Synthesis and properties of a new tetraaza macrocyclic ligand containing one N-acetic acid pendant arm and its copper(II) and nickel(II) complexes

ELSEVIER

Inorganica Chimica Acta 274 (1998) 24-31

Synthesis and properties of a new tetraaza macrocyclic ligand containing one N-acetic acid pendant arm and its copper(II) and nickel(ll) complexes Shin-Geol Kang "'*, Seong-Jin Kim ~, Kiseok Ryu a, Jinkwon Kim ~' "Department OfChemist~'. Taegu University. Kyungsan 712.714, Soufh Korea Department of C'hemist~%Ktmg/u National University. g~m:~314.701. South Korea Received 5 December 1996; revised 4 June 1997; accepted In July 19~17

Al~r~'t

A new monofunctionalized tetraaza macrocycle C-meso-5.16-dimethyl-2.6,13,17-tetraazatricyclo.[16,4,0,0~ '-']docosane-2-acetic acid t HL~). in which one acetic acid group is appended, was prepared by the one-step reactionof the tetra~a macrocycleC-meso-3,14.dimethyl2,6,13,17.tetraazatricyclo[ 16.4,0,0~' ~]doco~ne {L~) with an excess of bromoaceticacid, The copper( I! ) and nickel( II) complexes of HL-' were synthesi~,edand characterized. Two types of copper{II) complexes [Cu(HL:) I ( CIO~).~.0.SH,O and ICuLa ]CIO~.5H.~O ( L~"is a d~protonated form of HL~) can be i~lated m~ler acidic and basic conditions respectively. However, only one lbrm of nickel{il ) complex I NIL:(H~O) ]1210~was i,~olaledeven under acidic conditions. The crystal structureof ICu( HL" ) I ( CIO~)~. 0.5H~O shows thai the pendant a~elic acid group is cooMinatedto the metal ion thl~)ughthe oxygen atom of the cart~mylunit: tile complex has a somewhat distorted square. pyramidal coordination geometry, The acetic acid IFoup in ICu{HI.~) I ~' is also c(~rdinated to the metal ion in nitromethane, ace~onitrile, and >_0.$ M HCIO.~aqueou,~ solutions, but i,~ deprolonated to province [CuL'~] ' even in pure water. The macrocycle HL~' reacts with copier( II ) ion~ more slowly than I.', Crystal data of (Ca( HL~) ] (CIO~)~.0,5H~O: monoclinic, space gr.up P2~/n with a - 8. It)7( I ), h-= 21+48~14). c - 1~.339(7) A. B = ql 3R(I) ° and Z--4. © IqgX Elsevier Scie,ce S.A. All rights re~erved.

I, introduction There hu,~been considerable interest in the synthesis, structures, and properties of various types of N-functionalized polyaza macrocyclic ligands and their metal complexes. In particular, the interest in macrocyclic compounds containing N-acetic acid groups is still growing, because such coma pounds often exhibit remarkable Sl~'cific metal ion selectivity and are important for the design of medical imaging agents such as magnetic resonance imaging (MRI) contrast agents [ I ~ ) . Most polyaza macrocyclic ligands containing N-acetic acid pendant arms react with transition metal ions In produce complexes in which the acetic acid gn~p i~ dcprotonatcd and Ih¢ metal ion is bonded to the resulting N-acetate form I 1~16]. As tar as we know, examples of transition metal complexes containing bonds between the central metal ion and the acetic acid group have not ~'en rep~med to date, "Ct~s~ing

author, Fax: + 82-53-8.~0 (~44~),

1102t1~1~3/98/$19,00 © 1998 El,~vier Scie~'c S,A, All rights r~,~,,ed, PIt SO0~O- 16~)¢ q? ) 0~98~.¢)

H

Lt

RI"R~m H

HL4 : RI=IR~iI~I;RsgH;

nlmH

H~.~ nt ~1~ a IVle;

R~~% - CI'ECOOH

The Noalkylation of a i~dyaza macrocycle ix strongly alTccted by the substituents at the carbon atoms next to the secondary amino groups and by the nature of the alkylating agent, For example, although direct reaction of I A,8.1 Ilettuazacyclotetradecane (cyclam) with an excess of alkyl bromide usually forms quaternary ammonium salts [ 17 ]. the reaction of L' {C-mesa-3,14-dimethyl-2,6.13,1 7-tetraazatricyclo[ 16,4,0.0~ ~'~]-docosane) containing two cyclohexane

S..G. Kang el al. I btorganica Chbnica A('la 274 ¢1998)24-31

subunits and two C-methyl groups with a large excess of RBr (R = Et or n-Pr) produces a fully N-alkylated macrocycle in which only one alkyi group is bonded to each nitrogen I 18 ], However, the only product isolated from the one-step reaction of L t with a large excess of 2-bromoethanol in basic acetonitrile medium was the di-N-hydroxyethylatea macrocycle L 3 [ 191. In this work, the one-step reaction of L t with an excess of bromoacetic acid was attempted, to investigate the effects of the C-suhstituents and the alkylating agent on the substitution reaction. Interestingly, the major product obtained from the reaction was the macrocycle HL2 containing only one Nacetic acid pendant arm. Furthermore. the coordination behaviors of HL-"in its copper( 11) complex are quite different from those in the nickel(!i) complex. The properties of HL-" also differ from those of other related macrocycles containing N-acetic acid groups. This paper reports the synthesis and properties of HL-" and its copper(ll) and nickel(!I) complexes. The crystal structure of I Cu( HL-") ] (CIO4),. 0.5 H,O was also determined, to investigate the unusual coordination behavior of the complex.

