Indian Jou rnal of Chemistry Vol. 45A, June 2006, pp. 1395- 1399

Synthes is and characterization of a new Schiff base ligand deri ved from benzo-15-crown-5 and its complexes with cobalt(II),

nickel(II) and copper(II)

ibrahim Erden*, Nebahat Demirhan & Ulvi Avclata

Yi ldiz Tcchni ca l Univcrsity. Facu lty of Arts and Scienccs Chemi stry Department. 342 10 Esenler, Istanbul , Turkey

Emai l: ierden@yi ldi z.cdu.tr

Received.') Septelllber 2005; revised 30 March 2006

A new Sch iff base ligand , N-quino[8 ,7-b]azin-5-yl-2 ,3,5,6,8, 9.11 , 12-octahydrobenzo [b][ 1.4,7. 1 0. 13lpentaoxacyclopentade­cin- 15-ylmeth ani mine (1) has been sylllhesized from thc reaction of 5-ami no- l , 10-phenanth roline wi th 4 '- formylbcnzo- 1 5-c rown-5. The li gand reacts with Co(l l). Ni(ll ) and Cu(l l) salts to form complexes. The ligand and the compl exes havc been characterized by FTiR. 'H NMR (DMSO-dr,) . UV-v is, elcmcntal analysis, mass spectra (LC-MS) and magnetic measuremen ts. The metal to the li gand ratio of the Co(l l). ' i(lI ) and Cu(lI ) complexes have been found to be 1:2. Protonatiun constallls of thc ligand and overall formation constants of the complexes have becn calcu lated from potcntiometric data using the computer program TITFIT.

IPC Code: lnl. CI 8 C07F I/08 : C07F I 5/04; C07 15106: C07C25 1102

Different kinds of crown ethers have been synthes ized in order to produce molecules wi th superior properti es and proper applicati on in various areas l

-4

. 1,10-Phenanthroline is a we ll -known N-heterocyclic chelating agen t wi th a ri gid planar structure . It has been used to develop bi omimetic models of metaloenzymes and to prepare supramolecules, se lf­assembling systems or meta l complexes with interestin g anticancer properti es5

-9

.

Recentl y. Schiff bases conta ining a secondary site for coordinati on have attracted special attention. Crown ethe r-containing Schiff bases are known to bi nd cations in the crown ether cavity in addition to the coordinati on of a transition metal cenle r through the NxOy donor atoms IO

-13

.

T he synthes is and characteri zation of aldehyde conta ining crown ether and 1, lO-phenanthro li ne­containing Schiff base ligand and the ir complexes with Co(Il ), C u(II). N i(II) are described here. T he structures of the ligand and the complexes were determined by their elemental analys is . UV -vis. F TlR . IH N MR (DMSO-d6 ) and mass , pectra (LC-MS).

Protonation constants of the li gand (1) and formation constants of the complexes have been calculated using the computer program TITFlT

,·u 5.

Experimental Doubly di still ed and deioni zed water was used

throughout for the potentiometri c experiments under an atmosphere of nitrogen. Unless spec ified otherwi se. reagent grade reactants and solvents were used as received. Hi gh purity potassium nitrate was used as supporting electrolyte. The ionic medium was 1.0 M KN03 at the beginning of each potentiometric titration .

The FTIR spec tra (KBr di scs) were recorded in the 4000-400 cm-I range on a Mattson 1000 FTIR spectrometer. The spec tra and absorbance measurements were recorded on Agi lent 8453 UV -vi s spectroscopy system. Proton NMR spectra were recorded on Brucker AC-200 MHz (DMSO-clc,) spec tromete r. The e lementa l ana lyses and mass spec tra (LC-MS) were dete rmined in the TUBITAK Laboratory (Center of Sc ience and Technology Research of Turkey). Magneti c susceptibiliti es were determined on Sherwood sc ientific magneti c susceptibility balance. M e lting points were obtained wi th Gallenkamp CAP MPD-350 apparatus in open capi lIari es. Potentiometri c measurements were carried

1

N

N

1 4

I~ N

(1 )

1396 INDIAN J CHEM . SEC A, JUNE 2006

out using a ti tration system with a Metrohm E-415 dosi mate and Melrohm E-51O pH meter. A Metrohm 6.0204.000 combi ned glass electrode was used fo r potenti ometric titration s, pH and EMF measurements. A thermostated titration vessel of 100 mL capacity was used. The electrode system was cali brated us ing standard buffer solutions (pH 4.0017.00).

