of [Cu2(L1)2(l-g
2-SO4)] in 4.
The
s
parameters calculated for 1 (0.11); 2 (0.12); 3 (0.30, 0.23) and
molecules interlink oxygen atoms of sulfate ion, from two RR or
SS units, to a chain along the a-axis using hydrogen bonds viz.,
O5ꢁ ꢁ ꢁO10ꢁ ꢁ ꢁO9ꢁ ꢁ ꢁO11ꢁ ꢁ ꢁO6. These are in turn hydrogen bonded to
O7, O8, O11, O12 and O13 atoms that are filled up in channels hav-
ing hydrophilic and hydrophobic environments. The Oꢁ ꢁ ꢁO dis-
tances are within the range of other reported water chains
[47,48]. Two RR and SS units are cross-linked by hydrogen bonding
4 (0.19, 0.13) are imperative of the distorted square pyramidal
geometry [46].
In the packing diagram of 3, dimers having RR and SS combina-
tions are packed alternatively along the c-axis generated by inver-
sion center, but identical RR or SS combinations are packed over
each other along the a-axis. The O9, O10 and O11 atoms of water

160
H.S. Jena, V. Manivannan / Inorganica Chimica Acta 390 (2012) 154–162
Table 3
Complex 5 crystallizing in the P21/n space group, contains a
hexa-coordinated dinickel complex having {Ni2( -OP)2( -OAc)}
Selected bond distances (Å) in 3 and 4.
l
l
unit, in which two Ni(II) atoms are bridged by an acetate ion and
by two phenoxo groups. Coordination by L2, acetate ion and OP
bridging brings about the same penta coordination environment
around two nickel centers, but differ in the sixth coordination site
which is completed by methanol oxygen atom in Ni1 and by cya-
nide nitrogen atom of dicyanamide ligand in Ni2. Therefore, both
nickel centers have distorted pseudo-octahedral geometry and a
perspective view of SS-[Ni2(L2)2(OAc)(DCA)(CH3OH)] unit is dis-
played in Fig. 7. The acetate ion is slightly asymmetrically bridging
having Ni–O distances of 2.011(2) and 2.024(2) Å, which is lying
within the range 2.01–2.07 Å observed in few other cases [49–
53]. The Ni2O2 unit has a butterfly shape with the angles between
planes containing Ni1Ni2O1 and Ni1Ni2O2 atoms being 157.45°,
while between Ni1O2O1 and O1Ni2O2 atoms being 158.87°. The
non-bonded Niꢁ ꢁ ꢁNi distance observed in 5 is 3.018(1) Å is consid-
erably shorter by 0.092(1) Å than that reported in a closely related
compound [13]. Selected bond distances observed in 5 are listed in
Table 5. The four coordination bonds arising from the ligand L2 is
slightly shorter at Ni1 than at Ni2 centers and this may be due to
poor coordinating ability of methanol at Ni1. In the packing dia-
gram, RR and SS dimers are arranged alternatively into chains
3
4
Cu1–N1
Cu1–N2
Cu1–O1
Cu1–O2
Cu1–O3
Cu2–N3
Cu2–N4
Cu2–O1
Cu2–O2
Cu2–O4
Cu1ꢁ ꢁ ꢁCu2
1.976(3)
1.939(2)
1.921(2)
2.339(3)
1.971(2)
1.980(3)
1.940(3)
2.515(3)
1.901(2)
1.953(3)
3.179(7)
1.959(7)
1.935(7)
1.924(5)
2.308(4)
1.947(6)
1.956(7)
1.941(7)
2.517(5)
1.882(6)
1.956(6)
3.112(2)
interactions and notable among them is presence of a planar
six-membered ring involving O5 atom of sulfate ion, O7 and O8
atoms of water molecules (Fig. 5). In the packing diagram of 4,
RR and SS combinations form discrete dimeric units linked by
hydrogen-bonding interactions involving solvated water and
methanol molecules, as shown in Fig. 6. The relevant Dꢁ ꢁ ꢁA dis-
tances found in 3 and 4 are listed in Table 4.
Fig. 5. Packing diagram showing the hydrogen bonding interactions present in 3, on viewing along a-axis.
Fig. 6. Existence of discrete dimeric RR and SS combination linked by hydrogen-bonding interactions in 4.

