Controlling the self-assembly of homochiral coordination architectures of CuII by substitution in amino acid based ligands: Synthesis, crystal structures and physicochemical properties

Article abstract of DOI:10.1039/c4dt03643c

Through the strategic design of ligands based on amino acids, structural diversity in chiral coordination architectures of Cu^II is demonstrated with six new examples: {[Cu(l-HTyrbenz)₂]·CH₃OH·H₂O}_n (1), {[Cu(l-HSerbenz)₂]·3H₂O}_n (2), {[Cu(l-HTyrthio)₂]·H₂O}_n (3), [Cu(l-HTyr4-pyr)₂(H₂O)]·2H₂O (4), [Cu(l-HSerthio)₂(H₂O)] (5), and [Cu(l-Phethio)₂(H₂O)]·3H₂O (6) [where l-H₂Tyrbenz = l-N-(benzyl)-tyrosine, l-H₂Serbenz = l-N-(benzyl)-serine, l-H₂Tyrthio = l-N-(methyl-2-thiophenyl)-tyrosine, l-H₂Tyr4-pyr = l-N-(methyl-4-pyridyl)-tyrosine, l-H₂Serthio = l-N-(methyl-2-thiophenyl)-serine and l-HPhethio = l-N-(methyl-2-thiophenyl)-phenylalanine]. For these 1:2 metal-ligand complexes, the availability of a donor atom (either from the phenolic OH group or the carboxylate group of one of the ligands) for bridging between the Cu^II centers results in the formation of coordination polymers (1-3), while no such availability allows a water molecule to occupy the fifth site around the Cu^II center to generate hydrogen bonded supramolecular assemblies (4-6). In 1, a coordination polymer is formed via a syn-anti bridging carboxylate, and the phenolic group has no role in its formation. To further emphasize this point, l-tyrosine in 1 is replaced with l-serine to form 2, in which an anti-anti bridging by the carboxylate group is observed. On the other hand, the formation of {[Cu(l-HTyrthio)₂]·H₂O}_n (3) results from the growth of a spiral polymer via the unique phenolic bridging with a distance of 10.806(9) ? between two Cu^II centers. On changing from the l-H₂Tyrbenz ligand to the l-H₂Tyr4-pyr ligand (1vs.4), the strong hydrogen bonding of the pyridyl nitrogen with the phenolic group does not allow the latter to bind to Cu^II. Similarly, on changing from l-H₂Tyrthio to l-H₂Serthio (3vs.5), the length of the -CH₂OH group in the latter is much less than the distance between the two Cu^II centers, therefore this group cannot occupy the fifth site and thus a water molecule is coordinated. This is further confirmed by reacting 5 with 2 eq. of l-H₂Tyrthio in methanol to form 3, while the reverse is not possible. All these compounds are characterized by a number of analytical methods, such as elemental analysis, FTIR, UV-Vis and circular dichroism spectroscopy, polarimetry, powder and single crystal X-ray diffraction and thermogravimetric analysis. Photoluminescence properties of all ligands containing the l-tyrosine group and their metal complexes (1, 3 and 4) are compared in solution at room temperature. This journal is

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DOI: 10.1039/C4DT03643C
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ARTICLE TYPE
Controlling the self-assembly of homochiral coordination architectures
II
of Cu by the substitution in amino acid based ligands: synthesis, crystal
structures and physicochemical properties
a
a,#
a
Navnita Kumar, Sadhika Khullar and Sanjay K. Mandal*
5
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
DOI: 10.1039/b000000x
II
Through the strategic design of ligands based on amino acids, structural diversity in the chiral coordination architectures of Cu is
.
.
.
demonstrated with six new examples: {[Cu(LꢀHTyrbenz) ] CH OH H O} (1), {[Cu(LꢀHSerbenz) ] 3H O} (2),
{[Cu(Lꢀ
2
3
2
n
2
2
n
.
.
.
HTyrthio) ] H O} (3), [Cu(LꢀHTyr4ꢀpyr) (H O)] 2H O (4), [Cu(LꢀHSerthio) (H O)] (5), and [Cu(LꢀPhethio) (H O)] 3H O (6) [where
2
2
n
2
2
2
2
2
2
2
2
1
1
2
2
0
5
0
5
LꢀH Tyrbenz = LꢀNꢀ(benzyl)ꢀtyrosine, LꢀH Serbenz = LꢀNꢀ(benzyl)ꢀserine, LꢀH Tyrthio = LꢀNꢀ(methylꢀ2ꢀthiophenyl)ꢀtyrosine, and Lꢀ
2 2 2
H Tyr4ꢀpyr = LꢀNꢀ(methylꢀ4ꢀpyridyl)ꢀtyrosine, LꢀH Serthio = LꢀNꢀ(methylꢀ2ꢀthiophenyl)ꢀserine and LꢀHPhethio = LꢀNꢀ(methylꢀ2ꢀ
2
2
thiophenyl)ꢀphenylalanine]. For these 1:2 metalꢀligand complexes, the availability of a donor atom (either from the phenolic OH group
II
or the carboxylate group of one of the ligands) for bridging between the Cu centers provides the coordination polymers (1ꢀ3) while no
II
such availability allows a water molecule to occupy the fifth site around the Cu center for generating hydrogen bonded supramolecular
assemblies (4ꢀ6). In 1, the coordination polymer is formed via a synꢀanti bridging carboxylate showing no role of the phenolic group in
its formation. To further emphasize this point, Lꢀtyrosine in 1 was replaced with Lꢀserine to form 2 where an antiꢀanti bridging by the
.
carboxylate group is observed. On the other hand, the essence in the formation of {[Cu(LꢀHTyrthio) ] H O} (3) lies in the growing of
2
2
n
II
the spiral polymer via the unique phenolic bridging with a distance between two Cu centers of 10.806(9) Å. In changing from Lꢀ
H Tyrbenz ligand to LꢀH Tyr4ꢀpyr ligand (1 vs 4), the strong hydrogen bonding of the pyridyl nitrogen with the phenolic group does not
2
2
II
allow the latter to bind to Cu . Similarly, in changing from LꢀH Tyrthio to LꢀH Serthio (3 vs 5) the length of the –CH OH group in the
latter is much less than the distance between the two Cu centers to occupy the fifth site and thus a water molecule is coordinated. This is
2
2
2
II
further confirmed by reacting 5 with 2 eq of LꢀH Tyrthio in methanol to form 3 while the reverse was not possible. All these compounds
2
are characterized by a number of analytical methods, such as elemental analysis, FTIR, UVꢀVis and circular dichroism spectroscopy,
polarimetry, powder and single crystal Xꢀray diffraction and thermogravimetric analysis. Photoluminescence properties of all ligands
containing the Lꢀtyrosine group and their metal complexes (1, 3 and 4) are compared in the solution at room temperature.
Introduction
cular assemblies through chemical modifications in the ligand
system will allow one to understand the structure and bonding in
these species and to provide further directions in the rational
design of improved materials. In this regard, a strategic design of
a set of ligands can be a way to do so.
In the last 15 years, strategic design of diverse coordination
architectures have been the subject of immense interest for their
diverse structural aesthetics and for their possible roles in various
5
5
6
6
0
5
0
5
3
3
4
4
0
5
0
5
1
2ꢀ3
applications, such as catalysis, luminescence,
molecular
On the other hand, induction of chirality in such networks has
been sought due to their usefulness in asymmetric catalysis, chiral
3,4a,4b
4a,4b,5
3,4
separation,
gas and liquid adsorption,
magnetism, etc.
The construction of such coordination architectures that include
coordination polymers (CPs) and supramolecular assemblies
depends on coordination bonds and supramolecular interactions,
such as hydrogen bonds, πꢀπ stacking of aromatic moieties or Cꢀ
H…O interactions, etc. In CPs coordination bonds provide the
major contribution in their constructions while the formation of
supramolecular assemblies of higher dimensionality occurs
through the association of discrete precursors, such as monomers
and dimers, by strong supramolecular interactions. Modulation of
the contribution of coordination bonds and hydrogen bonds has
resulted in numerous diverse (structural and functional)
13ꢀ
recognition and enantiomeric separation, nonꢀlinear optics, etc.
16
One of the ways to make chiral coordination architectures is
the selfꢀassembly of optically pure chiral organic ligands with the
metal ions. In addition to their low cost and easy availability,
amino acids are also preferred in making chiral ligands due to
their abilities to act both as hydrogen bond donors and acceptors
and to show different binding modes with the metal centers
through various functionalities present in these ligands, e.g.,
13ꢀ16
carboxylate, hydroxy, etc.
One such set of ligands that has
been utilized to some extent is the reduced Schiff base ligands of
17ꢀ34
various amino acids.
However, their use in making
6
ꢀ12
coordination architectures in recent years.
the parameters that control the formation of CPs or supramoleꢀ
Thus establishing
coordination architectures under hydrothermal conditions is
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DOI: 10.1039/C4DT03643C
3
5
limited due to their poor thermal stability.
45 such as elemental analysis, FTIR, UVꢀVis and circular dichroism
spectroscopy, polarimetry, powder and single crystal Xꢀray
crystallography and thermogravimetric analysis. Furthermore,
due to the presence of the Lꢀtyrosine group three ligands (Lꢀ
H Tyrbenz, LꢀH Tyrthio and LꢀH Tyr4ꢀpyr) and their metal
Lꢀtyrosine is one of the few amino acids with three functional
groups (hydroxy, amino and carboxylate) that can provide diverse
binding modes (chelating, bridging, etc.); however, a limited
number of coordination architectures is reported so far using this
5
0
5
0
5
0
5
0
2
2
2
21,
amino acid or particularly its Schiff base derivatives.
50 complexes (1, 3 and 4) were studied for their photoluminescence
properties in the solution at room temperature.
