E L S E V I E R Inorganica Chimica Acta 282 (1998) 42-49

Lanthanide(III) complexes of two oxaazadiamine macrocyclic ligands derived from 2,6-diformylpyridine: the crystal structures of

a reduced macrocyclic ligand and the corresponding diprotonated macrocycle

Laura Valencia ", Rufina Bastida "*, Andres de Bias b, David E. Fenton ~, Alejandro Mac~as a Adolfo Rodr~guez a, Teresa Rodriguez-Blas b Alfonso Castifieiras ~'

• ' Departamento de Qm'mica im~rgdnic~a. Unit'er.~idad de Sautiugo. Avenida de las Ciencias Jn. 157th5 Sunttu.~o de Compo.~'tefa. Spuin "Departamenu, tie Qm'mtca Ftmdamet~tal c bt&lxtrial. Universidad de Lu Coru~a. Campus th' la Zapateini s/n. 15071 l.u C,,rmiu, Spain

• Department t!t'(?hemistry. The Univer.~io'. $3 7HFSheffieht. UK

Received 5 January 1998; receixed in revised fi~ml 3 March 1998: accepted 25 Starch 1998

Abstract

New macrocyclic lanthanide( ill ) complexes were obtained with two oxaazadiamine macrocycles derived from 2.6-diformylpyridine: ( i I mononuclear complexes of an I 8-membered sexidentate N ~O~ macrocycle ( L a ) derived from 1.5-bis( 2-aminophenoxy )-3-oxapentane; ~ ii ) mononuclear complexes of a 16-membered pentadentate N ,O: macrocycle (L-') derived from 1.3-bis(2-aminophenoxy) propane. The com- plexes were characterized by elemental analysis, molar conductivity, mass spectrometry. IR and ~H NMR spectroscopy, thermogravimetry and magnetic measurements. The crystal structures of the L-" macrocycle and the corresponding diprotonated ligand are also reported. © 1998 Elsevier Science S.A. All rights rese~.ed.

IG, vword.~: Lanthanide complexes: Oxaazadiamine complexes: Crystal structt|re~.

1. I n t r o d u c t i o n

The stability of metal complexes with polydentate ligands depends on a range of factors such as the number and type of donor atoms present and their relative positions within the ligand, the itature o f the ligand backbone, and the number and size of the chelate rings formed on complexation, if the ligand is a macrocycle, then the ring size ~s a further factor that will influence complex stability. Ccmsequently. macro- cyclic iigand~ provide an excellent basis for the study of molecular recognition phenomena since their cavity size, shape, and components can be varied readily [ 1 I.

Within the area of macrocyclic chemistry, we are interested in the synthesis and characterization of ianthanide( !11 ) com- plexes with mixed N,O, donor-atom macrocycles containing aromatic, head and lateral units [ 2-51. Most efforts to date have focused on the use of Schiff-base macrocycles or tetra- azapolyamine macrocycles as complexing agents for transi-

* Corresponding author. Fax: 34-81-597 525.

lion metal ions or for lanthanide( III ) ions. In contrast, little has been reported on lanthanide complexes with oxaazapoly- amine macrocycles [ 6 -10 ] .

In previous papers we have reported the template synthesis of |anthanide( Ill ) complexes with related Schiff-base macro- cycles containing pyridine [2,3,5] or furan [4l head units. As an extension of this work, we have investigated the reac- tions between hydrated lanthanide nitrates or perchlorates and the 18-membered oxaazadiamine macrocycle L' , containing an N~O~-donor set, derived from 2,6-diformylpyridine and 1,5-bis( 2-aminophenoxy)-3-oxz 9entane, and the ! 6-mem- bered oxaazadiamine macrocycle L-', containing an N,O_,-donor set, derived from 2,6-diformylpyridine and 1,3- bis( 2-aminophenoxy ) propane. Ligands o f this type provide a series of compounds o f intermediate rigidity. The selective complexation and transport of metal ions may be facilitated by macrocyclic iigands of intermediate rigidity (that is, suf- ficient rigidity to present a donor set with a defined geometry to a metal ion. but flexible enough to encourage favourable kinetics of metal ion incorporation and release ).

0020-169319815 - ~ee front matter ,,~.~ 1998 Elsevier Science S.A, All rights reserved. PII S0020-1693(98 ~00186-8

.I¢_ L t k d e n c i u t't ul./Im,rgunica C h i m U , A c t a ~ ~ t ! 9 9 1 ¢ / 4 2 - - 4 9 43

v ~O O" v t.vo..P

L I L 2

The object of this work aimed at evaluating how modifi- cations introduced in these ligands led to increased ligand flexibility and how changes in the aliphatic bridge length could affect the coordination capacity towards lanthanide ions.

2. Exper, mental

2.3. Preparations

2.3.1. Synthesis o f the diamine macroc3"cles L I and L'- The metal-free reduced macrocycles were synthesized by

a modification of previously reported procedures I 15 l- They were prepared directly f rom an "in situ" reduction in metha- nol. with excess o f sodium tetrahydroborate, o f the corre- sponding metal di imine complexes , the lead( II ) perchlorate for L t. o r the manganese( ii ) perchlorate for L-'. The reaction solutions were refluxed for 1 h, then they were al lowed to reach room temperature, and filtered. The products obtained were stirred with dichloromethane under reflux, filtered while hot, and the solutions concentrated to dryness to give the crude products, which were recrystallized from acetonitrile.