2. Experimental 2. I. Materials All chemicals used in syntheses were of reagent grade. The macrocycle L ~ was prepared as described previously 1201. Safety note: although we experienced no problems with the compounds reported in this work, perchlorate salts of metal complexes with organic ligands are often explosive and should he handled with great caution.

2.2. Synlhe,~'i,sof tll.:. HBr, H:O An absolute methanol suspension ( ~ 30 ml) of bromo. acetic acid ( 3. I g, 22.2 mmol) and KOH ( 1.3 g. 22.2 mmol ) was stirred for 20 rain at room temperature. After addition of L I (3.0 g, 8.9 mmol) and Na~CO~ (2.4 g, 22.2 mmolL the mixture was heated to reflux over 48 h. The reaction mixture was filtered off', and the filtrate was evaporated on a rotary evaporator to dryness. To the residue was added water ( ,-, 60 ml) and then the resulting mixture was allowed to stand overnight. The white solid formed was filtered off, washed with cold water, and dried in air. A second crop was obtained after the volume was reduced further ( to -,, 15 ml ) and the solution allowed to stand for several hours. The product was used without further purification. Total yield ,-, 60%. Anal Calc. for C,-,H4.~N4BrO~: C, 53.55; H. 9.15: N, 11.35. Found: C, 53.20; H. 8.90; N, 11.35%. FAB mass: m/z 395 ( [ M - H:O-Br] ~ ). IR: 3300-3500 ( vO-H ), 3240 ( vN-H ). 3280 (uN-H), 2700 ( vNH, + ). 1700-1600 (t,C--O) c m ~. IH NMR (CD3OD): 8 !.27 (d, Me), 1.50 (d, Me) ppm. ~C NMR (CD3OD): 8 14.0 (Me), 15.4 (Me), 22.4. 25.2. 25.3 (d), 25.4, 27.5, 27.8, 30.9. 34.1.40.5. 50.4, 5i.5, 51.6. 52.4.

25

55.9, 59.0, 59.6 (d), 65.4 (CH,COOH), ! 79.6 (COOH) ppm.

2.3. Synthesis of lCufHL2)l(ClO4):.O.5H_,O A methanol solution ( 20 ml ) of Ca ( O2CMe ) 2" H20 ( 2.0 g, 8.0 mmol) and HL2-HBr-H20 (2.5 g, 5.0 retool) was heated to reflux for I h and then cooled to room temperature. After water ( 10 ml ) and an excess of HCIO4 had been added, the mixture was stored in a refrigerator. The dark purple crystals formed were filtered offand washed with cold water. The product was recrystailized from hot O.1 M HC104 watermethanol (3:1) mixture. Yield "-90%. Anal. Calc. for C22H43N4CuC1200os: C, 39.65; H, 6.45; N, 8.40. Found: C, 39.95; H, 6.60; N, 8.40%. IR: 3550 ( vOH of H.,O). 3370 ( ~,OH of COOH), 3200 ( uNH, br), 1710 (vC---O) cm-

2.4. Synthesis of lCuL"]ClO#. 5H:O fL: is the monodeprotonated fi~rm of HL") To a minimum volume of hot aqueous solution of ICu(HL")I(CIO4L,.O.5H.,O (I.0 g) were added NaOH (0.3 g) and an excess of NaCIO4. After the mixture had been filtered off. the filtrate was stored in a refrigerator to produce blue-purple crystals. The product was filtered off, washed with methanol, and dried in air. Yield ,-, 80%. Anal. Calc. for C.,_~H.~IN4CuCIOII: C, 40.85; H, 7.95; N, 8.65. Found: C, 40.50; H. 7.70; N, 8.50%. FAB mass: m/= 557 ([M * 5H,,OI + ), 458 ( [M-CIOa-5H:O] ÷ ). IR: 3520 (uH:O), 3240 (),NH). 3210 (I, NH). 3190 (),NH). 1640-1(gX)

(vCO~)cm ),

,~ynthestso.1INtL°(H:O)]CIO,~ This complex was prepared by ,'mmethod similar to thai for the copper(ll) complex [Cu(HL~)](CIO4):.O.5H~O. except that N i( O:CMe )~. 4H~O ( 2.0 g ) was reacted instead of Cu(O,CMe),. H:O. The pale purple solid was recrystallized from hot water-methanol ( 3:1 ) mixture. Yield ~ 90¢;~. Anal. Calc. l'or C2,,H4~N4NiCIO7 ( 569.75 ): C. 46.38: H. 7.61; N, 9.83. Found: C, 46.72; H. 7.45: N. 10.02c,~. FAB mass: m/z 551 (IM-H.~OI +), 451 (IM-H..O-CIO~]*). IR: 3450 (vOH of H.~O), 3270 (vNH). 3250 (vNH). 3230 (~NH). 1620-1600 ( vCO~ ) cm ~. Magnetic moment/.L~,: 2.82 Ix, at 20°C.