2
3a,23c,25,34,36ꢀ38
In our laboratory, using reduced Schiff base ligands
of Lꢀtyrosine a systematic study was carried out to show how the
formation of CPs or supramolecular assemblies of Cu under
nonꢀhydrothermal conditions can be effected by the substitution
in it. Further modifications in the ligand using Lꢀphenylalanine
and Lꢀserine instead of Lꢀtyrosine provided the concrete support
II
Experimental section
1
1
2
2
3
3
4
Materials and methods
All chemicals and solvents used for synthesis were obtained from
in understanding the formation of supramolecular assemblies 55 commercial sources and were used as received, without further
over CPs. In doing so, we observed that the presence or absence
of a coordinated water molecule at the fifth site around fiveꢀ
purification. All reactions were carried out under aerobic
2
1
17,18
conditions. The ligands LꢀH Tyrbenz , LꢀH Serbenz
and Lꢀ
2
2
II
19
coordinated square pyramidal Cu in all complexes, except 2
HPhethio
procedures.
were prepared using the modified literature
II
where the Cu center is distorted octahedral, due to strategic
chemical modifications in the ligand is responsible for the
formation of such diverse networks. This is particularly important
to note that for the ligand LꢀH Sersal (where LꢀH Sersal = LꢀNꢀ
6
0
Physical Measurements
1
H NMR spectra of LꢀNa
Tyrbenz, LꢀNa Serbenz, LꢀNa Tyrthio,
2 2
3
3
2
(2ꢀhydroxybenzyl)ꢀserine) and its derivatives, where these act as
LꢀNa
obtained in D
spectrometer; chemical shifts are reported relative to the residual
2
Tyr4ꢀpyr, LꢀNa
2
Serthio and LꢀNaPhethio ligands were
◦
dianions due to the presence of a 2ꢀhydroxy group, the complexes
having a metal to ligand ratio of 1:1 are CPs with coordinated
2
O solution at 25 C on a Bruker ARXꢀ400
12e
39
water molecules. Similarly, the CP reported by Vittal et al. is 65 solvent signals. The elemental analysis (C, H, N) was carried out
a 1:1 metal to ligand complex with an alternating bis(phenoxo)
core and contains coordinated water molecules. Thus, in the
current study the importance of a coordinated water molecule in a
using a Mettler CHNS analyzer; thermogravimetric analysis was
carried out from 25 to 500 C (at a heating rate of 10 C/min)
under dinitrogen atmosphere on a Shimadzu DTGꢀ60. IR spectra
◦
◦
ꢀ
1
1
:2 metalꢀligand complex is demonstrated for the first time.
were measured in the 4000ꢀ400 cm range on a PerkinꢀElmer
Herein, we report six new Cu complexes as the outcome of 70 Spectrum I spectrometer with samples prepared as KBr pellets.
proposed work described above: {[Cu(Lꢀ
UVꢀVis spectra of the compounds in methanol (a typical
concentration of mM) were recorded in an Agilent
II
the
.
.
.
HTyrbenz) ] CH OH H O} (1), {[Cu(LꢀHSerbenz) ] 3H O} (2),
{
1
2
3
2
n
2
2
n
.
.
[Cu(LꢀHTyrthio) ] H O} (3), [Cu(LꢀHTyr4ꢀpyr) (H O)] 2H O
Technologies Cary60 UVꢀVis spectrophotometer using a cuvette
of path length 10 mm. Emission spectra were obtained using a
2
2
n
2
2
2
(
4),
[Cu(LꢀHSerthio) (H O)]
(5),
and
[Cu(Lꢀ
2
2
.
Phethio) (H O)] 3H O (6) [where LꢀH Tyrbenz = LꢀNꢀ(benzyl)ꢀ 75 Perkin Elmer Fluorimeter (LS55) with a cuvette of 10 mm path
2
2
2
2
tyrosine, LꢀH Serbenz = LꢀNꢀ(benzyl)ꢀserine, LꢀH Tyrthio = Lꢀ
length. For photoluminescence spectra, 0.5 mM methanolic
solutions of the compounds were prepared. Optical rotations were
recorded using Anton Paar Modular circular Polarimeter (MCP
300). Measurements were carried out using a glass cell with 50
2
2
Nꢀ(methylꢀ2ꢀthiophenyl)ꢀtyrosine, and LꢀH Tyr4ꢀpyr = LꢀNꢀ
2
(
methylꢀ4ꢀpyridyl)ꢀtyrosine, LꢀH Serthio
=
LꢀNꢀ(methylꢀ2ꢀ
2
thiophenyl)ꢀserine and LꢀHPhethio = LꢀNꢀ(methylꢀ2ꢀthiophenyl)ꢀ
phenylalanine]. Fig. 1 shows the structures of all chiral ligands 80 mm path length. CD spectra were recorded on a Chirascan
that are made for this study. All these chiral compounds are
structurally characterized by a number of analytical methods,
spectropolarimeter (Applied Photoꢀphysics, Leatherhead, Surrey,
UK) using quartz cuvettes with a 2 mm path length. ESI mass
spectrometry was performed using either Waters HRMS
instrument or Thermo Scientific LTQ XL LCꢀMS instrument for
the 50ꢀ2000 amu range.
O
OH
O
OH
OH
O
8
9
9
5
0
5
N
HN
N
H
H
HO
Synthesis of L-H Tyrbenz
S
2
OH
L-H Tyrbenz
To a solution of 500 mg of Lꢀtyrosine (2.8 mmol) and 220 mg of
NaOH (5.6 mmol) in 14 mL of a methanol:water mixture (v/v
1:1) was added 0.28 mL (2.8 mmol) of benzaldehyde. The
resulting solution was refluxed for 1h. The yellow reaction
mixture was brought to room temperature prior to addition of 105
OH
L-H
Serbenz
2
2
L-H Tyrthio
2
OH
O
OH
O
OH
O
mg of NaBH (4.8 mmol) at 0 °C. The solution was stirred until
4
N
the yellow color disappeared. The pH of the solution was
adjusted to 5 using (~2 mL) glacial acetic acid and stirred for half
an hour. A white precipitate was filtered, washed with water and
air dried. Yield: 350 mg (47%). HRMS (ESIꢀTOF): m/z calcd for
N
H
N
H
H
HO
S
N
S
OH
L-H
Serthio
L-HPhethio
[(LꢀH Tyrbenzl)H] , 272.1287; found, 272.1278. M.pt. 263 C.
+
o
L-H Tyr4-pyr
2
2
2
1
H NMR (D O): δ 2.62 (d, 2H), 3.17 (t, 1H), 3.41 (d, 1H), 3.60
Fig. 1 Structure of various chiral ligands synthesized and used in this
2
study.
100 (d, 1H), 6.43 (d, 2H), 6.83 (d, 2H), 7.16 – 7.28 (m, 5H). Selected
2
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ꢀ
1
o
1
FTIR peaks (KBr, cm ): 3174(s), 3011(w), 2827(w), 2747(w),
C. H NMR (D O): δ 3.05 (t, 1H), 3.56 (d, 2H), 3.75 (d, 1H),
2
1
8
603(w), 1580(br), 1516(s), 1437(m), 1396(s), 1253(s), 1106(s), 60 3.87(d, 1H), 6.87ꢀ6.89 (m, 2H), 7.22ꢀ7.23 (dd, 2H). Selected
2
0
ꢀ1
28(s), 743(s), 697(s). Specific rotation [α] D
= +12.50
FTIR peaks (KBr, cm ): 3251(br), 3079(w), 2989(w), 2424(w),
(
0.018%, H O).
1622(s), 1567(s), 1479(s), 1443(m), 1368(s), 1328(s), 1214(s),
1160(s), 1086(s), 855(s), 722(s), 545(s). Specific rotation [α] D
2
2
0
5
0
5
0
5
0
5
0
5
0
5
Synthesis of L-H Serbenz
It was prepared following the procedure described for Lꢀ
= ꢀ22.73 (0.018%, H O).
2
2
65
H Tyrbenz except 500 mg (4.7 mmol) of Lꢀserine was used
Synthesis of L-HPhethio
It was prepared following the procedure described for Lꢀ
2
instead of Lꢀtyrosine. In this case, the resulting yellow Schiff
base solution was refluxed for 8 h. A white precipitate was
filtered, washed with water and air dried. Yield: 300 mg (32%).
HRMS (ESIꢀTOF): m/z calcd for [(LꢀH Serbenz)H] , 196.0973; 70 tyrosine and benzaldehyde, respectively. In this case, the
found, 196.0970. M.pt. 219 C. H NMR (D O): δ 2.51 (t, 2H),
1
1
2
2
3
3
4
4
5
5
H Tyrbenz except 500 mg (3 mmol) of Lꢀphenylalanine and 0.28
2
mL (3 mmol) of thiophenealdehyde was used instead of Lꢀ
+
2
o
1
resulting yellow Schiff base solution was reflux for 24 h. A white
precipitate was filtered, washed with water and air dried. Yield:
362 mg (46%). HRMS (ESIꢀTOF): m/z calcd for [(Lꢀ
2
3
.00 (t, 1H), 3.42 (d, 1H), 3.58 (d, 1H), 6.30 (d, 2H), 6.69 (d,
ꢀ
1
2H), 7.20 (d, 2H), 7.91 (d, 2H). Selected FTIR peaks (KBr, cm ):
+
o
1
3
1
245(br), 3197(s), 3063(s), 1625(s), 1596(s), 1534(s), 1471(s),
455(w), 1276(s), 1201(s), 1080(s), 758(s), 648(w). Specific 75 NMR (D O): δ 2.69ꢀ2.76 (m, 2H), 3.20 (t, 1H), 3.63 (d, 1H), 3.79
HPhethio)Na] , 284.1655; found, 284.0726. M.pt. 227 C. H
2
2
0
rotation [α] D = +14.77 (0.018%, H O).
(d, 1H), 6.81 (d, 1H), 6.83ꢀ6.86 (m, 1H), 7.06 (d, 2H), 7.12 (d,
2
ꢀ
1
1
H), 7.18ꢀ7.20 (m, 3H). Selected FTIR peaks (KBr, cm ):
Synthesis of L-H Tyrthio
3418(br), 3179(s), 3010(w), 2806(w), 2689(w), 1603(w),
1586(br), 1515(s), 1438(m), 1397(s), 1346(s), 1252(s), 1106(s),
2
It was prepared following the procedure described for Lꢀ
2
0
H Tyrbenz except 0.26 mL (2.8
mmol) of 2ꢀ 80 827(s), 746(m), 550(s). Specific rotation [α] D
= +30.40
2
thiophenecarboxyaldehyde was used instead of benzaldehyde. In
this case, the resulting yellow Schiff base solution was refluxed
for 3 h. A white precipitate was filtered, washed with water and
air dried. Yield: 581 mg (76%). HRMS (ESIꢀTOF): m/z calcd for
(0.018%, H O).
2
.
.
Synthesis of {[Cu(L-HTyrbenz) ] CH OH H O} (1)
In a 10 mL round bottom flask, 25 mg (0.092 mmol) of Lꢀ
2
3
2
n
+
o
1
[
(LꢀH Tyrthio)H] , 278.1785; found, 278.0851. M.pt. 248 C. H 85 H Tyrbenz and 5 mg (0.092 mmol) of KOH were dissolved in 3
2
2
NMR (D O): δ 2.59 (d, 2H), 3.16(t, 1H), 3.61 (d, 1H), 3.75 (d,
mL methanol. To this was added 11.5 mg (0.046 mmol) of
2
.
1
H), 6.38 (d, 2H), 6.76ꢀ6.85 (m, 4H), 7.18 (d, 1H). Selected FTIR
CuSO 5H O with stirring. The reaction mixture turned blue and
4
2
ꢀ
1
peaks (KBr, cm ): 3435(br), 3178(s), 3006(w), 2692(w),
was stirred for 6 h. After filtering off the K SO precipitate, the
2 4
blue filtrate was evaporated to dryness to obtain the product.
2
8
624(w), 1581(br), 1517(s), 1436(s), 1393(s), 1262(s), 1105(s),
21(s), 717(m), 533(s). Specific rotation [α] D = ꢀ2.27 (0.018%, 90 Yield: 24 mg (75%). Anal. Calc. (%) for C H N O Cu (MW
2
0
33
38
2
8
H O).