L ' . Yield 54%. Anal. Found: C, 65.6; H, 6.3; N, 9.8%. Calc. for C_,~H_,~N~O~- ! ,75H20: C. 65.3; H. 6.3: N, 9.9,%. Mass spectral parent peak (FAB) nd:: 392. IR (KBr disc 9: ~'(HzO) 3537 cm ': v( NH ) 3410 and 3288 cm " ~. t H NMR ( DMSO-d , ) I see Table I ).

2. !. Meusuremen£v

Elemental analyses were carried out on a Fisons Instrument EA1108 CHNS-O elemental analyser. The IR spectra were recorded as KBr discs, using a Mattson Cygnus 100 spectro- photometer . Fast a tom bombardment mass spectra were recorded on a Kratos MS50TC mass spectrometer. The matrix used was 3-nitrobenzyl alcohol. Melting points of the [ L n L I [ N O s l ~ complexes were determined using a Biichi capillary melt ing points apparatus.

Magnetic measurements were determined at room temper- ature on a vibration sample magne tomete r ( V S M ) Digital Measurement Sys tem 1660 with a magnet ic field of 5000 G. Conduct ivi ty measurements were carried out in 1 0 - ' mol dm ~ d imethyl formamide or acetonitrile solutions at 20°C using a W T W LF3 conductimeter . Thermograms were obtained with a Shimadzu TGA-50 thermogravimetr ic sys- tem under normal conditions, and with a Setaram T G A 92-16.18 (heat ing rate 5 K min ~; a tmosphere He, 6t) cm ~ m i n ~ ) . 'H NMR spectra were recorded on a Bruker WM-300 spectrometer.

2. 2. Chemicals and starting materials

2,6-Diformylpyridine was prepared according to the liter- ature method [ 11,121. The diamines 1,5-bis(2-aminophen- oxy)-3-oxapentane and 1 ,3-bis(2-aminophenoxy) propane were prepared by reduction of the corresponding dinitro pre- cursor using a procedure similar to that described previously [ 13,141.

Lan than ide( l l i ) nitrates and perchlorates were commer- cial products from Alfa and Aldrich laboratories and were used without further purification. Solvents used were o f rea- gent grade and were purified by usual methods.

Caution! Perchlorates are potentially explosive.

Table I 'H NMR spectra o f L' and I L a L ' I [ C t O ~ I ,-6H.,O in DMSO-d~. L: and [ LaL-" I [ CIO~ I ~ 3H.O in CD ,CN. and [ L-" H_, ] I CIO~ i., in DMSO-d~

Assignment ,5 ( p p m | lnlegration 6 f p p m ) Multiplicity

L: [ L a L : | [ C I O . i ~- 6H_,O

Ha 7.711 t~ IH 7.831t) 1H Hb 7.39( d ~ 2H 7 .47(d) 2H Hc 4.36c d ) 4H 4.39t s ~ 4H Hd 5.42( t ~ 2H Aromatics 6.85--6.50c m~ 8H 6.84--6.57t m) 8H He 4 .11I ra ) 4H 4 .101ml 4H HI 3.851 m ) 4H 3.851 m) 4H

L-" [ LaL: t [CIO, I ,- 3 H : O

Ha 7.781t) | H 8 . 4 t ( t l IH Hb 7.34( d ) 2H 7 .84(d) 2H Hc 4.50( db 4H 4 .78(s ) 4H Hd 5.95( t ~ 2H Aromat ics 6.65--.6.951m~ gH 6.64--7.13t m) 8H He -1.281 t i 4H 4.40( t ~ 4H Hf 2.451 q j 2H 2.38 ( q ) 2H

[ L:H., ] [ CIO,] :

Ha 8.221t) IH Hb 7.80q d | 2H Hc 4.78( t ) 4H Hd 8.291 t ) 4H Aromatics 7 . 7 5 - 7 . 0 5 ( m ) 8H He 4.421 t ) 4H Hf 2.471q ) 2H

s: singlet, d: doublet, t: triplet, q; quintuplet, m: muhiplet .

Hal

~ z J

.] L, !

44 L. Valencia et el./Inorganica Chimica Acta 282 (1998) 42--49

L -~. Yield 32%.Ana l . Found: C, 73.5; H, 6.4; N, 11.8. Calc. for C,__,H,.~N,Oz: C, 73. ! ; H, 6.4; N, ! 1.6%. Mass spectral parent peak ( F A B ) nff:.: 362. IR ( K B r disc) : u ( N H ) 3389 c m - t. I H N M R (CD~CN) (see Table 1).