2.6. Measttremettts IR spectra were recorded as either Nujol mulls or KBr pellets on a Shimadzu IR-440 spectrophotometer. NMR spectra with a Bruker WP 300 FT NMR spectrometer, electronic spectra with a Shimadzu UV-160 spectrophotometer, and conductance measurements with a Metrohnl Herisau conductometer E518. Magnetic susceptibilities were measured with a Johnson Matthey MK-I magnetic susceptibility balance. Molar susceptibilities were corrected for diamagnetism of the

S,.G. Kang et al. / Inorganica Chimica Acta 274 (1998) 24-31

26

ligand and the anion by use of Pascal's constants. Elemental analyses and mass spectra were performed at the Korea Basic Science Institute, Seonl, Korea. Kinetic measurements of the formation of the copper( I11 complexes of L t and HL 2 were carried out in acetate buffer solutions ( p H 5.7) of methanol-water (1:11 at 25°(=. The initial concentrations of HL-~-HBr.H20 and C u ( N O s ) 2 3H20 in the reaction mixtures are 2.0 X ! O - "~and 1.0 X ! 0 - 2 M, t~tpectively. The reaction was monitored using the in--in absorbance at 520 ( L ' ) o r 5 5 3 n m (L21.

2. 7. Crystal structure determination

A purple crystal of [Cu(HL =) ] (CLOD2.0.5H20, obtained from water=acetonitdle, was mounted on a thin glass fiber on an Enraf=Nonius CAD4 diffractometer. Unit cell parameters were determined from a least.~uares fit of 23 accurately centered reflections (22 ° < 20 < 29°). Tbe~ dimensions and other para~ters, including conditions of dam collection, are summarized in Table I. Data were collected at 297 K in the tt~2O scan mode. Three inten~ reflections were monitored every 200 reflections to check stability. Of the 3652 unique reflections measured, 3265 were considered obmrved (Fo> 4~r(Fo) ) and were used in sub.~quent SlrUCtUreanalysis, Data were corrected for Lorentz and polarization effects. Empirical 9' absorption cowection was applied. Maximum and minimum transmission were 99.68 and 89.75%, respeclively, l~e SHELXSo86 program was utilized for tbe heavy atom method { 21 ], The SIftlCIUI~refinements were performed with T~bie I C i ~ l l l lind ~ftnemem g~t~ for I Cu(ttL') I 1C10~);,0,~H31 Formul~

M

C~H~,CI:N~CuO,,,, ~,114

Space~rt~p

~ ) !.

tteA) blA) r (A) B 1o)

8,197111 21.485141 16,339(7 ]1 913811 )

g I ) ~ 18 em ~) (era-)) C~s~tl ,~l~e(mini Ttmtsmls~ioncoefficients ,~(Mo K~t) (At Sc~ mode 2~ limi~1~) No, unlq~ tktt~ No, ob~rved d~l~ (F,, > 4~y~F,,) ) No, v ~ l e ~ RI" WR2b Goodness of fit

4 1,538 10 0,2 ×0,2 xO,4 0,897=0,~17 0,71073 o~2~ 46 36S2 3265

387 O,O437 0,1169 I,! 13

* RI ~11K, t = IF, I I/~:lF,.I, ~wR2" I T,wI K,'~=I:,~I~/T,~'( t~,:):I"~:, '= I/Io'~(E, ~) + (O,05~P) " + 2.~,~Pl~ P= lr~ut(F.~,OI + ~',," 113,

the SHELXL-93 program on F 2 data [ 22 I. Heavy atoms (Cu and CI) were located by use of the heavy atom method. Other non-hydrogen atoms were found from successive difference Fourier map calculations. Two oxygen atoms in one perchlorate anion are disordered. These atoms were refined with a fixed site occupation factor of 0.5. All non-hydrogen atoms were refined anisotropically. A peak was observed in well isolated space; it was included as half-weight oxygen (i.e. water). Hydrogen atoms of water were not found. All hydrogen atoms bonded to carbon atoms were included in calculated positions. This C-H bond distance was fixed at !.00 and U values were assigned based approximately on that of the attached atom. The other hydrogens (N-H) were included in located positions with U=0.07/~2. A final dilL ference Fourier map~ was essentially featureless, the largest peak being 0.46 e A ='~. Final RI (based on F) and wR2 (based on F-') values are shown in Table I. Positional and equivalent isotropic thermal parameters are listed in Table 2. Table 2 Atomic co,ordinates and equivalent isotropic thermal parameters for

