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Division of Inorganic Chemistry, Department of Chemistry, Aligarh Muslim ..... F. A. Cotton, G. Wilkinson, Advanced Inorganic Chemistry, 5th Ed., Wiley, New York ...
J. Serb. Chem. Soc. 70 (11) 1273–1281 (2005) JSCS–3367

UDC 54–71–034:546.562:542.42:543.42 Original scientific paper

Metal ion promoted synthesis of pentaazamacrocyclic complexes of a few first row transition metal series derived from 2,6-diaminopyridine TAHIR ALI KHAN*, SHABANA TABASSUM, NISHAT BEGUM and POONAM CHINGSUBAM Division of Inorganic Chemistry, Department of Chemistry, Aligarh Muslim University, Aligarh-202002 India (e-mail: [email protected]) (Received 9 February 2004, revised 20 January 2005) Abstract: A new series of dichloro/dinitrato (2,6,9,13,18-pentaazacbicyclo [12.3.1]octadeca-1(18),14,16-triene) metal (II) [MLX2] (M = Mn(II), Co(II), Ni(II) and Zn(II); X = Cl or NO3) and (2,6,9,13,18-pentaazacyclo[12.3.1]octadeca-1(18),14,16-triene) copper(II) dichloride/dinitrate [CuL]X2 (X = Cl or NO3) have been synthesized by the template condensation reaction of 2,6-diaminopyridine with 1,2-diaminoethane and 1,3-dibromopropane. The complexes were studied by elemental analysis, magnetic susceptibility and conductivity measurements. Various spectroscopic techniques, viz. IR, 1H-NMR, EPR, UV/Vis, were used to establish their structures. Except for the complexes of copper(II), which are square planar, all other complexes have octahedral structures. Keywords: pentaazamacrocyclic ligands, transition metal complexes/template condensation, spectroscopic studies. INTRODUCTION

The coordination chemistry of macrocyclic ligands is a fascinating area of research. The synthetic, kinetic and structural aspects1,2 of polyazamacrocyclic complexes have received considerable attention and a variety of such systems have been synthesized.3–7 The polyazamacrocycle complexes, particularly those of tetraazamacrocycle along with the pentaaza and higher polyazamacrocycles, have been widely studied in view of their potential for binding more than one metal ion.8,9 The relationship of electronic properties and reactivities of these synthetic macrocyclic complexes to those of naturally occurring macrocycles, such as porphyrins10 and corrins, continues to promote great interest in their design and preparation. Studies of macrocyclic complexes have shown that some are involved in important biological processes,11,12 such as photosynthesis and dioxygen transport,13,14 in addition to *

Author for correspondence.

doi: 10.2298/JSC0511273K

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their catalytic properties,14,15 which may lead to important industrial applications. Their enhanced kinetic and thermodynamic stabilities led to a widespread study of the features which also influence their potential applications as metal extractants,16,17 radiotherapeutic,18 medical imaging agents,19 MRI contrast agents20,21 and as effective sequestering agents for toxic metals.22 Cyclic tetraamines have received considerable attention owing to their coordination properties towards various metal cations.23 Metal template synthesis was found to be an effective method to synthesize macrocyclic complexes. Thereby, the steric course of the condensation reaction resulting in ring closure is directed.8,24 Here, the synthesis and characterization of pentaazamacrocyclic complexes [MLX2] [M = Mn(II), Co(II), Ni(II), Zn(II)] and [CuL]X2 (X = Cl or NO3) obtained from the template condensation reaction of 2,6-diaminopyridine with 1,2-diaminoethane and 1,3-dibromopropane, are reported. EXPERIMENTAL The metal salts MnX2.4H2O, CoX2.6H2O, NiX2.6H2O, CuX2.2H2O (X = Cl or NO3), ZnCl2 and Zn(NO3)2.6H2O (all BDH) were commercially available pure samples. The chemicals 2,6-diaminopyridine (Aldrich) and 1,2-diaminoethane, 1,3-dibromopropane (E. Merck) were used as received. Synthesis of dichloro/dinitrato (2,6,9,13,18-pentaazacbicyclo [12.3.1]octadeca-1(18),14,16-triene) metal(II) [MLX2] (M = Mn(II), Co(II), Ni(II), Zn(II); X = Cl or NO3) and (2,6,9,13,18-pentaazacbicyclo [12.3.1]octadeca-1(18),14,16-triene) copper(II) dichloride/dinitrate [CuL]X2 (X = Cl or NO3) A mixture of 2,6-diaminopyridine (0.01 mol) and 1,2-diaminoethane (0.01 mol) in methanol (50 cm3) was stirred for about 24 h. Finally a methanolic solution (25 cm3) of a metal salt (0.01 mol) and 1,3-dibromopropane (0.02 mol) were added simultaneously. The resultant mixture was refluxed for about 8 h, giving a solid product, which was washed several times with methanol and dried in vacuo. Methodology The elemental analyses were obtained from the microanalytical laboratory of the Central Drug Research Institute Lucknow, India. The 1H-NMR spectra in DMSO-d6 using a Brucker Ac200E NMR spectrometer with Me4Si as the internal standard, were obtained from Guru Nanak Dev University, Amritsar, India. Metal and chloride estimations were done volumetrically25 and gravimetrically,26 respectively. The IR spectra (4000–400 cm-1) were recorded as KBr discs on a Perkin Elmer 621 spectrophotometer. A Pye-Unicam 8800 spectrophotometer was used for obtaining the electronic spectra of the compounds in DMSO. The EPR spectra were recorded on a JEOL JES RE2X EPR spectrometer. Magnetic susceptibility measurements were performed using a Faraday balance at 25 oC. The electrical conductivities of 10-3 M solutions in DMSO were obtained on a Systronics type 302 conductivity bridge equilibrated at 25.00 ± 0.01 oC. RESULTS AND DISCUSSION

