Indian Journal of ChemistryVol. 35A, August 1996, pp. 671-676

Studies on the interaction of iron(II), nickel(II), copper(II) and zinc(II)with tetraazamacrocycles

Mohammad Shakir", Saji P Varkey & Omar S M Nasman

Division of Inorganic Chemistry, Department of Chemistry, Aligarh Muslim University, Aligarh 202 002

Received 23 March 1995; revised lOJanuary 19ge

The condensation of aliphatic diamines H2N(CH2)nNH2 (n = 2-3) with dicarboxylic acidHOOC - (CH2)n- COOH (n = 1-2) in the presence of dicyclohexyl-carbodiirnide and 4-(dimethylarni-no)pyridine results in new types of 14-18 membered tetraamide macrocyclic ligands la-ld. These com-pounds on reduction with LiAlH4 yield a series of tetraazamacrocycles 2a-2d which form complexeswith Fe(II), Ni(Il), Cu(II) and Zn(II). The ligands and their complexes have been characterized by ele-mental analyses, mass, lR, IH NMR, UV/Vis, EPR spectroscopic, molar conductance and magnetic mo-ment data. An octahedral geometry around the metal ion is suggested for [M2aCl2][M2dCI2], whereM = Fe(II) and Ni(II) while a square-planar and a tetrahedral geometry is proposed for [M2a)CI2-[M2d)C12 for M =Cu(II) and Zn(II).

The growing need for macrocyclic ligands andtheir complexes has stimulated research efforts fortheir efficient preparation I and many preparativemethods of macrocyclic compounds have beendeveloped+'. The amide macrocyclic ligands areof interest because their metal complexes functionsimilarly to porphyrin analogues in catalysing or-ganic oxidation reactionst". As our programmefor the development of polyaza and mixed polyazamacrocycles, we have recently reported? a-d thetransition metal complexes of various macrocycles.Recent studies have established" that [dicyclohex-y1carbodiimide) (DCe). and . [4(dimethylami-no}pyridine) (DMAP) can act as good condensingreagents for the condensation of primary amineand carboxylic acid.

Generally, the macrocyclic polyamide ligand isprepared's'? by the reaction of polyarnines witheither the diester salt of a dicarboxylic acid or thedicarboxylic acid dichloride, In most cases, the po-lyamide tnacrocycles thus formed on reductionwith B2H6 01' LiAIH4 lead to the formation oftheir corresponding polyazamacrocyclesv'l-'?which may be used to construct various macropol-ycyclic systems. In this paper we report an effi-cient route for the preparation of a new series ofpolyamide macro cycles obtained by the condensa-tion of dicarboxylic acids with primary diarninesusing condensing reagent DCC and DMAP. Thepolyoxomacrocycles thus obtained on reductionwith LiAIH4 resulted in the formation of the

corresponding tetraazamacrocyc1es. The complex-ation behaviour of these presynthesized macrocy-cles 2"a-2d have also been carried out with Fe(II),Ni(II), Cu(II) and Zn(II) meta} ions.

Materials and MethodsThe metal chlorides (all BDH) used were com-

mercially available pure samples. The dicarboxylicacids, malonic and succinic acids; Dce andDMAP (all Fluka) were used as purchased. 1,2-Diaminoethane, 1,3-diaminopropane and LiAIH4were purchased from E. Merck and used as such.

Synthesis of ligands2,4,9,11- Tetraoxo- 1,4,8,12-tetraazacyc!otetra-(La)

Dicyclohexy1carbodiimide (11.10 mmol) and ca-talytic amount of 4-(dimethylarnino )pyridine indichloromethane (50 rnl) at O°C were kept on amagnetically stirred two necked 250 ml RB flask.To this stirred solution was added simultaneously,1,2-diaminoethane (5.10 mmol) and malonic acid(5.10 mmol) in dichloromethane (50 ml). The re-sultant reaction mixture was stirred for another 8h. The solid product thus obtained was filteredand washed several times with dichloromethane.The product was obtained as a chalky white solidafter recrystallization from methanol and dried invacuo.

