Molecular structures of dinuclear zinc(II) complexes of chiral tridentate imine and amine ligands: Effect of ligand geometry on diastereoselectivity

Article abstract of DOI:10.1016/j.ica.2012.06.041

Racemic mixtures of Schiff bases (L1H and L2H) were reduced to respective amines (L1′H and L2′H). Compounds of composition [Zn ₂(L1)₂(NCO)₂] (1), [Zn(L1)N₃] _n (2), [Zn₂(L2)₂(NCO)₂] (3), [Zn₂(L1′)₂(NCO)₂] (1′), [Zn ₂(L1)₂(N₃)₂]·2DMF (2′·2DMF) and [Zn₂(L2′)₂(NCO) ₂]·DMF (3′·DMF) were synthesized using these ligands, Zn(NO₃)₂·6H₂O and NCO ^- or N₃^- ions. Molecular structures of all six compounds have been established. Both imine and amine ligands have N ₂O donor set, but coordinate, respectively, in meridional and facial fashions. First four complexes are monochelates and last two are bis-chelates. The Zn₂O₂ unit in 1-3 has RS combination of imine where as in 1′ has RR(SS) combinations of amine. In 2′ and 3′, zinc(II) bis-chelates have cis,cis,trans-(O_P)₂(N _A)₂(N_Y)₂ stereochemistry and cis-(O_P)₂ disposition further coordinate to tetrahedral zinc. Compound 1′ exhibits 1D hydrogen-bonded polymer by enantioselective H-bonding interaction. In 2′, DMF molecules assemble RR and SS bis-chelates through N-H?O interactions.

Full text of DOI:10.1016/j.ica.2012.06.041

Inorganica Chimica Acta 394 (2013) 210–219
Contents lists available at SciVerse ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Molecular structures of dinuclear zinc(II) complexes of chiral tridentate imine
and amine ligands: Effect of ligand geometry on diastereoselectivity
⇑
Himanshu Sekhar Jena, Vadivelu Manivannan
Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781039, India
a r t i c l e i n f o
a b s t r a c t
Racemic mixtures of Schiff bases (L1H and L2H) were reduced to respective amines (L10H and L20H). Com-
pounds of composition [Zn2(L1)2(NCO)2] (1), [Zn(L1)N3]n (2), [Zn2(L2)2(NCO)2] (3), [Zn2(L10)2(NCO)2] (10),
[Zn2(L1)2(N3)2]ꢀ2DMF (20ꢀ2DMF) and [Zn2(L20)2(NCO)2]ꢀDMF (30ꢀDMF) were synthesized using these
Article history:
Received 31 March 2012
Received in revised form 22 June 2012
Accepted 26 June 2012
ꢁ
ligands, Zn(NO3)2ꢀ6H2O and NCOꢁ or N3 ions. Molecular structures of all six compounds have been
Available online 25 July 2012
established. Both imine and amine ligands have N2O donor set, but coordinate, respectively, in meridional
and facial fashions. First four complexes are monochelates and last two are bis-chelates. The Zn2O2 unit in
1–3 has RS combination of imine where as in 10 has RR(SS) combinations of amine. In 20 and 30, zinc(II) bis-
chelates have cis,cis,trans-(OP)2(NA)2(NY)2 stereochemistry and cis-(OP)2 disposition further coordinate to
tetrahedral zinc. Compound 10 exhibits 1D hydrogen-bonded polymer by enantioselective H-bonding
interaction. In 20, DMF molecules assemble RR and SS bis-chelates through N–Hꢀ ꢀ ꢀO interactions.
Ó 2012 Elsevier B.V. All rights reserved.
Keywords:
Schiff base
Racemic mixture
Tridentate ligand
Hydrogen bonding
Self-assembly
Diastereoselectivity
1. Introduction
We have been interested in the synthesis and coordination
chemistry of ligands containing a pyridyl ring [47–52]. As its con-
Zinc(II) ion is essential for all living organisms and is found to be
present in all six major classes of metalloenzymes [1–2]. In most of
these enzymes, bivalent zinc has distorted four- or five-coordina-
tion. Compounds have been synthesized using tetradentate tripo-
dal ligands to model the structural and functional properties of
zinc enzymes [3–6]. The active site of carboxypeptidase A, car-
boxypeptidase B and thermolysin enzymes consists of zinc(II) ion
surrounded by a donor set of N2O from the protein residue and a
water molecule at the fourth site [7–11]. Model studies with tri-
dentate ligands containing N, O and/or S donor atoms have been
reported [12–19]. Phenoxo bridged transition metal complexes
having M2O2 core containing N2O type donor imines and amines
find applications in electrical conductivity, magnetism, host–guest
chemistry, molecular separation, gas storage, sensors, photolumi-
nescence and catalysis [20–34]. Zinc complexes in particular have
antibacterial and antifungal activities [35–37]. The reported phen-
oxo bridged centrosymmetric/noncentrosymmetric zinc dimer of
imines and amines do not have chiral center and hence lack of dia-
stereoselectivity [38–42]. Inclusion of a chiral center in imine and
amine ligand moiety enhances diastereoselectivity around metal
center. Since secondary amines are flexible, prefer to bind in facial
[43–45] than meridional manner but with an exception [46].
tinuation, Schiff bases (L1H, L2H) and their reduction products
(L10H, L20H), each having a chiral carbon, 2-pyridyl ring and pheno-
lic group, were synthesized. These ligands upon treatment with
Zn(II) ion in presence of coligands NCOꢁ or N3ꢁ, afforded mono-
and bis-chelates of bivalent zinc, all compounds having binuclear
entities. Herein we report the structural characterization of these
complexes that reveal the role of ligand geometry on self-assembly
of racemic imine and amine ligands around the bivalent zinc.
2. Experimental
2.1. Materials and methods
A Perkin-Elmer Spectrum One spectrometer (4000–450 cmꢁ1),
Perkin-Elmer Series II CHNS/O Analyzer 2400, waters Q-TOF pre-
mier mass spectrometer and Bruker 400 MHz spectrophotometer
were used for obtaining relevant data. Thermogravimetry 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 7 °C/min in the noted tempera-
ture 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
Corresponding author. Tel.: +91 361 258 2306.
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.2012.06.041

H.S. Jena, V. Manivannan / Inorganica Chimica Acta 394 (2013) 210–219
211
program [53,54]. All the structures were solved by direct methods
using SHELXS-97 [55]. Non-hydrogen atoms located from the differ-
ence Fourier maps were refined anisotropically by full-matrix
least-squares on F2, using SHELXS-97 [55]. All hydrogen atoms were
included in the calculated positions and refined isotropically using
a riding model.
2-Acetylpyridine, 2-benzoylpyridine, NaNCO, (Aldrich, USA);
Zn(NO3)2ꢀ6H2O, NaN3, NaBH4, hydroxylamine hydrochloride, Zn
dust (Merck India Ltd.) and solvents were used as received without
further purification. (R,S)-1-(2-pyridyl)ethylamine, (R,S)-2-((1-(2-
pyridyl)ethylimino)methyl)phenol (L1H) were prepared using our
earlier reported procedure [50].
780(m), 757(s), 696(s), 678(m), 657(w), 621(s), 611(w), 576(s),
540(s), 480(w), 464(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. Anal. Calc. for
C19H16N2O: C, 79.14; H, 5.59; N, 9.72. Found: C, 79.02; H, 5.46;
N, 9.67%.
2.2.4. (R,S) 2-((1-(2-pyridyl)ethylamino)methyl)phenol (L10H)
(R,S)-1-(2-pyridyl)ethylamine (0.6 g, 5 mmol) and 2-hydroxy-
benzaldehyde (0.6 g, 5 mmol) in MeOH (50 mL) were stirred for
1 h at ambient conditions. The resultant yellow solution was
cooled in an ice bath and solid NaBH4 (0.57 g, 10 mmol) was added
with stirring, which turned the color of the solution to colorless
and stirring was continued overnight. The volatiles were removed
in vacuum and the residue was dissolved in water (50 ml), ex-
tracted with CH2Cl2 (3 ꢃ 20 ml), dried over anhydrous Na2SO4
and L10H was obtained as colorless oil after removal of the solvent.
Yield: 1.08 g (95%), ESI-MS: m/z Calc. for C14H16N2O+ 228.13.
