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Indian Journal of Chemistry Vol. 43A. March 2004. pp. 556-561 Synthesis and physico-chemical studies on transition metal complexes of macrocyclic ligand derived from 2,6-diacetylpyridine dihydrazone Mohammad Shakir*, Poonam Chingsubam, Hamida-Tun-Nisa Chishti, Yasser Azim & Nishat Begum Division of Inorganic Chemistry. Department of Chemistry. Aligarh Muslim University, Ali garh 202 002, Indi a Received 27 December 2002; revised 3 Nowmber 2003 A novel series of Schiff base decaaza macrocyc lic comp lexes 1 [ML X,] [M = Mn(ll), Fe( ll ). Co(ll). Ni( ll ) and Zn (II )] ; and [CuL' ]:X 2 ( X = Cl. N0 3) have been synt hesized by the reaction between pre-synthesized 2.6-diacetylpyridine dihydrazone (L) and formaldehyde in th e presence or metal ions in methanol medium at room temperature. The formation of li ga nd (L) and the proposed macrocyclic complexes have been confirmed from the results of elemental analyses. the comparative band pos itions for v(C=N) and appearance of proton resonance peaks for secondary amine 1 group (N-NH-C) in H NMR spectra of compl exes. The nature of the comp lexes and th eir overall geometry have been infe1Ted from electrical conductivity data, observed band positions in electronic spectra and magnetic moment values. The importance of macrocyclic complexes in coordination chemistry is because of its various 1 7 applications · , in biol :lg ic al processes such as 8 photosynthesis and dioxygen tran s port ; cata lytic 9 properties ; potential appl ications as metal extractants 10 and as radio-therapeutic and medical imaging agents. In macrocyclic complexes, both the metal ion and the size of the ring play an important role. Lindoy and co. wor kers have reporte d ll ·12 a senes o f' stu d'res on t he selective complexation of transition metal ions by polydentate ligands . Metal ions act as templates , directing the steric course of the condensation reaction . . nng . rn c Iosure 13 · 19 . Th ere f ore, t I1e meta I resu Ittng template method has been recognized as high yielding and se lective routes to new ligands and their 20 21 complexes ' . Several macrocyclic ligands derived 12 ~ "4 from hydrazine precursors have bee n reported - - . Recently. divalent metal che lates of macrocycle derived from dihydrazide and aromatic diketone have 25 also been reported • We report herein, a novel series of decaazamacrocyclic complexes derived from the 26 29 condensation reaction of 2,6-di acety lpyridine . , hydrazine hydrate, formaldehyde and metal ions structure directing agent. Experimental II II II The metal salts MX, .nH,O (M =Mn , Fe , Co , 11 11 11 Ni , Cu and Zn ; X= Cl,- NO: and n=lJ,6) (all BDH) were commercially pure samples. The chemicals such as 2, 6-diacetylpyridine (A ldrich), hydrazine hydrate 85l'/r; (Sigma) and formaldehyde so luti on 37 % (E. Merck) were used as received. Solvents were dried before use. Preparation of 2,6-diacetylpyridine dihydrazone, 'L' To a stirring solution of 2 ,6-diacetylpyridine (0.3264 g, 2 mmol) in methanol (- 20 ml) was added a solution of hydrazine (0.242 ml, 4 mmol) dissolved in methanol(- 20 ml). The stirTing continued for 6-8 h, resulting in a colourless so lution . The resultant reaction mixture was allowed to stand for48 h resulting in the isolation of microcrystalline solid. Synthesis of dichloro/nitrato (1,3:11,13-dipyridyl-4,10,14,20tetra methyl- 2,5,6,8,9,12,15,16,18,19-decaaza-4,9,14,19tetracne cycloeicosane) metal (II), [ML' X,] (M =Mn", Fe", Co", Ni" and Zn 11 ) and [CuL'] X, (X=CI, NO,). To a stirTing methanolic solution (-20 ml) of 2, 6diacetylpyridine dihydrazone, 'L'(0.668 g, 4 mmol), solutions of formaldehyde (0.298 ml , 4 mmol) taken in 20 ml methanol and MX 2.nHz0 (X=C I, N0 3 , n= 1,3,6) (2 mmol ) dissolved in 20 ml of methanol were added simultaneously. The reaction mixture was further stilTed overnight affording the isolation of solid product, wh ich was filtered, washed several times and vacuum dried. E lemental analyses were obtained from the microanalytical laboratory, Co llege of Sciences King Saud University Riyadh (KSA). Metals and chloride 1 0 were determined volumetricall/ and gravimetricall/ respectively. The electronic spectra of the compounds in DMSO were recorded on a Pye-Un icam 8800 spectrophotometer at room temperature. EPR spectra were record e d on a JEOL JES RX2X EPR spectrophotometer. Magnetic s uscepti bi Ii ty NOTES N1· II and Zn II ; X=CI, NO) have been prepared by the template condensation reaction of2-6-diacetylpyridine dihydrazone, ' L ' and formaldehyde in methanol medium in a 2:2 ratio (Scheme 1). An attempt was made to synthesize metal free macrocyclic li gand which resulted in an oily product. All the complexes are found to be stable to atmo s phere at r oom temperature. These complexes are soluble in distilled water, DMSO and DMF. The results of eleme ntal analyses (Table 1) correspond to the proposed macrocyclic framework. The low conductivity data ascertain the non-electrolytic nature of these measurements were carried out using a Faraday 32 Balance at 25°C. The electrical conductivities of 3 10· M solutions in DMSO were obtained on a Digital conductivity meter APX 185 equilibrated at 25 °C ± 0.05. 1H NMR spectra were recorded in DMSO-d6 using a Jeol , Eclipse 400 with Me 4 Si as an internal 1 standard. The IR spectra (4000-200 cm- ) were recorded as KBr discs on a Perkin-Elmer 2400 spectrophotometer. Results and discussion A new series of decaazamacrocyclic complexes I I II II II [ML X 2] and [CuL] X 2 (where M = Mn , Fe , Co , Me ra y~~~ 0 Me 557 + 0 HCHO ~ Me HN y \ A"-';:~----:-l Scheme I N /L-NNHH ~Cu~ HN-N~ Me c"x,ru<,o ) N-NH N~"l~ ~ Me I 2+ INDIAN 1 CHEM, SEC A, MARCH 2004 558 Table 1- Analytical data and molar conductance values for the compounds Compound Yield M.pt ( 0 C) Colour Calcd (Found) % M Cl 1\_, c H N 56.54 (56.53) 6.80 (6.79) 36.64 (36.62) 45.19 (45.17) 4.89 (4.88) 26.36 (26.34} 15 41.09 (41.07) 4.45 (4.43) 28.76 (28.75} 15 45 . 11 (45.10) 4.88 (4.87) 26.31 (26.30) 23 41 .02 (41.01) 4.44 (4.43) 28.71 (28.70) 23 45.02 (45.01 ) 4.87 (4.86) 26.26 (26.24) 18 40.95 (40.93) 4.43 (4.41) 28.66 (28.65) 18 44.85 (44.83) 4.85 (4.84) 26.16 (26.15) 14 40.81 (40.80) 4.42 (4.41) 28.57 (28.55) 14 44.44 (44.42) 4.81 (4.80) 25.92 (25.91) 100 40.47 (40.45) 4.38 (4.36) 28.33 (28.32) 115 44.28 (44.27) 4.79 (4.78) 25.83 (25 .81) 18 40.33 (40.31) 4.36 (4.34) 28.23 (28.22) 18 (cm 2 ohm·' mor') L 45 150 White [MnL' CI:J 50 290 Dull green 10.16 ( 10.15) [MnL' (N03 ) J 52 290 Dull green 9.24 (9.23) [FeL' Cl2 ] 60 >300 Wine red 10.33 (10.31) fFeL' (N0 3) 1J 55 >300 Wine red 9.40 (9.39) [CoL' Cl 2] 40 >300 Dark brown 10.50 ( 10.49) [CoL' (N0,) 2] 45 >300 Dark brown 9.55 (9.54) [NiL' CIJ 38 185 Rust 10.84 ( 10.83) [NiL' (NO)J 45 200 Rust 9.86 (9.85) [CuL'q] 55 220 Yellow 11.66 ( 11.65) [CuL' ](N03) 2 60 200 Yellow 10.62 (10.61 ) [ZnL' Cl 2] 55 >300 Colourless 11 .99 (11.97) [ZnL' (N0 3 ) 2] 65 >300 Colourless 10.92 (10.91) complexes, except that of copper compl.exes, which }? were found to be 1:2 electrolyte -. The preliminary information regarding the formation of 'L ·has been inferred from bands observed in its IR spectrum. The disappearance of band corresponding to v(C=O) and appearance of a new .J strong intensity band at 1625 em assigned to v(C=N) of imine group srrongly suggest the formation of 'L' . •J A strong doublet around 3360 em may be assigned to v(N-H) stretching mode of uncondensed primary amine group of hydrazine moiety. The appearance of 13.37 ( 13.35) 13.34 (13.33) 13.32 ( 13.30) 13.27 ( 13.25) 13. 14 ( 13.13) 13.09 (13.07) .J bands at 2925 and 985 em may be assigned to v(C-H), and v(N-N) stretching vibration respectively in 'L'. TheIR spectra of all the complexes exhibit no band corresponding to v(C=O) of formaldehyde group rather a new strong intensity band appears in the region 32103260 em·' anributable 33 to the v(N-H) stretching mode of secondary amines. This suggests that condensation between CO of formaldehyde moiety and NH 2 of hydrazine moiety has occurred in presence of metal ion. The IR sp ~ctra of all the macrocyclic complexes NOTES exhibit a medium intensity band in the region 15901 34 37 1620 cm- which may be assigned - to a coordinated imine v(C=N) stretching vibration. The band in the 1 region 1140-1220 cm- may reasonably, be assigned to v(C-N) stretching vibration. An absorption band 1 appears in the region 2850-2920 cm - in all the complexes, may reasonably be ascribed to the v(C-H) stretchi ng vibrational modes. A medium intensity band 1 around 940-975 cm- may be ascribed to the v(N-N) 38 stretching mode • All the comp lexes show bands 1 around 403, 601 and 1578 cm- consistent39 A0 with the pyridine ring vibrations assignable to out-of-plane ring deformation and in-plane ring deformation, respectively. These vib rations do not suffer signiticant shift towards higher frequencies suggesting that pyridine nitrogen in the macrocyclic complexes is not 41 coordin ated to the metal atom • The presence of band 1 in the region 330-490 cm - may be due to the 42 3 v(M-N) .4 _ Bands observed in the regions 207-220 559 1 1 44 cm- and 228-240 cm- may be assigned to v(M-CI ) and v(M-0) stretching vibrations respectively. However, in the copper complex additiona l bands 1 observed at 1630, 1280, 870 and 705 cm- may be reasonably assigned to the free nitrate group. 1 The H NMR spectrum of 'L' shows peaks at 2.63 ppm which may be assigned to the methyl protons (CH 3 ; 6H) of the 2,6-diacetylpyri,dine moiety. Multiplets in the region 7.75 and i38 ppm may be 45 assigned to aryl protons (Hu) and to (2H~) of 'L'. 46 Multiplets in the region 4.99 ppm may be attributed 1 to (N-NH,; 4H) protons of 'L' _ The H NMR spectra of the Zn(II) complexes show a major peak at 7.747.77 ppm and 7.35-7.39 ppm which may be assigned ~~ to the ary l · protons (2Hu) and (4H11 ) respectively. A singlet at 2.68-2.70 ppm may be reasonably assigned to the methyl (CH 3 ; l2H) protons of the 2, 6diacetylpyridine moiety. The multiplets observed at 3.11-3.13 ppm may be assigned to the meth ylen e Table 2- Magnetic moment values, electronic spectral data assignments and EPR data or the compound Compound J..l.n(B .M .) Band position(cm·') EPR Assignments G 5.80 [MnL' Cl2] [MnL' (N0 3 ) 2] 5.78 22,300 18.750 6 22.350 18,800 6 6 A 1g ~ 'T,g 4 A 1g ~ T 1g A 1g ~ 7~g 4 A 1g ~ T 1g 4 6 [FeL' Cl 2] 5.44 11,450 5 T2g ~ Eg [FeL' (NO,) ,l 5.40 II ,850 5 T 2g ~ Eg [CoL' C I2] 