2.3.2. General me thod f o r the ~ 'nthesis o f lanthanide( l l l ) complexes

A methanol solution { 10 cm ~) of L n X 3 - n H 2 0 (0.50 mmol ) ( X ffi NO.~ - or CIO4 - ) was added slowly to a warm stirred acetonitri le solution (50 cm ~) o f the ligand (0.50 m m o l ) . The re:.ultant solution was refluxed for about 4 h, filtered while hot and concentra ted to -- ! 0 cm ~. Then diethyl ether was added to precipitate the complex. When the com- plex did not precipitate, it was necessary to evaporate the solvent and to add diethyl ether to the resulting oil. The product was filtered off, washed with methanol :diethyl ether ( I:! 0) and dried under vacuum. The complexes appear to be air stable, soluble in acetonitrile, d imethyl sulfoxide, d ime- thy l formamide and acetone, modera te ly soluble in methanol , ~thanol and dichloromethane, and insoluble in water, diethyl ether and carbon tetrachloride. All at tempts to prepare com- plexes o f L -~ with lanthanide(I I I ) nitrates were unsuccessful .

ILnLt l (CIO4)~-xHaO. IR {KBr disc) : u ( C = C ) and u(C----N) 1450, 1600, 1 6 2 6 c m - ~ ; u(CIO.s- ) 626,636, 1087. I 118, 1143 c m - '; v(H_~O) 3400 c m - ~. Mass spectra (posi- t ive-ion FAB) : observed peaks for J LnL' ( CIO.~ ) _, 1 ' and [ LnL I ( CIO4 ) l +

[LnLtI(NO~).~-xH_~O. IR ( K B r disc) : v ( C = C ) and i , ( C = N ) 1450, 1600, 1 6 2 6 c m -~; ~,(NO~ ) 742, 815, 1035,

Table 2 Crystal data and structure refinement for L-" and L"Hd CIO~ I_-

1325, 1384, 1500 cm - ~; v(H_,O) 3400 c m - ~. Mass spectra (posi t ive-ion FAB) : observed peaks for [LnL'(NO~)_~I + and [LnL~(NO~) 1 +

[LnL21(CIO4).,.xH_~O. IR ( K B r disc): u ( C = C ) and v ( C = N ) 1450, 1602, 1 6 2 0 c m - i ; v (CIOa- ) 626,636, 1087, 1120, ! 143 c m - ~; v(H_~O) 3400 cm - '. Mass spectra (posi- tive-ion FAB) : observed peaks for [LnL-'(CIO.~)_,] + and [ LnL:( CIO.; ) ] +

2.4. Cr3,stai structure data and determinat ion

Crystal data and exper imental condit ions for L ~- and L-'H: [CIOa ] : are listed in Table 2. The molecular structures are illustrated in Figs. 1 and 2. Selected bond lengths and angles, with standard deviat ions in parentheses, are presented in Tables 3 and 4.

A colourless prismati-: crystal of C_,,H_, ~N ~O., and a yel low prismatic crystal o f [ C:aH2~N~O a ! I CIO~ ] _, were mounted on a glass fibre and used for data collection. Cell constants and an orientation matrix for data collection were obtained by least-squares ref inement o f the diffraction data from 18 and 25 r e fec t ions in the range 9 0 < 0 < 4 3 ° and 5 ° < 0 < 19 ° respect ively in an Enraf-Nonius MACH3 automatic diffrac- tometer [ 16]. Data were collected at 293 K, using the to-2# scan technique for L-" and the to scan technique for LZH,[C104]> and corrected for Lorentz and polarization effects [17] . An empirical absorption correct ion was also made [ 18 ].

Empincal formula C : :H,. ,N ,0: C :,H.,,CI :N ,0,,, Formula weight 361.43 562.35 Temperature (K) 293(2) 293(2) Wavelength (/~ ) 1 54184 0.71073 Crystal system orthorhombic triclinic Space group Pnma P- I Unit cell dimensions

a ( A 1 21.467(2) 8.476( 2 ) b (A) 15.0445(5) 10.824(9) c CA) 5.8033(4) 14.149110) a (°1 80.82(7)

(01 81.23(3)

Y (°) 81.30(3) Volume ( ,/k'l 1874.2(2) 1255.8( 14 ) Z 4 2 Density (calc. ) ( Mg m ' ) ! .281 1.487 Absorption coefficient (mm ' ) 0.666 0.320 F(000) 768 584 Crystal size (ram) 0.40×0.10×0.10 0.35 ×0.15 ×0.15 0 Range for data collection (°) 4.12 to 64.94 3.70 to 22.82 lndexranges - 2 5 < h < 0 . 0 ~ k < 1 7 . - 6 < / ~ 0 - 9 < h < 0 , - I I < k _ < l l . -15_<1<15 Reflections collected ! 652 3653 Independent reflections 1652 3381 ( R,n, = 0.1438) Data. parameters 1652, 177 3381, 305 Goodness-of-fit on F: 0.978 0.965 Final R indices (!> 2o'(1) ) R, =0.0486, wR, =0.1039 R, = 0.0738, wR_, =0.1014 Extinction coefficient 0.0004(2) 0.0008 (7) Largest difference peak, hole ( e A ') 0.157, - 0. ! 33 0.373. - 0.362

L Valencia et a L / lnorgan ica Ch imica Ac ta 282 ¢ 1998.) 4 2 - 4 9 45

Tr A _L,:

-~ I W ct°

Fig_ I- Cry~tal smacturc of L: showing the atom labelling.