Found: (M++H) 229.14. IR (KBr, cmꢁ1): 3285(w), 3048(w),
3009(w), 2970(m), 2926(w), 2855(w), 2720(w), 2637(w),
1614(w), 1590(s), 1572(w), 1488(w), 1471(w), 1455(w), 1434(m),
1372(w), 1257(s), 1185(m), 1150(m), 1103(s), 1035(s), 993(w),
977(s), 932(s), 842(m), 788(s), 752(s), 720(w), 627(s), 553(w),
500(s). 400 MHz 1H NMR (d (J, Hz), CDCl3): 13.23 (OH, s), 8.56
(1H, d, 2.8), 7.61 (1H, t, 7.8), 7.17 (1H, t, 8.4), 7.12 (1H, t, 7.6),
7.10 (1H, d, 7.6), 6.85 (1H, d, 6.0), 6.82 (1H, d, 6.0), 6.71 (1H, t,
7.2), 3.86 (1H, q, 9.8), 3.64 (2H, d, 6.2), 3.23 (NH, b), 1.39 (2H, d,
5.6). 100 MHz 13C NMR (d, CDCl3): 161.7, 157.9, 149.1, 136.2,
128.1, 122.5., 121.8, 121.6, 118.5, 115.9, 56.7, 53.2, 49.6, 22.0. Anal.
Calc. for C14H16N2O: C, 73.66; H, 7.06; N, 12.27. Found: C, 73.52; H,
6.96; N, 12.01%.
2.2. Syntheses
2.2.1. Phenyl(2-pyridyl)ketoxime
To a mixture of phenyl(2-pyridyl)ketone (10.0 g, 55 mmol) and
NH2OHꢀHCl (6.0 g, 86 mmol) in methanol (50 mL), an aqueous
solution (50 mL) of NaOH (11.0 g, 275 mmol) was added and stir-
red 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 fil-
tered, washed with water and dried in desiccators. Yield: 9.51 g
(87%). IR (KBr, cmꢁ1): 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. Anal. Calc. for C12H10N2O: C, 72.71; H, 5.08; N, 14.13. Found:
C, 72.64; H, 4.98; N, 14.02%.
2.2.2. (R,S) Phenyl(2-pyridyl)methaneamine
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, cmꢁ1):
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. Anal. Calc. for C12H12N2: C, 78.23;
H, 6.57; N, 15.21. Found: C, 77.64; H, 5.98; N, 15.13%.
2.2.5. (R,S) 2-((phenyl(2-pyridyl)methane)aminomethyl)phenol (L20H)
L20H was synthesized by following the procedure described for
L10H by using (R,S)-phenyl(2-pyridyl)methaneamine (0.755 g,
4 mmol) and 2-hydroxybenzaldehyde (0.5 g, 4 mmol) in MeOH
(50 ml). Yield of the solid product: 1.12 g (97%), ESI-MS: m/z Calc.
for C19H18N2O+ 290.14. Found: (M++H) 291.13. IR (KBr, cmꢁ1):
3328(s), 3263(w), 3058(w), 3043(w), 3008(s), 2916(w), 2902(w),
2854(m), 2717(w), 1614(w), 1588(s), 1570(w), 1492(w),
1471(m), 1455(w), 1443(w), 1415(w), 1362(s), 1342(w),
1318(m), 1253(s), 1190(s), 1148(m), 1121(m), 1104(m), 1096(w),
1076(w), 1047(m), 988(m), 977(s), 930(s), 896(s), 869(w), 842(s),
801(s), 752(s), 716(w), 702(s), 667(m), 633(m), 608(m), 567(m),
543(s), 470(s). 400 MHz 1H NMR (d (J, Hz), CDCl3): 11.23 (OH, s),
8.59 (1H, d, 4.8), 7.55 (1H, d, 8.0), 7.31 (2H, d, 6.8), 7.23 (1H, t,
4.6), 7.13 (1H, t, 8.0), 7.11 (1H, d, 7.6), 6.86 (2H, t, 7.4), 6.73 (1H,
t, 8.4), 4.90 (1H, s), 3.86 (2H, s), 3.42 (NH, b). 100 MHz 13C NMR
(d, CDCl3): 160.3, 158.2, 149.3, 141.3, 136.8, 128.9, 128.7, 127.8,
123.0, 122.9, 122.5, 119.1, 116.5, 66.0, 50.43. Anal. Calc. for
C19H18N2O: C, 78.59; H, 6.25; N, 9.65. Found: C, 78.34; H, 6.11;
N, 9.42%.
2.2.3. (R,S) 2-((phenyl(2-pyridyl)methylimino)methyl)phenol (L2H)
A
mixture
of
phenyl(2-pyridyl)methaneamine
(4.5 g,
2.2.6. [Zn2(L1)2(NCO)2] (1)
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%). ESI-MS: m/z Calc.
for C19H16N2O+ 288.13. Found: (M++H) 289.10. IR (KBr, cmꢁ1):
3081(s), 3009(s), 2896(s), 1623(s), 1586(s), 1464(s), 1431(s),
1383(w), 1313(s), 1279(s), 1215(w), 1200(s), 1151(s), 1118(m),
1053(s), 1028(s), 988(s), 938(w), 914(w), 893(w), 859(s), 846(w),
To L1H (0.226 g, 1.0 mmol) dissolved in DMF (10 mL), solid
Zn(NO)3ꢀ6H2O (0.300 g, 1.0 mmol) was added and stirred for
10 min. To this colorless solution, aqueous (5 mL) NaCNO (0.65 g,
1.0 mmol) was added and stirred for another 30 min. Colorless sin-
gle crystals of 1 suitable for X-ray diffraction study were obtained
from this DMF-H2O solution on standing for about one week time.
Yield: 0.58 g (87%). IR (KBr, cmꢁ1): 3022(w), 2981(w), 2906(w),
2873(w), 2187(s), 1649(s), 1606(w), 1597(m), 1575(w), 1548(s),

212
H.S. Jena, V. Manivannan / Inorganica Chimica Acta 394 (2013) 210–219
1470(s), 1448(s), 1397(s), 1380(w), 1337(w), 1316(w), 1287(s),
1198(m), 1146(w), 1130(m), 1101(m), 1072(w), 1052(m),
1026(w), 1015(w), 969(w), 901(s), 857(w), 814(w), 785(m),
759(s), 746(m), 676(w), 647(m), 620(w), 581(w), 543(w), 517(w),
468(w). Anal. Calc. for C30H26N6O4Zn2: C, 54.16; H, 3.94; N, 12.63.
Found: C, 54.04; H, 3.91; N, 12.57%. ESI-MS: m/z Calc. for
2.2.11. [Zn2(L20)2(NCO)2]ꢀDMF (30ꢀDMF)
Yield: 0.72 g (83%). IR (KBr, cmꢁ1): 3295(s), 3064(w), 2926(w),
2866(w), 2243(s), 2220(s), 1668(s), 1596(s), 1572(m), 1484(s),
1452(m), 1441(m), 1331(m), 1274(s), 1194(m), 1155(m),
1089(m), 1063(w), 1046(m), 1015(s), 984(s), 906(s), 871(s),
860(w), 773(w), 756(s), 743(m), 728(w), 700(s), 676(w), 640(m),
617(s), 586(m), 562(w), 534(m). Anal. Calc. for C43H40N7O5Zn2: C,
59.66; H, 4.66; N, 11.33. Found: C, 59.61; H, 4.64; N, 11.28%. ESI-
MS: m/z Calc. for {64Zn(L20)}+, 353.06. Found: 353.10. 400 MHz
1H NMR (d(J, Hz), DMSO-d6): 8.53 (1H, d, 4.2), 7.73 (2H, t, 7.6),
7.46 (2H, d, 5.6), 7.32 (1H, t, 7.2), 7.24 (2H, m), 7.08 (1H, d, 7.2),
7.06 (1H, d, 8.0), 6.82 (1H, d, 7.2), 6.53 (1H, s), 4.97 (2H, s).
{
64Zn(L1)}+, 289.03. Found: 289.04. 400 MHz 1H NMR (d (J, Hz),
DMSO-d6): 8.64 (1H, d, 3.6), 8.41 (1H, s), 7.95 (1H, t, 8.4), 7.49
(1H, d, 7.6), 7.44 (1H, t, 6.0), 7.19 (1H, d, 8.0), 7.15 (1H, t, 7.8),
6.70 (1H, d, 8.8), 6.46 (1H, t, 7.2), 4.78 (1H, q, 6.2), 1.58 (3H, d, 6.8).