4.55 16.800 22,200 'T,g(F) ~ A 2g(F) 4 4 T 1g(F) ~ T1 g(P) [CoL' (NO,) 2] 4.54 16,500 22,400 4 [NiL' Cl 2] 3.05 11,500 17,850 1 [NiL' (NO)J 3.06 12,000 17.400 -'A ,g(F) ~ ' T,g(r) 3 3 A 2g(F) ~ T 1g(P) [CuL' Cl2 ] 1.76 13.000 16,100 21,950 2 1.77 12, 100 16,200 21,600 5 5 4 T 1g( F) ~ A 2g( F) 4 T 1g( F) ~ T 1g( P) 4 4 A 2g(F) ~ -'T,g(F) A 2g(F) ~ -'T,g(P) 3 2 B ,g --+ l3 2g 2 ' B,g ~ A 1 g 2 2 B 1g ~ Eg 2.22 2.06 3.66 's,g ~ ' s ,g 2 l3 1g ~'A,g 2 'B,g ~ Eg 2.24 2.07 3.42 INDIAN J CHEM, SEC A, MARCH 2004 560 protons (N-CH 2-N; 4H) of the aldehyde moiety. The multiplets observed at 6.83-6.84 ppm may be assigned to the secondary amino group of the hydrazine moiety. But, no NMR signal has been observed in the 1 complexes [Zn Cl 2] and [Zn L (N0 3)z) which correspond to the NH 2 protons of 'L' suggesting that condensation has taken place (Scheme 1.) The EPR spectra of both the polycrystalline Cu(II) macrocyclic complexes were recorded at room temperature, and their g 11 and gj_ values were calculated. Neither of the decaazamacrocyclic Cu(II) complexes studied shown any hyperfine splitting, but gave only a derivative curve giving g 11 and gj_ values, (Table 2), as 48 characteristic of square planar copper (II) complexes. This suggests that the unpaired electron is present in 49 the dx 2-y 2 orbital as g 11 > g j_ > 2.02 • In an axial symmetry, the g values are related by the expression G=(g 11 -2)/(gl - 2), which measures the interaction between copper centres in the unit cell. The calculated 'G' values for the present complexes appeared in the 50 range 3.42 and 3.66, suggest the existence of a considerable exchange interaction between copper, as G<4. All the complexes show g 11 < 2.3. It should be 51 noted that for an ionic environment while for a covalent environment g 11 < 2.3 , indicating that the present complexes exhibit considerable covalent character. T he appearance of two bands in the electronic spectra (Table 2) of the manganese complex in the regions 18,750-18,800 em·' and 22,300-22,350 em·' may reasonably COITespond 52 to the 6A 1 ~ -~ 4 T1 ~ an d 4 6 A18, -7 T2-~ transitions, respectively consistent with an octahedral geometry around the manganese (II) ion. The electronic spectra of the iron complexes exhibit a weak intensity (d-d) transition in the region 1 1,45011 ,850 em·' , which may be reasonably assigned to the 5 5 T 28 -7 E~ transition , consistent with a high-spin octahedral environment around iron (II) ion. However, the electronic spectra of the cobalt complexes exhibit two bands in the regions 16,500-16,800 em·' and 22,200-22,400 em·' which may reasonably correspond 4 4 4 to th_e_ T 1s(F) -7 _ A 2 _.(F) and ~T 1 §~F) -7 T 1 _~(P) transitions, respectively, suggestmg· an octahedral geometry for the complexes. The ligand tield spectra for nickei(II) macrocyclic complexes show two bands in the regions 11,500- 12,000 em·' and 17,400-17,850 4 3 em·' which may be ascribed 5 to the 3A 2 /F) -7 T1 ~(F) and 3A 2 _~(F) -7 3T 1/P) transitions, ·rt"spectively, indicating an octahedral environment around the e nickei(II) ion. The copper complexes gave three bands in their electronic spectra in the regions 12,100-13,000 em-'; 16,100-16,200 em·' and 21,600-21,950 em·' and 2 these bands may reasonably assigned to the 8 1 ~ -7 2 2 2 2 2 B2R; B,R-7 A '·• and B,_~ -7 E~ transitions respecti~ely. The above results are consistent with the square planar geometry of copper (TI) complexes. 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