Salih İlhan a, *, Hamdi Temel b, Murat Sunkur c & İbrahim Teğin a a Siirt University, Faculty of Art and Sciences,

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1 Indian Journal of Chemistry Vol. 47A, April 2008, pp Synthesis, structural characterization of new macrocyclic Schiff base derived from 1,6-bis(2-formylphenyl)hexane and 2,6-diaminopyridine and its metal complexes Salih İlhan a, *, Hamdi Temel b, Murat Sunkur c & İbrahim Teğin a a Siirt University, Faculty of Art and Sciences, Chemistry Department, Siirt, Turkey b Dicle University, Faculty of Education, Chemistry Department, Diyarbakır, Turkey c Batman University, Faculty of Technical Education, Batman, Turkey salihsiirt@gmail.com; salihilhan@dicle.edu.tr Received 25 January 2008; revised 17 March 2008 A macrocyclic ligand has been synthesized by reaction of 2,6-diaminopyridine and 1,6-bis(2-formylphenyl)hexane. Its complexes with Cu(II), Ni(II), Pb(II), Zn(II), Cd(II) and La(III) have been synthesized by the reaction of ligand and Cu(ClO 4 ) 2.6H 2 O, Ni(ClO 4 ) 2.6H 2 O, Pb(ClO 4 ) 2.6H 2 O, Zn(ClO 4 ) 2.6H 2 O, Cd(ClO 4 ) 2.6H 2 O and La(ClO 4 ) 3.6H 2 O, respectively. The ligand and its metal complexes have been characterized. All complexes are diamagnetic while the Cu(II) complex is binuclear. IPC Code: Int. Cl. 8 C07F1/08; C07F3/06; C07F3/08; C07F5/00; C07F7/00; C07F15/04 The coordination chemistry of macrocyclic ligands is a fascinating area in inorganic chemistry 1. Transition metal macrocyclic complexes have received much attention as active part of metalloenzymes as biomimic model compounds due to their resemblance with natural proteins like hemerythrin and enzymes 2,3. Schiff base macrocycles have been of great importance in macrocyclic chemistry 4. There is a continued interest to synthesize macrocyclic complexes 5-7 because of their potential applications in fundamental and applied sciences 7-9 and importance in the area of coordination chemistry 10,11. The development of the field of bioinorganic chemistry has been another important factor in spurring the growth in interest in macrocyclic compounds 12. We report herein the synthesis of a new dialdehyde 1,6-bis(2-formylphenyl)hexane derived from 1,6-dibromohexane with salicylaldehyde and K 2 CO 3. The new macrocyclic Schiff base has been synthesized by reaction of 2,6-diaminopyridine and 1,6-bis- (2-formylphenyl)hexane. Its Cu(II), Ni(II), Pb(II), Zn(II), Cd(II) and La(III) complexes have been synthesized by template effect by reaction of the ligand and Cu(ClO 4 ) 2. 6H 2 O, Ni(ClO 4 ) 2. 6H 2 O, Pb(ClO 4 ) 2. 6H 2 O, Zn(ClO 4 ) 2. 6H 2 O, Cd(ClO 4 ) 2. 6H 2 O and La(ClO 4 ) 3. 6H 2 O, respectively. Spectral and magnetic properties of the new compounds have also been studied in detail. Experimental Elemental analysis was carried out on a LECO CHNS (model 932) elemental analyzer. 