2,4,10,12- Tetraoxo- 1,5,9, 13-tetraazacyclohexa-decane{lb)

672

cooling, 10 ml of water, 10 ml of 15% aq. NaOHand then 20 ml of water were added successivelyto the mixture at O'C. The solid material was fil-tered and the residue washed with hot THF. Thefiltrate and THF washings were concentrated un-der reduced pressure to give 2a as viscous liquid.The liquid thus obtained was thoroughly washedwith THF and dried in vacuo.

INDIAN J CHEM, SEe. A, AUGUST 1996

HH °tYrO{ 2 DCClOMAP\ + -4H20'-H HO OHH2 .

la ,1.,0, X'(CH2~;Y'CHz

lb ,1.,0; X· (CH2l]; Y.CH2

Ie •••• 0; X' (CHZ)Z; Y,(CHZ)Z

Id ••••0, X·(C~)) ,Y'(CHZ)Z

Za ••• = HZ; X· (CHZ)Z ; Y' CHZ

n .•.'.H2' X= (CHZ)) ; Y= CH2

ze •••• HZ' X='CHZ)2, y.(CH2)2

2d •••= H2' X· (CH2)); Yz(CH2)2:

104 • FoW) and Hi(Jt) 104' Culll) ana z-unSeh __ I

This compound was prepared by adopting thesame procedure described above. Instead of 1,2-diaminoethane, 1,3-diaminopropane (5.1O mmoI)was added.

2,5,10,13- Tetraoxo- 1,6,9, 14-tetraazacyclohexa-decane{le)

This preparation was exactly analogues to theprevious ones. Here the diamine and diacid em-ployed was 1,2-diaminoethane (5.1O mmol) andsuccinic acid (5.1Ommol),

2,5,11,14- Tetraoxo- 1,6, 10,15-tetraazacycloocta-decane{ld)

These compounds were prepared by adoptingthe above mentioned method using 1,3-diaminop-ropane {5.1Ommol} and succinic acid {5.1Ommol}.

The purity of all these compounds (la-Id) werechecked by TLC in DMF using pet. ether (2:3 viv) as eluents.

1,5,S, 12-Tetraazacyc!otetradecane (2a)A solution of compound 1a (7.8 mmol) in 50

ml of THF was added to a stirring solution of Li-AIH4 (0.26 mol) in 200 rnl of THF at o-c Themixture was stirred under reflux for 56 h. After

1,5,9,13- Tetraazacyclohexadecane (2b)The procedure adopted for this preparation was

similar to that for the preparation of 2a. Here thecompound lb (7.S rnrnol) was used for the prepar-ation of the' above title compound.

1,6,9,14- Tetraazacyclohexadecane (2c).This preparation was carried out using the de-

tailed procedure mentioned for the preparation of2a. The tetraamide compound used for this pre-paration was Ic (7.S mmol).

1,6,10,15- Tetraaracyclooctadecane (2d)This compound was prepared from the above

mentioned procedure using the compound ld {7.8mmol}. "The purity of the above prepared (2a-2d)compounds were checked by TLC using ethylacet-ate-methanol (3:2 vIv) as eluents.

Synthesis of complexes

Dichiara (1,5,8, 12-tetraazacyclotetradecane)meta~ll), [M2aC~1 [M= Fell and Nl1

To a stirred methanolic solution of metal{ll)chloride (l rnrnol) was added a solution of 2a(1.11 mmol) in methanol. The mixture was stirredfor 7 h. The solid product obtained was filteredoff and washed with methanol and then dried invacuo.

Dichloro..l ,5,9, 13-tetraazacyclohexadecane)nzeta~ll) lM2bC/2J [M= Fell and Nil1

These complexes were prepared as describedfor [M2aCIJ Instead 'of 2a a methanolic solutionof 2b (1.11 mmol) was added to the metal salt so-lution (I rnmol).

Dichloro; 1,6,9,14- tetraazacyclohexadecaneimetaVl) [M2cC~l [M= Nf1

This preparation was carried out using theprocedure mentioned for [M2aCI21. Here insteadof 2a, the compound 2e was added.