The followin g solu tions were prepared to obta in the pH-titration curves: Soluti on A: HClO~ (2.5 mL, 0.1 M ), KNO} (5 mL. 1.0 M). Solu tion B: Solu tion A + solution of the ligand in ethanol (2 .5 mL, 0.01 M). Solution C-E: So lution B + 2.5 mL, 0.01 M metal sa lt soluti on (i. e. CuCl ~ · 2H}0 , NiC I2 · 6H20, CoCl 2'

6H}0) in ethano l. Suffi cient amounts of ethanol were added to make up the tota l volume Va' whi ch was 25±0. 1 mL maintaining temperature at 25.0 ± O.I °C.

To the ti tration vesse l. a known volume of ligand solut ion , an exact volume of metal chloride. then the requ ired quantiti es of KN03 (used as support ing electro lyte) were used to minimi ze variations of the ;Jcti vity coeffi cients in spi te of wide changes in the concentrations of the reagents. The ionic strength (I) was kept constant at 1.0 M KN03.

These soluti ons were titrated by progress ive additi on of standardi zed carbonate-free 0.1 M NaOH titran t in increments of 0.1 mL and the correspond ing change in the pH of the so lution was measured.

Synthcsis of N-quino[8,7-b]azin-S-yl-2,3,S,6,8,9,l l ,I2octa­hydrobcllzu[h][1 ,4,7, I II, 13]pcn taoxa t"ydopentad ccin-lS-yl­II1cthanimine (1)

The solution of 5-amino-l,l O-phenanthroli ne (0.03 g. 0.153 mmol) in SO mL absolute ethanol was added dropwi se to the solu tion of 4'-formylbenzo-1 5-crown-5 (0.045 g, 0.152 mmol) in 10 mL absol ute ethanol and the mi xture was sti rred for 9 h at 90°C. The ethanol was evaporated to l/3rd of the initial volume and petrol eum ether was added at room temperature. A bright ye llow precipitate was obtained when the so lution was cooled to room temperature. It was filtered and then recrystalli zed from cold ethanol. Yield 0.0 16 g (55 %); m.pt.J90- 192 0c. lR (KBr): 1651 (C=NpheIlJ 1625 (C=N imill), 2953-2876 (CHaliph) ' 1140 (C-O-Caliph), 1268 (C-O-CromJ IH NMR (DMSO-{h) . 8 8.77 (s , H, H-C=N)(appeared with D20), 3.5-4.3 (m, 16 H, O-CHrCHr O) (deformati on with D20), 7.2-7.6 (m, 9 H, Ar-H). LC-MS: 474 /M+l]. Ana l. Caled for C27Hn N30 s (473): C, 68.48; H, 5.75 ; N, 8.87; 0 , 16.89 %. Found : C. 68.54; H, 5.59; N, 8.32; 0 , 16.92 %.