2
653.5): Calc. C, 58.76; H, 5.81; N, 4.28. Found: C, 59.13; H,
ꢀ
1
5
.80; N, 4.29. Selected FTIR peaks (KBr, cm ): 3269(s),
Synthesis of L-H Tyr4-pyr
3019(w), 2931(w), 1634(s), 1592(w), 1514(s), 1454(m), 1359(m),
1271(w), 1240(s), 1171(w), 806, 701. UVꢀVis [λmax, nm]: 204,
2
It was prepared following the procedure described for Lꢀ
2
0
H Tyrbenz except 0.26 mL (2.8
mmol) of 4ꢀ 95 225, 278, 590. Specific rotation [α] D
= +56.0 (0.025%,
2
pyridinecarboxyaldehyde was used instead of benzaldehyde. In
this case, the resulting yellow Schiff base solution was stirred for
6 h. A white precipitate was filtered, washed with water and air
dried. Yield: 670 mg (89%). HRMS (ESIꢀTOF): m/z calcd for
CH OH).
3
.
Synthesis of {[Cu(L-HSerbenz) ] 3H O} (2)
2
2
n
In a 10 mL round bottom flask, 12 mg (0.065 mmol) of
+
o
.
[
(LꢀH Tyr4ꢀpyr)H] , 273.1239; found, 273.1245. M.pt. 250 C. 100 CuSO 5H O was dissolved in 1 mL water. To this was added a
2
4
2
1
H NMR (D O): δ 2.64 ꢀ 3.68 (m, 2H), 3.13 (t, 1H), 3.50 (d, 1H),
clear solution of LꢀKHSerbenz prepared by using 25 mg (0.13
2
3
.71 (d, 1H), 6.43 (d, 2H), 6.83 (d, 2H), 7.17 (d, 2H), 8.30 (d,
mmol) of LꢀH Serbenz and 7 mg (0.13 mmol) of potassium
2
ꢀ
1
2H). Selected FTIR peaks (KBr, cm ): 3161(br), 2808(w),
hydroxide in 2 mL of water. The reaction mixture turned blue and
was stirred for 3h. A blue precipitate was filtered off, washed
2
1
359(w), 1614(s), 1518(s), 1449(m), 1385(s), 1332(s), 1234(w),
20
104(s), 872(s), 801(s), 573(m). Specific rotation [α] D = +9.09 105 with water and air dried. Yield: 23 mg (71%). Anal. Calc. (%) for
C H N O Cu (MW 506.11): Calc. C, 47.47; H, 5.98; N, 5.54.
(0.018%, H O).
2
20 30
2
9
Found: C, 46.71; H, 5.81; N, 5.37. Selected FTIR peaks (KBr,
ꢀ
1
Synthesis of L-H Serthio
cm ): 3375(br), 3277(s), 1623(s), 1496(w), 1457(m), 1372(m),
1358(s), 1345(w), 1278(m), 1146(w), 1079(s), 972(m), 753(w),
2
It was prepared following the procedure described for Lꢀ
H Tyrbenz except 500 mg (4.7 mmol) of Lꢀserine and 0.45 mL 110 694(s). UVꢀVis [λmax, nm]: 205, 254, 589. Specific rotation [α]
2
D
20
(4.7 mmol) of thiophenecarboxyaldehyde was used instead of Lꢀ
= +51.0 (0.025%, CH OH).
3
tyrosine and benzaldehyde, respectively. In this case, the
resulting yellow Schiff base solution was stirred for 3 h at room
temperature. A white precipitate was filtered, washed with water
.
Synthesis of {[Cu(L-HTyrthio) ] H O} (3)
It was prepared following the procedure described for 2 except Lꢀ
2
2
n
and air dried. Yield: 445 mg (42%). HRMS (ESIꢀTOF): m/z calcd 115 KHTyrthio, prepared by using 25 mg (0.09 mmol) of Lꢀ
+
for [(LꢀH Serthio)Na] , 224.1292; found, 224.0357. M.pt. 216.9
H Tyrthio and 5 mg (0.09 mmol) of potassium hydroxide in 2 mL
2
2
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DOI: 10.1039/C4DT03643C
of water, was used instead of LꢀKHSerbenz. A purple precipitate
was filtered off, washed with water and air dried. Yield: 24 mg 60 the product, it was confirmed that the product isolated was 3.
84%). Anal. Calc. (%) for C H N O S Cu (MW 634.22): Calc.
(60%). Based on the comparison of the FTIR and PXRD data of
(
2
8
30
2
7 2
C, 53.03; H, 4.77; N, 4.42. Found: C, 52.57; H, 4.68; N, 4.26.
Selected FTIR peaks (KBr, cm ): 3371(br), 3252(w), 3220(w),
Single crystal X-ray data collection and refinements
Following the practices of this laboratory published earlier,
ꢀ
1
12a
5
0
5
0
5
0
5
0
5
0
5
1
1
2
636(w), 1614(m), 1603(m), 1515(s), 1445(m), 1376(m),
initial crystal evaluation and data collection were performed on a
269(s), 1108(w), 881(m), 846, 714. UVꢀVis [λmax, nm]: 229, 65 Kappa APEX II diffractometer equipped with a CCD detector
2
0
79, 585. Specific rotation [α] D = +46.0 (0.025%, CH OH).
(with the crystalꢀtoꢀdetector distance fixed at 60 mm) and sealedꢀ
3
tube monochromated MoKα radiation using the program
.
40
1
1
2
2
3
3
4
4
5
5
Synthesis of [Cu(L-HTyr4-pyr) (H O)] 2H O (4)
It was prepared following the procedure described for 2 except Lꢀ
KHTyr4ꢀpyr, prepared by using 25 mg (0.092 mmol) of Lꢀ 70 within a randomly oriented region of reciprocal space surveyed to
H Tyr4ꢀpyr and 5 mg (0.09 mmol) of potassium hydroxide in 2
mL of water, was used instead of LꢀKHSerbenz. A green
precipitate was filtered off, washed with water and air dried.
Yield: 20 mg (61%). Anal. Calc. (%) for C H N O9.5Cu (MW
6
5
with 2.5 water molecules. Selected FTIR peaks (KBr, cm ):
3434(br), 3237(s), 1644(s), 1612(s), 1517(s), 1453(s), 1379(s),
1
6
APEX2. For each sample, three sets of frames of data were
2
2
2
collected with 0.30° steps in ω and an exposure time of 10 s
the extent of 1.3 hemispheres to a resolution of 0.85 Å. By using
2
40
the program SAINT for the integration of the data, reflection
2
2
profiles were fitted, and values of F and σ(F ) for each reflection
were obtained. Data were also corrected for Lorentz and
3
0
37
4
40
68.5): Calc. C, 53.85; H, 5.53; N, 8.38. Found: C, 53.71; H, 75 polarization effects. The subroutine XPREP was used for the
.46; N, 8.50. Despite our best effort, the CHN data could be fit
processing of data that included determination of space group,
ꢀ
1
40
application of an absorption correction (SADABS) , merging of
data, and generation of files necessary for solution and
refinement. The crystal structures were solved and refined using
264(s), 1088(s), 980(s), 798. UVꢀVis [λmax, nm ] 224, 259, 282,
2
0
41
00. Specific rotation [α] D = +96.0 (0.025%, CH OH).
80 SHELX 97. In each case, the space group was chosen based on
3
systematic absences and confirmed by the successful refinement
of the structure. Furthermore, Flack parameters of all the
structures confirmed the correct absolute configurations.
Positions of most of the nonꢀhydrogen atoms were obtained from
Synthesis of [Cu(L-HSerthio) (H O)] (5)
It was prepared following the procedure described for 2 except Lꢀ
KHSerthio, prepared by using 25 mg (0.113 mmol) of Lꢀ
H Serthio and 6.5 mg (0.113 mmol) of potassium hydroxide in 2
mL of water, was used instead of LꢀKHSerbenz. A blue
precipitate is filtered off, washed with water and air dried. Yield:
18 mg (66%). Anal. Calc. (%) for C H N O S Cu (MW
4
4
2
2
85
a
direct methods solution. Several fullꢀmatrix leastꢀ
2
squares/difference Fourier cycles were performed, locating the
remainder of the nonꢀhydrogen atoms. All nonꢀhydrogen atoms
were refined with anisotropic displacement parameters except
where mentioned. In order to obtain reasonable thermal
1
6
22
2
7 2
82.05): Calc. C, 39.86; H, 4.60; N, 5.81. Found: C, 40.16; H,
ꢀ
1
.42; N, 5.75. Selected FTIR peaks (KBr, cm ): 3327(br), 90 parameters compared to other atoms, the lowest residual factors
3
1
212(m), 1642(m), 1629(s), 1444(s), 1421(w), 1391(m),
348(w), 1300(w), 1216(w), 1099(w), 1016(m), 716(s), 673(w).
and optimum goodness of fit with convergence of refinement,
adjustments to the structures of 4 and 5 were done accordingly. In
4, the occupancy factor of the lattice water molecule O6 was
adjusted to 0.5. In 5, one of the thiophene rings was modelled for
the 2ꢀfold disorder, where the S1, C6, C7 and C8 atoms were
allowed to occupy at two different sites (S1A/S1B, C6A/C6B,
C7A/C7B and C8A/8B with final occupancy factors 0.605 and
0.395, respectively); all atoms in the ring were refined
isotropically with further constraints to have the expected bond
20
UVꢀVis [λmax, nm]: 235, 276, 586. Specific rotation [α] D
+
=
74.0 (0.025%, CH OH).
3
95
.
Synthesis of [Cu(L-Phethio) (H O)] 4H O (6)
2
2
2
It was prepared following the procedure described for 2 except Lꢀ
KPhethio, prepared by using 25 mg (0.096 mmol) of LꢀHPhethio
and 5 mg (0.09 mmol) of potassium hydroxide in 2 mL of water,
was used instead of LꢀKHSerbenz. A purple precipitate was 100 lengths and thermal parameters. In each structure, all hydrogen
filtered off, washed with water and air dried. Yield: 15 mg atoms were placed in ideal positions and refined as riding atoms
46.5%). Anal. Calc. (%) for For C H N O S Cu (MW 674.28): with individual isotropic displacement parameters.
(
2
8
38
2
9 2
Calc. C, 49.8; H, 5.68; N, 4.15. Found: C, 49.2; H, 5.5; N, 4.0.
Selected FTIR peaks (KBr, cm ): 3375(br), 3277(s), 1623(s),
1
1
2
Crystallographic parameters and basic information pertaining to
data collection and structure refinement for all compounds are
ꢀ
1
4
2
496(w), 1457(m), 1372(m), 1358(s), 1345(w), 1278(m), 105 summarized in Table 1. All figures were drawn using Olex2 and
43
146(w), 1079(s), 972(m), 753(w), 694(s). UVꢀVis [λmax, nm]:
MERCURY 3.0 and hydrogen bonding parameters were
2
0
44
12, 235, 275, 582. Specific rotation [α] D
= +62.0 (0.025%,
generated using PLATON. The final positional and thermal
CH OH).
parameters of the nonꢀhydrogen atoms for all structures are listed
in the CIF files (ESI†).