Dichlord 1,6, 10,15-tetraazacyclaoctadecane)meta(ll) [M2dC~l [M= Fell and Nil1

These complexes were prepared by adopting

SHAKIR et al.: INTERACTION OF Fe(II), Ni(II), Cu(II) & Zn(n) WITH TETRAAZAMACROCYCLES 673

the same procedure as used for [M2aCl21. Here in-stead of 2a., the compound 2d was employed forcomplexation.

Synthesis of[ Cu(2a-2d)]Cl2To a stirred solution of CuCl2'2H20 (l mmol)

in methanol was added a solution of the com-pound (2a-2d; 1.11 mmol) in methanol. The re-sultant mixture was stirred for 6 h.

Synthesis of[Zn(2a~2c)lCl2These compounds were prepared using the

above method except that the ligands employedfor complexation was the compounds 2a-2c.

The elemental analysis and mass spectra(JMSD-300) were obtained from the Micro-analyt-ical Laboratory of CDRl, Lucknow. The 'H NMRspectra were determined in DMSO-do using aBruker AC 200E NMR spectrometer with Me4Sias an internal standard. Metals and chloride weredetermined volumetrically I.' and gravimetrically I~

respectively. The IR spectra (4000-200 cm -I)were recorded as KBr discs on a Perkin Elmer62] spectrophotometer. The electronic spectra inDMSO were recorded on a Pye-Unicam 8800spectrophotometer at .room temperature. EPRspectra were recorded on a JEOL JES RE2XEPR spectrometer. The electrical conductivitiesof 10-3 M solution in DMSO were obtained on aSystronic type 302 conductivity bridge equilibrat-ed at 25 + 0.1 "C. Magnetic suscepribility measure-ments were carried out using a Faraday balance at25°C.

Results and DiscussionA new series of tetraamide macrocycles, la-ld

have been prepared by the condensation reactionof dicarboxylic acids with primary diamines usingthe condensing reagent, DCC and DMAP asshewn in Scheme 1. However, an attempt to syn-thesize these macrocyclic ligands without the useof DCC and DMAP failed to give the products. Inaddition to this, the ligands corresponding to 0-

phenylenediamine could not be formed. Thecorresponding tetraaza macrocycles have been iso-lated successfully on reduction of these tetraamidemacrocycles with LiAIH4 (Scheme 1). The resultsof elemental analysis and molecular ion peaks(Table 1) in the mass spectra are consistent withthe proposed macrocyclic framework. All massspectra of the ligands showed molecular ion peaksfor the 2:2 reaction product with no peaks abovethem. The miz values appeared at 256, 282, 288and 310 for the ligands la, Ib, Ic and ld respect-ively. All the iron complexes are found to be airsensitive. The analytical data of the macrocyclic

complexes suggest their 1:1 (metal:ligand) stoichi-ometry as shown in Scheme I. The molar conduc-tivity values for all the complexes except copperand zinc in DMSO medium are in the range of 17-22 ohm - 1 ern-mol" 1 suggesting them to be non-electrolytes while that of copper and zinc com-plexes observed in the range <)K-122ohm - 1 ern-mol" 1 suggest their 1:2 electrolytic na-ture ".

In the IR spectra of the complexes, bands dueto hydroxyl and primary amine groups are ahsent.This information together with the appearance offour bands in the 1680-1710, 1530-1570, 1250-1260 and 650-670 em - 1 regions assignable?" toamide I (vC = 0); amide II (vC = N + oNH); amide(III) (oNH) and amide IV (~C =0) hands, respect-ively, suggest the formation .of the proposed rnac-rocyclic framework. A single sharp band observedfor the amide ligands in the region 3 2K5- 3 310cm-I may be assigned to v{N - H) of amidegroup. The absorption bands appearing in the re-gion 2880-2930 and 1410-1460 em - 1 in all the li-gands may reasonably be assigned to the CHstretching and CH bending vibrational modes re-spectively.