C 4

'--~... ~<~--J" "~'~'%r-~ ~.~ "© ~ - ? .,

\\ ~ ~ C23

22 22

Table 3 Selected bond lengths ( A ) and angles (~) for L"

O - C ( 7 ) ! .373(4) O - C ( 1 2 ) 1.428(5) N( I )--C(2) 1.329(4) N( 2 )==C( 61 1.37215 ) N121=-C(51 1.462(51 C( 2 )-=C( 3 ) 1.388(6) C( 21-C( 51 1.499(5 ) C( 3 )-C141 1.373161 C ( 6 ) - C ( I 1 ) 1.391(6) C(6) - -C(7 ) 1.410(5) C( 7 l - C ( 8 ) 1.372461 C181-C191 1,381171 C ( 9 ) - C ( 101 1.364( 71 C( 10)-C( t I ) 1.387f61 C( 121--C( 131 1.500161

C(71-O. .C( 121 i I6.7141 C( 21'-N( I )=-C( 2 ) 118.215 ) C461-N121-C(51 120.114) N( I ) - C 1 2 1 - C ( 3 ) 123.0151 N( I )-.C( 21-C(51 117.7(4) C( 31-C( 21-C( 5 ) 119.3(51 C ( 4 ) - C ( 3 ) - C ( 2 ) ! 17.8161 NI 2 )-C(51--C( 2 ) 110.6(4) N( 2 ) - C ( 6 ) - C ( I I ) 123.6(5) N( 2 )--C(6 )-C( 7 ) 119.2(4) C( I I ) -C( 6 ) - C ( 7 ) 117.215) C( 8 ) - - C ( 7 ) - 0 125.8(51 C( 8)-(?( 7 )--C(6) 120.715) O-C(71-C161 113.6141 C( 7 )-.CI g)-C'( 9 ) 120.616) C( I01--C(9)-C181 120.2(61 C191--C( tO)--C( 11 ) 119.715) C( tO)--C( I I 1--C, 61 121.7151 O-=C( 121-=C( 131 109.415) C( 12 ) ' -C( 13) -C(12) 118.9(7)

Symmetry transformations used to generate equivalent atoms: ( i t x, - y + I /2 . z.

0=9

26

(b) Fig. 2. Two different views of L:H: [ CIO4 ] _. showing the atom labelling.

The structures were solved by direct methods [ 19 ] which revealed the position o f all non-hydrogen atoms, and refined on F-" by a full-matrix least-squares procedure using aniso- tropic displacement parameters for all non-hydrogen atoms [201. The hydrogen atoms were located on a difference

Table 4 Selected bond lengths ( A ) and angles (°) for L:H: [ CIO= ! ".

O( 151=-C(14) 1.37121 O( 15)--.C( 161 1.4211 ) O( 19)--C(20) 1.37(2) O( 19) -C(18) ! .42(2) N( I )--=C(61 1.33121 N( i ) - C 1 2 ) 1.36121 N181--C(9) 1.47(2) N( 8)--C(7) !.51( I ) N( 261 =-C(25) 1.4612) N ( 2 6 ) - C ( 2 7 ) 1.50{ I ) C(2')=.C(3) 1.37121 C( 2 )-=C(27) 1.48( 21 C ( 3 ) - C 1 4 ) 1.38(2) C( 41-=C151 1.4212) C(5) - -C(6) 1.34(2) C(61--C(71 1.51(21 C(0)-- .C(I0) 1.3312) C(9)-=C(14) 1.39(2) C( 10)-C( 11 ) 1.39(2) C( I I ) -C( 121 1.40121

(¢on t imtcd)

• .16 L. Vtde,r'ia et aL /lnrwganica Chimira Acta 282 (i 998J 42--49

Table 4 I continued )

C( 121-C( 131 C( 131~_'( 141 C( 161-C1171 C( 171--171181 C( 2111-C1251 C( 2(I)424 21 ) C(211-C(22) C( 22 )--('( 23 ) C(23 ]-C(24) C~ 24 ~-C( 25 I

C1141-O( 15 I--C1161 C ( 2 0 ) - O l 19)-Cc lg) C{6~-N( I p--CI 2) C( 9 ~-N( 8 I -C( 7 ) C( 25 )-N( 261-C( 27 Nt I )-CI 2 I--C( 3 ) N( I )--Ct 2 ~--C( 271 C13 ~--C(2)-Ct 27~ C~ 2 )-C( 3 )-C14 ~ C131--C141-C15~ C(6 ~-C~ 5 )--(_'( 4 , Nt I ~-C(61--C151 N( I 1-('(61---C(7 ) C~ 5 ~-C.( 61-C( 7 ) NIg)-CI 7 ~--C(6I C( I O ) - C I q ) - C ( 14 ) C(101-C(9)-N(8) C(14)-C19l-N!8) C(9)--Ct I O ) - C ( I I ) CI IO)--C( I I ) -C(12) C( 131-C( 1 2 ) - C ( I i ) C( I4)-C( 13)-Ct 12) O( 15~-C(141--CI9) O( 15)-C1 14,-C1131 C(91--C1141-C( 13 ) Ol 15)--C( 16~-C( 171 C( 161-C( 171--C(IS) O( 191-C( 18)-.C117~ C(25 ~-C. ( 20 ~-0(It)) Ct 25 v-C(2() ~--Ct 21 O1191-C( 201-C~ 2t ) C[ 22)-C~ 21 ~-C( 20~ C121 ~-Ct 221-C(23) CI 22 )-C( 23 I-C(24) C(25 ~-C~ 241-C(23) C( 24 )-C( 25 I-C( 20 C124 i--C( 25 )-N~ 261 C~ 20 )--C( 25 )-N( 26 ) C( 2 )-C( 27 )-N(26)