3
Conversion of 5 to 3
In a 10 mL round bottom flask, 30 mg (0.12 mmol) of 5 was
dissolved in 3 mL methanol. To this was added 35 mg (0.06
mmol) of LꢀH Tyrthio with stirring. The reaction mixture was
110
Powder X-ray studies
Data were recorded on a Rigaku Ultima IV diffractometer
equipped with a 3 KW sealed tube Cu Kα Xꢀray radiation
(generator power settings: 40 kV and 40 mA) and a DTex Ultra
2
stirred for 24 h. After filtering off the white precipitate
(confirmed to be H Serthio by FTIR spectroscopy), the blue 115 detector using parallel beam geometry (2.5° primary and
2
filtrate was evaporated to dryness to obtain 3. Yield: 24 mg
secondary solar slits, 0.5° divergence slit with 10 mm height limit
4
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Dalton Transactions
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slit). For each sample, a fine powder was packed on a glass
sample holder that was placed on the sample rotation stage (120
respectively) and two lattice solvents (one methanol molecule and
one water molecule) and three water molecules, respectively.
rpm) attachment. The data were collected over an angle range 5° 60 Both are carboxylatoꢀbridged 1D coordination polymers but the
II
to 50° with a scanning speed of 1° per minute with 0.02° step.
difference in geometry around the Cu center arises from the
II
substitution in the ligand. As shown in Fig. 2a, the Cu center in
5
Results and discussion
1 has a distorted square pyramidal geometry with a coordination
environment of O N type ꢀ out of the four equatorial sites two
3
2
Synthesis
6
7
7
5
0
5
are occupied by the nitrogen atoms (N1 and N2) of the amine
groups whereas the other two are occupied by the oxygen atoms
Out of the six ligands used in this study, three (LꢀH Tyrthio, Lꢀ
2
(O3 and O5) of the carboxylates of two ligands, and the apical
H Tyr4ꢀpyr and LꢀH Serthio) are new. A general methodology
2
2
site is occupied by the oxygen atom (O4') of the carboxylate of
the ligand bound to the adjacent metal center. The carboxylate
group of one ligand binds in a monodentate fashion (with oxygen
atom O3) while the carboxylate group of the second ligand (with
oxygen atoms O4 and O5) bridges in a synꢀanti fashion between
1
1
2
2
3
3
4
4
5
5
0
5
0
5
0
5
0
5
0
5
was developed to synthesize the ligands. In all cases, the sodium
salt of the respective Lꢀamino acid and the appropriate aldehyde
were stirred or refluxed depending upon the reactivity of the
aldehyde to obtain the respective Schiff base. One can correlate
the reaction conditions with respect to the substitution in the
aldehyde; however, it was not the case for several of these and
thus optimized conditions were obtained through design of
experiments. The Schiff base was further reduced using sodium
borohydride. The desired products were obtained by the addition
of glacial acetic acid to the sodium salt of the reduced Schiff
bases of the Lꢀamino acids (as shown in Scheme S1, ESI†). H
NMR (Figs. S1ꢀS6, ESI†) and FTIR (Figs. S7ꢀS12, ESI†) spectra
of all the ligands are reported.
Metal complexes were synthesized via a twoꢀcomponent selfꢀ
assembly reaction of CuSO 5H O and the respective
II
two Cu centers forming the 1D coordination polymer chain (see
II
Fig. 3a). On the other hand, the Cu center in 2 (see Fig. 2b) has a
distorted octahedral geometry having the sixth position occupied
II
by the hydroxymethyl group of one of the ligands (Cu ꢀOH bond
length: 2.723(1) Å).
1
.
4
2
monopotassium salt of the ligand in a 1:2 ratio under ambient
conditions; the solvent for the reaction was chosen based on the
solubility of the product and the byꢀproduct K SO . Unlike all
2
4
other compounds, 1 was found to be moderately soluble in water.
For 1, the reaction was carried out in methanol to separate the byꢀ
product via filtration allowing its isolation by evaporating the
filtrate under reduced pressure. On the other hand, for 2, 3, 4, 5
and 6 water was chosen as the reaction solvent in which the byꢀ
product K SO was soluble to obtain these as direct precipitates.
(a)
2
4
Interestingly, in the absence of any additional ancillary ligands
the isolation of divalent metal (Co and Zn ) complexes with a
metal to ligand ratio of 1:2 for tyrosine have been reported
while [Cu(LꢀPhꢀTyr)(phen)(ClO )] (where LꢀPhꢀTyr = LꢀNꢀ
II
II
38
2
1
4
(b)
(benzyl)ꢀtyrosine, which is abbreviated as LꢀH Tyrbenz in the
2
present work, and phen = 1, 10ꢀphenanthroline) is a 1:1 complex. 80 Fig. 2 Coordination environment around Cu(II) in (a) 1 and (b) 2.
Similarly, for the ligand LꢀH Sersal and its derivatives that act as
3
dianion due to the presence of 2ꢀhydroxy group, the 1:1 metalꢀ
ligand complexes are obtained;
CPs with coordinated water molecules.
Unlike 1, the bridging carboxylate group of the ligand in 2 that
1
2e, 39
thus these complexes are
forms the 1D coordination polymer chains as shown in Fig 3b is
II
in an antiꢀanti binding mode between two Cu centers. Examples
8
9
9
5
0
5
of carboxylate bridging by Lꢀtyrosine or Lꢀtyrosine based ligands
Description of the structures
38
to form 1D CPs are limited in the literature: {Co(Lꢀtyrosine)} ,
n
38
45
{
Zn(Lꢀtyrosine)} , [Cu(Lꢀtyrosine) ] , {[Zn(Lꢀtyrosine) (H O)]
n 2 n 2 2
Crystals of 1-5 suitable for the single crystal Xꢀray study were
grown from the slow evaporation of the respective methanolic
solution: 1 in 10 days, 2 in 7 days, 3 in 5 days, 4 in 7 days and 5
in 3 days. Despite numerous attempts, crystals of 6 suitable for
data collection could not be obtained; however, a comparison of
its spectroscopic data (UVꢀvis, CD and FTIR) with those of 4 and
45
39
(
H O)} , and {[Cu (LꢀHTyrsal) (H O)](H O)}
(where Lꢀ
2
n
2
2
2
2
n
H Tyrsal = LꢀNꢀ(2ꢀhydroxybenzyl)ꢀtyrosine); unlike the first four
2
II
complexes where the carboxylate group bridges between the Cu
or Zn centers, respectively, the last one with the Lꢀtyrosine
II
based Schiff base ligand the carboxylate group bridges the
bis(phenoxo)dicopper units in the polymeric structure. In 1, the
CuꢀNamine bond distances are 2.015(3) Å and 2.022(3) Å,
5
indicates their structural similarities (vide infra).
Compound 1 and 2 crystallize in the chiral monoclinic space
comparable to 2.022(3)
Å
reported for [Cu(LꢀPhꢀ
group P2 and orthorhombic space group P2 2 2 , respectively.
21
1
1
1
1
Tyr)(phen)(ClO )];
4
however, the CuꢀO(monodentate
carboxylate)
II
The asymmetric unit of 1 and 2 consists of one Cu center
surrounded by two ligands (LꢀHTyrbenz and LꢀHSerbenz,
distance in [Cu(LꢀPhꢀTyr)(phen)(ClO )], 1.958(3) Ǻ, is
4
comparable to one of the CuꢀO(bridged carboxylate) distances of
This journal is © The Royal Society of Chemistry [year]
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DOI: 10.1039/C4DT03643C
.
{
[Zn(Lꢀtyrosine) (H O)] (H O)} , the phenolic ꢀOH group is
2 2 2 n
directly hydrogen bonded to the uncoordinated oxygen atom of
4
5
4
4
5
5
6
6
7
7
8
8
9
0
5
0
5
0
5
0
5
0
5
0
the
monodentate
carboxylate
group.
In
{[Cu (Lꢀ
2
.
HTyrsal) (H O)] (H O)} , the phenolic ꢀOH group is involved in
2
2
2
n
both intrachain and interchain hydrogen bonding. It connects one
of the oxygen atom of the bridging carboxylate groups to the
lattice water molecule to form the 1D chain. For the interchain
hydrogen bonding, the lattice water molecule and the phenolic ꢀ
39
II
II
OH groups are involved. In 1, the Cu ...Cu distance is 5.833(6)
Å, which is similar to that (5.763(6) Å) found in {[Cu (Lꢀ
HTyrsal) (H O)](H O)} though the Cu centers in the latter are
2
II
2
2
2
n
a)
part of the bis(phenoxo) moieties that alternates in the CP chain;
this distance is much shorter (4.93(7) Å) in [Cu(Lꢀtyrosine)2]n
due to the antꢀanti bridging mode of the carboxylate group. On
the other hand, the Cu...Cu distance in 2 is 5.495(3) Å.
In addition to hydrogen bonding, various CꢀH...O interactions
like C26ꢀH12A..O6 and C26ꢀH12B..O4 with a donorꢀacceptor
distances of 2.989(7) Å and 3.102(7) Å, respectively, further
strengthens the association of the 1D CPs in 1. All hydrogen
bonding parameters for 1 are listed in Table 2.
In 2, all three lattice solvent molecules (water) forming a triad
are involved in connecting these 1D chains through strong
hydrogen bonding. However, each set of three lattice water
molecules for each 1D chains are not connected to each other. For
the hydrogen bonding within each 1D chain (see Fig. S14, ESI†),
two out of the three lattice water molecules (O1S and O3S) are
involved: O3S acts both as a hydrogen bond donor and a
hydrogen bond acceptor. As a donor, O3S is hydrogen bonded to
b)
Fig. 3 Comparison of the carboxylate bridging in the polymeric structures
of (a) 1 and (b) 2.
5
0
5
0
5
0
5
1
.957(3) Å in 1 but is slightly longer than the CuꢀO(monodentate
bond of 1.931(3) Å in 1. For 1, the bond angle
carboxylate)
O(carboxylate)ꢀCuꢀN(amine) for each ligand is 82.68(14)˚ and
8
Tyr)(phen)(ClO )]. The selected bond distances and bond angles
4.76(16)˚, which are similar to that of 83.25(9)˚ in [Cu(LꢀPhꢀ
–
OH (O5) of the –CH OH (OꢀꢀꢀO distance: 2.915(4) Å) and the
2
1
1
2
2
3
3
4
uncoordinated oxygen atom (O3) of the monodentate carboxylate
of the ligand (OꢀꢀꢀO distance: 2.858(4) Å). As an acceptor, O3S
is hydrogen bonded to the nitrogen (N1) of the amine part of the
ligand (NꢀꢀꢀO distance: 3.516(4) Å). O1S shows a three center
bifurcated hydrogen bonding with uncoordinated (O3) and
coordinated (O2) oxygen atoms of the monodentate carboxylate
for 1 and 2 are listed in Tables S1 and S2 (ESI†), respectively.