Same procedure was followed for the synthesis of 2–3 and 10–30
by using appropriate ligand and coligand in the same molar ratio.
2.2.7. [Zn(L1)(N3)]n (2)
3. Results and discussion
Yield: 0.652 g (71%). IR (KBr, cmꢁ1): 2866(w), 2066(s), 1650(s),
1596(s), 1549(s), 1481(w), 1469(m), 1447(m), 1389(s), 1284(s),
1198(s), 1130(m), 1101(m), 1052(m), 900(m), 854(m), 784(m),
759(s), 747(m), 657(m), 517(m). Anal. Calc. for C14H13N5OZn: C,
50.54; H, 3.94; N, 21.05. Found: C, 50.42; H, 3.91; N, 20.98%. ESI-
MS: m/z Calc. for {64Zn(L1)}+, 289.03. Found: 289.05. 400 MHz 1H
NMR (d (J, Hz), DMSO-d6): 8.69 (1H, d, 4.2), 8.41 (1H, s), 7.95
(1H, t, 7.6), 7.49 (1H, d, 7.4), 7.44 (1H, t, 7.2), 7.22 (1H, t, 7.2),
7.15 (1H, d, 7.2), 6.75 (1H, d, 8.4), 6.50 (1H, t, 7.4), 4.79 (1H, q,
7.0), 1.63 (3H, d, 6.8).
3.1. Synthesis and spectroscopic studies
Condensation of racemic 1-(2-pyridyl)ethylamine or phenyl(2-
pyridyl)methaneamine with salicyladehyde afforded imine ligands
L1H and L2H, which on reduction with NaBH4 gave the corre-
sponding amine ligands L10H and L20H. By reacting the racemic
mixture of these two Schiff bases with Zn(NO3)2ꢀ6H2O and coli-
gands such as cyanate and azide ions, compounds of composition
[Zn2(L1)2(NCO)2] (1), [Zn(L1)N3]n (2) and [Zn2(L2)2(NCO)2] (3),
were isolated. In
a
similar manner, [Zn2(L10)2(NCO)2] (10),
2.2.8. [Zn2(L2)2(NCO)2] (3)
[Zn2(L10)2(N3)2]ꢀ2DMF (20) and [Zn2(L20)2(NCO)2]ꢀDMF (30) were
isolated from their reduced bases (Scheme 1). These reactions
yielded complexes in which zinc(II) ion are being shown to have
coordination numbers ranging from 4 to 6 having distorted
tetrahedral, square pyramidal, trigonal bipyramidal and octahedral
geometries (vide infra). Imine function is planar due to the sp2
hybridization for the nitrogen atom, hence ligands L1H and L2H
bind to the metal ion in meridional fashion where as amine func-
tion is pyramidal due to the sp3 hybridization for the nitrogen atom
and as a consequence ligands L10H and L20H span the facial posi-
tions around the metal center. Thus by isolating racemic mixtures
of a pair of tridentate ligands containing a chiral carbon atom that
can bind the metal ion in meridional and facial fashions, an oppor-
tunity exists to explore the nature of their coordinating behaviors.
In addition phenolate group has the potential to bridge two metal
centers and as a result a Zn2O2 unit can be anticipated. In order to
satisfy the coordination environment around M2O2 core, a chiral
imine/amine interact with another molecule either of same
chirality (homochiral dimer) or of opposite chirality (heterochiral
dimer) leaving some vacant sites for solvent or coligands [56–60]
to occupy. This preferred interaction between components of the
same or opposite chirality leads to spontaneous selection of
enantiomers from the racemic mixture. Thus the self-assembly of
racemic imines or amines will be very important for self-sorting
processes.
Yield: 0.65 g (82%). IR (KBr, cmꢁ1): 3295(s), 3063(w), 2925(m),
2221(s), 2189(s), 1668(s), 1627(s), 1599(s), 1572(m), 1549(m),
1483(s), 1442(s), 1405(m), 1331(w), 1291(w), 1277(m), 1197(m),
1151(m), 1127(m), 1046(m), 1019(m), 906(w), 871(s), 789(m),
757(s), 743(w), 701(s), 640(s), 620(s), 587(s), 547(m), 468(m). Anal.
Calc. for C40H30N6O4Zn2: C, 60.85; H, 3.83; N, 10.64%. Found: C,
60.65; H, 3.81; N, 10.59%. ESI-MS: m/z Calc. for {64Zn(L2)}+,
351.05. Found: 351.10. 400 MHz 1H NMR (d (J, Hz), DMSO-d6):
8.62 (1H, d, 4.0), 8.54 (1H, s), 7.98 (1H, t, 7.2), 7.56 (1H, t, 5.6),
7.45 (1H, d, 7.6), 7.34 (1H, t, 8.0), 7.29 (1H, d, 6.8), 7.19 (1H, t,
7.6), 7.13 (1H, d, 7.2), 6.61 (1H, d, 8.4), 6.40 (1H, t, 7.2), 6.04 (1H, s).
2.2.9. [Zn2(L10)2(NCO)2] (10)
Yield: 0.55 g (82%). IR (KBr, cmꢁ1): 3330(s), 3057(w), 2982(w),
2920(w), 2862(w), 2210(s), 1609(m), 1595(m), 1572(w), 1482(s),
1467(w), 1451(s), 1355(w), 1310(s), 1289(w), 1271(s), 1156(m),
1130(w), 1095(m), 1054(s), 1023(s), 971(w), 941(w), 927(s),
892(m), 873(s), 814(w), 785(m), 757(s), 731(s), 645(m), 623(m),
582(m), 556(w), 545(s). Anal. Calc. for C30H30N6O4Zn2: C, 53.83;
H, 4.52; N, 12.55. Found: C, 53.72; H, 4.50; N, 12.48%. ESI-MS: m/
z Calc. for {64Zn(L10)}+, 291.05. Found: 291.42. 400 MHz 1H NMR
(d(J, Hz), CD3OD): 8.20 (1H, d, 4.0), 7.45 (1H, t, 8.4), 7.09 (1H, d,
6.4), 6.95 (1H, t, 5.8), 6.77 (1H, t, 7.8), 6.64 (1H, d, 7.2), 6.46 (1H,
t, 4.0), 6.39 (1H, d, 7.6), 5.15 (NH, s), 3.60 (1H, q, 7.0), 3.47 (2H,
d, 7.2), 1.09 (2H, d, 6.8).
In IR spectra, conversion of L2H to L20H can be inferred by the
presence of a strong and sharp mN–H peak at 3328 cmꢁ1 in L20H.
However in L10H, the mN–H peak is obscured by a broad band of
mO–H probably due to involvement of O–H and N–H groups in
2.2.10. [Zn2(L10)2(N3)2]ꢀ2DMF (20ꢀ2DMF)
Yield: 0.71 g (87%). IR (KBr, cmꢁ1): 3252(s), 3069(w), 2922(w),
2857(w), 2076(s), 1662(s), 1596(s), 1573(m), 1484(s), 1450(s),
1381(w), 1348(m), 1284(m), 1260(s), 1154(m), 1135(w), 1096(m),
1054(m), 1021(s), 998(w), 936(m), 872(s), 781(m), 757(s), 735(s),
644(m), 617(w), 581(m), 541(m), 502(m). Anal. Calc. for C34H44N12-
O4Zn2: C, 50.07; H, 5.44; N, 20.61. Found: C, 49.98; H, 5.41; N,
20.57%. ESI-MS: m/z Calc. for {64Zn(L10)}+, 291.04. Found: 291.12.
400 MHz 1H NMR (d (J, Hz), CD3OD): 8.16 (1H, d, 4.0), 7.41 (1H, t,
8.4), 7.05 (1H, d, 6.4), 6.93 (1H, t, 5.8), 6.74 (1H, t, 7.8), 6.58 (1H,
d, 7.2), 6.42 (1H, t, 4.0), 6.37 (1H, d, 7.6), 5.10 (NH, s), 3.55 (1H, q,
7.0), 3.42 (2H, d, 7.2), 1.05 (2H, d, 6.8).
hydrogen bonding interactions. In imine ligands, the mC
@
for
N
imine group is present as
a strong and sharp peak at
ꢂ1623 cmꢁ1. This peak was replaced by a weak mN–H deformation
peak at ꢂ1614 cmꢁ1, in amine ligands. In amine ligands a new
strong peak due to the
nato complexes show mC
m
C–N was observed at ꢂ1255 cmꢁ1. The cya-
„
peak in the range 2187–2243 cmꢁ1
.
