Inui an Joum;i1 or Chcmistry Vo L '+S ;\ . Octohcr 2006. pp. 222.+-2228

Synthesis, spectra , electroch8mi stry and single crys tal X-ray strllCl:Ure oC

l Co( cx-Nai El)2(N:J z]' cx- Nai El = I-cth yl-2-(naphthyl-cx-azo)i midazole

Deb~lsis Banerj ee & .Chitt;lr;lnj ;ln Sin ha '"

Inmgan ic Chemi stry Sectio n. J)ep:lnlllent o r Chemi stry. Jaua vpur _Uni vers it y. J;lu;lvpur. Kolkata 700032. Inu ia

Email : c_ r_s inh;l @y:i1lOo.colII

/( ecl'il 'cd 12 Mllr 2000: 1'1' I ·i .l' l'i/ 25 !I IIg 11.1 I 2()()0

Reaction or 1-;i1k yl-2-(naphth yl-u-al.o) illlid;;zo les I (f.-N:li R. ( 1) where R = i'vlc (a). [[ (h ) . Ih (t: ) 1 with m h:i1t ( ll ) acetate and N;IN~ ill lIIet hanol ,o lution res ults in hi s-chcl;lted. al.i uo COlllpIeX. lC'o(u-NaiR HN')2 1 (2). The X- r:IY stru cture shows ui sto ncd oc­taheural CONI, coo ruin:ll ion sphere with 11'II1I .Hl'll n .H/ 'II1 I.1' (t il ) 2h \\'ith rei'crence to scqucnCl: o r coord inati on p;lirs o r al. iuo- N. al.o­N alld illliua'l.o lc-N. The structul'l; is a li rsl e.,am ple or III type conligura tion in 3d mctal comp le xcs or al.o illline runction. Rc:Jox propeni es 01' the co mple xes have hee n exam ined hy cyc l ic vo lt ­am mc try and sho w hi gh pote ntia l Co(III )/Co(ll ) coupl e ;i1ong with li gand reuucti ons.

IPC Cod(,: In l. CLx C07f7IS106

A ry lazoheterocyc les possess deloca li sed, Thtcidic azo imine (-N=N-C=N-) chelating functi on I.e. For de­signing imidazole contain ing no systems, we ha ve

synthesised ary lazoimidazo !csJ. The n-acidity of che­

lating functi on is largely dependent on the nature of heterocyc le, ring size, number o f heteroatoills. and substitutents in the aryl group.!. Usc o f naphthy lamine during diazo coupling w ith imidazo le results in the synthesis of naphthylazoi midazole whi ch has higher steri c crowding and beller electron donating property than 2-(pheny lazo) imidazo!csJ

. The coord ination and cyc lometallated compounds of naphthy lazo imidazo les have already been reported by us5

.').

In continuati on of our earli er studi es on the cOOl'd i­nat ing properti es of azo imidazo les, the synthes is and characterisation o f cobalt ( II )-azide complexes of 1-

alky l-2-(naphthy l-a-azo ill1idazo les), a-Na iR (1 ), are reported here. The structura l confirmation has been carried out for one complex by single crys tal X-ray difrracti on study.

Expcrimcntal Co(OAch,4HeO and NaN, were purcha sed from

Loba Chemi , 80mbay. I -A lky l-2-naphthy lazoimda­

zo les (a -Na iR) we re prepared as reported ~tlread/ . A ll other chemica ls and solven ts w,:r.:: of reage nt grade. The so lvents were used after dryingl O

Microana lyses (C, H, N) were per fOl' llled using a Perkin -E lmer 2400 CHNO/S elenlental anal yzer. Spectroscopic mea surements were c arri ~d out using Lambda 25 Perkin-Elmer spec trophOlOlneter ror UV­Vi s spec tra . RX- I Perk in-Elmer FT-IR spec tropho­tometer for Ff-JR spectra (K8r di sk, 4000-450 C lll-

I).