1 H NMR and 13 C NMR spectra were recorded using a Bruker Avance DPX-400 NMR spectrometer. IR spectra were recorded on a Midac 1700 FTIR spectrometer on KBr discs in the range cm -1. Electronic spectral studies were conducted on a Shimadzu (model 160) UV-vis spectrophotometer in the range nm, using 10-3 M solution of the complex in DMSO. Molar conductivity was measured with a WTW LF (model 330) conductivitymeter, using 10-3 M solution of the complex in DMSO. Electrospray ionization mass spectrometric analyses (ESI MS) were obtained on the Agilent 1100 MSD spectrometer. 1,6-Bis- (2-formylphenyl)hexane was prepared derived from 1,6-dibromohexane with salicyaldehyde and K 2 CO 3 as reported in literature 13. All the other chemicals and solvents were of analytical grade and used as received. Synthesis of 1,6-bis(2-formylphenyl)hexane To a stirred solution of salicylaldehyde (24.4 g, 0.2 mol) and K 2 CO 3 (13.8 g, 0, 1 mol) in DMF(100 ml), was added dropwise 1,6-dibromohexane (24.4 g 0.1 mol) in DMF (40 ml). The reaction was continued for 4 h at C and then for 4 h at room temperature (Scheme 1). Then, 200 ml distilled water was added and the mixture kept in a refrigerator. After 1 h, the precipitate was filtered and washed with 500 ml water. It was dried in air and recrystalized from EtOH and filtered under vacuum. Yield: 49 g (75%), M. pt: C, Color: white. Anal.: Calcd for C 20 H 22 O 4 : C, 73.60, H, Found: C, 73.75, H, C NMR (DMSO-d 6, δ ppm): CH 2 CH 2 CH 2 : 25.64, CH 2 CH 2 O: 28.87, CH 2 CH 2 O: 68.71, HC=O: , Aromatic: , , , , , H NMR (DMSO-d 6, δ ppm): 1.54 (t, 4H, J = 7.4 Hz, CH 2 CH 2 CH 2 :), 1.81 (p, 4H, J = 6.2 Hz, CH 2 CH 2 O), 4.14 (t, 4H, J = 6.4 Hz, CH 2 CH 2 O),

2 NOTES (m, 8H, Ar-H), (s, 2H, HC=N). Selected IR data (KBr, ν cm -1 ): 3070, 3035 ν(ar-ch), 2951, 2854 ν(alf.-ch), 1681 ν(c=o), 1489, 1458 ν(ar-c=c), 1284, 1246 ν(ar-o), 1192, 1046 ν(r-o), 760 ν(substituted benzene). Synthesis of the macrocyclic Schiff base (L) The macrocyclic ligand (L) was prepared by the dropwise addition of a solution of the 2,6-diaminopyridine (0.22 g, 2 mmol) in methanol (40 ml) to a stirred solution of 1,6-bis(2- formylphenyl)hexane (0.65 g, 2 mmol) in methanol (60 ml). After the addition was completed, stirring was continued for 2 h. A yellow colored precipitate (Scheme 2) was filtered and washed with methanol. Yield: 0.44 g (55.14%). Color: yellow. Anal.: Calc. for C 25 H 25 N 3 O 2. H 2 O: C, 75.16, H, 6.31, N, Found: C, 75.38, H, 6.41, N, C NMR (DMSO-d 6, δ ppm): CH 2 CH 2 CH 2 : 22.59, CH 2 CH 2 O: 28.66, CH 2 CH 2 O: 68.65, HC=N: , Aromatic: , , , , , , , , H NMR (DMSO-d 6, δ ppm): 1.52 (4H, CH 2 CH 2 CH 2 ), 1.81 (4H, CH 2 CH 2 O), 4.16 (4H, CH 2 CH 2 O), (m, 11H, Ar-H), (s, 2H, HC=N). Selected IR data (KBr, ν cm -1 ): 3379 (H 2 O), 3062, 3035 ν(ar-ch), 2935, 2862 ν(alf.