N
Presence of coordinated azide in 2 and 20 can be inferred by a peak
in the range 2066–2076 cmꢁ1. The ESI mass spectra showed char-
acteristic m/z peaks for the monochelated fragments {64Zn(L1)}+ at
289.04 (for 1), 289.05 (for 2); {64Zn(L2)}+ at 351.10 (for 3);
64Zn(L10)}+ at 291.42 (for 10), 291.12 (for 20) and Zn(L20)}+ at
64

H.S. Jena, V. Manivannan / Inorganica Chimica Acta 394 (2013) 210–219
213
Scheme 1. Schematic representation for the synthesis of 1–3 and 10–30.
353.10. The 1H NMR spectra of all the six complexes are nearly
identical to that of free ligands spectra.
Compound 1 crystallized in space group P21/n and ORTEP dia-
gram of the centrosymmetric dimeric unit, [Zn2(L1)2(NCO)2], is dis-
played in Fig. 1. The zinc(II) ion is bound by mono anionic end-cap
ligand L1 and nitrogen end of ambidentate cyanate ion, in the
square plane. The axial site is occupied by bridging OP from an-
other [Zn(L1)(NCO)] unit. Thus penta coordination around zinc cen-
ters can be described as distorted square pyramidal geometry
3.2. Molecular structures
The molecular structures of 1–3, 10, 20ꢀ2DMF and 30ꢀDMF were
determined using single crystal X-ray diffraction techniques. The
crystallographic data and refinement parameters are listed in Ta-
ble 1. Selected bond parameters are listed in Table 2 (for 1–3)
and Table 3 (for 10, 20ꢀ2DMF and 30ꢀDMF). The conventions followed
in discussions are: L1 = 2-((1-(2-pyridyl)ethylimino)methyl)phe-
nolate ion; L2 = 2-((phenyl(2-pyridyl)methylimino)methyl)pheno-
late ion; L10 = 2-((1-(2-pyridyl)ethylamino)methyl)phenolate ion;
L20 = 2-((phenyl(2-pyridyl)methane)aminomethyl)phenolate ion;
OP = phenolate-O; NY = pyridyl-N; NI = imine-N; NA = amine-N;
NC = cyanate-N and NZ = azide-N.
based on the calculated
s value of 0.38 [61]. The two trans angles
N2–Zn1–N3 and N1–Zn1–O1, in the square plane are smaller than
expected for a regular square base. As a consequence of the OP
bridge a Zn2O2 unit exists which has a planar rectangular shape
having unequal Zn–O distances, implying that OP bridge is unsym-
metrical in nature. The Zn2O2 unit has a center of symmetry in it
and as a consequence exists as heterochiral dimer. The OP bridge
also brings about a butterfly shape to the overall ligand moiety.
In the coordination sphere, the trend Zn–NY > Zn–NI > Zn–NC, in
Table 1
Crystallographic and refinement parameters of 1–3 and 10–30.
1
2
3
10
20ꢀ2DMF
30ꢀDMF
CCDC No.
Chem formula
Formula wt.
Temp. (K)
Cryst. syst.
Space group
a (Å)
863807
863808
C14H13N5OZn
332.66
863809
C40H30N6O4Zn2
789.48
296 (2)
Monoclinic
P21/c
8.6555(4)
11.6319(6)
17.4024(9)
863810
C30H30N6O4Zn2
669.38
296 (2)
Monoclinic
P21/n
9.039(2)
11.126(4)
31.323(10)
863811
C34H44N12O4Zn2
815.59
296 (2)
Monoclinic
P21/c
11.8857(9)
19.1656(14)
18.9389(12)
863812
C43H40N7O5Zn2
865.60
C
30H26N6O4Zn2
665.35
296 (2)
296 (2)
296 (2)
Monoclinic
P21/n
8.6765(12)
16.646(2)
10.0095(14)
Triclinic
Triclinic
ꢀ
ꢀ
P1
P1
6.2073(11)
10.5477(19)
11.406(2)
67.647(12)
87.400(13)
79.832(12)
679.6(2)
2
9.0463(3)
11.3639(4)
20.4068(8)
97.960(2)
92.802(2)
102.032(2)
2025.43(13)
2
b (Å)
c (Å)
a
(°)
b (°)
94.381(7)
94.858(3)
91.162(19)
116.113(4)
c
(°)
V (Å3)
1441.4(3)
2
1.711
1.533
3588
1745.78(15)
2
1.426
1.502
3037
3149.2(16)
4
1.566
1.412
5518
3873.9(5)
4
1.291
1.398
7752
Z
l
(mmꢁ1
)
1.813
1.626
3098
1.238
1.419
7060
qcalc. (g cmꢁ3
No. of unique rflns
)
No. of rflns. (I P 2
r
(I))
2755
3097
2752
3755
5644
6197
b
R1a, wR2 (I P 2
r(I))
0.0274, 0.0733
0.0381, 0.0799
1.005
0.243/ꢁ0.239
0.0398, 0.0967
0.0398, 0.0967
1.000
0.442/ꢁ0.897
0.0365, 0.0817
0.0627, 0.0950
1.087
0.393/ꢁ0.219
0.0434, 0.0918
0.0715, 0.1031
1.022
0.307/ꢁ0.307
0.0402, 0.1083
0.0627, 0.1255
1.030
0.882/ꢁ0.930
0.0366, 0.0918
0.0636, 0.1052
1.042
0.542/ꢁ0.319
b
R1a, wR2 (all data)
Goodness-of-fit (GOF) on (F2)
Largest peak/hole (e Åꢁ3
)
a
R1
wR2 = [
=
R
||Fo| ꢁ |Fc||/
R|Fo|.
b
2
R
w(Fo ꢁ Fc2)2/
R .
w(Fo2)2]1/2

214
H.S. Jena, V. Manivannan / Inorganica Chimica Acta 394 (2013) 210–219
Table 2
Selected bond lengths (Å) and bond angles (°) in 1–3.
1
2
3
Zn1–N1
Zn1–N2
Zn1–N3/N3A
Zn1–O1
2.159(2)
2.065(2)
1.969(2)
2.105(1)
2.016(1)
3.108(1)
2.707(2)
2.167(4)
2.124(3)
2.086(3)/2.388(3)
2.067(3)
2.131(3)
3.199(1)/3.534(1)
2.720(5)
2.720(5)
2.155(4)
2.066(3)
1.954(5)
2.128(3)
1.999(3)
3.193(1)
2.618(3)
Zn1–O1A
Zn1ꢀ ꢀ ꢀZn1/Zn1A
O1ꢀ ꢀ ꢀO1
N3ꢀ ꢀ ꢀN3
N1–Zn1–N2
N1–Zn1–N3/N3A
N1–Zn1–O1
77.78(6)
94.37(7)
163.25(6)
106.14(6)
140.06(7)
85.57(6)
113.48(6)
97.26(7)
106.35(7)
82.09(5)
76.2(1)
88.5(1)/94.1(1)
158.2(1)
94.3(1)
88.2(1)/161.6(1)
83.0(1)
77.8(1)
100.2(2)
160.2(1)
102.4(1)
125.2(2)
84.3(1)
118.4(1)
97.0(2)
115.5(2)
78.7(1)
N1–Zn1–O1A
N2–Zn1–N3/N3A
N2–Zn1–O1
N2–Zn1–O1A
O1–Zn1–N3/N3A
O1A–Zn1–N3/N3A
O1–Zn1–O1A
N3–Zn1–N3A
Zn1–O1–Zn1A
95.2(1)
97.6(1)/107.7(1)
176.0(1)/101.1(1)
80.8(1)
75.8(1)
99.2(1)
Fig. 1. ORTEP diagram (30%) and atom labeling scheme in 1 (all H-atoms except H6
are omitted for clarity).
97.91(6)
101.3(1)
Table 3
Selected bond lengths (Å) and bond angles (°) in 10–30.
