Indian Journal o f C he mi stry Vo l. 43A. April 2004. pp. 793-79 8

Synthesis and characteri zation of novel N-functionali zed macrocyclic

dioxotetraamines bearing 8-hydroxyquinoline and its metal

complexes: Stability in aqueous solutions

Xiaojun Zhao*"·h, Xuncheng s ua, Encui Yang", Ying Wangh, Huakuan Li n"", Shourang Zhu &

Hongwei Sun

"Department o f C hemi stry. Nankai Uni vers ity, T ianji n 30007 1, P. R. Ch ina

"Co llege o f C he mi stry and Life Sc ience, T ianj in Normal Uni vers ity. T ianji n 300074, P. R. C hi na

Received 20 March 2003: revised 28 Jal/llary 2004

Nove l 4-(5'-8' -hyd roxyqu ino l i ne)methy lene- I ,4,7. 1 O-te traaza­cyc lotridecane- 11.I 3-di one ligand (L ) has been sy nthes ized by simple method, and characte ri zed by e lementa l analyses , IR and IH NMR. It has two chelating s ites eac h ab le to reac t w ith a

transiti on metal ion to fo rm complexes. At 2S .0i O. 1 0c, I = 0. 1 mol/dm' NaNO" po tentiometri c titra tio ns have been perfo rmed to de termi ne the protonation o f L-S- R- I , I O-phe nanthro line-Cu(lI ) (R = C H, . H, C I, N02) and the stabi li ty co nstants of C u(ll) and Co(l l). T he results show that fo r C u(U) and Co(U) comp lexes, 8-hydroxyquino line is a stronger che lating reagent th an tetra­amine [ 13Jene macrocycles. Mo lecula r mechani cs (MM +) calcul ations have been perfo rmed to assess the stab ility o f te rnary mi xed system 0 11 CO(II )- L-S -substi tuted- I, 10-phe na nth ro line­Cu (ll ) and C U(II )-L-S-substitu ted-I. I O-phenanth ro line-C u(ll ). T he coordination abil ity fo r diffe re nt coordinatio n sites and fo r d iffe rent metal ions (Co(l l) and C u(l l» at the same s ites have been compared. The calc ulated resul ts agree w ith those obta ined ex perimenta lly.

IPC Code: InI. CI.7 C07F 1/08; C07F 15/06

During the past few decades much attentio n has been foc used on po lyamine macrocycl ic molecules ' . As an important li gand , d ioxote traamines have been discussed extensively' '' and many new methods fo r the synthes is of d ioxopo lyamines have been repo rted". However, the pendant-arm groups introduced into the parent macrocycles have no more than o ne donor ato m. Consequently, their ro le of group or pendant arm in such compo unds can o nly be ax ial coordinatio n or steric with respect to the central metal ion. 8-Hydroxyq uino line and its de ri vati ves, that are known to be a good chelating reagent , have been widely studi ed J . Many metal complexes of 8-hydroxyquinoline are very stable and exhi b it

inte resting properti es . 8- Hydroxyquino line can be introduced into dioxotetraamine, which may functio n as versatile ligands due to the two bi nding components hav ing independent coordinati on functio n.

I , IO- Phenanth roline is a ki nd of li gand with wide coordinatio n ability and its complexes playa vi ta l ro le in many fie lds4

.7

. 1, IO-Phenanth ro line is known to coord inate wi th Cu(U) ions quantitati ve ly in the pH range 2-8 (ref. 8). Since coo rdination abil ity o f 8-hydroxyquino line and 1, 1O-phenanthroline is higher

d d · . 8 9 I I' d compare to loxotetraamllle " t 1ese 19an s coordinate wi th C u(l l) and fo rm stable complexes in acid ic condi tion. T hus, pH titration deprotonates dioxote traamine. When other metal io ns are added into the solution, po lynuclear mi xed systems can be fo rmed 10. S tudy ing the stability of these kinds o f complexes and the re lationship between the ligands and the metal io ns in so lu tion is a worthy goa \. Recently, 8-hydroxyquinoli ne pendants have been introduced into the dioxotetraamines using a simple method 10. The stability of the correspo nding metal co mplexes in aqueous solutio n has been determined and possible structures are di scussed in thi s note . T he re lated compounds are g iven in Structure I. The results show that fo r CuOI) and Co(II ), 8-hyd roxyquino line is a stro nger chelating reagent than d ioxotetraamin [1 3]ene macrocycles.