Moreover, the involvement of the phenolic group in the ligands
for the hydrogen bonding network is very different in these
complexes compared to 1. The 1D CP chains in 1 are involved in
extensive intermolecular hydrogen bonding with the lattice water
and methanol molecules giving rise to a 2D supramolecular array.
Out of the two phenolic groups (O1 and O6) of the LꢀHTyrbenz
ligands in 1, one (O6) is involved in connecting the 1D chains to
generate the 2D network. In this hydrogen bonding network,
there are two sets: (a) between the oxygen atom (O7) of the
lattice methanol molecule and –OH (O1) of the phenol group (Oꢀꢀ
(
distances: O1SꢀꢀꢀO3, 3.577(4) Å; O1SꢀꢀꢀO2, 2.752(4) Å) and
oxygen atom (O6) of the bridging carboxylate (O1SꢀꢀꢀO6
distance: 2.864(4) Å) of the ligand. The third lattice water
molecule (O2S) plays a very significant role. Although it is not
directly involved in the intraꢀchain hydrogen bonding but as
shown in Fig 5, it bridges between the two lattice water
molecules O1S and O3S (O2SꢀꢀꢀO1S distance: 2.953(5) Å) (O2Sꢀ
ꢀꢀO3S distance: 2.865(6) Å) from different triads of different 1D
chains to form the interꢀchain hydrogen bonding, thus extending
the dimensionality. Further reinforcement of the network is by the
interꢀchain hydrogen bonding between the two oxygen atoms (O1
and O5) of the ꢀCH OH groups of the two ligands coordinated to
each Cu centers and oxygen atom of a lattice water molecule
O1S) (O1ꢀꢀꢀO1S distance: 2.777(4) Å) and the uncoordinated
oxygen atom (O3) of the monodentate carboxylate (O5ꢀꢀꢀO3
distance: 2.972(4) Å) of the ligand, respectively. Thus both
ꢀ
(
O distance: 2.672(6) Å) and the uncoordinated oxygen atom
O2) of the monodentate carboxylate of the ligand (OꢀꢀꢀO
distance: 2.667(8) Å) as shown in Fig. S13, (ESI†), and (b)
between the oxygen atom (O8) of the lattice water molecule and
oxygen atom (O5) of the bridged carboxylate (OꢀꢀꢀO distance:
2
.985(8) Å) as well as the oxygen atom (O6) of the phenol part of
2
the ligand (OꢀꢀꢀO distance: 2.652(8) Å). O8 is also hydrogen
bonded to the oxygen atom (O7) of the lattice methanol molecule
(OꢀꢀꢀO distance: 3.049(7) Å). Thus the O8 atom, which acts as a
donor (bifurcated) as well as acceptor, connects the two 1D
chains through O6 (see Fig. 4) forming a R (29) motif. This
2
II
(
4
46
4
CH OH groups from two LꢀHSerbenz ligands are involved in
2
9ꢀmembered ring consists of four donor atoms (O6, O8, O6’,
connecting these 1D chains for the overall network in 2. This is
very different from the involvement of the phenolic groups of the
LꢀHTyrbenz in 1. All these hydrogen bondings in 2 lead to the
formation of four different motifs: R (11), R (11), R (14) and
R (10). Both the elevenꢀmembered motifs consist of four
O8’), four acceptor atoms (O5, O8, O5’, O8’) and some part of
the ligand skeleton. In {Co(Lꢀtyrosine)} , and {Zn(Lꢀtyrosine)} ,
n
n
the phenolic –OH is deprotonated and thus the phenoxo group
4
4
4
3
4
5
3
8
coordinates with another metal center. In [Cu(Lꢀtyrosine) ] and
2
46
2
n
2
6
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DOI: 10.1039/C4DT03643C
Fig. 4 Two 1D chains connected via lattice water molecules in 1.
4
acceptor atoms (O1, N1, O2S and O2S’in R (11) and O2S, O3S,
in a spiral chain is 10.806(9) Å. Each 1D spiral chain is further
extended by the intraꢀchain hydrogen bonding. The oxygen
atom(O1S) of the lattice water molecule acts as a hydrogen bond
4
4
5
0
5
0
5
0
5
O5 and N2 in R (11)); however, these vary in number of donor
atoms (O1S, O3S, O3S’ and O1S’in R (11) and O3S, O3 and
O2S in R (11)). The R (14) motif comprises of four acceptor 40 acceptor showing bifurcated hydrogen bonding with the oxygen
3
4
4
4
4
3
5
atoms (N1, O6, O3S, O1S) and five donor atoms (O3S, O1S, O3,
atom (O3) of the coordinated phenol (OꢀꢀꢀO distance: 2.672(7) Å)
and nitrogen (N2) atom of the amine part of the ligand (OꢀꢀꢀN
distance: 3.009(6) Å). This lattice water molecule (O1S) also acts
as a hydrogen bond donor and shows hydrogen bonding with the
2
O1S’ and O2). The tenꢀmembered ring in R (10) has two donor
2
1
1
2
2
3
3
atoms (O6 and O2) and two acceptor atoms (O1S and O1S’). In
all these motifs, rest of the ring is made of some portion of the
ligand skeleton. All hydrogen bonding parameters for 2 are listed 45 oxygen atom (O1) of the carboxylate (OꢀꢀꢀO distance: 2.730(6)
in Table 2. Å) of the ligand. This reinforcement of hydrogen bonding within
Compound 3 crystallizes in the monoclinic chiral space group
2
1
each spiral chain forms two motifs labeled as R (21) and R (6)
2
2
46
2
P2 . The asymmetric unit of 3 comprises of a pentacoordinated
(see Fig. S16, ESI†). The 21ꢀmembered motif R (21) consists
1
II
2
Cu center surrounded by two LꢀHTyrthio ligands and one lattice
of two donor atoms (O1S and O3) and two acceptor atoms (O5
II
1
water molecule (as shown in Fig. S15, ESI†). The Cu center has 50 and O1S). The sixꢀmembered motif R (6) consists of O3 as
2
a distorted square pyramidal geometry with an O N coordination
acceptor and O1S and N2 as donor atoms. The remaining parts of
both the motifs are made up of some part of the ligand. The
lattice water O1S is also involved in interꢀchain bifurcated
hydrogen bonding with the oxygen atoms (O1 and O2) of the
3
2
environment. The four equatorial sites are occupied by the two
nitrogen atoms (N1 and N2) of the amine group and two oxygen
atoms (O2 and O4) of the carboxylates of the two ligands.
Unlike 1 and 2, both the carboxylates in 3 bind to the metal 55 carboxylate of the ligands of the next chain (distances: O1SꢀꢀꢀO1,
center in a monodentate fashion. The sulphur atoms in the two
thiophene rings of the mononuclear unit point towards each other.
The apical site is occupied by the phenolic oxygen (O3') of the
3.195(7) Å; O1SꢀꢀꢀO2, 2.787(6) Å) (see Fig. 7). All hydrogen
bonding parameters for 3 are listed in Table 2.
Compound 4 crystallizes in the monoclinic chiral space group
II
II
ligand coordinating to the next metal center (Cu ꢀOH bond
C2. A 2ꢀfold axis that passes through the Cu center and the
length: 2.704(5) Å) generating a spiral 1D coordination polymer 60 coordinated water molecule generates the whole molecule from
(as shown in Fig. 6). The selected bond distances and bond angles
the asymmetric unit. There are two lattice water molecules per
II
for 3 are listed in Tables S1 and S2 (ESI†), respectively. This
mononuclear unit. The Cu center with an O N2 coordination
3
kind of phenolꢀbridged coordination polymer is limited in the
environment has a distorted square pyramidal geometry (see Fig.
S17, ESI†) where two equatorial sites are occupied by the
47
literature. The other phenolic groups (O6) of the second
LꢀHTyrthio ligand shows a bifurcated hydrogen bonding with 65 nitrogen atoms of the amine group and the other two equatorial
oxygen atoms (O4 and O5) of the monodentate carboxylate of the
ligand (O6ꢀꢀꢀO4 distance: 3.035(7) Å) (O6ꢀꢀꢀO5 distance:
sites are occupied by the oxygen atoms of the carboxylates of the
two ligands. The apical site is occupied by a water molecule
(O2). Both the carboxylates bind to the metal center in a monoꢀ
dentate fashion. The selected bond distances and bond angles for
II
3.018(7) Å) coordinating to Cu of the adjacent coordination
II
polymer. The Cu...Cu distance between two adjacent Cu centers
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Fig. 5 3D supramolecular array in 2 involving 1D chains and lattice water molecules.
5
Fig. 6 1D helical structure of 3.
are listed in Table S1 and S2 (ESI†), respectively. The nitrogen 15 with coꢀcrystals of 4,4′ꢀbipyridineꢀNꢀmonoxide (BPMO) and pꢀ
4
atom (N2) of the pyridyl moiety is hydrogen bonded to the
oxygen atom (O1) of the phenol moiety of the second ligand (Nꢀꢀ
ꢀO distance: 2.673(6) Å) and viceꢀversa, resulting in the
formation of a network in the x direction (as shown in Fig. 8,
coumaric acid (PCA), the NꢀꢀꢀO distance 2.689(3) Å and an angle
48
of 175˚. In another coꢀcrystal system of resorcinol and methyl
ester of acrylic acid, two types of OꢀH..N bonding is observed
10
49
(NꢀꢀꢀO distances: 2.787(4) Å and 2.800(4) Å). The NꢀꢀO
top). Few examples of this kind of hydrogen bonding between 20 distances in both the systems are comparable to the NꢀꢀO distance
4
8ꢀ49
phenolic OꢀH and pyridyl N are also known.
In the system
in 4. The oxygen atom (O2) of the coordinated water molecule is
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Table 1 Crystal Structure Data and Refinement Parameters for 1, 2, 3, 4 and 5.
Compound
1
2
3
4
5
Chemical Formula
Formula Weight
C
33
H
38CuN
654.19
2
O
8
C
20
H
30CuN
506.00
2
O
9
C
28
H
30CuN
2
O
7
S
2
C
30
H
36CuN
660.17
4
O
9
16 2 7 2
C H22CuN O S
634.2
482.01
Temperature (K)
Wavelength (Å)
Crystal System
260(2)
296(2)
296(2)
0.71073
250(2)
296(2)
0.71073
0.71073
0.71073
0.71073
Monoclinic
P2
Orthorhombic
P2
Monoclinic
Monoclinic
Monoclinic
Space Group
a (Å)
b (Å)
c (Å)
a (°)
1
1
2
1
2
1
P2
1
C2
12.0163(8)
7.7380(5)
P2
1
12.7195(19)
9.7533(14)
14.170(2)
90
9.2543(6)
10.0380(8)
23.8749(19)
90
10.2891(10)
9.0692(9)
14.9871(17)
90
10.6279(19)
7.9827(14)
23.447(4)
90
17.1859(14)
90
107.324(2)
90
β (°)
115.087(9)
90
90
91.668(7)
90
94.130(3)
90
γ (°)
90
Z
2
4
2
2
4
3
V (Å )
1592.1(4)
1.365
2217.9(3)
1.515
1397.9(3)
1.507
1525.49(19)
1.437
1988.6(6)
1.610
3
Density (mg/cm )
ꢀ1
ꢁ
(mm )
0.739
1.039
0.980
0.776
1.349
F (000)
686
1060
658
690
996
Theta (°) Range
1
.59 to 25.26
1.71 to 25.14
1.98 to 25.14
2.48 to 25.04
1.92 to 24.96
for Data Coll.