I CuL-'I(CIO~),.O.SH=,O AIom

x

Cu N( I 1 N( 2 ) N(31 N141 O( I ) O( 21 0131 C1 I1 C121 C1;11 Cl 41

-0.0757(41 0.11)72(4 ) 0.1912141 0,0020(41 0.2472(4 ) 11.24"/915 ) i]1,111141 ~ 0,2265151 ~0,1q27161 ": 0,13761~) 11,0~481 ~ I

ClOt C171 C181 C191 C(10) C{ I I ) CI 121 C1131 C11411 CII3• C1161 CI 17) C1181 C( 191 C12111 C1211 C1221 CI(II I"1121 OI4t 0151 0161 017) 0181 0191

O(I0) O(11)

y 0.1}633815 )

11,1~8=~1? I i),28891? ) 11,2777151 0,2178151 0.M21(3) 0.3083( 3 ) 0.~117415 I 0,t]1173151 ~ 0.0343161 ~0,1180161 ~ 0,2I~AOI31 ~(]1,2143(3 ) -0.1277(31 -0.2908161 0.3823(6) 0,0238(51 0.1839161 0,1fl411 !1 -!1,21t7111) 0,0~31($1 0,0984(61 0,3224(51 0,1821181 -0,226417t -0,332017) -0.058( l ) -0,293121

0.1369812) 0.1545(21 0,11447( 2 ) 0.1241121 0.231~( 2 ) 0,107012 0.0934( 2 0,149319 0,1141112 11,11451112 11,i120~12 11,1124312

; 11,i14+I 12 = 0+111912 + 0,0311fll2 03139112 11.11~63( 2 0.161712: 0,230812 (I.257012 0,2~07(21 I),3273t 2 ) 0.3558( 2 ) 0,3167(21 11,24t~12 ) 0,221312) 0,0355131 0.2446( 3 ) 0.1447(21 0.1127121 0.4287215 ) 0.20035171 0,447813 ) 0.447113 ) 0,455612 l 0,365312 ) 0,1989131 0.2193141 0,202( I ) 0.1383171

~

U,,q

0.2831113) 0.3841121 0.2691(2) O. 1809( 2 ) 0.277712) I),384512 ) 0.5208(2) 0,08911 ) 0.384713 ) 11,378'113) 11,21131113) 11,18~9131 11,1748131 0.(~13131 0,07~ 14 t 11,083413I 11,1696131 0,1751131 0,1766131 0.2582( 31 0,3502121 0,3334131 0,4059( 3 ) 0,4290131 0.446313 ) 0.373612) 0,2302131 0,3268( 31 0,461013) 0.4~95 ( 3 ) 0.11289171 0,0935217 ) 0,0461(31 0.1869(31 0,104013) 0.1093(41 0.1773(31 O,O495131 O,Ob9( I )

0.032212) 0.033218) 0.038218 ) 0.036618 ) 0.031117) 0.051418) 0,072( I ) 11.2811) 0,04~11 i 0,11~211) 0,0~0( I ) 11,(140iI ) 0.03311 I 0,116211) 0,0~712) 0,05311 ) 0.114011I 11.1~911I 0,04511 ) 11.1141111 0,033419 ) 11.047( I ) 11,114911) 0,04811 ) 0,114511) 0.0325191 0.065(2) 0,(~3 ( 2 ) 0,047( I ) 0,134611) 0.048013 ) 0,05111141 0.098(2) 0.111121 0.09411 ) 0.127121 0.13212) 0.164131 0,155181 0.146( 5 )

0.0714(8)

27

S.-G. Kang et al, I hu~rganh'a Clmniea Acta 274 ¢ 1998j 24-31 3. Results and discussion

3.1. Synthesis

The mono-N-functionalized macrocycle HL-'. HBr-H,O was readily prepared in high yield ( ---60%) by one-pot reaction of an absolute methanol solution of L ~and an excess of bromoacetic acid in the presence of KOH and Na2CO3. It is interesting to observe that the introduction of only one pendant acetic acid group is achieved by the one-step reaction of L ~with an excess of bromoacetic acid. This result is different from that observed for the reaction e l L ~with 2-bromoethanol in a i :2.5 molar ratio: the major product in the reaction was the di-N-hydroxyethylated macrocycle L ~ 1191. One of the reasons for the easy synthesis of the monofunctionalized macrocycle HL'- in this work may be the steric hindrance caused by the methyl groups and the cyclohexane rings fused to the macrocycle. Another important factor affecting the substitution reaction of L ~with bromoacetic acid. compared with 2-bromoethanol, may be the stronger interactions between the secondary amino groups and the functional group such as hydrogen bonding, which retard the reaction. The macrocyclic ligand HL-'. HBr. H,O is extremely stable in the solid state, is readily soluble in methanol and is slightly soluble in water at room temperature. The ~H NMR spectrum of HL". HBr. H,O shows two doublets centered at ~51.27 and 1.50 for the two C.methyl groups. The ~3C NMR spectrum shows 22 peaks ( see Section 2 ). The NMR spectra, together with the elemental analysis and the IR spectrum, are consistent with tile structure of I,,II. ~, which was conlirmed by the crystal structure of its copper( II I complex ( see below ). Reaction of HL". HBr. H,O with Ni( O~CMe ):. 4H,O in refluxing methanol followed by the addition of FICIO,~produced the octahedral complex [ Nil.~( H~O)]CIO,~, in which tile acetate group of' tile ligand is axially coordinated to the