L

Experimental

(M=C u,Co) Comp lexes

Reagent or analytical grade commercial materials were used wi tho ut furth er puri fication, unless otherwi se stated. All o ther materials used in the

794 INDI AN J CHEM. SEC A. APRIL 2004

ex periments such as NaOH, HN0 3, and meta l ion solu tion of Cu(NOJh, Co(N03h were prepared in redi stilled water. The concentrati on of NaOH used for titration was established with potassium hydrogen phthalate. The compounds 5-chl oromethyl-8-hydroxyquinoline and 1,4,7 , 10-tetraazacyclo-tridecane-II , 13-di one were prepared according to the li terature l l

.12.

The Fourier-Transform I R spectra were taken on a FT-JR 170SX (N icolet) spectrometer, elemental analyses were made on a Perkin- Elmer 240C analyzer. MS was conducted on a VG ZAB-HS instrument. I H NMR spectra were recorded on a Bruker AC-P200 200 MH z spectrometer at 25°C in CDCI] or DMSO-d6 solution with tetramethylsil ane as internal standard. Titrati on was carri ed out with a Beckman (<l>71 model) equipped with 3948 1 type combination glass electrode.

Potentiometri c determinati on was carri ed out in a 50 ml jacked cell thermostated at 25.0±0.l oC. Anaerobic conditi ons were maintained using pre­purified N2 as an inert atmosphere, and the ionic strength of so lu tion was maintained at 1=0.1 mol dm'] by addition of KN03 . The cali brati on of the glass electrode was done as described in the literatures. The values of kw= 1.68 X 10- 14

, y;, =0.851 for water were used fo r calcul ati on.

Synthesis of 4-(5' -8' -hydroxyquinoline)methyJene-l ,4,7,10-tetraaza-cyclotridecane-Il ,13-dione (L)

5-Chloromethyl-8-hydroxyquinoline (2.5 g) and anhydrous K2C0 3 (2 g) were di ssolved on heating in dry DMF (100 ml ) with stirring. After 5 min 1,4,7,10-tetraazacyclotridecane-ll ,13-dione (2 g) and anhydrous K2C03 (2 g) were added, and the mi xture was constantly stirred at 80- 90°C under nitrogen. After 3 days, the mi xture was filtered under vacuum to give a light ye llow solution. DMF was then removed from the solution under reduced pressure. The residue was purified by chromatoghraphy on silica gel using with CHCliCHJOH . The eluate was concentrated to give a brown red solid, which was recrystallized from ethanol to give a white powder with 34% yield . 'H NMR (DMSO): J 2.68-2.85 (l4H), 4.64 (2H), 7.12-8.90 (6H). IR (KBr pellet): 3386, 3242, 1677 and 1559 cm· l

. Anal. Calcd for L-2H20: C, 56.01 , N, 17.19, H, 7.17%. Found: C, 55.81 , N, 16.93, H, 7.14%.

Potentiometric titrations 5-R-I,10-phenanthrolines (Rphen where R = CH3,

H, CI , N02) were combined with Cu(II) in the ratio

I: I, to form Cu(II )-Rphen complexes(L) . Then ligand L was mi xed with Cu(Il)-Rphen in I: I ra tio. Potenti ometric equilibrium measurements of the L' in the presence of M(I1 ) (Cu(IJ) or CI)(lI)) ions were carri ed out respectively with a Beckman p H meter (Model <l>7l) equipped with a type 3984 1-combi nation electrode. Typical concentrati ons of ex perimental solutions were Ix 10-3 mol dm-3 fo r both the ligand and metal ions. Redisti lled (in quartz equipment) water was used fo r preparing all the solutions. NaNO" Cu(N03h, CO(N03) 2 were recrystallized fro m H20 before use. The concentrations of Cu(II ) and Co(ll) in the stock solution were analyzed by EDTA tit ration methods. The ioni c strength was adjusted to 0.1 mol dm-.1 with NaN03 . All titrati ons were carried out under N2 at 25°C. Computation of equilibrium constants was done using the program based on the improved TITFIT technique J3

. For each system, at least. two titrations were perfo rmed and each titrat ion contained at least 45 experimental points.