Reflections Collected
15183
5589
13150
3868
8182
4273
5711
2469
17388
6862
Independent
Reflections
Reflections
with I >2σ(I))
4
668
3282
3435
2291
4195
R
No. of
Parameters refined
int
0.0435
07
0.0506
309
0.0435
371
0.0322
218
0.0768
514
4
2
GOF on F
0.936
.0378/0.0762
0.916
0.941
0.936
1.002
a
b
Final R
I >2σ(I))
/wR (all data)
1 2
/wR
0
0.0341/0.0616
0.0411/0.0776
0.0582/0.0858
0.0336/0.0691
0.0590/ 0.1251
0.1118/ 0.1490
(
R
1
2
0.0507/0.0831
0.0480/0.0675
0.0378/0.0711
Flack Parameter
Largest diff. peak
0.027(9)
0.249
0.014(10)
0.284
0.011(13)
0.283
0.022(11)
0.182
ꢀ0.001(13)
0.578
ꢀ
3
and hole (eÅ )
and ꢀ0.245
and ꢀ0.315
and ꢀ0.309
and ꢀ0.196
and ꢀ0.729
ꢀ
ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ
a
b
2
2 2
c
2 2 1/2
2
2
2
2
2
c
R = Σ||F | − |F ||/Σ|F |. wR = [Σw(F − F ) /Σw(F ) ] , where w = 1/[σ (F ) + (aP) + bP], P = (Fo + 2F )/3
1
o
c
o
2
o
o
o
5
0
5
hydrogen bonded to the uncoordinated oxygen atom (O4) of the
monodentate carboxylate of the ligand (OꢀꢀꢀO distance: 2.743(4) 20 C5ꢀH5..O4 and C11ꢀH11...O6 with donorꢀacceptor distances
Å) to have the network propagated in the y direction, as shown in
Fig. 8, bottom. The 2D assembly in 4 has extensive hydrogen
bonding thus forming a network with variable pore sizes. One of
the lattice water molecules (O5) connects the phenolic oxygen
distance: 3.146(8) Å). The CꢀH…O interactions C2ꢀH2A..O5,
3.410(5) Å, 3.371(6) Å and 3.358(8) Å, respectively, provide an
additional strength to the network. Various hydrogen bondings
4
5
46
1
lead to two kinds of motif formation in 4: R (61) and R (49).
4 3
4
The 61ꢀ membered motif R (61) consists of four acceptor atoms
4
atoms (O1) of the ligand via hydrogen bonding (O5ꢀꢀꢀO1 25 (O1, O1’, O1’’, O1’’’) and four donor atoms (N2, N2’, N2’’,
5
distance: 2.934(6) Å). The other lattice water molecule (O6) is
hydrogen bonded to the nitrogen (N1) of the amine (NꢀꢀꢀO
distance: 3.182(7) Å) as well as to the coordinated oxygen (O3)
and uncoordinated oxygen atom (O4) of the monodentate
N2’’’) whereas 49ꢀmembered motif R (49) consists of five
3
acceptor atoms (O2, O5, O5’, O5’’, O5’’’) and three donor
atoms(O4, O1 and O1’). Again, in both the cases the motifs were
completed by the ligand skeletons. All hydrogen bonding
1
carboxylate of the ligand (O6ꢀꢀꢀO3 distance: 2.719(8) Å; O6ꢀꢀꢀO4 30 parameters for 4 are listed in Table 2.
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2
2
2
Compound 5 crystallizes in the monoclinic chiral space group
R (8); O7 and O7’ in R (4) and O1 and O6 in R (9) except the
2
2
2
2
P2 . The asymmetric unit of 5 consists of two independent
sixꢀmember R (6) motif which consists of three donor atoms
1
3
molecules (see Fig. S18, ESI†). Each mononuclear unit consists
(O2, O3 and O3’). Like all the motifs, these also consist of some
II
of a pentacoordinated Cu center bound to two LꢀHSerthio 45 part of the ligands. In addition to the hydrogen bonding
II
5
ligands. The Cu center has a distorted square pyramidal
geometry with an O N coordination environment; two equatorial
interactions observed in the first 1D chain, for the second 1D
chain the coordinated water molecule (O8) shows hydrogen
3
2
bonding with the oxygen atom (O12) of the –CH OH of the
2
ligand (O8ꢀꢀꢀO12 distance: 2.962(12) Å). Similar to the first
5
5
6
6
7
7
8
8
9
9
0
5
0
5
0
5
0
5
0
5
chain, the oxygen atoms (O14 and O11) of the –CH OH of two
2
ligands coordinated to same metal center are hydrogen bonded to
the uncoordinated oxygen atoms (O10 and O13, respectively) of
the carboxylate of the adjacent molecules in an intermolecular
fashion (O14ꢀꢀꢀO10 distance: 2.630(14) Å; O11ꢀꢀꢀ O13 distance:
2.725(13) Å). These hydrogen bondings give rise to three motifs
2
2
46
within this chain: two R (10) and one R (12). All motifs
2
2
2
consist of two donor atoms (O17 and O18 in R (10); O13 and
O10 in R (12)) and two acceptor atoms (N3 and N4 in R (10);
O18 and O17 in R (12)) along with some parts of the ligands.
2
2
2
2
2
2
2
All hydrogen bonding parameters for 5 are listed in Table 2.
Effect of the substitution on the ligands
In this study, a systematic change in the reduced Schiff base
derivatives of Lꢀamino acid ligands has been used to investigate
the formation of products under similar reaction conditions.
Fig. 7 Interꢀchain hydrogen bonding in 3 involving the lattice water
molecule (two chains are shown with different colors).
II
Clearly, the coordination of a water molecule to the Cu center is
controlled by the nature of substitution present in the ligand. This
10
15
20
25
30
35
40
sites are occupied by the nitrogen atoms of the amine group
whereas the other two equatorial sites are occupied by the
carboxylate oxygens of the ligands. The apical site is occupied by
a water molecule. Both the carboxylates binds to the metal center
in a monodentate fashion. The selected bond distances and bond
angles for 5 are listed in Tables S1 and S2 (ESI†), respectively.
The two independent molecules in the asymmetric unit not only
differ in the arrangement of sulphur atoms in the two thiophene
rings (in one molecule these point towards each other whereas in
the other molecule these point away from each other), see Fig.
S18 (ESI†) but also vary in their hydrogen bonding interactions.
Each molecule forms a unique 1D supramolecular chain via
intermolecular hydrogen bonding as shown in Fig. 9. In the first
in turn forms either the CPs (1, 2 and 3) with a general formula
.
{[ML ] Y} , or the supramolecular assemblies (4, 5 and 6) with a
2
n
.
general formula [ML (H O)] Y, where L is the ligand and Y
2
2
represents the lattice solvent molecules. Their formation is purely
based on the coordination chemistry of a 1:2 metal to ligand
complex. After having four sites occupied by two ligands the fifth
II
site around Cu is occupied by the donor atom (either from the
phenolic OH group or the carboxylate group) that is available in
1
ꢀ3 while a water molecule occupies in 4ꢀ6. In {[Cu(Lꢀ
.
.
HTyrbenz) ] CH OH H O} (1), the coordination polymer is
2
3
2
n
formed via bridging carboxylate showing no role of the phenolic
group in its formation. To further emphasize this point, Lꢀ
tyrosine was replaced with Lꢀserine to form another CP, {[Cu(Lꢀ
1
–
D chain, the two oxygen atoms (O6 and O7, respectively) of the
.
HSerbenz) ] 3H O} (2).
2
2
n
CH OH of one mononuclear unit shows an intermolecular
2
In changing from LꢀH Tyrbenz ligand to LꢀH Tyr4ꢀpyr ligand
2
2
hydrogen bonding with the uncoordinated oxygen atoms (O5 and
O3, respectively) of the carboxylates of the next mononuclear
units in an intermolecular fashion (O6ꢀꢀꢀO5 distance: 2.686(12)
Å; O7ꢀꢀꢀO3 distance: 2.687(12) Å). The oxygen atom (O1) of the
coordinated water molecule shows intermolecular hydrogen
bonding with two coordinated oxygen atoms (O2 and O4) of the
two carboxylates of two different molecules (O1ꢀꢀꢀO2 distances:
.868(11) Å and O1ꢀꢀꢀO4 distance: 2.918(11) Å, respectively).
The nitrogens (N2 and N1) of the amine part of the ligands of one
mononuclear unit are hydrogen bonded to the oxygen atom (O1)
(
1 vs 4), the strong hydrogen bonding of the pyridyl nitrogen with
II
the phenolic OH does not allow the latter to bind to Cu . The
structural assortment of compounds such as 4 can be accredited to
the presence and position of the hetero atom in the ring. For
II
example, as reported earlier the use of LꢀH tyrꢀ2pyr with Cu
2
results in the formation of a supramolecular assembly [Cu(Lꢀ
50
II
Htyr2ꢀpyr)2].
But the environment around Cu and the
2
hydrogen bonding interactions present in the 4 is distinctly
different from the supramolecular array in [Cu(LꢀHtyr2ꢀpyr) ]. In
2
II
4
[
, Cu is pentacoordinated with an O N environment, whereas in
Cu(LꢀHtyr2ꢀpyr) ], hexacoordinated Cu is surrounded by an
2
3
2
of the coordinated water and oxygen atom (O6) of the –CH OH
2
II
part of the ligand of the next unit respectively (distances: N2ꢀꢀꢀ
O1, 3.240(12) Å; N1ꢀꢀꢀO6, 3.014(13)Å). These hydrogen
O N environment. In both the cases, the nitrogen of the amine
2
4
2
2
and oxygen of the carboxylate of the ligand bind to the metal
bondings lead to the formation of four motifs: R (6), R (8),
3
2
2
2
46
center. In addition to that, the pyridyl nitrogens also coordinate to
R (4) and R (9). All four motifs consist of two acceptor atoms
(O1 and O1’in R (6); O1 and O1’ in R (8); O1 and O1’in R (4)
and N1 and N2 in R (9)) and two donor atoms (O2 and O7 in
2
2
II
2
2
2
the Cu in case of [Cu(LꢀHtyr2ꢀpyr) ] whereas in 4, the fifth
2
3
2
2
II
2
coordination of the Cu center is completed by a water molecule.