The template reaction of metal salts with 2,6-diaminopyridine, 1,2-diaminoethane and 1,3-dibromopropane in a 1:1:1:2 mole ratio resulted in the formation of a new class of pentaazamacrocyclic complexes with stoichiometries [MLX2] [M = Mn(II), Co(II), Ni(II), Zn(II)], and [CuL]X2 (X = Cl or NO3). The elemental analysis results (Table I) are consistent with the proposed 1:1 metal to ligand stoichiometry (Fig. 1). All the complexes were non-electrolytes27 in DMSO, except the copper complexes which were 1:2 electrolytes.

SYNTHESIS OF PENTAAZAMACROCYCLIC COMPLEXES

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Fig. 1. Reaction scheme for the synthesis of the macrocyclic complexes.

IR Spectra The IR spectra of all the complexes (Table II) showed no bands corresponding to primary amine stretching vibrations. The bands at ca. 3200 cm–1, assignable28 to the coordinated secondary amino stretching vibrations, indicated that the proposed condensation had occurred. All the complexes showed bands in the 1160–1200 cm–1 regions, which may be reasonably assigned to n(C–N). The bands observed in the 2890–2940 and 1430–1480 cm–1 regions can be ascribed to n(C–H) and d(C–H), respectively. The pyridine moiety exhibits three important ring vibrations,29,30 i.e., 6a and 8a vibrations (in-plane ring deformation) appearing at 603–610 and 1580–1600 cm–1, respectively,29 while the 16b vibration (out-of-plane ring deformation) is observed in the 404–412 cm–1 region. Moreover, a medium intensity band at 420–450 cm–1 for all the complexes is due to n(M–N) vibrations.31 The spectra of the nitrato complexes gave additional bands around 1230, 1020, and 890 cm–1, which are consistent with the monodentate nature of this group. Bands appearing in the nitro and chloro complexes in the regions 235–255 and 300–360 cm–1 are assignable to n(M–O) and n(M–Cl), respectively.32,33 EPR Spectra The EPR spectra of the polycrystalline copper(II) complexes (Table III) were recorded at room temperature. They showed only a single broad signal, while hyperfine splitting signals were absent in all cases. The absence of hyperfine sig-

C13H23N7O6Zn

[ZnL(NO3)2]

C13H23N5ZnCl2

[ZnLCl2]

C13H23N7O6Cu

[CuL](NO3)2

C13H23N5CuCl2

[CuL]Cl2

C13H23N7O6Ni

[NiL(NO3)2]

C13H23N5NiCl2

[NiLCl2]

C13H23N7O6Co

[CoL(NO3)2]

C13H23N5CoCl2

[CoLCl2]

C13H23N7O6Mn

[MnL(NO3)2]

C13H23N5MnCl2

[MnLCl2]

Compounds

Bright green

432.30

Dark green Dark green Olive green Olive green

436.91

385.64

438.74

Light green

383.81

432.07

Light green

Bright green

379.19

378.97

Pale grey

Pale grey

Colour

428.30

375.20

F.W. (Calcd.)