The disappearance of all the amide bands havebeen noticed in the IR spectra of tetraazacrocycleswhen compared to their tetraamide macrocycles.However, a slight negative shift in NH stretchingvibration have been observed. All other hands donot show appreciable change as compared to theiramide Iigands. The major change noticed in the IRspectra of macrocyclic complexes as compared totheir corresponding Jigands is the slight negativeshift in the v{N - H) which appeared in the region3240-3285 ern - 1 and thus can be ascribed tocoordinated NH stretching vihration. The appear-ance of a new medium intensity band in the region410-455 cm-I assignable to v(M-N) further con-firms the involvement of nitrogen in coordination.All the complexes show a band - 280 ern 1 as-signed to v{M - Cl) vihrations.

The 'H NMR spectra of Ia-Ld macrocyclic li-gands do not show any signal corresponding toprimary amino and alcoholic protons suggestingthat the proposed macrocyclic skeleton has beenformed through condensation reaction. The mac-rocyclic ligands la-ld show a multiplet in the re-gion 8.41-8.56 ppm which can be assigned if, toamide (HN - CO, 4H) protons. This clearly showsthat the condensation has indeed taken place. Amultiplet appearing in the region 3.37-3.67 ppmmay be ascribed to the methylene protons.(CO - N - CH2, 8H) which are adjacent to the ni-trogen atoms. However, a multiplet in the region

674 INDIAN J CHEM, SEe. A, AUGUST 1996

Table I-Analytical and physical data of the complexes

Compound ~dt M.pt.(OC) Found (Calcd), % Am(Colour) (8M) yield(%) ern-ohm - 'mol- ,

M CI C H N

C'OH'fiN40. (Ia) l'.lll 46.8 6.3 21.8

White 30 ~46.7) (6.2) (21.8)

C"H",N40. (Ib) 210 50.'.l 7.2 1'.l.5White 28 (50.7) (7.0) ( 1').7)

C'2H",N 40. (Ie) 218 50.4 7.4 1'.l.4

White 32 (507) (7.0) ( 1'.l.7)

C,.H,.N404 (Id)· 205 53.5 7.5 11l.1lWhite 33 (53.1l) (7.7) (17.9)

CI!IH24N4 (2a) 5').') 11.1l 27.1lYellowish brown 22 (5'.l.7) ( 11.'.l) (27.'.l)

C"H'MN. (2b) 63.0 12.1 24.6Yellowish brown 26 (63.2) ( 12.3) (24.6)

C"H2XN4 (2e) 63.2 12.2 24.0

,Yellowish brown 22 (63.1 ) ( 12.3) (24.6)

C,.H]2N4 (2d) 65.4 12.4 21.4

Yellowish brown 24 (65.6) (12.5) (21.'.l)

[Fe2aCl21 5.35 231l 17.3 22.0 36.5 7.3 17.3 IIIReddish brown 24 (17.1 ) (21.7) (36.7) (7.3) (17.1 )

[Ni2aCl21 3./0 l'.lO IIl.O 21.4 36.3 7.0 16.1l 21

Red 20 (17.8) (21.5) (36"+) (7.3) (17.0)

[Zn2aICl, 161l 1'.l.3 20.') 35.5 6.'.l 16.7 112

White 26 ( 1'.l.4) (21.1 ) (35.7) (7.1 ) (16.6)

[Cu2a1Cl2 1.73 240 IX.1l 21.5 35.6 7.0 16.6 121

Green 28 (1'.l.0) (21.2) (35.9) (7.2) ( 16.7)

[Fe2bC121 5.33 1116 15.5 1'.l.1l 40.S 7.7 15.6 17

Reddish u. ( 15.7) (20.0) HO.6) (7.'.l) (15.1l)

[N~2bCl2j 3.14 l'.lll 16.3 l'.l.'.l 40.5 7.7 15.5 22

Red 22 (16.9) (19.8) (40.2) (7.8) (15.6)

[Zn2bjCll 218 11l.1 I '.l.6 3'.l ..1 7.6 15.5 '.lll

White 20 ( 17.9) (19.5) (3'.l.5) (7.7) ( 15..+)

[Cu2b]CI2 1.80 261l 17.6 1'.l.4 3lJ.lJ 7.6 15.6 122

Green 29 ( 17.5) (19.6) (3'.l.7) (7.7) ( ISA)

INi2cCl,] z.vs 156 16.2 20.0 40.4 1l.0 15.6 IlJ

Red 32 ( 16..+) (19.8) (40.3) (7.8) ( 15.7)