2
1
0
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Fig. 8 Hydrogen bondings in x (top) and y (bottom) directions for the formation of the 2D supramolecular network in 4. Other lattice water molecule (O6)
is omitted for clarity.
5
0
5
In [Cu(LꢀHtyr2ꢀpyr)2] the supramolecular assembly grows
through the hydrogen bonding which involves the phenolic OH,
oxygens of the carboxylates and the lattice solvent (water)
molecules. In 4, the above mentioned hydrogen bonding do exist
along with another typical hydrogen bonding between the pyridyl
nitrogen and the phenolic –OH of the ligand (vide supra). Thus
the 2ꢀpyr derivative forms a polymeric structure because no such
pyr..HO(phenol) hydrogen bonding is possible. Similarly, in
changing from LꢀH Tyrthio to LꢀH Serthio (3 vs 5) the length of
reacting 5 with 2 eq of LꢀH Tyrthio in methanol to form 3 as
established by PXRD (see Fig. S21, ESI†) while the reverse was
not possible. To further illustrate the significance of the phenolic
2
part, the LꢀTyrosine part in the ligand LꢀH tyrthio is supplanted
2
1
25 with LꢀPhenylalanine and the resultant ligand LꢀHPhethio gives
.
[Cu(LꢀPhethio) (H O)] 3H O (6). Although the crystal structure
2
2
2
of 6 is not obtained even after several attempts, the values for the
carboxylate stretching frequencies in its FTIR spectrum
advocates the presence of monodentate carboxylate
2
2
ꢀ
1
1
the –CH OH group in the latter is much less than the distance 30 (ꢀυ = υasym−υsym = 267 cm ) and thus implicate no carboxylateꢀ
2
II
45,53
between the two Cu centers to occupy the fifth site and thus a
bridged CP formation.
The absence of the phenolic ꢀOH
water molecule is coordinated. Thus the essence in the formation
group in LꢀPhethio further insinuate the formation of any
phenolic bridged CP, thus confirming 6 to be a supramolecular
assembly and not a CP.
.
of {[Cu(LꢀHTyrthio) ] H O} (3) lies in the growing of the spiral
2
2
n
polymer via the unique phenolic bridging with a distance between
II
2
3
0
5
two Cu centers of 10.806 Å. This is further confirmed by
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Fig. 9 Two independent 1D supramolecular chains in 5 (Chain 1: top; Chain 2: bottom).
5
0
5
Powder X-ray data analysis
UV-Vis and Circular Dichroism (CD) spectroscopy
UVꢀVisible and CD studies were carried using ~1 mM
To confirm whether the single crystal structure corresponds to the
bulk material or not, powder Xꢀray diffraction patterns were 20 methanolic solution of 1ꢀ6. In the visible part of the spectra for 1ꢀ
recorded for 1-5 at room temperature. The experimental and
simulated (from the single crystal data) patterns were similar to
each other (see Figs. S19ꢀS23, ESI†). Powder pattern of 6 was
also recorded to check the crystalline nature of the compound
–1.
–1
6, major peaks are at 590 nm (ε = 159 L·mol cm ), 589 nm (ε =
–
1.
–1
–1.
–1
1
144 L·mol cm ), 585 nm (ε = 200 L·mol cm ), 600 nm (ε =
–1.
–1
–1.
–1
174 L·mol cm ), 586 nm (ε = 152 L·mol cm ) and 582 nm (ε
–1.
–1
= 153 L·mol cm ), respectively (as shown in Fig. 10a). These
II
2
2
51
(see Fig. S24, ESI†). The patterns obtained confirm that the 25 peaks are due to the dꢀd transition in Cu ( E to T ). In the
g 2g
single crystal and bulk material are the same. It also confirms the
phase purity of the bulk sample.
CD spectrum (400ꢀ700 nm) for 1, the positive Cotton effect is
observed at 445 and 632 nm. The corresponding peaks for other
1
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Table 2 Hydrogen Bonding Parameters for 1, 2, 3, 4 and 5.
DꢀH…A
r(DꢀH) (Å)
r(H…A) (Å)
r(D…A) (Å)
∠DꢀH…A (°) Symmetry
1
O1ꢀH2..O7
O6ꢀH5..O8
O8ꢀH12C..O7
O8ꢀH12D..O5
O7ꢀH51..O2
0.82
0.82
0.75
0.87
0.82
1.86
1.84
2.31
2.17
1.86
2.672(6)
2.652(8)
3.049(7)
2.985(8)
2.667(8)
168
171
169
157
167
x,ꢀ1+y,z
1ꢀx,ꢀ1/2+y,ꢀz
ꢀx,1/2+y,ꢀz
C5ꢀH20..O6
C10ꢀH26B..O5
2
0.93
0.97
2.53
2.43
3.263(8)
3.317(6)
136
152
1ꢀx,ꢀ1/2+y,ꢀz
ꢀx,1/2+y,ꢀz
O1ꢀH1..O1S
O1SꢀH1SB..O6
N1ꢀH1A..O3S
N2 ꢀH2..O2S
O1SꢀH1SA..O2
O2SꢀH2SB..O1S
O2SꢀH2SA..O3S
O5ꢀH5..O3
O3SꢀH3SB..O3
O3S ꢀH3SA..O5
C13ꢀH13B..O4
3
0.82
0.85
0.98
0.98
0.85
0.85
0.86
0.82
0.85
0.85
0.97
1.96
2.03
2.56
2.10
1.91
2.11
2.01
2.24
2.05
2.10
2.44
2.777(4)
2.864(4)
3.516(4)
3.078(5)
2.752(4)
2.953(5)
2.865(6)
2.972(4)
2.858(4)
2.915(4)
3.322(5)
171
167
165
172
171
173
177
149
159
161
151
ꢀx,ꢀ1/2+y,1/2ꢀz
ꢀx,ꢀ1/2+y,1/2ꢀz
ꢀ1+x,y,z
ꢀ1/2+x,1/2ꢀy,ꢀz
1/2ꢀx,1ꢀy,1/2+z
1ꢀx,ꢀ1/2+y,1/2ꢀz
ꢀ1/2+x,1/2ꢀy,ꢀz
1+x,y,z
1/2+x,3/2ꢀy,ꢀz
O1SꢀH1SB..O1
N2ꢀH2..O1S
O1SꢀH1SA..O1
O1SꢀH1SA..O2
O3ꢀH3..O1S
O6ꢀH6..O4
O6ꢀH6..O5
4
0.85
0.98
0.86
0.86
0.82
0.84
0.84
1.90
2.23
2.57
1.95
1.87
2.24
2.29
2.730(6)
3.009(6)
3.195(7)
2.787(6)
2.672(7)
3.035(7)
3.018(7)
166
135
131
165
167
156
145
1ꢀx,1/2+y,1ꢀz
1ꢀx,1/2+y,1ꢀz
1+x,y,ꢀ1+z
1+x,y,ꢀ1+z
x,y,1+z
ꢀ1+x,y,z
ꢀ1+x,y,z
N1ꢀH1..O6
O1ꢀH1A..N2
O2ꢀH2..O4
O5ꢀH5A..O1
O6ꢀH6A..O4
O6ꢀH6B..O3
C2ꢀH2A..O5
C5ꢀH5..O4
0.98
0.82
0.84
0.87
0.84
0.84
0.93
0.93
0.93
2.35
1.87
1.91
2.07
2.33
1.94
2.55
2.47
2.48
3.182(7)
2.673(6)
2.743(4)
2.934(6)
3.146(8)
2.719(8)
3.410(5)
3.371(6)
3.358(8)
142
164
171
172
164
154
154
162
157
ꢀ1/2+x,1/2+y,z
1/2ꢀx,ꢀ1/2+y,1ꢀz
ꢀ1/2+x,1/2+y,z
x,ꢀ1+y,z
1/2ꢀx,ꢀ1/2+y,ꢀz
1/2+x,1/2+y,z
ꢀ1/2+x,ꢀ1/2+y,z
x,1+y,z
C11ꢀH11..O6
5
N1ꢀH1..O6
O1ꢀH1C..O4
O1ꢀH1D..O2
N2ꢀH2..O1
O6ꢀH6..O5
0.98
0.85
0.85
0.98
0.82
2.18
2.11
2.03
2.40
1.87
3.014(13)
2.918(11)
2.868(11)
3.240(12)
2.687(12)
142
158
167
143
173
1ꢀx,ꢀ1/2+y,1ꢀz
1ꢀx,ꢀ1/2+y,1ꢀz
1ꢀx,1/2+y,1ꢀz
1ꢀx,1/2+y,1ꢀz
1ꢀx,ꢀ1/2+y,1ꢀz
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DOI: 10.1039/C4DT03643C
O7ꢀH7..O3
0.82
0.85
0.82
0.82
0.97
0.97
1.92
2.28
1.84
1.92
2.40
2.57
2.686(12)
154
138
160
169
136
136
1ꢀx,1/2+y,1ꢀz
2ꢀx,ꢀ1/2+y,ꢀz
2ꢀx,1/2+y,ꢀz
2ꢀx,ꢀ1/2+y,ꢀz
1ꢀx,1/2+y,1ꢀz
1ꢀx,1/2+y,ꢀz
O8ꢀH8C..O12
O14ꢀH14A..O10
O11ꢀH11..O13
C1ꢀH1F..O7
2.962(12)
2.630(14)
2.725(13)
3.166(15)
3.335(15)
C17ꢀH17A..O10
2
2
3
3
4
4
5
5
6
6
0
5
0
5
0
5
0
5
0
5
In the CD spectrum of 1 (200ꢀ400 nm), the positive Cotton
effect is observed at 217, 240 and 273 nm. The corresponding
peaks for other complexes are as follows: 2, 210 and 234 nm; 3,
2
00 and 246 nm; 4, 260 nm; 5, 200 and 251 nm; 6, 200 and 285
nm. For 1, the negative Cotton effect is observed at 200 nm and
224 nm. The corresponding peaks for other complexes are as
follows: 2, 200 nm; 3, 224 nm; 4, 217 and 277 nm 5, 229 nm; 6,
2
27 and 285 nm (as shown in Fig. 11b).
FT-IR spectroscopy
The IR spectra of 1ꢀ6 (see Figs. S25ꢀS30, ESI†) were recorded in
solid state using KBr pellets. In the FTꢀIR spectra of 1ꢀ6, the
ꢀ
1
broad peak in the range of 3300ꢀ3400 cm is due to the lattice
ꢀ
1
ꢀ1
water molecules. The peak at 3269 cm (1), 3252 cm (3) and
ꢀ
1
3269 cm (4) is due to phenolic –OH of the ligands. The sharp
ꢀ
1
ꢀ1
ꢀ1
a)
peak observed at 3237 cm (4), 3257 cm (5) and 3277 cm (6) is
due to coordinated water molecule. The hydroxyl peak of the
ꢀ
1
ꢀ1
–
CH OH for 2 and 5 appears at 3111 cm and 3212 cm ,
2
ꢀ
1
respectively. The peaks in the range of 2930ꢀ2950 cm are for the
NꢀH of amine part of the complexes. The presence of two types
of asymmetric and symmetric stretches for the carboxylate group
in 1 and 2 are well in accordance with the presence of two types
of carboxylate binding modes (monodentate and bridging) in 1
and 2. The various FTIR peaks for the carboxylates in 1ꢀ6 are
4
5,53
listed in Table S3 (ESI†).