220

254

320

310

187

198

272

235

265

250

M.p./oC

51

49

43

39

46

40

50

42

48

45

Yield/% M

(14.9)

14.4

(16.9)

16.5

(14.5)

14.0

(16.5)

16.0

(13.5)

13.1

(15.4)

15.2

(13.6)

13.8

(15.5)

15.7

(12.8)

12.3

(14.6)

14.2



(18.3)

18.7



(18.4)

18.6



(18.7)

18.4



(18.6)

18.1



(18.8)

18.4

Cl

(35.5)

35.0

(40.4)

40.0

(35.7)

35.3

(40.6)

40.2

(36.1)

36.6

(41.2)

41.5

(36.1)

36.5

(41.1)

41.6

(36.4)

36.8

(41.6)

41.3

C

H 6.5

(5.2)

5.6

(6.0)

6.4

(5.3)

5.0

(6.0)

6.5

(5.3)

5.8

(6.1)

6.4

(5.3)

5.7

(6.1)

6.3

(5.4)

5.2

(6.1)

Found (Calcd.)/% N

(22.3)

22.7

(18.1)

18.4

(22.4)

22.8

(18.2)

18.6

(22.6)

22.9

(18.4)

18.6

(22.6)

22.9

(18.4)

18.2

(22.8)

22.4

(18.6)

18.2

23

20

106

102

18

25

16

22

19

24

Molar conductance/W-1 cm2 mol-1

TABLE I. Formula weight (calcd.), colour, yield, melting point (oC), elemental analyses and molar conductance values of the compounds

2920 2905

3220

3180

3205

[CuL](NO3)2

[ZnLCl2]

[ZnL(NO3)2]

2895

2898

2900

3205

3200

[CuL]Cl2

2915

2940

[NiL(NO3 )2]

3194

[NiLCl2]

2900

3200

3210

[CoLCl2]

[CoL(NO3)2]

2935

3180

[MnL(NO3)2]

2890

3190

[MnLCl2]

1190

1200

1170

1185

1165

1180

1200

1160

1175

1186

1604

1620

1630

1610

1625

1630

1620

1605

1615

1630

1458

1440

1480

1450

1465

1470

1435

1430

1452

1480

425

440

430

420

445

435

450

420

442

425

240







235



255



245





355







360



350



300

n(C–H) n(C–N) d(N–H) d(C–H) n(M–N) n(M–O) n(M–Cl)

n(N–H)

Complex

TABLE II. IR vibration frequencies (cm-1) of the complexes

610

605

608

603

606

610

609

605

607

604

(6a)

407

404

408

409

405

407

412

410

405

408

(16b)

1580

1600

1594

1590

1600

1595

1593

1585

1590

1580

(8a)

In-plane ring Out-of-plane ring In-plane ring deformations deformations deformations

Pyridine ring

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nals may be due to a strong dipolar and exchange interaction between the copper(II) ions in the unit cell.34 The g|| and g were calculated and observed in the 2.15–2.23 and 2.05–2.08 regions, respectively, which support35 that the ground state (g|| > g^ > 2.02) may be the dx2-y2. The g values are related by the expression G = (g|| – 2)/(g^ – 2), which is a measure of the exchange interaction between copper centres in the polycrystalline solid.36 If G > 4, the exchange interaction is negligible and if G < 4, considerable exchange interaction is present in the solid complexes.37 In the present case, G appeared in the 2.87–3.00 range, suggesting an exchange interaction in these complexes. All the copper complexes showed considerable covalent character,38 as the g|| values are less than 2.3. TABLE III. Magnetic moments, electronic spectral and EPR data of the complexes. Complex

meff/mB

[MnLCl2] [MnL(NO3)2] [CoLCl2] [CoL(NO3)2] [NiLCl2]

5.78 5.76 4.55 4.57 3.20 3.12

18,400/16.58

1g

®

4T

22,600/15.00

6A

1g

®

4T

18,750/13.90

6A

4 1g ® T1g

22,440/18.20

6A

1.80

4T

4 1g(F) ® T1g(P)

14,800/14.01

4T

® 4A2g(F)

21,700/16.12

1g(F) ® 1g(P) 3A (F) ® 3T (F) 2g 1g 3A (F) ® 3T (P) 2g 1g 3A (F) ® 3T (F) 2g 1g 3A (F) ® 3T (P) 2g 1g 2B ® 2B 1g 2g 2B ® 2A 1g 1g 2B ® 2E 1g g 2B ® 2B 1g 2g 2B ® 2A 1g 1g 2B ® 2E 1g g

11,250/18.36 11,400/19.10 11,400/107

11,800/125 16,440/142 20,800/165

1H-NMR

1g(F)

1g(F)

4T

g||

g^

G





































2.15

2.05

3.00

2.23

2.08

2.87

2g

® 4A2g(F)

21,800/15.59

21,500/150 1.95

®

2g

14,600/14.45

15,900/134 [CuL](NO3)2

1g

4T

1g

4T

17,550/18.63 [CuL]Cl2

Assignments 6A

17,640/17.19 [NiL(NO3)2]

EPR data

UV/Vis bands/cm-1/e/M-1 cm-1

4T

Spectra 1H-NMR

The data (Table IV) for all the mononuclear zinc(II) complexes show a multiplet in the 6.94–6.98 ppm region, which can be assigned to the secondary amino (C–NH–C; 4H) protons of the 1,2-diaminoethane and 1,3-dibromopropane moiety.39 Two multiplets observed in the 2.50–2.52 ppm region may