Room temperature magnet ic moment was measured using v ibrating sample 155 magnetometer at 298 K.

Molal' conductance ( i\~ I ) wa s measured by Sys tronics conductivity meter 304 model using c(/ . 10.

1 M solll­ti ons in MeOH. Electroc hemical me:lSlIrements were ca rri ed out w ith the use of compu ter cont roll ed EG&G PA RC VersaStat mode l 250 dec troc hemica l instrument ha ving a Pt-di sk working electrode. T he so lu tion wa s JR compensated and the results were collected at 298 K . The reported resul ts are referenced to SCE in acetonitri le and arc uncorrected for juncti on potential. Estimati on o f coba lt was .:al'ried out by

I ... I d lo comp exometnc titrati on met 10 .

Call/ion : A zide complexes of transit ion metal ions containing organic li gands are potentiall y ex plosi ve. Onl y a small amount o f the mater ial s should be pre­pared, and handled w ith ca re.

Preparation or his-t:hclat('d azido t:omplcxes, l CII(a-NaiEt)!(N.lhl (2h)

I-Ethy l-2-(naphthl y l-a -azo) imidazole (a-Nai Et ) (0.06 g, 0.50 I11mol) in M eOH ( I () mL) was added dropwi se to a stirred so luti on o f Co(OAc)2 ---+H 20 (0.062 g, 0.25 mmol) in MeOH ( 10 mL) at 298 K. The brown so lution was stirred for 15 min . T hen. Na .1 (0.03 g, 0.50 11111101) in MeOJ-l ( 10 mL) was added to the brown solution. The co lOI' changed fro l11 brown to deep brown. The solution \-vas filtered and

a-NaiR ( I); R = Me (a), El (b), Bz (e) 2 (tlt isomer)

NOTES 2225

then le rt undi sturbed ror a week resulting in the pro­ducti on of clark brown crystals. It was washed with water, methanol, ether and dried ill \ '([CIIO . Yi eld 0.12 g (75%) . The microanal ytical data of the complex [Co(a-NaiEthCN,hl (20) : Anal. Found: C, 55.71 ; H, 4.45; N, 30.28; Co, 9. 12. Calcd for C,(J H 2R NI ~ Co: C, 55.99; H, 4.35; N, 30.48; Co, 9.16%.

All other co mplexes were prepared by the sa me procedure. I n all cases, crys tal I i ne products were ob­tained. The yield va ri ed from 75-80% and microana­lytical data of the complexes: lCo(a-NaiMeMN3h J (2a): Ana l. Found: C, 54.71; H, 4.0 I; N, 3 1.78; Co, 9.50. Cedcd for C2X H 2~ N I~ Co: C, 54.64; H, 3.90; N, 3 1.87; Co, 9.58 %. [Co(a-NaiBz)c(NJhJ (2c): Anal. Found: C, 60.0 I ; H, 4.40; N, 27. 19: Co, 8. 12 . Calcd for C'6H .'2 NI ~Co: C, 60.08; H, 4.45 ; N, 27.26 ; Co, 8.19%.

X-ray crystal structurc analysis

The crys tal s were grow n by slow evaporati on of reac ti on mi xture for a week. Data were collected with Siemens SMART CCD diffractometer using graphite­monochrornati zed Mo-Ka radi ati on (A. = 0.71073 A) at 183 K. U ni t ce ll parameters were determi ned from least-squares refinement of setting angles of 30 12 re­flections with 28 in the range 4.14::; 28 ::; 52°. A summary of the crystall ograph ic data and structure refinement parameters are given in Table I. Rell ec­tion data were recorded usin g the (JJ scan technique. Data were corrected for Lorentz polarization effects and for I i near decay . Semi-empi rical absorption cor­rections based on lV-scans were applied . The structure was solved by heavy atom methods using SHELXS-97 (ref. II) and success ive difference Fourier sy nth e­ses. All non-h yd roge n atoms were refilled anisotropi­ca ll y. The hyd roge n atoms were fi xed geo metricall y and refined using the riding mode l. In the final differ­ence Fourier map, the res idual maxima and minima

o -1 0 -1 [~IIlax (e A . ), 1.289 and ~IIlill (e A . ), -1.226] were car-ried out using SHELXL-97. All calculati ons were car­ried out using SIIELXL-97 (ref. 12), ORTEP-32 (ref. 13) alld PLATON-99 (ref. 14) prog rams.