The stretching frequency for the CꢀO is observed at 1240 cm
ꢀ
1
ꢀ
1
ꢀ1
ꢀ1
ꢀ1
(
1), 1278 cm (2), 1244 cm (3), 1264 cm (4), 1254 cm (5)
ꢀ
1
ꢀ1
and 1278 cm (6). In the spectrum of 3, the peaks at 1198 cm
ꢀ
1
and 714 cm are due to C=S and CꢀS present in the thiophene
ring of the ligand. The corresponding peaks for 5 appear at 1177
ꢀ
1
ꢀ1
54
cm and 716 cm , respectively.
Thermogravimetric analyses
b)
Fig. 10 a) UV spectra and b) CD spectra for 1ꢀ6 in wavelength range from
Thermal stabilities of 1ꢀ6 were studied as a function of
temperature in the range of 25ꢀ500 ˚C (see Fig. S31, ESI†). Since
5
0
5
400 to 700 nm.
1
, 2 and 3 are CPs, their profiles show thermal stabilities up to
complexes are as follows: 2, 453 and 653 nm; 3, 434 and 650 nm;
, 453 and 671 nm; 5, 459 and 658 nm; 6, 454 and 657 nm. For 1,
the negative Cotton effect is observed at 537 nm. The
corresponding peaks for other complexes are as follows: 2, 522
nm; 3, 524 nm; 4, 533 nm; 5, 527 nm; 6, 530 nm (as shown in
Fig. 10b). The peaks in the range of 520ꢀ540 nm are due to dꢀd
2
00 ˚C with an initial loss of the lattice solvent molecules at
4
around 100 ˚C. For 1, it is a three step weight loss profile. The
first weight loss of 4.96% between 50ꢀ120 ˚C corresponds to loss
of two lattice water molecule (ca. 5.2%). The second step
showing weight loss of 15.4% between 120ꢀ220 ˚C indicates loss
1
52
of three lattice water molecules along with loss of a CO
2
transitions.
molecule from the ligand (ca. 14.9%). The third step showing
weight loss of 50.1% between 220ꢀ400 ˚C indicates loss of the
rest of the Cuꢀligand complex (ca. 51.9%). For 2, it is a two step
weight loss profile. The first weight loss of 10.2% between 50ꢀ
In the UV region of the spectra of 1ꢀ6 (200 to 400 nm), the
peaks at around 200 nm (пꢀп*) and 225 nm (nꢀп*) are due to the
ligand. The peaks within the range of 250ꢀ275 nm in various
spectra are due to the various substitutions in the aldehyde part of
the ligands (as shown in Fig. 11a).
1
1
1
00 ˚C corresponds to loss of three lattice water molecule (ca.
0.7%). The second step showing weight loss of 64.7% between
1
4
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2
00ꢀ400 ˚C indicates loss of the ligand (ca. 69.4%). For 3, it is a
profile. The first weight loss of 3.44% between 50ꢀ150 ˚C
corresponds to loss of one water molecule (ca. 2.87%). The
second step showing weight loss of 6.01% between 150ꢀ190 ˚C
30 indicates loss of three more water molecules (ca. 8.6%). The third
step showing weight loss of 59.7% between 200ꢀ400 ˚C indicates
further degradation of the compound.
three step weight loss profile. The first weight loss of 4.2%
between 50ꢀ170 ˚C corresponds to loss of two lattice water
molecules (ca. 4.2%). The second step showing weight loss of
12.9% between 160ꢀ230 ˚C indicates loss of a thiophene
molecule (ca. 13.4%). The third step showing weight loss of
5
0
5
3
3
9.1% between 230ꢀ400 ˚C indicates loss of left over ligand (ca.
6.4%). Each of 4 and 6 shows loss of both lattice as well as
Photoluminescence properties
coordinated solvent molecules at around 150 ˚C. For 4, it is a four
step weight loss profile. The first weight loss of 10.03% between
All tyrosine based ligands show good fluorescence as tyrosine
1
3
5
itself is a natural fluorophore. All the ligands were excited at 270
nm to show emission at 310 nm for LꢀNaHTyrbenz, 318 nm for
LꢀNaHTyrthio and 324 nm for LꢀNaHTyr4ꢀpyr. In the presence
of Cu(II) ions the fluorescence due to the ligands is quenched as
can be seen in the emission spectra of 1, 3 and 4 (Fig 12). This is
due to the fact that a transitionꢀmetal center can persuade the nonꢀ
radiative deactivation of adjoining photoexcited fluorophore by
dexter type energy transfer between the orbitals of appropriate
5
0ꢀ110 ˚C corresponds to loss of four uncoordinated water
molecules (ca. 9.96%). The second step showing weight loss of
.7% between 110ꢀ200 ˚C indicates loss of one uncoordinated
6
and one coordinated water molecules (ca. 6.3%). The third step
showing weight loss of 35.2% between 200ꢀ330 ˚C indicates loss
of a tyrosine molecule and a copper atom (ca. 33.8%). The fourth
step showing weight loss of 11.9% between 330ꢀ400 ˚C indicates
loss of a pyridyl group (ca. 12.5%). The TGA profile of 5, shows
1
40
II
55
energy of Cu and the respective fluorophores.
a)
45
Fig. 12 Emission spectra of Lꢀ NaHTyrbenz, LꢀNaHTyrthio, LꢀNaHTyr4ꢀ
pyr, 1, 3 and 4.
Conclusions
In this article we have demonstrated that the formation of diverse
chiral coordination architectures can be controlled by the strategic
substitution on the reduced Schiff base ligands of amino acids.
5
5
6
0
5
0
.
.
Those
({[Cu(LꢀHTyrbenz) ] CH OH H O}
(1),
{[Cu(Lꢀ
2
3
2
n
.
.
HSerbenz) ] 3H O} (2) and {[Cu(LꢀHTyrthio) ] H O} (3))
2
2
n
2
2
n
which do not have any coordinated water moelcule are 1D CPs
but their formation is through different functionalities of the
ligand (a synꢀanti bridging carboxylate and hydroxy group of the
Lꢀtyrosine part of the ligand in 1 and 3, respectively, and an antiꢀ
anti bridging carboxylate group of Lꢀserine part of the ligand in
2
0
b)
2
). On the other hand, each of the three complexes ([Cu(Lꢀ
Fig. 11 a) UV spectra and b) CD spectra for 1ꢀ6 in wavelength range from
.
HTyr4ꢀpyr) (H O)] 2H O (4), [Cu(LꢀHSerthio) (H O)] (5), and
[Cu(LꢀPhethio) (H O)] 3H O (6)) that contains a coordinated
2
2
2
.
2
2
2
00 to 400 nm.
2
2
2
it to be highly stable till 200˚C thus confirming the presence of
strong hydrogen bonding. The weight loss of 69.82% between
202ꢀ304 ˚C corresponds to loss of the coordinated water molecule
and the ligand (ca. 67.1%). For 6, it is a three step weight loss
water molecule are supramolecular assemblies via extensive
hydrogen bonding. Thus the involvement of the phenolic ꢀOH
group in the ligands derived from LꢀTyrosine in a coordination
bond is dictated by the substitution on the N atom of the ligand.
2
5
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For the methylthiophenyl containing ligands, the phenolic group
in LꢀHTyrthio is long enough to bridge the two Cu centers in 3
65
(c) S. Khullar and S. K. Mandal, CrystEngComm, 2013, 15, 6652; (d)
S. Khullar, V. Gupta and S. K. Mandal, CrystEngComm, 2014, 16,
II
5
705; (e) N. Kumar, S. Khullar, Y. Singh and S. K. Mandal,
but the much shorter length of the –CH OH group in LꢀHSerthio
2
CrystEngComm, 2014, 16, 6730.
Q. Wang, Y. Chen, P. Ma, J. Lu and X. Zhang, J. Mater. Chem.,
2011, 21, 8057.
is responsible for the formation of 5. Furthermore, the
significance of the phenolic part is observed when the LꢀTyrosine
1
3
5
0
5
70
1
4 T. Hang, W. Zhang, H. Y. Ye and R. G. Xiong, Chem. Soc. Rev.,
part in the ligand LꢀH tyrthio is exchanged with LꢀPhenylalanine
2
2
011, 40, 3557.
and the resultant ligand LꢀHPhethio gives 6. Therefore, these
ligands are found to play an important role in determining the
coordination architectures with diverse physicoꢀchemical
properties as determined by a number of analytical methods, such
as FTIR, Fluorescence, UVꢀVis and circular dichroism
spectroscopy, polarimetry, powder and single crystal Xꢀray
diffraction and thermogravimetric analysis. Based on the results
presented in the paper, we are currently conducting further work
involving other substitutions on the ligands to showcase the
generalization of this scheme.
1
1
5 W. Zhang and R. G. Xiong, Chem. Rev., 2012, 112, 1163.
6 W. Zhang, L. Z. Chen, R. G. Xiong, T. Nakamura and S. D. Huang,
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8
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5
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Acknowledgement
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000; (c) R. J. Biediger, W. George, J. M. Kassir, W. Li, V. Robert,
Funding for this work was provided by IISER, Mohali. N. K. is
grateful to MHRD, India, for a research fellowship. Central
facilities (Xꢀray, NMR, HRMS and CD) at IISER, Mohali, and
CIL, NIPER, Mohali for CHN are gratefully acknowledged.
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a
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and Research, Mohali, Sector 81, Manauli PO, S.A.S. Nagar, Mohali
(Punjab) 140306, INDIA
Fax: 91 172 2240266; Tel: 91 172 22 40124;
Eꢀmail: sanjaymandal@iisermohali.ac.in
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#
Current address: Department of Chemistry, DAV University, Jalandhar,
1
1
1
1
1
1
1
1
00
05
10
(Punjab) 144001, INDIA
†
Electronic Supplementary Information (ESI) available: Crystallographic
data of the structures 1, 2, 3, 4 and 5 in CIF format (CCDC no. 993632ꢀ
93636, respectively). NMR and FTIR spectra for the ligands, additional
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3
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Journal Name, [year], [vol], 00–00 | 17

Dalton Transactions
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DOI: 10.1039/C4DT03643C
Table of Contents – artwork and synopsis
II
5
In this paper we report six chiral ligands based on Lꢀtyrosine, Lꢀserine and Lꢀphenylalanine and their homochiral Cu complexes to study
the effects of various substitutions in the ligands on the formation of diverse coordination architectures. This has allowed us to identify
the factors involved in controlling the formation of either coordination polymers or supramolecular assemblies.
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