Synthesis of the Co(l l) complex

Ligand 1 (0.05 g, 0.1 mmol) was di sso lved in absolute ethanol (20 mL) and Co(CH,COOh' 4H}0 (0.013 g, 0.052 mlnol) in 10 mL of absolute ethanol was added to this solu tion. After addi tion of 0.01 M KOH solution in ethanol to raise the I IH to 8.0-8.5 , the mi xture was stirred on a water bath at 90°C fo r 3 h. A dark-brown precipitate was obta ined when the solution was cooled to room tempe rature. It was fi ltered, washed wi th diethyl ether. Yield 0.022 g. (44 %); m.pt. >350°C. LR (KBr): 1625 (C=N), 2953-2876 (CHaliph) , 11 40 (C-O-Caliph) , 1268 (C-O-Crom). Since the solubili ty of the complex in organ ic solvents is very low, IH NMR spectra could not be taken. Ana l. Caled for CS.jHSSOI 2N6CO (1041.9): C, 62.24; H. 5.6 1; N, 8.07 ; O. 18.43 %. Found: C. 63. 14; H. 6.84; N. 8.22; 0, 18.63 %.

Synthesis of the Cu(I1) complcx

Ligand 1 (0.05 g, 0.1 mmol ) was di ssolved in absol ute ethanol (20 mL) and CuCf}' 2H20 (O.Ol g, 0.05 mmol) in 10 mL of absolute ethanol was added to this solution . After addi ti on of 0.0 I M KOH solution in ethanol to raise the pH to 7.0-7 .5, the mi xture was stirred on a water bath at 90°C for 3 h. A dark-brown precipitate was obtained when the solution was cooled to room temperatu re. Jt was filtered, washed with diethyl ether. Yi eld 0.021 g. (42%) ; m.pt. >350°C. IR (KBr): 1625 (C=N), 2953-2876 (CHalil'h), 1140 (C-O-Cali ph), 1268 (C-O-Crom). Since the solubility of the complex in organ ic solvents is very low, IH NMR spectra could not be taken. Anal. Caled for Cs~Hs40 lON6Cu (l0 10.5): C. 64.18; H. 5.39; N, 8.32; 0, 15.83 %. Found : C. 65 .72; H. 5.52; N, 8.65; 0 , 18.92 %.

Synthesis of lhe 'i(I1) complex

Ligand 1 (0.05 g, 0.1 mmol ) was di ssolved in absolute ethano l (20 mL) and Ni(CH}COOh' 4H20 (0.01 3 g, 0.052 mmol ) in 10 mL of absolute ethanol was added to thi s s6 lution . After addi tion of 0.01 M KOH solution in ethanol to raise the pH to 8.0-8.5, the mi xture was stirred on a water bath at 90°C for 3 h. A dark-brown precipi tate was obtained when the s('l ution was cooled to room temperature. It was filtered, washed wi th diethyl ether. ' ield 0.024 g. (48 %); m.pt. >350°C. IR (KBr): 1625 (C=N), 2953-2876 (CHaliph), 11 40 (C-O-Caliph), 1268 (C-O-Crom). Si nce the solubility of the complex in organic solvents is ve ry low, IH NMR spectra could not be taken. Anal. Caled for C5.jHs40IoNGNi (1005.7): C, 64.49; H, 5.41 ;

NOT ES 1397

/011 \ o~ (0 0 I ~ H

~00 J I

Fig. I - Suggested structure or the Co(ll ) complex.

N. 8.36; O. 15.9 %. Found: C. 65.82: H. 5.50: N. 8.78; O. 16.52%.

Results and discussion The starting compound s. 5-amino- 1.10-

phenanthroline and 4 '-fo rmylbenzo- I 5-crown-5 were prepared accordi ng to known methods 16. 17 . 1 was synthesized from 5-ami no-I.I O-phenanthrol i ne and 4 '- formylbenzo- I 5-crown-5 with condensat ion reaction providi ng good yield. Its metal complexes were prepared by trea ting the li gand with the corresponding metal sa lts in 2: 1 rati o.