~ O 3

~

O2

C13(-'/~

ci0

ci

metal ion as usual. Unexpectedly, similar reaction of HL-'.HBr-H_,O with Cu(O_~CMe),-H,O followed by the addition of HCIO~ produced the square-pyramidal complex I Cu( HI,-") I (CIO4)e" 0.5H_,O containing the N-acetic acid group which is coordinated to the metal ion. The dep~oionated copper(ll) complex [CuL-"1CIO4- 5H20 was prepared by simple recrystallization of ICu(HL-') ]-'÷ in a basic aqueous solution. All attempts to prepare [ Ni ( HL-") ] (OO4)_, from acidic solutions of [NiL2(H_,O)]C104 were unsuccessful: the only product isolated as a solid was the reactant [ NIL-'(H_,O) 10 0 4 even in concentrated HCIO4 ( > 2.0 M ) solutions. The reasons for the different coordination behaviors between the copper( 11) and nickel ( I! ) complexes of HL-" are not clear at this time. However, one of the reasons for the easy formation of [ Cu ( HL-") I" +, in contrast to the nickel ( II ) complex, may be the stronger Lewis acidity of the Cu(!1) ion 123 l. The nickel( I1 ) and copper( I! ) complexes prepared in this work are stable in the solid state and are soluble in polar solvents such as water. 3.2. Crystal structure qf ICu(HL" JI(CIO4L," 0.51-1,.0

The crystal structure (Fig. I) of the complex cation I Cu( HL-") ] -"+ shows that the acetic acid group is attached to one of the less sterically hindered nitrogen atoms of the ligand. The complex has a somewhat distorted square-pyramidal geometry with four nitrogens in a plane and one apical oxygen of the pendant acetic acid group. The macrocyclic ligaml adopls the trans-III stereoche,nistry. The acetic acid group and the methyl group in the same si x-membered chelate ring are anti with respect to the plane. Tile cyclohexane rings and the six-membered chelate rings adopt a cllair conlormao lion. Tile lattice water is not involved in coordination. Selected bond dislances and angles of the complex are summarized in Table3, The Cu=N bond distances

H2C20

// C1211 ~

c2

II-Ns

c3

ce

c8

c5

c7

c6

( )c19 Fig. I. An ORTEP drawing of I Cu( HL z ) i : ' with 511e~probability displacement eli )soids. The hydrogen atom H( 2 ) attached to O( 2 ) is included, together with the O(.3) alom of the lattice water. Hydrogen ;,toms of water wen: not fopnd. There is i)o interaction helween O( 3 ) and H ( 2 ).

S,.G, Kang et aL I Im)rgaaico Chimk'a Acta 274 (1998) 24-31

28

Tabt¢3 .~le~,'d bond distances IA) and angles (°) for ICu(HL:)I(CIO4),"

0.SH~,O Cu-N( I) Cu-N(3) Cu-O( 1 ) C(22)-O(2)

2.069(3) 2.018(3) 2,297(3) 1,317(6)

Ni-N(2) Ni-N(4) C( 22 )--O( 1 )

2.047( 3 ) 2.026( 3 ) 1.203(5)

N( I bCu.-N(2) N(3)-Cu-N(4) N( I)--Cu-N(3) NIl )--Cu-.O(I ) N( 3).-Cw-O( I ) C(21 )~C( 22)-O( l ) O( I )~4~(22)-O(2)

97.9(2) 92.1(2) 176.4(2) 80.9(2) 102,3(2) 124.1 (4) 125.6(5)

N(2)-Cu-N(3) N( I)-Cu-N(4) N(2)--Cu-N(4) N(2)--Cu-O(l) N( 4)--Cu-O( I) C(21).-C(22)-O(2) Cu-N( l )-C(21 )

84.0(2) 85.5(2) 169.2(2) 87.1(2) 103.6(2)

110.2(5) 110.2(2)