10
20ꢀ2DMF
30ꢀDMF
Zn1–N1
Zn1–N2
Zn1–N3
Zn1–N4
Zn1–O1
Zn1–O2
Zn2–N4
Zn2–N5
Zn2–N6
Zn2–N8
Zn2–O1
Zn2–O2
Zn1ꢀ ꢀ ꢀZn2
O1ꢀ ꢀ ꢀO2
2.081(4)
2.233(4)
1.938(5)
2.141(3)
2.148(3)
2.138(4)
2.155(3)
2.180(2)
2.127(2)
2.157(2)
2.154(2)
2.140(2)
2.158(2)
2.131(1)
2.107(1)
1.980(3)
2.127(3)
2.121(5)
2.189(4)
1.933(5)
1.973(4)
1.931(2)
1.915(2)
1.963(4)
1.969(2)
1.961(2)
3.142(1)
2.084(3)
2.002(3)
3.218(1)
2.531(5)
1.992(1)
1.990(1)
3.096(1)
N1–Zn1–N2
N1–Zn1–N3
N1–Zn1–N4
N1–Zn1–O1
N1–Zn1–O2
N2–Zn1–N3
N2–Zn1–N4
N2–Zn1–O1
N2–Zn1–O2
N3–Zn1–N4
N3–Zn1–O1
N3–Zn1–O2
O1–Zn1–O2
N4–Zn1–O1
N4–Zn2–N5
N4–Zn2–N6
N4–Zn2–O2
N5–Zn2–N6
N5–Zn2–N8
N5–Zn2–O1
N5–Zn2–O2
N6–Zn2–O1
N6–Zn2–O2
N8–Zn2–O1
N8–Zn2–O2
O1–Zn2–O2
O1–Zn2–O2
Zn1–O1–Zn2
Zn1–O2–Zn2
77.6(2)
114.1(2)
79.0(1)
176.0(1)
98.7(1)
88.70(9)
93.17(9)
98.6(1)
106.1(1)
88.9(1)
163.3(1)
78.8(1)
94.5(1)
90.0(1)
76.08(8)
164.3(1)
78.36(6)
177.1(1)
97.91(6)
89.99(5)
92.29(6)
101.69(6)
100.30(6)
90.70(5)
166.28(6)
79.18(6)
92.94(5)
88.16(6)
85.38(5)
167.53(6)
124.1(2)
93.7(2)
98.8(2)
88.6(1)
154.1(1)
Fig. 2. ORTEP diagram (30%) and atom labeling scheme in 2 (all H-atoms except H6
are omitted for clarity).
121.5(2)
107.0(2)
76.0(1)
93.7(2)
77.7(2)
117.3(2)
122.7(2)
98.1(2)
coordinate through nitrogen atom in a bent fashion with an angle
of 137.0(2)° at N3. Both the five- and six-membered chelate rings
are puckered with the former having a near-envelope shape. The
asymmetric carbon atom C6, lie in flap at a distance of 0.32 Å from
the slightly twisted plane containing other four atoms N2Zn1N1C5.
In the six-membered ring Zn1 atom lies at a distance of 0.51 Å from
the slightly twisted plane containing the atoms N2C8C9C14O1. In
89.6(1)
90.85(6)
114.6(1)
110.0(1)
113.0(1)
119.0(1)
156.8(1)
90.0(2)
105.0(2)
119.8(2)
116.34(8)
109.23(8)
109.58(7)
118.68(8)
117.6(1)
110.7(1)
the packing diagram, C–Hꢀ ꢀ ꢀ
p
interaction, C10–H10ꢀ ꢀ ꢀC13
(3.690(3) Å) and C–HꢀꢀꢀO interaction, C2–H2ꢀꢀꢀO2 (3.187(3) Å) are
76.5(1)
significant.
84.96(9)
98.34(9)
100.42(9)
85.38(5)
97.28(5)
98.13(6)
ꢀ
Compound 2 crystallized in space group P1 and the molecular
104.7(2)
102.3(1)
structure consists of neutral 1D coordination polymer having the
formula [Zn(L1)(N3)]n. This polymer is formed from a [Zn(L1)]2 di-
mer in which each zinc(II) ion is coordinated by L1, and both OP
atoms are involved in bridging the two metal ions. These
bond lengths was observable. The cyanate ion is slightly bent at the
carbon atom with the angle subtended at C13 being 177.6(3)° and
[Zn(L1)]2 units are further bridged by two azide ions in a
l
ꢁ 1,1

H.S. Jena, V. Manivannan / Inorganica Chimica Acta 394 (2013) 210–219
215
Fig. 3. ID coordination polymeric structure in 2.
fashion to a 1D coordination polymer. The ORTEP diagram with
atom numbering scheme of the repeating unit is displayed in
Fig. 2 and a representative view of the polymer in Fig. 3. The biva-
lent zinc is hexa coordinated and has a distorted pseudo octahedral
geometry. The coordination environment around bivalent zinc is
NINY(NZ)2(OP)2 and the stereochemistry for (NINY)(NZ)2(OP)2 being
cis,cis,cis. Thus the polymer contains rectangular shaped planar
Zn2O2 and Zn2N2 units, each having center of symmetry residing
in the unit. As a consequence, Zn2O2 unit is formed from a racemic
pair of L1. The coordination polymer is formed by edge-sharing of
two octahedral {ZnNINY(NZ)2(OP)2} units and the shared edges are
cis to each other with an angle at zinc atom being 134.38(2)°. Both
OP-linked Zn2O2 and NZ-linked Zn2N2 units are unsymmetrical. The
trend, Zn–NY > Zn–NI > Zn–NZ in the metal ligand bonds is also ob-
served. The L1 is bound to Zn(II) ion by a puckered five- and six-
membered chelate rings with the ligand being twisted. The asym-
metric carbon atom deviates from the five-membered chelate ring
having dihedral angle of 18.17° between C5C6N2 and C5N1Zn1N2
planes. The dihedral angle of 35.82° between the planes formed by
N2Zn1O1 and O1C14C9C8N2 suggests an out of plane displace-
ment of zinc from the envelope shaped six membered rings.
Compound 3 crystallized in space group P21/c and ORTEP dia-
gram with the atom labeling scheme is displayed in Fig. 4. Ligands
L1 (R = Me) and L2 (R = Ph) differ in the substitution at the asym-
metric carbon atom but the coordination environment remain
identical. Hence compounds 1 and 3 are isostructural, but with
subtle differences. Five-coordinate zinc centers are highly distorted
value of 160.2(1)°. The Zn2O2 unit has a planar rectangular shape
having unequal Zn–O distances, implying that OP bridge is unsym-
metrical in nature. Since the unit also has the center of symmetry
in it, exists as heterochiral dimer. Among the coordination bonds,
the trend Zn–NY > Zn–NI > Zn–NC in bond lengths was observable.
Ligand L2 is bound to the zinc atom by a five-membered and a
six-membered chelate ring and both rings are puckered, resulting
in an open book shape for the ligand moiety. The asymmetric car-
bon atom deviates from the puckered five-membered chelate ring
and dihedral angle between the two planes C5C6N2 and
C5N1Zn1N2 being 8.8°. The dihedral angle of 29.36° between the
planes formed by N2Zn1O1 and O1C14C9C8N2 suggests an out
of plane displacement of zinc from envelope shaped six membered
rings. In the packing diagram, C12–H12ꢀ ꢀ ꢀO2 (3.478(6) Å) and
C16–H16ꢀ ꢀ ꢀ
p(C20) (3.668(7) Å) interactions connects the dimers
in head-to-tail fashion to a 1D structure (Fig. 5) in which an isotac-
tic arrangement of the asymmetric carbon centers are present.
Compound 10 crystallized in space group P21/n and asymmetric
unit contains the neutral dinuclear complex [Zn2(L10)2(NCO)2]. The
molecule is non-centrosymmetric in nature and ORTEP diagram
with the atom labeling scheme is displayed in Fig. 6. Both the zinc
centers are penta coordinated and each bound by a mono anionic
tridentate ligand in facial fashion. Other two coordination sites
are occupied by NC and bridging OP. Coordination geometry around
both zinc centers is highly distorted as evident from calculated
s
values of 0.56 and 0.50. However, the geometry around both zinc
centers can be regarded as distorted trigonal bipyramidal with NC-
NY and coordinated-OP forming the trigonal plane while NA and
bridged-OP atoms occupying axial sites. The sum of three angles
in the trigonal planes at Zn1 and Zn2 are 359.7(2)° and 359.8(2)°,
respectively. But the trans angles at Zn1 and Zn2 are, respectively,
154.1(1)° and 156.8(1)°, deviate largely from linearity. The Zn2O2
unit is slightly non planar with the dihedral angle between
O1Zn1O2 and O1Zn2O2 planes being 6.9° and that between
Zn1O1Zn2 and Zn1O2Zn2 being 8.7°. The Zn2O2 unit has oblique/
diamond shape as can be inferred from the bonding and non-bond-
ing distances around it. The Zn2O2 unit in 10 does not have the cen-
ter of symmetry inside the dimeric form and hence lead to the
formation of a homochiral dimer having the combination as either
RR or SS for the asymmetric C-atom. However the crystal lattice, in
overall has an equal mixture of dimers containing RR and SS com-
binations, due to the center of symmetry that lies outside the mol-
ecule. On complexation, nitrogen atom of the secondary amine
group in L10 also becomes chiral. In 10, if the absolute configura-
tions of both the NA centers are RR then C-centers are SS and vice
versa. The trend Zn–NA > Zn–NY > Zn–NC in the metal ligand bond
distances is observed. The ligand forms a five-membered chelate
ring with bite angle of ꢂ77.7(2)° and six-membered chelate ring
with bite angles of 88.6(1)°, 90.0(2)° and both rings are puckered.