1.40( 2 1.4(R 2 ) 1 .47(2) 1.51121 1.3712 ) 1.38t 2 ) 1.36t21 1.36121 1.43121 1.34121

118f I 11611 118(2 113( i 11541 t21t I !!511 12312 11912 11912 11712 12512 1t5(2 12112 1091 I 12412 12312 11412 120( 2 11912) 121(2) 11912b 1!9(2~ 124(21 118(21 109( 1 ) 1 t 9 ( 2 ) |091 I ) 115(2) 1t8(2) 127q2) 12112b 122(29 119121 11712) t24121 i 19121 117~21 1(}7.3(8~

Fourier map and refined (so(topically ( w = I / Is"(F, , 2) + ( 0 . 0 5 1 3 P ) 2 + 0.0()00Pi where P = ( F,'- + 2F,-" ) / 3 ) for L: , and were located in their calculated posi t ions ( C - H 0 . 9 3 - 11.97 A,, N - H 0.90 A) and refined using a riding model for L2H_, [ CIO.~] _,. A secondary extinction correct ion was only applied for L" [ 20 !- After all shif t /e .s .d, natios were less than 0.001. the refinement converged to the agreement factors listed in Table 2.

For both structures, atomic scattering factors were taken from the International Tables for X-ray Crysta l lography

[211. Molecular graphics were from Z O R T E P and S C H A K A L [ 22] .

3 . R e s u l t s a n d d i s c u s s i o n

3. I. I_xmthanide( l l l ) complexe.~

In a previous paper, Fenton and coworkers [ t5] reported the synthesis and characterization of mononuclear C u ( l l ) nitrate complexes with the L ~ and L-" macrocycles . W e inves- tigated the above reaction using the less s tereochemical ly demanding Ln( I I I ) cations in order to make a compar ison be tween the potential coordinat ion behaviour of the reduced macrocycl ic ligands and their Schiff-base macrocycl ic pre- cursors and to analyse whether the modificat ion o f the number of donor atoms, the change in the aliphatic bridge length, and the reduction of the (mine groups could affect the synthesis and stability of the complexes .

W e have found that the reactions be tween L t and hydrated lanthanide nitrates or perchlorates in molar ratio 1:1. as descr ibed in Section 2, gave, in general, good yields of analytically pure products [ LnL' 1 [ C I O ~ ] , - x H 2 0 ( Ln = La, Ce, Pr, Nd, Eu, Gd, Tb, Ho or Er) and [Lnl,I1 - [ NO~ 1~" xH_,O - vEt ,O ( Ln = La, Ce, Pr, Nd, Eu, Gd, Tb, Dy, Ho, Er or Lu) . The complexes I LnL-'I ! CIO, ] ~.xH_,O ( Ln = La, Ce, Pr, Sm, Eu, Gd, Ho or Er) were obtained by reaction of L 2 with hydrated lanthanide perchlorates but we were unable to obtain complexes in the react ions at tempted with L'- and the Ln ( ! ! I ) nitrates where in all cases the free macrocycle and unreacted metal salts separate out from the reaction med ium on cool ing to room temperature.

The complexes were characterized by elemental analysis (C. N, H ) , molar conduct ivi ty , magnet ic moment measure- ments, thermal analyses ( nitrate complexes ) , mass spectrom- etry, IR spect roscopy, and 'H N M R spec t roscopy for the diamagnet ic lanthanum complexes . W e did not perform ther- mal analysis o f the perchlorate complexes because o f the explos ive behaviour shown in earlier work { 21.

The analytical data and yields o f the reactions are presented in Table 5. Compar i son o f these results with those obtained for the related diimine macrocyc les containing pyridine [ 2,3 ! indicates that reduction o f the (mine groups increases the ligand flexibility, leading to an enhancement o f the complex- at(on capaci ty of both reduced systems, This effect is espe- cially important at the end o f the lanthanide series, with the smaller lanthanide cations, where flexibility o f the ligand is necessary in order to al low the full set o f donor atoms from the macrocyc le to approach the metal ions,

The results also show that the ligand der ived from 1,5- b i s (2 -aminophenoxy) -3 -oxapen tane and containing a pyri- dine head unit provides a l igand f ramework capable o f forming more stable lanthanide(I i i ) complexes than when the furan head unit is used. In earlier work we were unable to synthesize lanthanide complexes o f the furan-containing analogue o f L j 141.