-ch), 1689 ν(ar-c=c), 1288, 1238 ν(ar-o), 1161, 1045 ν(r-o), 752 ν(substituted benzene). UV-vis (λ max, nm) (DMSO)): 267, 323, 378. Mass spectra (m/z): 399 [L] +. Synthesis of the complexes To a stirred solution of ligand in chloroform (60 ml), was added dropwise M(ClO 4 ) n.6h 2 O (2 mmol, if M = Cu, 4 mmol) in methanol (40 ml). After the addition was completed, the stirring was continued for 2 h. Then, the precipitate was filtered and washed with CHCl 3, and then methanol, and dried in air (Fig. 1). Characterization of [Cu 2 (L)(ClO 4 ) 2 ][ClO 4 ] 2. H 2 O Color: brown. Yield: 0.43 g (22.8%). Anal.: Calc. for Cu 2 C 25 H 25 N 3 Cl 4 O 18. H 2 O: C, 31.85, H, 2.87, N, Found: C, 32.04, H, 3.01, N, H NMR (DMSO-d 6, δ ppm): 1.55 (CH 2 CH 2 CH 2 ), 1.83 (CH 2 CH 2 O), 4.15 (CH 2 CH 2 O), (Ar-H), (HC=N). Selected IR data (KBr, ν cm -1 ): 3348 (H 2 O), 3066 ν(ar-ch), 2931, 2862 ν(alf.-ch), 1651 ν(ar-c=c), 1242 ν(ar-o), 1103 ν(r-o), 756 ν(substituted benzene), 1103, 621 ν(clo 4 - ). Λ M = 197 Ω -1.mol -1.cm 2. UV-vis (λ max, nm) (DMSO): 271, 325, 377. Mass spectra (m/z): 824 [[Cu 2 (L)(ClO 4 ) 2 ][ClO 4 ] 2 -H] +. Characterization of [Ni(L)(ClO 4 ) 2 ]. 2H 2 O Color: yellow. Yield: 0.16 g (11.6%). Anal.: Calc. for NiC 25 H 25 N 3 Cl 2 O 10. 2H 2 O: C, 43.35, H, 4.19, N, Found: C, 43.46, H, 4.31, N, H NMR (DMSO-d 6, δ ppm): 1.56 (CH 2 CH 2 CH 2 ), 1.92 (CH 2 CH 2 O), 4.17 (CH 2 CH 2 O), (Ar-H), (HC=N). Selected IR data (KBr, ν cm -1 ): 3383 (H 2 O), 3069 ν(ar-ch), 2935, 2866 ν(alf.-ch), 1646 ν(ar-c=c), 1292, 1242 ν(ar-o), 1091, 1046 ν(r-o), 752 ν(substituted benzene), 1113, 629 ν(clo 4 - ). Λ M = 25 Ω -1.mol -1.cm 2. UV-vis (λ max, nm) (in DMSO): 274, 326, 375. Mass spectra (m/z): 658 [Ni(L)(ClO 4 ) 2 +2H] +. Characterization of [Pb(L)(ClO 4 )][ClO 4 ]. 2H 2 O Color: yellow. Yield: 0.48 g (28.5%). Anal.: Calc. for PbC 25 H 25 N 3 Cl 2 O 10. 2H 2 O: C, 35.67, H, 3.45, N, Found: C, 35.82, H, 3.79, N, H NMR

3 562 INDIAN J CHEM, SEC A, APRIL 2008 Fig. 1 Proposed structure of the complexes (X=ClO 4 ). could not be taken because of the low solubility Selected IR data (KBr, ν cm -1 ): 3348 (H 2 O), 3070 ν(ar-ch), 2931, 2858 ν(alf.-ch), 1651 ν(c=n), 1598 (C=N(pyridine)), 1489, 1454 ν(ar-c=c), 1288, 1238 ν(ar-o), 1161, 1099 ν(r-o), 751 ν(substituted benzene), 1108, 621 ν(clo 4 - ). Λ M = 88 Ω -1.mol -1.cm 2. UV-vis (λ max, nm) (in DMSO): 274, 326, 377. Mass spectra (m/z): 594 [Pb(L)(ClO 4 )]-H] +. Characterization of [Cd(L)][ClO 4 ] 2. 3H 2 O Color: yellow. Yield: 0.63 g (44.7%). Anal.: Calc. for CdC 25 H 25 N 3 Cl 2 O 10. 3H 2 O: C, 42.61, H, 4.40, N, Found: C, 42.77, H, 4.67, N, H NMR (DMSO-d 6, δ ppm): 1.68 (CH 2 CH 2 CH 2 ), 1.92 (CH 2 CH 2 O), 4.18 (CH 2 CH 2 O), (Ar-H), (HC=N). Selected IR data (KBr, ν cm -1 ): 3371 (H 2 O), 3070 ν(ar-ch), 2931, 2858 ν(alf.-ch), 1647 ν(ar-c=c), ν(ar-o), 1161, 1099 ν(r-o), 756 ν(substituted benzene), 1106, 621 ν(clo 4 - ). Λ M = 169 Ω -1.mol -1.cm 2. UV-vis (λ max, nm) (DMSO (1:1)): 273, 376. Mass spectra: 668 [[Cd(L)](ClO 4 ) 2 ] +. Characterization of [La(L)(ClO 4 ) 3 (H 2 O)]. H 2 O Color: yellow. Yield: 0.55 g (31.6%). Anal.: Calc. for LaC 25 H 27 N 3 Cl 3 O 15. H 2 O: C, 34.44, H, 3.33, N, Found: C, 34.56, H, 3.61, N, H NMR (DMSOd 6, δ ppm): 1.55 (CH 2 CH 2 CH 2 ), 1.91 (CH 2 CH 2 O), 4.18 (CH 2 CH 2 O), (Ar-H), (HC=N). Selected IR data (KBr, ν cm -1 ): 3363 (H 2 O), 3070 ν(ar-ch), 2931, 2862 ν(alf.