IZn2cjCl2 IlJ2 111.1 IlJ.5 3'.l.3 7.7 15.5 115

White 24 ( 17.'.l) ( 19.5) (3'.l.5) (7.7) (15.4)

ICu2elCl21.71 216 17.6 1'.l.5 40.0 7.6 15.6 11'.l

Green 23 ( 17.5) (19.6) (39.7) (7.7) ( 15..+)

[Fe2dCl,j., 5.40 11l'.l 14.5 11l.5 44.1 8.3 14.4 III

Brown 27 (14.6) (18.5) (43.9) (8.4) (14.6)

[Ni2dCl2] :U5 Z06 15.0 18.3 43.6 8.4 14.5 20

Red 24 (15.2) ( 18.4) (43.5) (8.3) (14.5)

[Cu2:;1jCI, 1.78 262 16.5 18.3 42.'.l 8.2 14.2 114

Green 28 (16.3) (18.2) (43.0) (8.2) (14.3)

1.99-2.03 ppm for the ligand Ib and Id is as- ppm -for the Jigands la and lb and another singletsigned as middle methylene protons of 1,3-diamin- at 3.30-3.31 ppm for the ligands Ic and Id mayopropane moiety. A singlet in the region 2.80-3.18 be assignable" to methylene protons of dicarbox-

SHAKIR et al.: INTERACTION OF Fe(I1),Ni(II), Cu(II) & Zn(II) WITH TETRAAZAMACROCYCLES 675

ylic acid moiety (CO -CH2 - CO, 4H) and(CO - (CH2)n - CO, 8H).

However, the IH NMR spectra of 2a-2d com-pounds do not show any band assignable to amideprotons. This suggest the reduction of carboxylgroups. The spectra of 2a- 2d showing two multip-lets in the region 6.21-6.40 and 2.51-2.98 ppmmay be assigned'? to the secondary amino protons(C - NH, 4H) and methylene protons(N - CH2 - C, 8H) of dicarboxylic acid moietywhich are adjacent to nitrogen atom. However, thecompound 2a and 2c gave a multiplet in the re-gion 3.18-3.21 ppm corresponding" to methyleneprotons (N - CH2, 8H) of amine moiety. The com-pounds 2a, 2b and 2d show a multiplet in the re-gion 1.91-2.31 ppm which may be atrribured " tothe central methylene protons [C - (CH2)n - C). Amultiplet appearing for the compounds 2c and 2drespectively at 1.89 and 1.96 ppm may be due tothe methylene protons (N - C - CH2, 8H) of dicar-boxylic acid moiety.

The 'H NMR spectra of macrocyclic zinc(U)complexes of 2a- 2c have also been recordedwhich were found to be comparable to their re-spective metal free ligand. The main change no-ticed is the shift of the signals towards lower fieldwhich is an identification of the coordination ofthe macrocycles.

The EPR spectra of the polycrystalline Cu2+complexes were recorded at room temperature.Except [Cu2d]CI2, all the copper complexesshowed hyperfine splitting and their gll' g l' All andA 1 values have been calculated. The absence ofhyperfine splitting in these complexes may be dueto the strong dipolar and exchange interaction be-tween copper(II) ions in the unit cell. The gn andg 1 values allows one to distinguish unambiguouslybetween d : _;. and d z2 ground state, The tetraa-zamacrocyclic complexes studied here show ~i andg 1 values in the 2.171-.2.01 and 2.037-2.048 re-gions, respectively which support that the d x2 _;..

may be the ground state. However, the All and A'Ivalues appeared in the region 88.94-112.50 and18.00-23.62 G respectively which are consistent"with the square planar environment around cop-per(Il) ion. All the complexes gave same spectralpattern and thus the ring size of the macrocyclicligand has little effect on the EPR spectral par-ameters, All the compounds that were studiesshow gll < 2~3. It should be noted for an ionic en-vironment " that gll> 2.3, while for a covalent en-vironment glf < 2.3, indicating that the presentcomplexes posses considerable covalent character.The g values are related by the expression,

G= (gll- 2)~gl - 2), which measure the exchangeinteraction between copper centres in the polyc-rystalline solid. If G> 4, exchange interaction isnegligible and G< 4 indicate considerable ex-change interaction in the solid complexes. In thepresent case, the axial symmetry parameter, G liesin the range 4.00-4.92 which indicate that the ex-change interaction is very less.