(2.018(3)-2.069(3) .~,) are comparable with those for copper(lI) complexes of other 14-membered tetraaza macrocycles containing N-acetate group(s) [ 9.1 l- 13 ]. The Cu-N(I)(tertiary) distance is longer than the Cu-N(secondary) distances, as usual. The Cu-O ( I ) bond distance (2.297(3) A) is also comparable with those for [CuLSl (LS~doubly deprotonated form of H,,Ls) (2.31 ,~) [9l and ICeL*I (L*-doubly deprotonated form of H.,L% (2,248( I ) A) [ ! I ]. indicating the coordination of the oxygen atom. Most interestingly, the C( 22)-O( I ) bond distance is 1.203(5) A, typical of a localized C=O double bond. and is distinctly shorter than tbeC(22)=O(2) distance(!.317(6) A~): the former and the latter distances t ~ quite similar to C - O double bond (1.181(9) A) and C-43 single bond (I.327(9) A) distances respectively of the pendant No CH~COOH group in the free ligand salt HL ~.2HBr. H:O [ 10}, Furthermore, the C(22)=O( I ) and C(22)--O(2) dis° lances are much shorter and longer, respectively, than the C=O bond distances (1,249(6) and 1,257(6) A) of ICuL~I containing Nonce(ate groups 19]. The C(21 )~C(22)=O( I l and O( I)=C(22)=,O(2) angles are 124. I(4) and 125.6(5)°, respectively, which are much larger than the C(21 )~C(22)~ 0(2) angle (110,2($)~). This confirms that the O( I ) atom is doubly bonded to the carbon: the C~O bond contains two pairs of bonding electrons and requires more space than the single C~C or C-O bond containing a single pair ofe!~ctrons, The bond angles about the metal ion deviate somewhat from ideal square-py~midal angles: N( I )-~u-N(3) and N(2 )Ca-N(4) angles are 176.4(2) and 169,2(2) °, respectively, The N( I )--Cu-O( I ) angle is much smaller than the other N~4:u-O angles, The above crystallographic results clearly show that the pendant arm of [CufHL")I '~ contains a carboxylic acid gro,p which is coordinated to the metal ion through the oxyo gun atom of the C ~ 0 unit, It has been reported that, for metal complexes of most polytua macrocyclic ligands containing pendant N-acetic acid group( s ) such as HL ~, H~L'*,and H,L ~, the N-acetic acid group is deprotonated and the resulting N~'etate group is bonded to metal ions in the solid state 19-. 161, To our knowledge, [Cu(HL-')I(CIO+h,0.SH20 is a rc.,ely characteda~l polyaza macrocyclic complex in which

the pendant acetic acid group is coordinated to the central metal ion through the carbonyl unit.

3.3. Spectraand properties of copper(H) complexes The IR spectrum of [ Cu ( HL 2) ] (OO4) 2" 0.5H20 obtained as either KBr pellets or Nujol mulls shows both vC=O and ~)--H of the coordinated pendant acetic acid group at " ! 710 and 3400 c m - ' , respectively. Bands corresponding to the stretching vibrations of the coordinated secondary amino groups and the perehlorate counter anions are observed at ~ 3200 and I 100 cm - ~,respectively. One peak at 3550 cm- ' corresponding to vO--H of the lattice water was also observed, in the spectrum of [CuL2]CIO+ • 5H:O, vCO:- of the coordinated pendant acetate group was observed at 16001640 cm- ~, together with vN-H of the secondary amino groups at ,,, 3200 c m - ~: no peak around 3400 or 1710 cm ~ assignable to vO-H or vC--O of the acetic acid group was observed. The molar conductances and electronic absorption spectra of the copper(ll) complexes are listedin Table 4. The molar conductances tbr ICufHL-')I(CIO~).,-0.5H20 in nitromethane (135 l l - ' c m : m o l - ' ) and ace(ant(rile (295 f~- *cm" real - *) indicate that the complex is a 1:2 electrolyte. However, the value measured in water was found to be 450 ft + ~cm: real -s which is much larger than that expected from a 1:2 electrolyte. The conductances for [CuL-'lCIO4.5H:O in nitromethane and acetonitrile correspond to a I:l electrolyte. However, the value in water is intermediate between I:l and 1:2 electrolyles. The electronic speclra of the copper( !1 ) complex of ItL: in nitromethane and ace(ohi(rile show a d=d hand at ~533 nm (~:~ 120 M ' cm '). The spectra are quite similar to that obtained in Nujol mull, This strongly indicates that in the non.aqueous solveuts the pendanl acetic acid group of I Cu(HL-') 1" ' is not deproton+ ated and is coordinated to the metal ion, likewise in the solid state, In the spectra of I CuL" ] + in the non-aqueous solvents, the band is observed at -- 570 nm, which is ~ 35 nm longer than that tbr ICu~HL 2) i z~ and corresponds to a squarepyramidal coordination geometry of the complex 124-26 }. Interestingly, the wavelength and molar absorption coefficient of the band tbr the complex of [Ca( HL 2) I ~+ in pure water are essentially the same as those of I CuL ~I ~ : the wavelengths of the bands for the former and the latter in water are -- 15 nm longer and 20 nm shorter, respectively, than those measured in the non-aqueous solvents, Furthermore, the value of pH measured in aqueous solution of ICu(HL:)I(CIO4),,0.5H~O (I,0× I0 ~'~ M) was ",3.0. The spectra of the two complexes in pure water were invariant with the addition of NaOH; the spectra were essentially the same as those obtained in 0.1-2.0 M NaOH aqueous solutions, Therefore, it is clear that the complex is deprotonated to produce [CuL~'I *, in which the resulting acetate group is coordinated to the metal ion, even in pure water. The shorter wavelength of the band for I CuL" ] + in aqueous solutions, compared with the non-aqueous solvents, may be related to