Results and discussion

The ligands (a-NaiR , 1), are unsy mmetri c, having N,N'-bidentate chelator where Nand N' refer to N(imidazole) and N(azo) donor centers, respectively. The react ion of methanolic so lution of a-NaiR , CO(OAC)2. 41-hO and NaN J in mole ratio [I : I :2, 1:2:2; I: I :excess (>4 mole)] affords bis-chelated rCo(a-

NaiRhCN,hJ (2) complexes. Studies 0 11 the cobalt (ll )­azide-complexes of I-al ky 1-2-(arylazo) i midazoles (RaaiR') has in spired us to set up similar reaction conditi on IS:

MeOtt Co(OAch + 2 a-NaiR + 2NaN, -------7

Stir. 298 K

[Co(N,)2(a-NaiR h l + 2NaOAc ... ( I) 2

The co mplexes are non-electrolyte in MeCN. The composition of the complexes is supported by C, H. N data. Roo m temperature (298 K) magneti c moment measurements show hi gh spi n data in the range 4.9-5 . 1 BM.

Structul'c description of lCo (a-NaiEth(N,hl (2b)

The molecular structure of [Co(a-Nai EtHN,)2 1 (20) is show n in Fig. I. Bond di stances and angles are provided in Table 2. The stru ct ure shows distorted octahedral arrangement about CoN(, coordinati on sphere. Co li es at the center of sy mmetry of the mo-

Table I - Summari sed crystallographic data for

ICo(a-Na i Et)~(N, )~ 1 (2b)

Empiri c:!1 formula

Formula weight

Temperature (K)

Crys[;ll system

Space group

Crystal sizc (mm).'

(/ (A)

b (A)

c (A)

an fJ (0)

yn V(Aj' z A(A) ~l (Mo-Ka) (Jl1n,- l)

De,,1e (mg III")

Refi ne parameters

C 'oH2RN 1-1 Co

0'+3.59

183(2) K

Triclinic

PI

O.82xO.58xO.36

8. 1299(2)

10.0938(2)

11.06 18(2)

63.699( I)

76.773( I )

73.20'+( 1)

773.67(3)

0.71073

().60 I

1.38 1

207

Total refl ection [ I > 20 ( I) [ 4834

Uniquc data

/?" [I > 20 ( I) J IIRh

Good ness of fit

"/?= LIFo - Fc I / L Fo .

30 12

0.0674

0.1768

1.052

I'l l'/? =rL \\'(F/ - F/)/ L IV FIJ-I [ I / ~ arc general but II' arc dilTcrcnl. IV = I / [o~ (F2)+(O.11 58 p)2J for 21J

2226 INDIAN .r CHc M . SEC A . OCTOl3ER 2006

lccular structure. Four N centers arc coming from two 0.- aiEt ligands and other two N-centres are coming from azide groups. Li gand acts as N(imidazolc),

(azo) bidentate chelator. Azide (N, ) serves as monodentate donorl(, li gand . The positi on of donor centers around Co(ll) sugges t fIW!S- (N , ),(N , ), fmll.\' ­

N( imidazo lc), N(imidazole), and fmlls-N (azo), N(azo) and has been named thereafter fmll s- froll s- fIW!S or IIf­lCo(a.-NaiEt)2(N,h l. Bis-chelated MX 2(RaaiR/