All the structures were full y optimized using Molecular Mechanics MM + method. The minimization was carri ed out using Polak-Ribiere Algorithm and the root mean squar , (RMS ) gradi ent of 0.04 1 84kJ/mol was used as tile terminati on conditi on. All the calculati ons were performed on a PlII computer using the Hyper Chem package program.

Results and discussion In the following text, each species wi II be denoted

by (p, q, r), where p is the stoichio:netric coefficient of the metal ion in the complex, q that of the li gand and r that of the hydrogen ions. A negati ve value of r indicates that the complex has released a proton (for instance from the amide group of the ligand or the coordinated H20 ). The reaction scheme is shown below, where ~lI o=[M(II )L/]/[M (II )][L/] (Scheme I)

Since ligand L has two independent coordination sites: 8-hydroxyquinoline and dioxotetraamine, it coordinates with transition metal ions and forms binuclear complexes under proper conditions. It has been proved9 that the coordination to 8-hydroxyquinoline is stronger than dioxotetraamine. 8-Hydroxyquinoline first coordinates with Cu(Il) ions while dioxotetraamine only partially coordinate with Cu(II ) ions in neutral and acidic conditions.

Generally, 8-hydroxyquinoline can only provide two coordination atoms in ligand L, so it can:t sati sfy the complete coordination for Cu(JI), while

NOTES 795

M

R

Scheme 1

phenanthroline can prov ide two nitrogen atoms with Cu(II) and form stable four-coordinated structures I O

.14

•

As the dioxotatraamine is free in L, protonation constants can be studied by utilizi ng potentiometric titration methods. I n this mixed system, the dioxotetraamine ligand can coordinate with the metal ions at suitable condition, so we are able to determine the stability constants of mi xed multinuclear complexes. The stabi lity constants are listed in Table I.

It is seen that changes of substituted group for 5-substituted-phenanthroline affects the protonation constants of the mixed complexes, it decreases with the increase in electron drawing abilities for substituted group. This is related to the Hammett substituted group effect 15 .

From Table I , it is seen that the stability constants of CO(II)-L-5-substituted-l , I O-phenanthroline-Cu(II) complexes are larger than those for Cu(IJ)-L-5-substituted-phenanthroline-Cu(U). This is abnormal according to Irving-Williams stability sequences l6

. It is possible as most complexes for Cu(II) are square planar with four coordination number while Co(JI) complexes are octahedral structure with six coordination number, the plane of aromatic rings 17 of 8-hydroxyquinoline taking part in the coordination

/ ~}i 0

;;~C~¢::< H "--1.1 H 0

H20

t;)c",-!;1 H L--I H 0

II

with Co(I1) in the mixed system, increases the stability of Co(II)-L-5-substituted-l , 10-phenanthroline-Cu(II), so its stability constants are larger than Cu(II)-L-5-substituted-phenanthroline­Cu(H). The effect of aromatic rings on Co(II)-L-5-substituted-l , lO-phenanthroline-Cu(lI) is shown in Structure II.

From Table I , it can be seen that the fine linear free energy relationships (LFERs) exist between 10g13co-L-RphenCll. the stability constants of ternary complexes, Co(II)-L-5-substituted phenanthrolines­ClI(lI) and 10gKRphe'H the protonation constants of 5-substituted phenanthrolines and between l og~co-L- R-Phen-Cu, the stability constants of ternary complexes, CO(II)-L-5-substituted phenanthrolines­Cu(II) and 10gKLRPhenCu the protonation constants of L-5-substituted phenanthrolines-Cu(lI).

The relevant linear regression equat ions and thei r con'elation coefficients are shown as follows:

Logf3coLRPhenCu = 4_985 + 0.591 10gKRphen r = 0.9940 Logf3coLRPhenCll = 1..1 84 + 0.868 10gKLRphenCll r = 0.9976 Log/3LRPhenCll = 4.025 + 0.682 10gKRphen r = 0.9986

From Table 2 it is seen that the energy of tetrahedral conformation is lower than that of the square planar conformation for different substituted groups in coordination site I . Hence, it is reasonable

Table I - Protonation constants for the ternary L-5-substituted-l, 1 O-phenanthroline-Cu(lI) complexes and stability constants of its complexes with Cu(II) or Co(U)