However other cis angle having the values of 122.7(2)° and
124.1(2)° is much wider. Two cyanato groups are oriented at tor-
sional angle of 28.1(3)°. The packing diagram of 10 reveals the
having a calculated
s value of 0.58, but the coordination geometry
can be best described as distorted trigonal bipyramid. The trigonal
plane is formed by OPNINC donor set with its angles lying in the
range 115.5(2)–125.2(2)° and the axial O1–Zn1–N1 angle has a
Fig. 4. ORTEP diagram (30%) and atom labeling scheme in 3 (all H-atoms except H6
are omitted for clarity).

216
H.S. Jena, V. Manivannan / Inorganica Chimica Acta 394 (2013) 210–219
Fig. 5. 1D chains formed by C–Hꢀ ꢀ ꢀO and C–Hꢀ ꢀ ꢀ
p
interactions with an isotactic arrangement of the asymmetric carbon centers present in 3.
Compound 20ꢀ2DMF crystallized in space group P21/c and OR-
TEP diagram with atom labeling scheme of 20, is displayed in
Fig. 8. The molecular structure of 20 consists phenoxo bridged neu-
tral molecule having the formula [Zn2(L10)2(N3)2]. There are two
zinc centers: (i) a hexa coordinated bis-chelate {Zn(L10)2}, in which
zinc(II) ion being coordinated by the facial tridentate ligand L10,
resulting in overall cis,cis,trans-(OP)2(NA)2(NY)2 stereochemistry
around the metal ion; (ii) a tetra coordinated zinc center in which
the bivalent zinc is coordinated by two end-on azide ions and by
the {Zn(L10)2}-unit through two OP atoms. It is relevant to note that
formation of such bimetallic centers using cis-(OP)2 disposition has
been reported [64]. Compound 20 is completely different from 10,
although it contains the same base L10, but the effect of changing
the coligand from cyanate ion (10) to azide ion (20), is reflected in
a drastic change in the coordination environment. The hexa- and
tetra- coordinated zinc centers, respectively, have distorted octahe-
dral and tetrahedral geometries. In the hexa coordinated center the
cis angles lie in the range 76.1(1)–106.1(1)° while the trans angles
lie in the range 163.3(1)–176.0(1)°. The three angles around the
metal center in tetra- coordinated zinc center are in the range
110.0(1)–119.0(1)° but the O1–Zn2–O2 (85.0(1)°) being acute
which is due to their bridging nature. The edge sharing between
the hexa- and tetra-coordinated zinc centers forms a rectangular
Zn2O2 unit in which the two planes containing the atoms
O1Zn1O2 and O1Zn2O2 angle by 4.4°. Since the center of symme-
try do not lie at zinc atom of hexa-coordinated center, the asym-
metric carbon atom in both L10 have the same absolute
configuration. As observed in 10, if the absolute configurations of
both the NA centers are RR then C-centers are SS and vice versa.
The Zn–NA bond lengths are longer than that of Zn–NY, while Zn–
NZ bond distances found in the tetra-coordinated zinc atom are
shorter than Zn–NI and Zn–NY bond distances found in hexa-coor-
dinated zinc atom. Solvent DMF molecules play an important role
in assembling RR and SS bis-chelates, by involving its oxygen atom
in H-bonding interaction with each of the two NA atom of the re-
duced Schiff bases {N2–H2ꢀꢀꢀO3, 2.80(1); N4–H4ꢀ ꢀ ꢀO4,
Fig. 6. ORTEP diagram (30%) and atom labeling scheme in 10 (all H-atoms except H6
and H20 are omitted for clarity).
presence of H-bonding interaction N5–H5ꢀꢀꢀO4, 2.984(7) Å between
the secondary amine hydrogen and cyanato oxygen atoms. This oc-
curs at N5O4Zn2O4 having a torsional angle of 24.4(3)°. This N5–
H5ꢀ ꢀ ꢀO4 interaction selectively links adjacent heterochiral dimers
to 1D H-bonded polymer {such as ꢀ ꢀ ꢀRRꢀ ꢀ ꢀRRꢀ ꢀ ꢀRRꢀ ꢀ ꢀ or
ꢀ ꢀ ꢀSSꢀ ꢀ ꢀSSꢀ ꢀ ꢀSSꢀ ꢀ ꢀ} as shown in Fig. 7. This type of H-bonding inter-
action has been termed as enantioselective H-bonding [62,63]. In
addition, two adjacent heterochiral dimers are also associated by
C17–H17ꢀ ꢀ ꢀO4; 3.40(1) and C17–H17ꢀ ꢀ ꢀ
p; 3.69(1) Å interactions.
The adjacent RR and SS H-bonded polymers are interlinked by H-
bonding interaction N2–H2ꢀ ꢀ ꢀN3, 3.435(6) Å and other weak inter-
action such as: C3–H3ꢀ ꢀ ꢀO3, 3.470(8); C10–H10ꢀ ꢀ ꢀO3, 3.392(8);
and C10–H10ꢀ ꢀ ꢀ
p, 3.554(9) Å, to a 2D sheet structure along a-axis.
Fig. 7. 1D H-bonded polymer representing ꢀ ꢀ ꢀSSꢀ ꢀ ꢀSSꢀ ꢀ ꢀSSꢀ ꢀ ꢀ sequence in 10.

H.S. Jena, V. Manivannan / Inorganica Chimica Acta 394 (2013) 210–219
217
Compound 30 is completely different from 3, as a result of changing
L2 to L20 and with the same coligand. It is also different from 10
(similar ligand and same coligand) but similar to 20 (similar ligand
and different coligand). The hexa- and tetra- coordinated zinc cen-
ters, respectively, have distorted octahedral and tetrahedral geom-
etries. In the hexa coordinated center the cis angles lie in the range
78.36(6)–101.69(6)° while the trans angles lie in the range
166.28(6)–177.07(6)°. The three angles around the metal center
in tetra-coordinated zinc center are in the range 109.3(1)–
114.6(1)° but the O1–Zn2–O2 (85.4(1)°) being acute which is due
to their bridging nature. The edge sharing between the hexa- and
tetra- coordinated zinc centers form a rectangular Zn2O2 unit in
which the two planes containing the atoms O1Zn1O2 and
O1Zn2O2 angle by 2.0°. Since the center of symmetry do not lie
at zinc atom of hexa-coordinated center, the asymmetric carbon
atom in both the L20 have the same absolute configuration and
the bis-chelates have RR or SS combinations. As observed in 10
and 20, if the absolute configurations of both the NA centers are
RR then C-centers are SS and vice versa. The Zn–NA bond lengths
are comparable that of Zn–NY lengths. But the Zn–NZ bond dis-
tances found in the tetra-coordinated zinc atom are shorter than
Zn–NI and Zn–NY bond distances found in hexa-coordinated zinc
atom. The Zn–OP bond distances in the hexa-coordinated zinc
atoms are longer than that found in the tetra-coordinated zinc
atom. Solvent DMF molecules do not involve in H-bonding interac-
tion but show some C–Hꢀ ꢀ ꢀO interactions {C23–H23ꢀ ꢀ ꢀO4,
3.247(3); C41–H41ꢀ ꢀ ꢀO4, 3.55(5); C25–H25ꢀ ꢀ ꢀO5, 3.574(5) Å} that
include oxygen and carbon atoms of DMF (Fig. 11).
Fig. 8. ORTEP diagram (30%) and atom labeling scheme in 20 (all H-atoms except H6
and H20 are omitted for clarity).
