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
1273
1274
KHAN et al.
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
1275
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
1278
KHAN et al.
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
1279
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.
1280
KHAN et al.
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)
REFERENCE 1.V. Alexander, Chem. Rev. 95 (1995) 273 2. R. M. Izatt, J. S. Bradshaw, S. A. Nielsen, J. D. Lamb, J. J. Christensen, Chem. Rev. 85 (1985) 271 3. S. C. Menon, A. Panda, H. B. Singh, R. J. Butcher, Chem. Commun. (2000) 143 4. T. Clifford. A. M. Danby, P. Lightfoot, D. T. Richens, R. W. Hay, J. Chem. Soc., Dalton Trans (2001) 240 5. B. Song, T. Storr, S. Liu, C. Orvig, J. Inorg. Chem. (2002) 685 6. A. K. .Mishra, J. F. Chatal, New J. Chem. 25 (2001) 336 7. M. B. Inoue, C. A. Villegas, K. Asano, M. Nakamura, M. Inoue Q. Fernando, Inorg. Chem. 31 (1992) 2480 8. M. P. Suh. W. Shin, K. Kim, J. Kim, Inorg. Chem. 23 (1984) 618 9. M. P. Suh. S. G. Kang, Inorg. Chem. 27 (1988) 2544 10. T. Chandra, B. J. Kraft, J. C. Huffman, J. M. Zalesk, Inorg. Chem. 42 (2003) 5158 11. J. J. R. Fraustoda Silva, R. J. P. Williams, The Biological Chemistry of the Elements. Clarendon Press, Oxford, 1991. 12. J. Liu, H. Zhang, C. Chen, H. Deng, T. Lu, L. Ji, J. Chem. Soc., Dalton Trans (2003) 114 13. D. Utz, F. W. Heinemann, F. Hampel, D. T. Richens, S. Schindler, Inorg. Chem. 42 (2003) 1430 14. Bioinorganic Catalysis, J. Reedijk, Ed., 2nd Ed; Marcel Dekker, New York, 1999. 15. N. R. Champness, C. S. Frampton, G. Reid, D. A. Tocher, J. Chem. Soc., Dalton Trans. (1994) 3031 16. K. R. Adam, M. Antotovich, D. S. Baldwin, P. A. Duckworth, A. J. Leong, L. F. Lindoy, M. McParlin, P. A. Tasker, J. Chem. Soc., Dalton Trans (1993) 1013 17. Y. Dong, S. Farquhar, K. Gloe, L. F. Lindoy, B. R. Rumbel, P. Turner, K. Wichmann. J. Chem. Soc., Dalton Trans. (2003) 1558 18. P. V. Bernhardt, P. C. Sharpe, Inorg. Chem. 39 (2000) 4123 19. J. W. Sibert, A. H. Cory, J. G. Cory, Chem. Commun. (2002) 154 20. R. Hovland. C. Glogard, A. J. Aasen, J. Klaveness, J. Chem. Soc., Perkin Trans 2 (2001) 929 21. S. J. A. Pope, A. M. Kenwright, V. A. Boote, S. Faulkner. J. Chem. Soc., Dalton Trans. (2003) 3780 22. M. N. Hughes, The Inorganic Chemistry of the Biological Processes, Wiley, New York , 1981 23. M. Meyer, G. V. Dahaoui, C. Lecomte, R. Guilard, Coord. Chem. Rev. (1978) 178 24. D. G. McCallum, L. Hall, C. White, R. Ostrander, A. L. Rheingold, J. Whelan, B. Bosnich, Inorg. Chem. 33 (1994) 924
SYNTHESIS OF PENTAAZAMACROCYCLIC COMPLEXES
1281
25. C. N. Reilley, R. W. Schmid, F. S. Sadak, J. Chem. Educ. 36 (1959) 619 26. A. I. Vogel, A Text Book of Quantitative Inorganic Analysis, 3rd Ed., Longmans, London, 1961, p. 433 27. W. J. Geary, Coord. Chem. Rev. 7 (1971) 81 28. M. P. Suh, S. K. Kim, Inorg. Chem. 32 (1993) 3562 29. N. S. Gill, R. H. Nuttal, D. E. Scarfe, D. W. A. Sharp, J. Inorg. Nucl. Chem. 18 (1961) 87 30. R. J. H. Clark, C. S. Williams, Inorg. Chem. 4 (1965) 350 31. M. Shakir, S. P. Varkey. Transition Met. Chem. 19 (1994) 606 32. V. B. Rana. P. Singh, D. P. Singh, M. P. Teotia, Polyhedron 1 (1982) 377 33. M. Shakir, S. P. Varkey, O. S. M. Nasman, Polyhedron 14 (1995) 1283 34. I. S. Ahuja, S. Tripathi, Indian J. Chem. 30A (1991) 1060 35. M. C. Jain, A. K. Srivastava, P. C. Jain, Inorg. Chim. Acta 23 (1977) 199 36. I. M. Proctor, B. J. Hathaway, P. Nicholls, J. Chem. Soc. A (1968) 1678 37. A. K. D. Mazumder, S. C. Das, P. K. Karmakar, N. K. Saha, K. D. Banerg, J. Indian Chem. Soc. 69 (1992) 761 38. D. Kivelson, R. R. Neiman, J. Chem. Phys. 35 (1961) 149 39. K. Burgess, D. Lim, K. Kantoo, C. Y. Ke. J. Org. Chem. 59 (1994) 2179 40. F. A. Bovey, NMR Data Tables for Organic Compounds, Vol. 1, Wiley Interscience, New York, 1967 41. L. Branco, J. Costa, R. Delgado, M. G. B. Drew, V. Felix, B. J. Goodfellow, J. Chem. Soc., Dalton Trans. (2002) 3539 42. F. A. Cotton, G. Wilkinson, Advanced Inorganic Chemistry, 5th Ed., Wiley, New York, 1988 43. A. B. P. Lever, Inorganic Electronic Spectroscopy, 2nd Ed. Elsevier Amsterdam, 1984, p. 318.
1276
KHAN et al.
SYNTHESIS OF PENTAAZAMACROCYCLIC COMPLEXES
1277
1277