FTIR data provides further useful in fo rmati on on the structure of 1 and it s compl exes. The free li gand shows charac teri sti c i mi ne stretchi ng bands at 1625 cm-I

. In the complexes. thi s band does not shi ft to the lower or hi gher wave numbers, suggesting that thi s imine group is not coordinated to the metal ions. Nitrogens of 1.1 O-phenanth ro l i ne stretching bands at 165 I cm-I shi ft to the lower wave numbers. suggesting that thi s nit rogen is coordinated to the metal ions. The aryl and alkyl ether bands of the li gands and compl exes are obse rved at 2850-2920. 1268- 1276 and 11 40- 1063 cm-I

• respec ti ve ly. Elemental analyses of 1 and its Co(U). Ni ClJ) and

Cu(TT ) complexes show good agreement with the proposed structures of the li gand and its complexes (Fig. I). The complexes of 1 could be prepared in good yield by reacting the di va lent metal salts and 1 in the rati o of 1:2. The cobalt center adopts a six­coordinate geo metry with the equatorial pl ane occupi ed by fo ur coplanar phenanthroline nitrogens and two water molecul es in axial posit ions. The ni cke l and copper centers adopt a four-coordinate geometry by four copl anar phenanthroline nit rogens l 2

The Co(Il ) comp lex possesses magnetic moment (Pell) 4.25 BM. which is in agree ment with octahedral geometry. Magneti c moment of the Ni (II) and Cu(l!) complexes show them to be diamagnetic. Cu(II ) and Ni(IT) complexes are sugges ted to possess a square planar environment in the complexes .

The IH NMR spectrum of li gand in DMSO-d6

confirmed the proposed structure showing one proton of 8.77 ppm for the H-C=N group upon D20-exchange. The 3. 5 and 4.3 ppm protons can be identifi ed easil y because they deform upon D20-exchange. The ass ignments of the protons are hi ghly complicated in the region 7.2 -7.6 ppm where the signals are due to the protons of aromati c group. The solubility of the metal complexes in organi c solvents was in suffi cient to obtai n IH NMR spectra and further in ves tigati ons were not poss ible.

The li gand and all complexes are stable at room temperature and are hygroscopi c. The li gand is soluble in common polar organi c so lvents. such as ethanol. methanol. chloroform but partiall y so luble in non-polar organic solvents such as. benzene and hexane. The UV -vis spectra of the li gand and meta l complexes were recorded in ethanol. chl oroform. methanol sol vents. The absorpti on spec tra of the ligand and complexes exhibit metal to li nand charne

'" '" transfer (MLCT) and li gand centered (LC) bands. The UV-vis spectra of the Schiff base li gand and complexes show low-energy absorpti on ba nds at approx imately 340-450 nm and hi gh energy bands at approx imately 225-276 nm. The electroni c absorpti on spectra of metal comp lexes arc dominated by the li gand-center 71:-71:* and n-71:* transiti ons of the Schiff base li gand .

1398 INDIAN J Cf-IEM , SEC A. JUN E 2006

The molecular ion peaks ml z 474IM+I] of the free li gands are present in the LC-MS spectra which supports the proposed structures. The most intense peaks at IIIl z 207 . 283. 299 and 4 17 correspond to the frangments I CI ~H9N,], IC I9H13N, J. IC19H1 2N301+ and I C2-lHllN30-lr. respectively. Mass spectral data confirm the proposed structure of 1.

The va lues of proton activity and pKI\' for these solutions have been calculated from solution A as 1.25 and -14.80. respecti vely. Protonation constants of the li gand were calculated by a potenti ometri c titration method with the TITFIT program. The calculated protonation and formation constants of the li gand are given in Table 1. The va lues of the protonation constants for the ligand are log KI = 9.06. log K2 = 7.12. log K3 = 5.57 and they correspond to the following equation s:

L + H+ ~ LH +

Titrat ion data obtained for L in the presence of Ni(U). CoCII) and CuCU ) ions were processed by the program TITFIT to observe the protonated and neutral complexes. The relative importance of the various species in each pH range is also shown by the di stribution di agrams in Figs 2-5.

As shown in Fig. 2 the li gand forms LH3·1+ between

pH: 2-7 . LH:',"+ between pH: 3-9. LHT between pH'" 5-11 and L between pH '" 6-12.