2.966(5) Å}. Other significant weak interactions (Fig. 9) that occur
between DMF and 20 are: N2–H2ꢀ ꢀ ꢀO3; 2.80(1), C21–H21ꢀ ꢀ ꢀO3;
3.36(1), C29–H29ꢀ ꢀ ꢀN5; 3.582(3) and C29–H29ꢀ ꢀ ꢀN6; 3.485(8) Å.
The packing diagram of 20, reveals weak interactions such as: C6–
The hexa-coordinated zinc centers in 20 and 30 are intrinsically
asymmetric in nature due to orientation of chelate rings. By view-
ing through the opposite NYNAOP pair of triangular faces, the RR
H6ꢀꢀꢀO10, 3.497(8) and C29–H29ꢀ ꢀ ꢀ
p, 3.77(1) Å exist between RR
bis-chelates have a
and the SS bis-chelates have
crystal lattice has an equal proportions of RR and SS bis-chelates,
and isomers are also in equal amounts.
Overall, the imine ligands are coordinated in meridional fash-
ion, forms OP bridged centrosymmetric binuclear structures and
hence compounds 1–3 have a RS combination of the ligand. But,
amine ligands span facial positions and form a non-centrosymmet-
ric Zn2O2 unit in 10 resulting in a RR or SS combination of amine.
However in 20 and 30, amine bis-chelates are present and two OP
groups occupy the cis positions which further act as bidentate li-
gand towards {Zn(CNO)2} and {Zn(N3)2} units. This leads to binu-
clear zinc complexes with edge-shared octahedron and
tetrahedron of zinc centers. The amine ligands show a wide range
D
configuration for the complex molecule
and SS bis-chelates. The C4–H4ꢀ ꢀ ꢀN7, 3.580(6); C7–H7ꢀ ꢀ ꢀO4,
3.581(6) and C33–H33ꢀ ꢀ ꢀC11; 3.691(7) Å interactions occur be-
tween two identical RR(SS) bis-chelates.
D
configuration. Since the overall
D
D
0
ꢀ
Compound 3 ꢀDMF crystallized in space group P1 and ORTEP
diagram with the atom labeling scheme of 30, is displayed in
Fig. 10. The molecular structure of 30 consists OP bridged neutral
dinuclear complex [Zn2(L20)2(NCO)2]. As observed in 20, there are
two zinc centers in 30 as well: (i) a hexa coordinated bis-chelate
{Zn(L20)2}, in which zinc(II) ion being coordinated by the facial tri-
dentate ligand L20 resulting in overall cis,cis,trans-(OP)2(NA)2(NY)2
stereochemistry around the metal ion; (ii) a tetra coordinated zinc
center in which the bivalent zinc is coordinated by two NC atoms of
cyanate ions and by the {Zn(L20)2}-unit through two OP atoms.
Fig. 9. Interaction of DMF with RR and SS bis-chelates in 20.

218
H.S. Jena, V. Manivannan / Inorganica Chimica Acta 394 (2013) 210–219
Fig. 10. ORTEP diagram (30%) and atom labeling scheme in 30 (all H-atoms except H6, H25, H2N and H4N are omitted for clarity).
Fig. 11. C–Hꢀ ꢀ ꢀO interactions of DMF with RR and SS bis-chelates in 30.
of NY–Zn–OP angles (88.2(1)–124.1(2)°). The observed angles,
122.7(2)–124.1(2)° (in 10) and 88.2(1)–90.0(1)° (in 20 and 30), are,
respectively, necessary for the demands of trigonal bipyramidal
and octahedral geometries. This is consistent with the flexible nat-
ure of the secondary amine function on coordination to transition
metal ions [45,65]. As such there is no perceptible coligand effect
observed in these complexes. They merely tend to bind to the site
left free by the tridentate ligands, may be due to domination of OP
bridging.
atmosphere of nitrogen. Freshly prepared samples were kept in
desiccators overnight prior to TG analysis and the profiles are dis-
played in Fig. S1. In compound 20, the weight loss of 9.19% (Calc.
8.96%) was observed in the temperature range of 105–143 °C, cor-
responding to the loss of one DMF molecule. Loss of second DMF
molecule is along with one azide ion occur for weight loss of
19.41% (Calc. 19.24%) in the temperature range 256–375 °C. From
the X-ray structure data (vide supra), it has been observed that
one of the DMF molecules exhibits a shorter H-bonding distance
of 2.804(1) Å than the other (2.966(5) Å) with NA atoms in com-
pound 20. It is consistent with the TG profile that the DMF molecule
having a shorter H-bonding distance could be lost at the higher
temperature range. In compound 30, the weight loss of 7.95% (Calc.
8.4%) was observed in the temperature range of 117–245 °C, that
3.3. Thermal analyses
The thermogravimetric analyses of 20ꢀ2DMF and 30ꢀDMF were
carried out in the temperature range 25–600 °C in
a static

H.S. Jena, V. Manivannan / Inorganica Chimica Acta 394 (2013) 210–219
219
[7] D. Pucci, I. Aiello, A. Bellusci, A. Crispini, M. Ghedini, M. La Deda, Eur. J. Inorg.
Chem. (2009) 4274.
[8] W.N. Lipscomb, Acc. Chem. Res. 3 (1970) 81.
correspond to the loss of one DMF molecule. Since the monoden-
tate coligands can be expected to lose prior to tridentate chelating
ligands, the weight loss of 19.31% (Calc. 11.2%) for cyanate ion can
be expected to occur in the temperature range 254–376 °C. Overall
in both compounds the Zn2O2 units are quite stable up to a calcu-
lated temperature of ꢂ375 °C.
[9] F.A. Quiocho, W.N. Lipscomb, Adv. Protein Chem. 25 (1971) 1.
[10] M.F. Schmidt, J.R. Herriott, J. Mol. Biol. 103 (1976) 175.
[11] B.W. Matthews, J.N. Jansonius, P.M. Colement, Nature 238 (1972) 37.
[12] J. Tisato, F. Refosco, F. Bandoli, Coord. Chem. Rev. 135 (1994) 325.
[13] P.A. Vigato, S. Tamburini, Coord. Chem. Rev. 248 (2004) 1717.
[14] Yu.E. Alexeeva, B.I. Kharisov, T.C. Hernandez Garcia, A.D. Garnovskii, Coord.
Chem. Rev. 254 (2010) 794.
[15] R. Ganguly, B. Sreenivasulu, J.J. Vittal, Coord. Chem. Rev. 252 (2008) 1027.
[16] X. Ran, L. Wang, Y. Lin, J. Hao, D. Cao, Appl. Organometal. Chem. 24 (2010) 741.
[17] X. Ran, L. Wang, D. Cao, Y. Lin, J. Hao, Appl. Organometal. Chem. 25 (2011) 9.
[18] G.G. Mohamed, M.M. Omar, A.A. Ibrahim, Eur. J. Med. Chem 44 (2009)
4801.
[19] V.G. Vaidyanathan, T. Weyhermuller, B.U. Nair, J. Subramanian, J. Inorg.
Biochem. 99 (2005) 2248.
[20] S.S.Y. Chui, S.M.F. Lo, J.P.H. Charmant, A.G. Orpen, I.D. Williams, Science 283
(1999) 1148.
[21] M. Albrecht, Chem. Rev. 101 (2001) 3457.
[22] M.A. Ali, S.E. Livingstone, Coord. Chem. Rev. 13 (1974) 101.
[23] T. Katsuki, Coord. Chem. Rev. 140 (1995) 189.
[24] R. Singh, A. Banerjee, E. Colacio, K.K. Rajak, Inorg. Chem. 48 (2009) 4753.
[25] R. Bagai, S. Datta, A. Betancur-Rodriguez, K.A. Abboud, S. Hill, G. Christou,
Inorg. Chem. 46 (2007) 4535.
[26] S. Naiya, H.-S. Wang, M.G.B. Drew, Y. Song, A. Ghosh, Dalton Trans. 40 (2011)
2744.
[27] P. Mukherjee, M.G.B. Drew, C.J. Gómez-Garíca, A. Ghosh, Inorg. Chem. 48
(2009) 5848.
[28] S. Basak, S. Sen, C. Marschner, J. Baumgartner, S.R. Batten, D.R. Turner, S. Mitra,
Polyhedron 27 (2008) 1193.