L. Valencia et al. /lnvrgt~nica Chim& a Actu 282 ~ 199b~j 42-49 47

Table 5 Analytical data, yields and molar conductance data (in DMF ()r CH,CN) for the comptexe~ ILnL ' I ICIO,1 , -~H:O. [LnLtI[NO.I , .xH:O "and I LnL-'I ! CIO4 l~ 'xH-O

x Analysis ( % ) ' Yield .l~t

C N H (C-) ( [ ! ~cm-'mol *)

ILnL' I [CIO, I , ..tH.,O 1_41 6 Ce 5 Pr 5 Nd 7 Eu 2 Gd 12 Th IO Fh) 12 Er 12

[ l - n L t 11 N O , l , ' xH,O La 5 Ce el. I, Nd h Eu 5 Gd 0.5 Tb Dy 3 Ho 3 Et )" Lu 5

[ LnL: l I CIO, l ," .d-I ~O La 3 Ce Pr 3 Sm Eu 4 Gd 7 Ht) 4 Er 5

29.2 129.41 4.6 (4.5) 4.11 (3.9) 53 419.9" 28.8 (28.81 4.4 14.41 3.2 13.61 79 392.1 29.9 (29.9) 4.5 14.5 ) "~.4 l 3.8 ) 88 373.8 28.7 ! 28.7) 4_5 (4.7) 3.4 (4.O) 711 388.9 31.9 { 31.41 4_4 (4.51 3.2 ( 3.31 68 415.2 25.5 ! 259) 3.8 (3.6) 3.6 (4.6) 65 457.6 26.4 ( 26.8 ) 4+0 ( 4.4 ) 3.5 ( 4 3 ) 76 485.3 25.4 t 25.8) 3.8 (3.7) 3.8 (4.5} 59 518,1 25.5 ( 25.7 ) 3.8 ( 3.8 ) 3.8 ( 4.5 ) 68 490.6

36.6 136.71 l i d ( I1.1 ) 3.7 {3.81 66 133.14 't 30. I ( 38.5 ) 12.3 ( I 1.7 ) 3.1 ( 3.4 ) 60 152.9 40_6 1411.21 8-g t £).71 4.5 (5.1) 17 169.5 30.2 139.51 10.6 (II .O) 4.0 (3.9) 16 183.7 33.3 {33.7) I I.I ( 10.21 3.5 {4.2; 81 170.4 36.9 ( 37.1 ) 116 I I 1.31 3.4 13.4) 5f) 172.0 36.7 ( 37.5 ) I i.O { I 1.4 ) 3.4 ( 3.41 78 ! 34.9 34.6 (34.8) 10.6 ( IO.61 3.4 (3.9) 61 156.0 34.7 134.6~ I 12 ( 10.51 3.8 1391 54 145.4 41.5 (40.7) t,)_8 ( 9 8 ) 3.5 14.71 13 113.1 3t.6132.71 11t.4 10.9) 4.1 (4.11 42 168.4

31).g t 30.91 5.2 (4.91 4.3 (3.4) 70 380.5" 329 ( 33.111 5.5 (5.2) 3.2 (2.~) 31 371.8 3O2 t 3O3) ) 5. l ( 4.9 ) 4.(1 ( 3.3 ) 62 420.3 33.1 132.61 5.5 {521 3.8 (2.81 54 364.5 2g.2 { 29.9 ) 4.9 ( 4.7 ) 3.5 ( 3.5 ) 59 412.4 27.7 ( 28.0 ) 4.5 { 4.4) 3.5 ( 3.9 ) 82 390.9 32.5 ~ 32.111 5.5 15.1 ) 3.8 12.81 63 416.2 28.7 '28+81 4.6 (4.6) 3.5 13.6t 73 413.5

-' Calculated values in parentheses. h With y Et:O molecules: 1.5 t Pr): 0 5 ( Nd ): i.5 (Er). " !0 ~ M in ace{on{{rile. '1 I0 ' M in dimethyl|'~lrmamide.

3.2. M a g n e t i c m e a s u r e m e n t s

T h e v a l u e s o f t he m a g n e t i c m o m e n t s o f t he [ L n L ' 1-

[ C I O 4 1 ~ c o m p l e x e s ( L n ~ Ce, Dr, Eu , G d , T b , H o a n d Er ;

tz,.( B M ) = 2 . 7 0 , 2 . 9 8 , 2 . 9 0 , 7 . 2 4 , 9 . 0 2 , 9 . 9 7 , 8 . 0 3 ) s h o w l i t t le

d e v i a t i o n f r o m the t h e o r e t i c a l v a l u e s f o r t r i p o s i t i v e l a n t h a n i d e

i o n s 1231 a n d t h o s e r e p o r t e d in t he l i t e r a tu r e 1 2 4 , 2 5 1 , s u g -

g e s t i n g tha t t he 4 f e l e c t r o n s d o no t p a r t i c i p a t e in b o n d f o r -

m a t { o n in t h e s e c o m p l e x e s .