-ch), 1651 ν(c=n), 1598 (C=N(pyridine)), 1489, 1454 ν(ar-c=c), 1292, 1242 ν(ar-o), 1103, 1049 ν(r-o), 756 ν(substituted benzene), 1106, 625 ν(clo 4 - ). Λ M = 34 Ω -1.mol -1.cm 2. UV-vis (λ max, nm) (in DMSO): 273, 323, 377. Mass spectra (m/z): 752 [La(L)(ClO 4 ) 2 (H 2 O)-H] +.

4 NOTES 563 Characterization of [Zn(L)(ClO 4 ) 2 ]. 2H 2 O Color: yellow. Yield: 0.18 g (12.9%). Anal.: Calc. for ZnC 25 H 25 N 3 Cl 2 O 10. 2H 2 O: C, H, 4.15, N, Found: C, 43.09, H, 4.21, N, H NMR (DMSO-d 6, δ ppm): 1.56 (CH 2 CH 2 CH 2 ), 1.90 (CH 2 CH 2 O), 4.16 (CH 2 CH 2 O), (Ar-H), (HC=N). Selected IR data (KBr, ν cm -1 ): 3363 (H 2 O), 3074 ν(ar-ch), 2935, 2862 ν(alf.-ch), 1647 ν(ar-c=c), 1292, 1242 ν(ar-o), 1049 ν(r-o), 756 ν(substituted benzene), 1107, 625 ν(clo 4 - ). Λ M = 24 Ω -1.mol -1.cm 2. UV-vis (λ max, nm) (in DMSO): 276, 323, 374. Mass spectra: 664 [Zn(L)(ClO 4 ) 2 +H] +. Result and discussion The ligand and complexes (Schemes 1 and 2) have been synthesized and characterized by elemental analysis, IR, 1 H and 13 C-NMR data, electronic spectra, magnetic susceptibility measurements, molar conductivity measurements and mass spectra. The IR spectra of the ligand (L) show a ν(c=n) peak at 1689 cm -1 and the absence of a ν(c=o) peak at around 1700 cm -1 is indicative of Schiff s base condensation. The IR spectra of all complexes shows ν(c=n) bands at cm -1 and it is found that the ν(c=n) bands in the complexes are shifted by about cm -1 to lower energy regions compared to that in the free ligand (L). This phenomenon appears to be due to the coordination of azomethine nitrogen to the metal ion 14. Also, a weak ν(h 2 O) band of free ligand at about 3380 cm -1 is observed because of hydrated water molecule. The IR spectra of the complexes are characterized by the appearance of a broad band in the region at cm -1 due to H 2 O groups 21. Also, infrared spectra of the metal complexes exhibit an intense band at approximately 1110 cm -1 along with a weak band at ca. 620 cm -1 which is assigned to ν(cl-o) of perchlorate anions 16. The IR spectra of the complexes clearly demonstrate that the COC and CCO stretching vibrations are altered compared to ligands due to conformational changes. The fact that the C-O-C absorptions of the complexes are shifted to lower wave numbers compared to that of the ligand also confirms the complex formation 17. The spectra of all the complexes are dominated by bands between cm -1 due to ν(alph.