)2 (X = hal ogen, M = Ru , Os) pseudooctahed ra l complexes can , in princip le, ex ist in five geo met rical isomeric forms' : eis-f rolls-f mils (c/ f ), f mlls-f mns-f mils (11/ ), fmll s-eis-eis ( fCC) , ei.\-c is-fmlls (ce f ) and c is -cis-cis

(cee) with reference to the sequence of coordinati on pairs X,X; N,N; N',N', res pec ti vely. Out of them, rour isomers (tce, efe, eel and eee) ha ve been charecterised . I ' ( II ) 1 "17 1s l l I ' In rutlenlum comp exes .. . . . . owever, tlere IS no report on the structura l characteri zati on having f mIlS-{ mlls-I mils geometry in the seri es of tra nsi ti on metal coordinati on complexes of azo heterocycles . The atomic arrange ments in chelate plane Co( I), N( I), C(3), N(3) , N(4) cons ti tute a good plane (dev ia­tion < 0.06 A) . The pendant naphthyl group is planar and makes dihedra l with che lated azo il1l ine fragment

Fig. I - ORTEP vicw or ICo(a-NaiEth (N,hl (2b).

(dihedra l 56.48( 10)°). The chelate angle subt ended by a.-NaiEt is N( I)-Co( I)-N(4), 74.34(8)° This is fo und to be th e lowest value in the se ri es of complexes or Co( ll )-azoimine fami ly' s.I!). There are three different Co-N bond di stances: Co-N(im idazoJe ) [Co( I )-N( I), 2. 1466( 19) AJ; Co-N(azo) [Co( I)-N(4) , 2.233(2) Al , and Co-N(azide) [Co( I )-N(5), 2.077(2) Al. The Co­N(azido) bond length is comparable wi th the reported data 15. The N=N bond length is 1.27 1 (3) A and is slightl y elongated from free li gand valll_cll. The N-N-N b I I·· I ' I 15 1(, Ollc parameters Ie Wit lin reportee range " .

Spectra l studies

The IR spectral bands were assigned on comparing with free li gand dataco. Most significan t observa ti on is the appearance of very strong sharp sing le band at -?034 · 1 ("I" bl· " ) '1'1 · .. , I ( I ) _ . cm d e.). lese COlt espollt to v,," III , .

Thi s supports mono-dentate N,'bond illg in the COIll­

pl exes l(, . The chelated ligand shows characteri stic transmission at 1600-450 cm·l. Moderately intense stretchings at - 1600 and - 1435 cm·1 are due to v(C=N) and v(N=N) , res pecti ve ly.

T able 2 - Sdcc tcd bond di stance U'\) ;\nd ang lcs (0)

1'0 1' ICo(a-Nai Et)2(N 1)2 1 (2b)

Bond di stancc (A) Bond ;lIlgle

n Co( I )-N( I ) 2.1 466( l lJ) N( I )-Co( I )-N(4) 7·1.3-1 (X)

Co( I )-N(4) 2.233(2) N(S)-Co( I )-N(S* ) 180.0

Co( I )-N(S) 2.077(2) N(S)-Co( I )-N( I ) XlJ.llJ(8)

N( I )-C(3) 1.33-1(3) N(S)-Co( I )-N( I *) lJ08 1(8)

N(3)-N(4) 1.27 1 (3) (.'5 "') -Co( I )-N( -I ) XS.2lJ(X)

N(3)-C(3) 1.37lJ(3) N(S)-Co( I )-N(-I ) lJ-I .7 1(X)

(4) -C(4) 1,426(3 ) N( I ")-Co( I )·N(-+) I05.Cl6(X)

N(S)-N(6) 1.199(3) N(4)-N(3 )-C,) I 122(2)

N(6)-N(7) 1. 152(4) N(3)- . (-I )-Co( I ) 11 6. 3X( 17)

N(6)-N(5)-Cu( I ) 122.32( I X)

N(7)- (6)-N() 17lJ S(3)