R -CH, -H -CI -N02

Species logK I (L-Rphen-Cu) 7.48±0.40 7.25±0.11 6.81±0. 11 6.39±0.24 L-Cu(lI ) logK 2(L-Rphcn-Cu) 3.99±0.20 3.97±0.06 3.98±0.06 4.24±0.1 7

logKRphcn 5.028 4.74:5 ' 4.125 3.437 L-Cu(II )-Cu(1I ) log{:ll io 7.74±0.1 6 6.37±0. 18 6.48±0.02 5.28±0. 19

log{:lI I_1 2.99±0.23 -4.47±0.19 -4.33±0.28 -5.11±0.20 L-Cu(II )-Co(lI ) log{:ll io 8.0 1±0.09 7.74±0.08 7.40±O. 1O 7.04±0. 11

log{:lI I_1 1.1 8±0.60 3.78± 1.8 1.02±0.60 -0.4 1±3.8 log{:lll _ , -3.83+0. 13 -4.01 +0.11 -4.20+0. 13 -4.63+0. 16

796 INDIAN J CHEM, SEC A, APRIL 2004

Table 2- The energy of different conformations at coordination site I for CU(II)-L-5-substituted-phenanthroline-Cu(lI) or Cu(lI)-L-5-substituted-phenanthroline- Co(Il) mixed coordination system(unit:kJ/mol)

Cu( I1 )- L-5-subst i tu ted-Ehenan thro I i ne-Cu(l I) Cu(I1)-L-5-su bsti tuted-Ehenanthrol i ne-Co(l I) R £1 £ 2 £1 £ 2

CI 909.9 6 18.6 926.0 636.7

H 908.3 618.6 924.8 636.7

CH, 919.0 644.2 935.1 662.3

N02 923.8 642.3 939.8 660.4

* EI stands for the energy of the square planar conformation £2 stands for the energy of the square tetrahedral conformation

Table 3- Selected bond distances(nm) and bond angle(O) of coordination for Cu(II)-L-5-substituted - I, 10-phenanthroline-Cu(II) complexes calculated by MM+

R Coordination site I Coordination site 2

CI Bond distances Cu-NI Cu-N2 Cu-03 Cu-N4

Bond angle L NI-Cu-N2 L N2-Cu-03 L 03-Cu-N4 L N4-Cu-NI

H Bond distances Cu-NI Cu-N2 Cu-03 Cu-N4

Bond angle L NI -Cu-N2 L N2-Cu-03 L 03-Cu-N4 L N4-Cu-NI

CH, Bond distances Cu-NI Cu-N2 Cu-03 Cu-N4

Bond angle L NI-Cu-N2 L N2-Cu-03 L 03-Cu-N4 L N4-Cu-NI

N02 Bond distances Cu-NI Cu-N2 Cu-03 Cu-N4

Bond angle L NI-Cu-N2 L N2-Cu-03 L 03-Cu-N4 L N4-Cu-NI

to suggest a tetrahedral conformation in site I.The coordination sites are shown in Structure III.

On Comparing the data of the two coordination sites from Tables 3 ·and 4, it can be seen that the bond distances of coordination site 1 are shorter than those for coordination site 2. For instance, in Table 3 the bond distances of Cu-Nl(0.1828) < Cu-N5(0.1904), Cu-N2(0.1827) < Cu-N6(0.1892), and in Table 4 Cu­Nl(0.1828) < Co-N5(0.1896), Cu-N2 < Co-N6

0.1828 Cu-N5 0.1904 0.1827 Cu-N6 0.1892 0.1779 Cu-N7 0. 1894 0.1826 Cu-N8 0. 1884 88.8 L N5-Cu-N6 76.8 120.6 L N6-Cu-N7 77.6 92.7 L N7-Cu-N8 89.9 118.3 L N8-Cu-N5 83.9 0.1827 Cu-N5 0.1904 0.1828 Cu-N6 0.1891 0.1779 Cu-N7 0.1894 0. 1826 Cu-N8 0.1884 88.8 L N5-Cu-N6 76.8 120.4 L N6-Cu-N7 77.6 92.7 L N7-Cu-N8 89.8 118.9 L N8-Cu-N5 83.9 0.1828 Cu-N5 0.1904 0. 1826 Cu-N6 0.1892 0.1779 Cu-N7 0.1894 0.1826 Cu-N8 0.1884 88.6 L N5-Cu-N6 76.8 120.4 L N6-Cu-N7 77.6 92.7 L N7-Cu-N8 89.8 118.4 L N8-Cu-N5 83.9 0.1828 Cu-N5 0.1904 0.1827 Cu-N6 0.1892 0.1779 Cu-N7 0.1894 0.1826 Cu-N8 0.1884 88.6 L N5-Cu-N6 76.8 120.4 L N6-Cu-N7 77.6 92.8 L N7-Cu-N8 89.9 119.0 L N8-Cu-N5 83.9