-ch) groups and a strong band appearing in the 1598cm -1 region is assigned to ν(c=n) pyridine mode. The ν(c=n) pyridine did not change in the complexes, indicating that azomethine group in the pyridine does not bind the metal ions H NMR and 13 C NMR of the 1,6-bis(2- formylphenyl)hexane, ligand and 1 H NMR of the complexes in DMSO-d 6 solution show that they are NMR active. The 1 H NMR spectrum of the 1,6-bis(2- formylphenyl)hexane showed a singlet at ppm due to the aldehyde protons, multiplet in the range approximately ppm due to the aromatic protons, at 1.66 ppm due to CH 2 CH 2 CH 2 protons, at 1.87 ppm due to CH 2 CH 2 O protons and at 4.16 ppm due to CH 2 CH 2 O protons (Scheme 1). 13 C NMR spectrum of the aldehyde showed at ppm due to the imine carbon, at ppm due to CH 2 CH 2 CH 2 carbon, ppm due to CH 2 CH 2 O carbon, at ppm due to CH 2 CH 2 O carbon, and at ppm due to aromatic carbon. The 1 H NMR spectrum of the ligand showed a singlet at ppm due to the imine protons, multiplet in the range approximately ppm due to the aromatic protons, at 1.66 ppm due to CH 2 CH 2 CH 2 protons, at 1.86 ppm due to CH 2 CH 2 O protons and at 4.16 ppm due to CH 2 CH 2 O protons. 13 C NMR spectrum of the ligand showed at ppm due to the imine carbon, at ppm due to CH 2 CH 2 CH 2 carbon, at ppm due to CH 2 CH 2 O carbon, at ppm due to CH 2 CH 2 O carbon and at ppm due to aromatic carbon. The 1 H NMR spectra of the complexes exhibited almost the same values as that of the ligand. Although we expected a shift on the position of CH=N signal for the NMR spectra of the complexes, no significant shift could not be observed. But the CH=N signal is observed in low intensity compared to the ligand 19. The electronic spectra of the ligand (L) in DMSO showed absorption bands at ca. 280, 320 and 370 nm. The bands are indicative of benzene and other chromophore moieties present in the ligand. The absorption bands of the complexes were shifted to longer wave numbers compared to that of ligand as expected. No d-d transitions for the complexes were observed probably due to low solubility of complexes. A moderately intensive band observed in the range of nm is due to π-π* transition, and the strong band observed in the range of nm is due to n-π* for these complexes 20. The observed room-temperature magnetic moment values for the binuclear Cu(II) and the other mononuclear complexes were found to be diamagnetic. The diamagnetic behaviour of the binuclear complex may be explained by a very strong anti-ferromagnetic interaction in the Cu-Cu pair The conductivity data in DMSO are reported in the range for 1:2 and 1:1 electrolytes. The complexes,

5 564 INDIAN J CHEM, SEC A, APRIL 2008 [Cu 2 (L)(ClO 4 ) 2 ][ClO 4 ]. 2 2H 2 O, [Cd(L)][ClO 4 ] 2.3H 2 O and [Pb(L)(NO 3 )][NO 3 ]. 2H 2 O have values of 197, 169 and 88 ohm -1 cm 2 mol -1 indicating 1:2 and 1:1 electrolytes, respectively. The other complexes are nonelectrolytes The mass spectra of complexes with ligand play an important role in confirming the monomeric [1+1] (dicarbonyl and diamine) nature of the complexes. The MS peaks are attributable to the molecular ions: 399 [L] +, 824 [[Cu 2 (L)(ClO 4 ) 2 ][ClO 4 ] 2 -H] +, 658 [Ni(L)(ClO 4 ) 2 +2H] +, 594 [Pb(L)(ClO 4 )]-H] +, 