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SYNTHESIS OF PENTAAZAMACROCYCLIC COMPLEXES

be assigned to the methylene protons of [N–(CH2)2–N; 4H] of the primary amine moiety. The middle methylene protons (C–CH2–C; 4H) of the propane chain of the complexes show a multiplet at 1.50 – 1.52 ppm. A triplet at 8.39–8.44 ppm and a doublet at 7.55–7.62 ppm may reasonably be assigned to the pyridine moiety40,41 of 2,6-diaminopyridine, corresponding to Ha and Hb of the pyridine ring, respectively. TABLE IV. 1H-NMR spectroscopic data of Zn(II) complexes, chemical shift (d/ppm) with multiplicities in parentheses* Pyridine ring proton

Complex

C–NH–C

N–CH2–CH2–N

C–CH2–C

Ha

Hb

[ZnLCl2]

6.98 (m)

2.52 (m)

1.50 (m)

8.44 (t)

7.55 (d)

[ZnL(NO3)2]

6.94 (m)

2.50 (m)

1.52 (m)

8.39 (t)

7.62 (d)

*m

= multiplets; d = doublet; t = triplet

Electronic spectra and magnetic data The spectral and magnetic moment data42,43 of all the complexes (Table III) are consistent with the proposed structures. The electronic spectra (Table III) of the manganese complexes exhibit two bands in the 18,400–18,750 and 22,440–22,600 cm–1 regions from 6Alg ® 4Tlg and 6Alg ® 4T2g transitions, respectively, corresponding to an octahedral geometry for the manganese ion.13 The cobalt complexes exhibit two bands in the 14,600–14,800 and 21,700–21,800 cm–1 regions, characteristic of 4Tlg(F) ® 4A2g(F) and 4Tlg(F) ® 4Tlg(P) transitions, respectively, corresponding to an octahedral geometry for the cobalt(II) ion.43 All the nickel complexes showed two bands in the 11,250–11,400 and 17,550–17,640 cm–1 regions, which may be assigned to 3A2g(F) ® 3Tlg(F) and 3A2g(F) ® 3Tlg(P) transitions, respectively, arising from the octahedral geometry of the nickel(II).43 The electronic spectra of the copper complexes showed a broad band centred at ca. 16,000 cm–1, assignable to 2Blg ® 2Alg transitions. However, two weak shoulders appearing in the regions 20,800 – 21,500 and 11,400 – 11,800 cm–1 may be ascribed to 2Blg ® 2Eg and 2Blg ® 2B2g transitions, respectively, suggesting a square planar geometry of the copper(II). The magnetic susceptibilities42 and electronic spectral data42,43 (Table III) obtained for all the complexes are consistent with an octahedral geometry for the Mn(II), Co(II), Ni(II) and Zn(II) complexes and a square planar geometry for the Cu(II) complexes. Acknowledgement: The chairman, Department of Chemistry, Aligarh Muslim University, Aligarh, India is acknowledged for providing the necessary facilities.

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IZVOD

SINTEZA PENTAAZAMAKROCIKLI^NIH KOMPLEKSA UZ POMO] NEKIH JONA METALA IZ PRVOG REDA GRUPE PRELAZNIH METALA POLAZE]I OD 2,6-DIAMINOPIRIDINA TAHIR ALI KHAN, SHABANA TABASSUM, NISHAT BEGUM i POONAM CHINGSUBAM Division of Inorganic Chemistry, Department of Chemistry, Aligarh Muslim University, Aligarh-202002, India

Sintetisani su novi nizovi dihloro/dinitrato (2,6,9,13,18-pentaazacbiciklo[12.3.1]oktadeka-1(18),14,16-trien)metal(II) [MLX2] (M = Mn(II), Co(II), Ni(II) i Zn(II); X = Cl ili NO3 i (2,6,9,13,18-pentaazacbiciklo[12.3.1]oktadeka-1(18),14,16-trien)bakar(II) dihlorid/nitrat [CuL]X2 (X= Cl ili NO3) kompleksa templatnom kondenzacijom 2,6-diaminopiridina sa 1,2-diaminoetanom ili 1,3-dibromopropanom. Kompleksi su karakterisani elementalnom analizom, merewem magnetne susceptibilnosti i elektri~ne provodqivosti, kao i razli~itim spektroskopskim tehnikama, kao {to su IR, 1H-NMR, EPR i UV/Vis. Osim kompleksa sa bakrom(II), koji su kvadratno-planarni, svi ostali kompleksi imaju oktaedarsku strukturu. (Primqeno 9. februara 2004, revidirano 20. januara 2005)

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