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

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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

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

n

2

1

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

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

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

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

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

6

0

5

0

5

3

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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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

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

2

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

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

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

: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

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

n

2

(

4),

[Cu(LꢀHSerthio) (H O)]

(5),

and

[Cu(Lꢀ

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

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

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

O

8

9

5

0

5

N

HN

N

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

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

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

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

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

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

2

3

4

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

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

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

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 [λ_m_a_x, 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

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^,ⁿ^m^]^:²⁰⁵^,²⁵⁴^,⁵⁸⁹^.^S^p^e^cⁱ^fⁱ^c^r^o^t^a^tⁱ^oⁿ^[^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

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

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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

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 [λ_m_a_x, 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

2

3

4

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

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

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 [λ_m_a_x, 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

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 [λ_m_a_x, 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

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

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 [λ_m_a_x, 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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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

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

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

2

3

4

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

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

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

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

CuꢀN_a_m_i_n_ebond 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

Tyr)(phen)(ClO )];

4

however, the CuꢀO₍_m_o_n_o_d_e_n_t_a_t_e

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₍_b_r_i_d_g_e_d_c_a_r_b_o_x_y_l_a_t_e₎distances of

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.

{

[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

5

6

7

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

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

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

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₍_m_o_n_o_d_e_n_t_a_t_e

bond of 1.931(3) Å in 1. For 1, the bond angle

carboxylate)

O₍_c_a_r_b_o_x_y_l_a_t_e₎_ꢀCuꢀN₍_a_m_i_n_e₎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

2

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

the phenolic –OH is deprotonated and thus the phenoxo group

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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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

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

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

2

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

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

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 N₂coordination

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)

0.71073

250(2)

296(2)

0.71073

Monoclinic

P2

Orthorhombic

P2

Monoclinic

Space Group

a (Å)

b (Å)

c (Å)

a (°)

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

91.668(7)

90

94.130(3)

90

γ (°)

90

Z

2

4

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

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

c

R = Σ||F | − |F ||/Σ|F |. wR = [Σw(F − F ) /Σw(F ) ] , where w = 1/[σ (F ) + (aP) + bP], P = (F_o+ 2F )/3

1

o

c

o

2

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.

This journal is © The Royal Society of Chemistry [year] [journal], [year], [vol], 00–00 | 9

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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

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

6

7

8

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

46

within this chain: two R (10) and one R (12). All motifs

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

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

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

n

CH OH of one mononuclear unit shows an intermolecular

2

In changing from LꢀH Tyrbenz ligand to LꢀH Tyr4ꢀpyr ligand

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

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

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

II

2

the Cu in case of [Cu(LꢀHtyr2ꢀpyr) ] whereas in 4, the fifth

2

3

2

II

2

coordination of the Cu center is completed by a water molecule.

2

1

0

| Journal Name, [year], [vol], 00–00

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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

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

ꢀ

1

the –CH OH group in the latter is much less than the distance 30 (ꢀυ = υ_a_s_y_m−υ_s_y_m= 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

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

This journal is © The Royal Society of Chemistry [year]

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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

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

This journal is © The Royal Society of Chemistry [year]

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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

0.75

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

0.85

0.86

0.82

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

ꢀ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

0.82

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

1+x,y,ꢀ1+z

x,y,1+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

0.93

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

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

0.98

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

[journal], [year], [vol], 00–00 | 13

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O7ꢀH7..O3

0.82

0.85

0.82

0.97

1.92

2.28

1.84

1.92

2.40

2.57

2.686(12)

154

138

160

169

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

3

4

5

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

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), 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

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

| Journal Name, [year], [vol], 00–00

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DOI: 10.1039/C4DT03643C

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

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

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

n

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

00 to 400 nm.

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

Journal Name, [year], [vol], 00–00 | 15

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DOI: 10.1039/C4DT03643C

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

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

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

5

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5

1

17 G. Verardo, P. Geatti, E. Pol and A. G. Giumanini, Can. J. Chem.,

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8

3

19 (a) R. J. Biediger, B. Dupre, L. K. Hamaker, G. W. Holland, J. M.

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1

Acknowledgement

2

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.

L. Ian, B. Dupre, L. K. Hamaker, N. Nguyen, E. R. Decker and C.

Wu, Propanoic acid derivatives that inhibit the binding of integrins to

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011, 71, 557.

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Notes and references

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a

Department of Chemical Sciences, Indian Institute of Science Education

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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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Ray, Cryst. Growth Des., 2007, 7, 1818; (d) M. A. Alam, M. Nethaji,

and M. Ray, Angew. Chem., Int. Ed., 2003, 42, 1940.

#

Current address: Department of Chemistry, DAV University, Jalandhar,

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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Journal Name, [year], [vol], 00–00 | 17

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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.

[journal], [year], [vol], 00–00 | 18

Article Doi

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

DOI: 10.1039/c4dt03643c

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