668 [[Cd(L)](ClO 4 ) 2 ] +, 752 [La(L)(ClO 4 ) 2 (H 2 O)-H] +, 664 [Zn(L)(ClO 4 ) 2 +H] + (refs 21-23). The complexes have no clearly defined melting point and begin to decompose in the temperature range C. The ligand is soluble in DMSO, DMF, CHCl 3, CH 2 Cl 2 and CH 3 CN but insoluble in H 2 O, EtOH and MeOH. The complexes are air stable, partly soluble in DMF, DMSO and insoluble CHCl 3, CH 2 Cl 2 and CH 3 CN and the crystals were unsuitable for singlecrystal X-ray structure determination. It is seen that the complex formation reaction between ligand and relatively large Cd(II) and Pb(II) metal ions result in the Cd(II) and Pb(II) complexes. The binding mode of the ligand for the Pb(II), Cd(II) and Cu(II) complexes are different than that of the other complexes. In the first case, the ligand behaves as a tetradentate ligand with the lone electron pairs of azomethine nitrogen atoms and the lone electron pairs of two oxygen in ether groups. In the second case, the ligand behaves as a bidentate ligand with the lone electron pairs of azomethine nitrogen atoms. The long distance binding process can be favored for very large Cd(II), Pb(II) metal ions but not other metal ions due to having smaller ion size than Pb(II) and Cd(II) metal ion. So, its coordination is - satisfied with two or three ClO 4 and one H 2 O for La(III) complex in the second case. Similar binding mode is known for Pb(II) and Cd(II) metal ions 18-20, 24,25. Also, infrared spectra of the metal complexes exhibit an intense band at approximately 1110 cm -1 along with a weak band at ca. 620 cm -1 which have been assigned to the perchlorate complexes are due to ν(cl-o) of perchlorate anions Also, the conductivity measurements of the Pb(II) and Cd(II) complexes in DMSO resulted in Λ M value 88 Ω -1 mol -1 cm 2 and 169 Ω - 1 mol -1 cm 2, which indicate that they are 1:1 and 1:2 electrolyte type, respectively. These results clearly verify different binding mode of ligand in the case of the Cd(II) and Pb(II) metal ions. As expected, in the case of the relatively smaller (Ni(II) and Zn(II)) metal ions, the ligand behaves as a bidentate ligand with the lone electron pairs of azomethine nitrogen atoms and the inner coordination sphere is donated with ClO 4 - ligands. The conductivity measurements showed that these complexes are nonelectrolyte. On the other hand, the diamagnetic behaviour of the binuclear complex can be explained by a very strong anti-ferromagnetic interaction in the Cu-Cu pair 18-20,22. Structure of the binuclear complex is given in Scheme 2. Some Co(II), Ni(II), Ag(II), Zn(II) or Pb(II) complexes prepared with similar ligands are already known 21. Suggested structure for Cu(II) complex is bipyramidal, for La(III) complex it is octahedral, for Pb(II) complex it is square pyramid, for Zn(II) and Cd(II) complexes it is tetrahedral and that for Ni(II) complex is square planar 18-20,22. 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