S,-G, Kanget al. I Inorganh'a OIhnh'a A('ta274 ¢i998124-31

29

Table 4 Electronic spectra and molarconductancedata " Complex

I Cu ( HL-" ) I ( CIO~ I.," O,SH:O

I CuL-"ICIO.~•5H.,O '

I NIL"( H,O ) i CIO.t

A.,,, I nm I ( e 1M - *c m *I l

.IM ({1 *cm-' mol ' )

535"

533 ( 120J • 535 (120) d 550 (152) 550 ( 1511 ¢ 530(1211 ' 568 h 568 (148) " 572 ( 1491 ') 550 ( 1501

135 • 295 J 450

104 204 153

520 112.51"

85"

503 111.5) ,I 330133 ) 'j 511719.(11.334 1301 537 ( 10.81 ", 339 1271 " 502 (9.7) ~, 331 (31]l v 496 (IO.6) h.3311130) '

205 " 255

In pure water at 20°C unless olherwise specilied, "Nujol mull. "In nitromethane, '*In acetonitrile, "in 2.0 M NaOH aqueous solulion. ' In 0,5 M HClO,aaqueous snluliou. In I,U M HCIOaaqueous solution. '~In 4.5 M HCIO~aqueous solution. ' The electronic spectra in 2.0 M NaOH and 0,5 M HCIO~are idenlical with those of ICu( l.lL-') I1CIO4~,,.0.SH:O tinder the same conditions, the coordination of the water molecule and/or strong interactions between the pembnt acetate group and water molecules.

3.5. Coordination geometr), change in solutimJs As

described

above,

tile

electronic

spectra

of

ICu(HL-') I ~~ or ICul:'] ' measured in basic aqueous solu° 3.4, Spevtra aud properties ,#'lNiL"tH,O)KTO~. SH,O The IR spectrum of the nickel(!1) complex shows ~,N-H of the coordinated secondary amino groups at 3230, 3250, and 3270 cm ~ '. The peaks corresponding to t,CO:- of the coordinated acetate pendant arm and v O - H of the coordinated water were observed at ~ 1610 and 3500 cm - ', respec. tively. The magnetic moment of the complex in the solid state is 2.82 P,t~ at 20°C, which is consistent with a d Kelectronic configuration in octahedral geometry. The electronic spectra ( Table 4) of the complex in various sol vents support the idea that the metal ion is in an octahedral environment. However, the spectra are affected by the nature of the solvent; the wavelength and molar absorption coefficient of the band in water are somewhat shorter and smaller, respectively, than those in nitromethane. The molar conductance of the complex measured in nitromethane is 85 [~~ * cm 2 t o o l - ' , indicative o f a I:l electrolyte. When the complex was dissolved in pure water, the molar conductance was 255 11-' cm-' mol~ ', which corresponds to a 1:2 electrolyte. Furthermore, the aqueous solution c,f the co;'nplex ( 1.0 × 10- ~ M ) was acidic ( pH ',,,5.0 ). it is likely that, in pure water, the complex exists as a mixture of [ N i L : ( H , O ) I + and [ N i L : ( O H ) I [ 101.

tions( I OH ] ~ 0. I-2.0 M) are essentially the same as thai in pure water. This indicates that the complex exists as the depromnaled form [ CuL ~} * under both conditions and Ihat the hydroxide ion is not involved in coordination even under basic conditions. However, the addition of strong acids such as HCIO,, to an aqueous solution of the copper(11) complex decreases the absorption at 550 nm ( Fig. 2 ). The spectrum obtained in 0.5 M HCIO4 solution is quite similar to that of

0.3 "' ~ i 0,2,

0.1 0.0 3O0

5O0

700 Wavelength I n m

Fi,-. 2. Electronic absorption spectra of I Cu{HL~)I(CIO4I~'0.SH.,O 1 2 . 1 x I 0 ~ M ) in aqueous solutions: [a) IHCIO41~-O.00 M: Ib) I ItCiO,)I =0.(15 M: (c) [ HCIO~ I --O In M: Id) [ HCIO4} --0.511M. The spectra measured in 2.0 M NuOH and 4.5 M HCIOj solutions are quile

similar to curves (a) and ( d ) respectively.