(0.1881). The I bond distance reflects strength or weakness of the coordination ability for different coordination site. This means that the coordination ability of the first site is stronger than that for the second, which is consistent with the expected results9

.

From Tables 3 and 4 it can be seen that the bond distances of coordination site 2 for Co(II)-L-5-substituted-I, 10-phenanthroline-Cu(II) are shorter than Cu(II)-L-5-substituted-l , 10-phenanthroline-

NOTES 797

Table 4-Selected bond distances(nm) and bond angle(O) of coordination for Co(II)-L-5-substituted-l, 10-phenanthroline-Cu(lI) complexes calcul ated by MM+

R Coordination si te I Coordination site 2 CI Bond di stances Cu-NI

Cu-N2 Cu-03 Cu-N4

Bond angle L NI-Cu-N2 L N2-Cu-03 L 03-Cu-N4 L N4-Cu-NI

H Bond distances ClI-NI Cu-N2 Cu-03 Cu-N4

Bond angle L NI-Cu-N2 L N2-ClI-03 L 03-Cu-N4 L N4-Cu-NI

CH) Bond di stances Cu-NI ClI-N2 Cu-03 Cu-N4

Bond angle L Nl-Cu-N2 L N2-Cu-03 L 03-Cu-N4 L N4-Cu-NI

N02 Bond distances Cu-NI Cu-N2 Cu-03 Cu-N4

Bond angle L NI-Cu-N2

L N2-Cu-03 L 03-Cu-N4 L N4-Cu-NI

R

III (M=Cu or Co, R=H, CH3, cr, NO'2)

Cu(Il), such as Co-NS (0. 1896)<Cu-NS(0.1904), Co­N6(0.1881)<Cu-N6(0. 1 892), which means the stability of Co(II)-L-S-substituted-l, lO-phenanthro­line-Cu(Il) is larger than Cu(lI)-L-S-substituted-l, 10-phenanthroline-Cu(II), This data supports the experimental results (Table 1).

0.1828 Co-N5 0 .1896

0.1827 Co-N6 0. 1881 0.1779 Co-N7 0.1885 0.1826 Co-N8 0.1875 88.8 L N5-Co-N6 87.7 119.2 L N6-Co-N7 80.8 92.7 L N7-Co-N8 75.5 120.2 L N8-Co-N5 84.0 0.1828 Co-N5 0.1896 0.1826 Co-N6 0.1881 0.1779 Co-N7 0.1885 0 .1826 Co-N8 0.1875 88.6 L N5-Co-N6 87.7 119.2 L N6-Co-N7 80.S 92.7 L N7-Co-NS 75.5 120.3 L N8-Co-N5 84.1 0 . IS28 Co-N5 0.1896 0.1827 Co-N6 0.1881 0.1779 Co-N7 0.1885 0.1826 Co-N8 0.1874 88.7 L N5-Co-N6 87.7 11 9.2 L N6-Co-N7 80.8 92.7 L N7-Co-N8 75.5 120.2 L. N8-Co-N5 84 .1

0. 1828 Co-N5 0 .1896 0.1827 Co-N6 0.1881 0.1779 Co-N7 0.1885 0.1826 Cu-N8 0.1875 88.6 L. N5-Co-N6 75.5

120.4 L N6-Co-N7 80.8 92 .8 L N7-Co-N8 87.7 119.0 L N8-Co-N5 84.1

Acknowledgement This project was supported by the National Natural

Science Foundation of China (No: 29971018), the Natural Science Foundation of Tianjin education commission (No: 20020901).

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