H.S. Jena, V. Manivannan / Inorganica Chimica Acta 390 (2012) 154–162
161
Table 4
Table 5
Selected Dꢁ ꢁ ꢁA interactions (Å) and their symmetry operators in 3 and 4.
Selected bond distances (Å) in 5.
3
5
O5ꢁ ꢁ ꢁO7
2.875(5)
2.865(5)
3.0(6)
x + 1, +y, +z
Ni1–N1
Ni1–N2
Ni1–O1
Ni1–O2
Ni1–O3
Ni1–O5
Ni1ꢁ ꢁ ꢁNi2
2.058(3)
Ni2–N3
Ni2–N4
Ni2–O2
Ni2–O1
Ni2–N5
Ni2–O4
2.062(3)
O5ꢁ ꢁ ꢁO8
2.018(2)
2.002(2)
2.124(2)
2.138(3)
2.019(2)
3.018(1)
2.019(2)
2.012(3)
2.196(2)
2.089(3)
2.009(2)
O5ꢁ ꢁ ꢁO10
O6ꢁ ꢁ ꢁO11
O7ꢁ ꢁ ꢁO8
2.66(12)
2.736(5)
2.735(7)
2.80(1)
2.89(6)
2.647(9)
2.92(2)
2.71(2)
ꢀx + 1, ꢀy + 2, ꢀz
O7ꢁ ꢁ ꢁO9
O8ꢁ ꢁ ꢁO12
O9ꢁ ꢁ ꢁO10
O9ꢁ ꢁ ꢁO11
O11ꢁ ꢁ ꢁO12
O12ꢁ ꢁ ꢁO13
x, +y + 1, +z
x ꢀ 1, +y, +z
x, +y ꢀ 1, +z
x, +y ꢀ 1, +z
linked zig-zag coordination chain which was previously observed
[13] with sterically less demanding methyl group substitution.
4
O2ꢁ ꢁ ꢁO7
O5ꢁ ꢁ ꢁO7
O6ꢁ ꢁ ꢁO8
O7ꢁ ꢁ ꢁO8
O8ꢁ ꢁ ꢁO10
2.864(9)
2.809(8)
2.99(1)
2.78(1)
2.67 (1)
x, +y + 1, +z
x, +y + 1, +z
4. Conclusion
x, +y, +z ꢀ 1
ꢀx + 1, ꢀy + 1, ꢀz + 1
Five complexes containing a dimetallic core was synthesized
using a racemic mixture of end-capping tridentate Schiff base li-
gand and bridging ligands. Determination of their molecular struc-
tures revealed that bridging ligands play a key role in recognizing
the chirality of the tridentate ligand. In 1 and 2, NO3 and Clꢀ,
ꢀ
(Fig. 8) in which two dimers are linked by hydrogen bonding inter-
action between coordinated methanol, lattice methanol (O3ꢁ ꢁ ꢁO6,
2.733(7) Å) and uncoordinated end of the dicyanamide group
(O6ꢁ ꢁ ꢁN7, 2.820(8) Å). It is also pertinent to note that phenyl group
substitution at the asymmetric carbon brings about steric crowd-
ing and this probably restricts the formation of dicyanamide ion
respectively act as a bridge between the two copper atoms. Hence
dicopper core can have the center of symmetry thus resulting in a
RS combination (heterochiral) of chiral ligands at two metal cen-
ters. However in 3–5 due to the presence of single sulfate or ace-
tate ion bridges, the dimetallic core cannot have the center of
Fig. 7. ORTEP diagram (30% probability ellipsoids) of SS-[Ni2(L2)2(OAc)(DCA)(CH3OH)] in 5.
Fig. 8. Chain containing alternating RR and SS dimers in 5.

162
H.S. Jena, V. Manivannan / Inorganica Chimica Acta 390 (2012) 154–162
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chiral tridentate ligand occur at the two metal centers in equal pro-
portions and thus retain the overall racemic nature. The observed
diaseteroselectivity in these dimetallic cores refers only to the solid
state structures. Also observed in compound 1 is a rare feature of
nitrate ion (l
-1,1-NO3ꢀ) bridge between two copper centers.
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Acknowledgments
We are grateful to the Department of Science and Technology
(DST), New Delhi, for financial grant and establishing single crystal
X-ray diffractometer facility under FIST scheme. The authors are
thankful to Mr. Babulal Das for the X-ray data and one of the
reviewers for helpful comments.
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Appendix A. Supplementary material
CCDC 831679–831683 contain the supplementary crystallo-
graphic data for compounds 1–5. These data can be obtained free
of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found, in the online version, at http://
dx.doi.org/10.1016/j.ica.2012.04.017.
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