It has been found that in the case of the Cu(Il)-L system (Fig. 3). complexation begins at pH '" 2.0 with the formation of [CuLH2l-l+ showing a maxi mum at pH'" 5. Then, [CuLH]3+ appears at pH> 4, [CU~H2]-l + appears at pH > 5 and the CuL"+ complex begins to form at pH'" 7 .5.

x OE-OS

., :3 .J.(JI-:-I)5

'-.J

2.(11':-0 5

2.(JO()

." •. -'1.000 ( .. no!) X.(JOO

I'll

----­.'

iO,f)()!) 12.{J(jO

Fi g. 2 - Typi cal distribution diagrams for the LHz systcms. (0 LH/+, " LI-I/+, + LH+, _ L).

Table I - Proionati on and ovcrall fO l'll1 at i o l ~ constants of the li gand and its complexes at 15°C ~lnd

ionic strength (/) : 1.0 M K 10 ,

M eta l ion Species log r:l IT (5Lill(lard Dcviat ion)

1-1 + L I-I+ 0.196

Lli / + 0196

LI-I,'+ J 11.75 0.196

Co(l l ) CoLz+ 00016

CoLI-I '+ 0.0016

CoLI-i / + 0.00 16

CoLzllz .1+ 19.50 000 16

Ni ( lJ ) Ni Lz, 0004

NiLI-I '+ 0.004

Ni LiI / + 21.50 0.004

Cu(lJ ) CuL!+ 0.0013

CuLI-I ' + 0.0013

Cu Ll-lz.j+ 0.0013

CuLzl-I /T 30.50 0.00 13

} (, Oi .- O~ c

:d .I.OL-05 C

2.1J()() ·1.000 (,.01111 ~ .tJOO 10J!Oi) 12.000 I'll

Fig. 3 - Typica l di stribut ion diagrams for thl: Cu (IJ )-L systems. (_ Cu!+. " CuLl 1' +. + CuL2+ . 0 CuLI-i / ' . 0 CuLzl-I / +).

7.91:-05

} (,,(11-:-05 c

;i 4.0E-05

G 2.0E-05

6 . 91':-05 ~~~~~~~::;:::~~~~~~I~~~~,~ 2.000 ".(JO() (-.(JO() ~ . () O(J J O.OO(J 12.0(JO

pll

Fi g. 4 - Typi cal distribution diagrams for the Co( IJ )-systems. (_ Co!+. " CoLHJ+. + COL1+. 0 COLI-i/+. 0 COL2I-1 l "+) '

NOTES 1399

I (1 . 'lI·. -(l~ ----_ •

I -I.Clli)

I ( l / ; ~ ~()

!

.,,­/~

..... ---,.,

r-._._._-Y--j(J.(hH l I:: J'( HI

Fig. 5 - Typi cal distribution diagrams for thc Ni(l l )-systcms. (_ Ni l + . ... Ni lH3+. + Nil1+. 0 NilH/ +).

Figure 4 shows the complex formation in solutions contai ning Co(ll)-L. Complexation begins at pH "" 2.0 with the formation of rCoLH2rl+ showing a maximum at pH "" 5.5. Then. the [CoLH]3+ complex begins to form at pH "" 4 showing a max imum at pH "" 6.5. [CuL2H2l l+ appears at pH > 5 and CoL2+ complex begins to form at pH"" 5.5.

Figure 5 shows the complex formation in solutions contain ing Ni (U)-L. Complexation begins at pH "" 2.5 with the formation of [N iLH]3+ showing a maximum atpH "" 5. Then, the [NiLH[3+ complex begins to form atpH "" 4 showi ng a maximum at pH "" 5.5. The NiL2+ complex begins to form at pH"" 5.

Acknowledgment The fin ancial support by the "Yildiz Technica l

Uni versity Research Fund" (Project No: 23-01-02-05) is si ncerely acknowledged.

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2

3

4

5

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