&.G. Ka~tg¢~aLI Inor&~inica Chimica Acta 274 ( i ~)8~ 24-3 i

30

ICu(HL-')i TM measured in Nujol mull, nilrometbane, or acetonitrile (see also Table 4). Interestingly, no further significant spectral change was observed in the solutions of > 0.5 M HCIO4; the spectrum in 0.5 M HCIO4 was essentially the same as that in 1.0-4.5 M HCIO4 solutions. This result supports the idea that in >0.5 M HCIO4 solutions the copper(il) complex exists as the protonated form ICu(HL2)] 2+. Moreover, it is also clear that the pendant acetic acid group of the complex is not removed from the coordination sphere even in 4.5 M HCIO4 solution. In < 0.5 M HCIO4 solution, the copper(ll) complex may exist as a mixture of [Cu( HL-' ) ] 2 + and [ CuL 2 ] ÷ ( Fig. 3). Fig. 4 shows that the addition of NaOH to the nickel(!!) complex I NiL-'(H:O)] " dissolved in pure water shifts the absorption band to longer wavelengths, On the other hand. the addition of perchloric acid to the solution shifts the band to ~orter wavelengths: the wavelength and molar absorption coefficient measured in 4.5 M HCIO4 are ~ o n e r "and larger. respectively, than tho~ in 1.0 M HCIO4 (see a l ~ Table 4). This result is different from that observed for the copper(!I) complex [ Cu(HL z) I ~'* or [ CuL-" I +, indicating that the pHdependent change in coordination geometry oftbe nickel(!i) complex in aqueous solutions is different from that of the copper(li) complex. The pH-dependent spectral change of the nickel(II) complex is quite similar to that observed tbr [NiL~(H~O)I + [10]. In basic solutions the coordinated water molecule of I N i L : ( H ; O ) ] * may be replaced by a hydroxide ion. whereas the acetate group of the nickel( II ) complex i~ protonated and the resulting acetic acid group is not directly involved in coordination in concentrated per+ chloric acid solutions [ 101,

OH •

Fig. 3, Structural¢¢~urva~{emen!of ICa{HL~~I"' in ~uc,us ~,olmiun~,,

0'i2

t

000

[}*00

-

_

4OO Fig-4, Ulec~mic ~ r ''~ in t~) 4,5 M HCI04, , ~ d (el 1,0M N~OII ~u~L~i,~,

J

--r----~

;----

6OO Wavelengtl~Inm ....~~f I NiL~(H~,O)ICIO~(~,5 x 10 ~M) ~0~, (~) pore w~le¢,id| 0 1 M N~OH,

3.6. Kinetic behavior

it has been reported that both the complex formation reaction of fully N-functionalized 14-membered tetraaza macrocycles such as ! ,4,8,1 l-tetrakis( 2-hydroxyethyl )- 1,4,8, I ltetraazacyclotetradecane with Cu 2 + and the dissociation of the resulting complex are much faster than those of the unsubstituted compound, i.e. cyclam. It was assumed that the functional pendant arms promote the reactions [ 27 ]. However, the di-N-functionalized macrocycle L 3 reacts with Cu -~+ ion more slowly than L ~ [ 19l. Furthermore, no apparent decom.nosition of the complex [CuL3] -~+ in concentrated strong acids such as HCIO4 was ob~rved for several hours [ 19 I. in order to investigate the effects of the acetic acid pendant arm on the complex formation reaction, we attempted to measure pseudo-first-order rate constants k for the complex formation of Cu: + with L * and HL 2 in sedium acetate buffer solutions (pH 5.7) at 25°C, Although the reaction rate is too fast to measure by the ordinary method, it could be observed that the reaction rate (approximate value k = 2.0 × 10--' s- m) for HL ~ is much slower than that for L ~ under the same conditions, This trend is rather similar to those reported for the diN-functionalized macrocycles L ~and H.~L"~19,191, confirming that the effects of the N-functional group on the complex formation for the partially N-functionalized macrocyclescontradict those observed for fully N-functionalized analogs. Unfortunately, the rate for the complex of Ni: ~ with L: under conditions similar to that for the copper( II ) complex could not be measured, because the absorption of the nickel(ll) complex in the visible region is weak and is obscured by the bands of the added nickel( !1 ) suit and/or butTer. Elecm)nic spectra of iCu(HL~)I : ' and INiL~I ' ( 1.0x 10= ~ M) in 0.5 M HCIO4 showed that less than 2~ of the complexes were decoml~sed in 10 h at 25~C, in aual~ o~y with the complexes of L* and L ~ I 19,20 I. This indic:ires that the dissociation rate is scarcely affected by the introduction of the functional group.

4. Conclusion The monooN°functionalized macrocycle HL ~ can be readily prepared in high yield by the one-step reaction of L* with bromoacetic acid. Two copper(II) complexes [ Cu( HL 2) 12. and [CuL ~I ~ can be obtained, whereas the only nickel( !1 ) complex isolated in the solid state is I NiLe'(H_,O) I ' . This work clearly shows that the carbonyl unit of the acetic acid group in [Cu( HL 2) 12 ,~ is coordinated to the metal ion in the solid state, in non-aqueous solvents such as nitromethane and acetonitrile, and in acidic aqueous solutions. However, the complex is deprotonated even in pure water to produce [CuL 2 i *, The pH-dependent coordination geometry change of the copper(il) complex is different from that of the nickel(it) complex, The N-functionalization of L' to give HL 2 reduces the formation rate of the copper(!!) complex.

S,-G, Kang et .1,/Inor,~oni('a Chmmi(~ Acta 274 ¢1998124-31

Acknowledgements This work was supported by the Basic Science Research Program (BSRI-96-3403 and BSRI-96-3429) administered by the Ministry of Education, Republic of Korea. The authors also wish to thank the Center for Molecular Science, Korea Advanced Institute of Science and Technology for X-ray data collection.

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