3.3, M o k i r conduc t i v i t i e s

T h e m o l a r c o n d u c t a n c e v a l u e s f o r t he p e r c h l o r a t e c o m -

p l e x e s o f L ' a n d L 2, m e a s u r e d in a c e t o n i t r i l e a t 25°(2 ( T a b l e

5 ) , l ie in t he r a n g e r e p o r t e d f o r 3: ! a n d 2:1 e l e c t r o l y t e s r e s p e c -

t i v e l y , T h i s s u g g e s t s t h a t in t he l a t t e r c o m p l e x e s , d e r i v e d f r o m t h e s m a l l e r N aO , d o n o r set , a d d i t i o n a l c o o r d i n a t i o n o c c u r s

v i a a p e r c h l o r a t e a n i o n . F o r t he n i t r a t e c o m p l e x e s t he v a l u e s ,

m e a s u r e d in d i m e t h y l f o r r n a m i d e , a r e in t h e r a n g e c h m a c t e r -

is{i t o f 2: I e l e c t r o l y t e s in th i s s o l v e n t , i n d i c a t i n g the w e a k e r

c o o r d i n a t i o n c a p a c i t y o f t h e p e r c h l o r a t e a n i o n [ 2 6 1 -

3.4. T h e r m o g r a v i m e t r i c a n a l y s i s

T h e r r n o g r a v i m e t r i c a n a l y s e s s h o w t h a t t he [ L n L ) ] [ N O ~ ] s

c o m p l e x e s p r o d u c e s i m i l a r t h e r m o g r a m s , a s a r e s u l t o f t h e i r

s i m i l a r s t r u c t u r e s . T h e T G A c u r v e s h a v e s t a g e s u p t o 2 0 0 ° C

w h i c h s h o w t h e y c o n t a i n s o l v e n t m o l e c u l e s , in a g r e e m e n t

w i t h t he f o r m u l a e p r o p o s e d f r o m t h e a n a l y t i c a l d a t a . O n l y

w i t h L n = N d , E u , G d o r H o axe t h e r e c l e a r l y d e f i n e d m e l t i n g

p o i n t s . T h e o t h e r c o m p l e x e s b e g i n t o d e c o m p o s e in t h e t e m -

p e r a t u r e r a n g e 1 8 0 - - 2 4 0 ° C ; th i s is l o w e r t h a n t h e t e m p e r a t u r e

r a n g e o b s e r v e d f o r t he r e l a t e d c o m p l e x e s o f t h e d i i m i n e

m a c r o c y c l e ( 3 5 9 - 3 9 2 ° C ) [ 21 .

48 L. Valencia et aL / h~organica Chimica A,'ta 282 t 1998) 42--40

3.5. l A B mass spectra o f the complexes

The FAB mass spectral data confirm the formation of the [ LnL! X, complexes. In all cases, peaks assignable to metal- containing fragments [LnL(CIO4)_,| ' , [LnL(CIO4) ] +, [ LnL( NO~)_, ! ~ and [ LnL( NO, ) 1 ' are present. Also, these fragments lose the metal ions to give the most intense peaks corresponding to the protonated ligand (m/z = 392 for L' or 362 for L"). Peaks also appear for the nitrate complexes with L n = L a , Eu, Gd and Er, and for the Cel llI) perchlorate complex, which cc~rrespond to [LnL~I ' and [CeL~'l ' respectively.

3.6. IR spectra

The 1R spectra of the L' and L z ligands exhibit, in both cases, t , (N-H) vibrations in the 3320-3425 c m i region. The spectrum of the L ~ macrocycle shows a splitting of this vibration which most probably reflects different hydrogen- bonding patterns for each of the secondary amine groups.

In the IR spectra of the complexes, the secondary amine stretches are unassignable because there is an intense broad band centred at -,- 3400 cm J consistent with the presence of water as suggested from the microanalyticai data. The water present in the complexes can arise from either lattice and/or coordinated water.

The bands at about 1600 and 1450 cm ~ are associated with ~,( C = N ) and v ( C = C ) vibrations from the pyridine ring which undergo a shift towards high frequencies on complex- ation, suggesting interaction between the metal and the pyr- idine nitrogen atom [ 27 ].

The perchlorate assignments were made by comparison with literature values [28.29]. The splitting of the bands attributable to the asymmetric CI-O stretching mode at -.- ! 100 cm - ~ ( t,~ ) and the asymmetric CI-O bending mode (t,~) at ",- 620 cm ~ suggests coordination of at least one of the C104- anions, as is also suggested by the conductance measurements. The higher-energy band consists of three maxima at ~ 1140. 1120 and 1080 c m t: a similar splitting of the ~,~ band has been observed for lanthanide(l l l ) com- plexescontaining bidentate chelating CIO4 [30].