The electronic spectra of the iron complexes ofthe ligand 2a, 2b and 2d gave a weak intensityband at 11350-11500 cm - 1 region which may, rea-sonably, be assigned IYto 5 T2g - 5 Eg transition, con-sistent with an octahedral geometry around themetal ion. However, the ligand field spectra ofnickel complexes of all the macrocyclic ligandsshow two bands in the region 11200-11350 and17100-17500 ern - 1 which may be ascribed to3A2g - 3 1;iF) and 3A2g - 3 TIi P) transitions. re-spectively suggesting!" an octahedral environmentaround nickel(II) ion. The copper complexes of allthe macrocyclic ligands have three bands in theirelectronic spectra at 12450-12650, 16200-16350and 21800-21900 cm - I regions which may be at-

. "B 'B' itnbuted to the -B1g-- 215' - Ig--Alg an"2 Big - 2 Eg transitions, respectively which are closein agreement?"!" with those expected for squareplanar geometry of copper(II) ion. The observedmagnetic moment values (Table 1) for all thesemetal complexes are in close agreement with theirelectronic spectral data which further support theproposed geometry.

AcknowledgementThe authors thank Dr. Alex Punnoose, Depart-

ment of Physics, AMU Aligarh for EPR spectra.Dr. Saji P V is thankful to the CSIR, New Delhi,for financial support.

References1 Corey E J & Nicolaon K C, J Am chern Soc, 96 (1974)

5614.2 Peterson I & Manusri M M, Tetrahedron, 41 (1985) 356,).3 Masamune S, Angew Chern Int Ed Engl, 16 (1977) 585.4 Che C M & Cheng W K, J chern Sac Chern Cornrnun

(1986) 1443.5 Drago R S, Cordon B B & Barnes C W. 1 Am chem Sac.

108(1986)2453.6 Sans sine L, Brazi E, Robine A, Mimoun H, Fischev J &

Weiss R, JAm chern Soc, 107 (1985) 3534.7 (a) Shakir M, Varkey S P & Hameed P S. 1 chem Res. II

(1993)442;(b) Shakir M, Varkey S P & Hameed P S, Polyhedron. 12(1993)2775.(c) Shakir M & Varkey S P, Polyhedron, 13 (1994) 7')1.(d) Shakir M & Varkey S P, Trans Met Chern, 1\1 (1\1\14)606.

R Dwyer T J. Geierstanger B H. Bathini Y. Lown J V &Wemmer D E,l Am chern Soc. 114(1992) 5911.

676 Il'\DIAN J ('HEM, SEe. A, AUGUST 1990

'J 1abushi 1, Okino tl & Kuroda Y, Ieuuhediou Leu, ~g(197(,)4339.

10 Alcock N W. Moorie P. Omar H A A & Reader C J. JCll£'III.\OI Dalton Iram. I IIJ~71 20·B.

II Dietrich P B, Lehn J M & Sauvage J P, Tetrahedron Leu,34(1969)211115

12 Graf E & Lehn J M . .1II m chem Soc. 20 (1975) 5022.U Rcillcv (",N. Schmid R W & Sadak I- A . .I chem LUlie, 30

t, 11J:'i'l I (>Iv.14 Vogel A I. Text hook of quantitative inorganic analysis

(Longmans. London) 1961. p 433.l:'i Geary W J. Coord chem Rev, 7 \ 11J71 ) ~2.16 Parka o, PulukkQd), K, Smith F C, Batsanov A & How-

ard J A K. J chem Soc Dalton Trans, (1994) 689.

17 Burge" K, Lirn D. Kanno K & Ke (' Y. .I org Chern, 59(1994) 2179.

III Ray R K & Kauffman G B. lnorg chim Acta. 207 (1990).I Y Lever A B P. Inorganic electronic spectroscopy (Elsevier,

Amsterdam) lY1)4.