4. Conclusion
Six zinc(II) complexes were synthesized using a racemic mix-
ture of tridentate imine and their reduced amine ligands. Determi-
nation of their molecular structures revealed the presence of a
Zn2O2 unit in all complexes. The tridentate imine and amine li-
gands, respectively, span meridional and facial positions due to
sp2 and sp3 hybridization on N-atom. Compound 1–3 have center
of symmetry in the Zn2O2 unit and has a RS combination of racemic
Schiff bases around zinc centers. Where as in 10, the Zn2O2 unit do
not have center of symmetry in it and has a RR(SS) combination of
amine ligand. In 20 and 30, hexa-coordinated zinc(II) bis-chelates of
amine are formed having RR(SS) combination of ligand. These two
complexes have a cis-(OP)2 disposition which coordinate to another
tetra- coordinated zinc(II) center. The Zn–NY bonds in imine com-
pounds are longer than Zn–NI bonds, but are shorter than Zn–NA
bonds in the amine complex. In these complexes no perceptible
coligand effect has been observed and they merely tend to bind
to the site left free by tridentate ligands, which may be due to
the domination of OP bridging. In 10, 1D polymeric chain exists that
are formed by enantioselective H-bonding interaction between
adjacent enantiomeric dimers. In 20 and 30, solvent DMF molecules
are involved in assembling RR and SS bis-chelates. Also the RR and
[29] E. Ruiz, P. Alemany, S. Alvarez, J. Cano, J. Am. Chem. Soc. 119 (1997) 1297.
[30] K.E. Jelfs, X. Wu, M. Schmidtmann, J.T.A. Jones, J.E. Warren, D.J. Adams, A.I.
Cooper, Angew. Chem., Int. Ed. 50 (2011) 1.
[31] C. Diedrich, R.J. Deeth, Inorg. Chem. 47 (2008) 2494.
[32] K.C. Gupta, A.K. Sutar, Coord. Chem. Rev. 252 (2008) 1420.
[33] R.H. Holm, P. Kennepohl, E.I. Solomon, Chem. Rev. 96 (1996) 2239.
[34] L. Canali, D.C. Sherrington, Chem. Soc. Rev. 28 (1999) 85.
[35] C.J. Chang, S.J. Lippard, Metal Ions Life Sci. 1 (2006) 321.
[36] S. Uhlenbrock, B. Krebs, Angew. Chem., Int. Ed. Engl. 31 (1992) 1647.
[37] E.M. Nolan, J.W. Ryu, J. Jaworski, R.P. Feazell, M. Sheng, S.J. Lippard, J. Am.
Chem. Soc. 128 (2006) 15517.
[38] S.S. Tandon, S. Chander, L.K. Thompson, Inorg. Chim. Acta 300–302 (2000) 683.
[39] S.S. Tandon, S. Chander, L.K. Thompson, J.N. Bridson, V. McKee, Inorg. Chim.
Acta 219 (1994) 55.
[40] C.R. Bhattacharjee, G. Das, P. Mondal, S.K. Prasad, D.S.S. Rao, Eur. J. Inorg. Chem.
9 (2011) 1418.
SS bis-chelates, respectively, have
D and D configurations.
Although we are not able to isolate pure RR or SS dimers from
the racemic mixture, the self-assembly observed here due to the
above noted factors will boost the understanding of self-sorting
process around the metal ion by racemic mixture of meridionally
and facially coordinating tridentate ligands.
[41] H. Keypour, M. Shayesteh, D. Nematollahi, L. Valencia, H.A. Rudbari, J. Coord.
Chem. 63 (2010) 4165.
Acknowledgments
[42] J.-Y. Miao, Acta Cryst. E67 (2011) m1598.
[43] L.L. Koh, J.D. Ranford, W.T. Robinson, J.O. Svensson, A.L.C. Tan, D. Wu, Inorg.
Chem. 35 (1996) 6466.
[44] F.D. Lesh, S.S. Hindo, M.J. Heeg, M.M. Allard, P. Jain, B. Peng, L. Hryhorczuk, C.N.
Verani, Eur. J. Inorg. Chem. (2009) 345.
[45] C. Imbert, H.P. Hratchian, M. Lanznaster, M.J. Heeg, L.M. Hryhorczuk, B.R.
McGarvey, H.B. Schlegel, C.N. Verani, Inorg. Chem. 144 (2005) 7414.
[46] A. Biswas, M.G.B. Drew, Y. Song, A. Ghosh, Inorg. Chim. Acta 376 (2011) 422.
[47] S.K. Padhi, V. Manivannan, Inorg. Chem. 45 (2006) 7994.
[48] V.K. Fulwa, R. Sahu, H.S. Jena, V. Manivannan, Tetrahedron Lett. 50 (2009)
6264.
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.
Appendix A. Supplementary material
[49] R. Sahu, S.K. Padhi, H.S. Jena, V. Manivannan, Inorg. Chim. Acta 363 (2010)
1448.
CCDC 863807–863812 contain the supplementary crystallo-
graphic data for 1–3, 10, 20ꢀ2DMF, 30ꢀDMF and a file containing TG
profiles of 20ꢀ2DMF and 30ꢀDMF, 1H NMR and ESI-Mass spectra of
1–3, 10–30. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/da-
ta_request/cif. Supplementary data associated with this article
can be found, in the online version, at http://dx.doi.org/10.1016/
j.ica.2012.06.041.
[50] H.S. Jena, J. Subramanian, V. Manivannan, Inorg. Chim. Acta 365 (2011) 177.
[51] H.S. Jena, V. Manivannan, Inorg. Chim. Acta 390 (2012) 154.
[52] R. Sahu, V.K. Fulwa, H.S. Jena, V. Manivannan, Polyhedron 33 (2012) 9.
[53] G.M. Sheldrick, SADABS, University of Gottingen, Gottingen, Germany, 1996.
[54] SMART and SAINT, Siemens Analytical X-ray Instruments Inc., Madison, WI,
1996.
[55] G.M. Sheldrick, SHELXS-97 and SHELXL-97, University of Gottingen, Gottingen,
Germany, 1997.
[56] O. Mamula, A. von Zelewsky, Coord. Chem. Rev. 242 (2003) 87.
[57] S.G. Telfer, R. Kuroda, Coord. Chem. Rev. 242 (2003) 33.
[58] E.J. Enemark, T.D.P. Stack, Angew. Chem., Int. Ed. 37 (1998) 932.
[59] J.M. Rowland, M.M. Olmstead, P.K. Mascharak, Inorg. Chem. 41 (2002) 1545.
[60] S.G. Telfer, T. Sato, R. Kuroda, J. Lefebvre, D.B. Leznoff, Inorg. Chem. 43 (2004)
421.
[61] A.W. Addison, T.N. Rao, J. Reedijk, J. Van Rijn, G.C. Verschor, J. Chem. Soc.,
Dalton Trans. (1984) 1349.
[62] Y. Ishida, T. Aida, J. Am. Chem. Soc. 124 (2002) 14017.
[63] A. Tessa ten Cate, P.Y.W. Dankers, H. Kooijman, A.L. Spek, R.P. Sijbesma, E.W.
Meijer, J. Am. Chem. Soc. 125 (2003) 6860.
References
[1] A. Galdes, B.L. Vallee, in: H. Sigel (Ed.), Role of Metal Ions in Biological Systems,
vol. 15, Marcel Dekker, New York, 1983, p. 1.
[2] R.S. Brown, J. Huguet, N.J. Curtis, in: H. Sigel (Ed.), Role of Metal Ions in
Biological Systems, vol. 15, Marcel Dekker, New York, 1983, p. 55.
[3] W.R. Kester, B.W. Matthews, J. Biol. Chem. 252 (1977) 7704.
[4] A. Trösch, H. Vahrenkamp, Eur. J. Inorg. Chem. (1998) 827.
[5] H. Adams, N.A. Bailey, D.E. Fenton, Q.-Y. He, J. Chem. Soc., Dalton Trans. (1996)
2857.
[64] X. Zhou, H. Fang, Y. Ge, Z. Zhou, Z. Gu, X. Gong, G. Zhao, Q. Zhan, R. Zeng, Y. Cai,
Cryst. Growth Des. 10 (2002) 4014.
[65] V.K. Muppidi, S. Das, P. Raghavaiah, S. Pal, Inorg. Chem. Commun. 10 (2007)
234.
[6] I. Rodriguez, E. Labisbal, A. Sousa-Pedrares, J.A. Garcia-Vazquez, J. Romero, M.L.
Duran, J.A. Real, A. Sousa, Inorg. Chem. 45 (2006) 7903.