Although assignment of the nitrate vibrations in the IR spectra of the { LnLI ] [ NO x ], complexes is more difficult, some information concerning the bonding mode of the nitrate ions can be obtained. In principle, ionic NO~ has three IR- active vibrational modes at 1390, 830 and 720 c m - '; upon coordination of the anion the vibrations of higher and lower energies are split into two components and the fourth vibra- tional mode becomes IR allowed, so that six IR absorptions should be observed, v.~ and v~ at 710, 740 c m - 0 ~,~, at 820 c m J. ~ a t 1030cm ~, ~,.~ and v~ at 1300, 1500cm-~ [311. The presence of several bands in the region associated with nitrate vibrations clearly identifies these species as containing coordinate nitrate groups [ 32]. In the spectra of all of the nitrate-containing complexes, the two most intense nitrate absorptions, associated with the v ( N = O ) and v~(NO_.),

appear at ~ 1500 and 1300 c m - t. The distinction between monodentate and bidentate nitrate groups is quite difficult, but the separation (A z,) of the two highest frequency bands has been used as a criterion to distinguish between the degree of covalence of the nitrate ,,,,ordination [33 ]. The magnitude of this separation of ~ 180 cm : may be indicative of a bidentate interaction of the nitrate anions with the lanthanide ions [34]. The appearance of an intense spectral band at ,-, 1380 cm I indicates the presence of some ionic nitrate

group [ 35.36 ].

3. Z N M R spectra o f the La( i l I ) complexes

The ~H NMR spectrum of the diamagnetic [ LaL' ] [ CIO~ ], complex was recorded immediately after its dissolution in (CD~)_,SO and shows the expected signals (Table I ); the spectrum shows no meaningful change with time. On com- parison with the spectrum of the free ligand, it can he seen that the signal assigned to the hydrogens of the amino groups does not appear, and that of the ¢t-CH: group to the amine is a singlet. The signals have almost the same position as in the free iigand, except for those of the pyridine hydrogen atoms which have been shifted downfield slightly. This behaviour contrasts with that observed for the corresponding Schiffbase ligand, which in the same solvent releases the metal ion slowly [2] . indicating that the increase in flexibility of the ligand leads to a more stable complex in the medium used.

The 'H NMR spectra of the [LaL ~ ] [NO~ ], complex were recorded immediately after dissolution in (CD~),SO and CD~CN. The spectra were complex and show many signals, suggesting competition between the solvent and the ligand for the lanthanum. This could result in removal of the metal from the macrocycle, behaviour which we have observed already in other systems [ 2,3 l.

The IH NMR spectrum for the [ LaL-" I [ CIO, ] , complex was recorded in CD,CN ( Table I ) and shows similar behav- tour to that described for the corresponding perchlorate com- plex with the L ~ macrocycle. There was no change in the spectrum of the complex after ,-- 24 h. This result indicates a greater stability of the lanthanum perchlorate complexes in solution with both ligands.

The complexes [LnL ~ ] [ClOt] ~-xH:O, Ln =Ce , Eu and Tb, were examined by cyclic voltammetry at l 0 ~ mol dm ~ in 10- ' tool d m - ~ EhNCIO~ in DMF: no oxidation-reduc- tion processes were detected.

3.8. The cr3.'stal struct, ,res o f L-" and L:H,ICI04I . ,

Single crystals of the macrocycle L~" suitable for X-ray analysis were produced by recrystallization in acetonitrile. The crystal structure is shown in Fig. I. The molecular geom- etry is characterized by a crystallographic mirror plane run- ning through CI3 and dividing the pyridine ring. The macrocycle is bent with the benzene rings at an angle of 36.7(2) ° to each other. Crystals of composition [C2_-H_~.~- N~O_,] [CIO412 were obtained by slow evaporation of an

L. Valencia et al. / hu~rganica Chimica At'ta 282 ¢ 1998,~ 42-49 49

acetonitrile solution of the [ LaL-" I [ CIO4 I," 3HzO complex. The diprotonated macrocycle is almost symmetrical, as shown in Fig. 2, although in this case there is no crystallo- graphic mirror plane relating both halves of the molecule.

The significant difference between the macrocycles lies in the environments o f the N atoms of the amino groups. The C - N ( a m i n o ) distances increase on protonation ( C - N ! .37- 1.46 A, and 1.46-1.51 ,~ for L-" and L-'H_, respectively). Also, and perhaps to 'accommodate' the perchlorate ions, the angles formed between the planes o f the benzene tings and those of the pyridine ring increase notably ( from 2 i ° to 45°). The perchlorate anions are involved in hydrogen bonding interactions with the NH_, groups ( N ( 8 ) - O ( 1 ! ) 2.90( i ), N ( 8 ) - O ( 2 2 ) 2.93( I ), N ( 2 6 ) - O ( 1 3 ) 2 .97(I ) . N ( 2 6 ) - O( 13 ~) 2 .91(I ) ,$,).

In both structures the remaining macrocyclic bond dis- tances and bond angles are within the expected range o f values.

4. Supp lementary mater ia l

Further details of the crystal structure determination can be ordered from Fachinformationszentrum Karlsruhe, 76344 Eggenstein-Leopoldshafen. under the depository numbers CSD-408134 and CSD-408135 for L-" and L-'t.t, [ CIO+I_, respectively.

A c k n o w l e d g e m e n t s

We thank La Xunta de Galicia ( X U G A 20903B96) and {he University of La Corufia for financial support.

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