Tab le 3 - UV-Vis spect ra". IR and magneti c Illolllcnt (p ) d;,ta of ICo(cllf:\-NaiI<H N')21 (2)

Compo

ICo(a- 'aiMcH N 1)2 1 (2a)

ICo(a-NaiEt)c( NJU (21J)

ICo(a-NaiBzJc(N,)cl (2c)

"Sol vcnt: MeCN

UV-Vi s spectral data (I,,,,,,,/nlll ) ( I ()'J EM" cm")

632(0.2-1). 452(7.76).422(8.7 1). 392( 12.24)

636(0.32). -1-1-1 (7.44) . 4 16(8. 13), 396( 14.2 1)

634(0.27). 4S0(6.X3). 4 17(7.lJ l ), 392( 14.48)

II< (clll " 2 u (N;) u(C=N)

2035 15n

2034 1600

2034 159X

Dipole Illoillent u ( =N ) ~t (13M )

1436 4.lJ l

1438 5.06

143-1 4.82

NOTES 2227

Table 4 - Cyc li c vo italllllletri e data of ICo(a-NaiRHN,)2l"

CO lllp. Co( III )/Co( ll ) Ligand red ucti ons (E I/2 ' V) (l!. Ep• IllV) (E ll, ' V) (l!. E". IllV )

ICo(a-NaiMc),(N,), 1 (2a ) [Co(a-Na iEtlc(N,h l (2b)

1.46 ( 120) -O.5R ( 120) -0.9R ( 130) - 1.30 ( 160) - 1.59 I>

1.43 ( 130) -0.62 ( 120) -0.95 ( 120) - 1.43 (140) - 1.(,0 I>

ICo(a-Na i BZ),(N,), I (2c)

1.47 ( 120) -0.60 ( 130) -0.90 ( 150) -1.3 l:\ ( 150) _1.60 1>

"Solven t. MeC N: lVorking electrode. Pt-di sk Illilli elec trode. Pt-wire aux ili ary. SCE reference: supporting elec trolyte [ n l3l1 .IN II~~IO.d: ,can rate 0.05 V S·I. potentia l EI/2 - 0.5(Ep"+E;x: ).l!.E,, - 1 Ep"-EI,,, I. IllV: Ep" = anodic peak potential. Elk' = cath odiC peak potential: Lpc __

2.0 1.6 1.2 0.8 0.4 0.0 -0.4 -0 .8 -1 .2 -1 .6 -2 .0 ·2.4 E(V) vs. SCE

Fig. 2 - Cycl ic voitallllllograill of Co(a-NaiMeH N')2 (2a).

The electronic spectra of the complexes were re­corded in methanol so luti on in the UV/V is region (250-900 nm). The data are li sted in Table 3. In the visible region , the complexes ex hibit intense band ::;400 nm. These transitions are li gand centred (LC) transiti ons'·21. There are three transitions in the range 4 15-640 IHn for the complexes. Intensity pattern of the bands are di fferent; the transi tions 4 15-425 and 440-455 nm are high (E -10.1 mOrICm·l

) and is sharp while transiti on 630-640 nrn is weak (E -180-450 1110r l cm· l

) and broad . Crys tall ograph ic data of [Co (ex­NaiEth(N,h] (2b) were used as the parameters for MO calculation to accoun t on the spectral properties of the complexes. The HOMO has only 5% Co orbi­tals while the HOMO-I bears 64% metal co ntribution. The LUMO and LUMO+ I are composed of 33% and < I % cobalt function , respectively. ex-NaiEt carri es two parts : imidazole-N=N- and naphthy l groups. Both of these groups contribute 44% (out of which 35% naphthyl and 48% azoimida70Jc) each to constitute HOMO. The LUMO has a share of onl y 5% from naphthyl ane! 56% from azoimie!azole group (out of which azo contributes 46%). The LUMO+ I is com­posed of >80% from imidazo le-N=N- (azo, 49% and on ly II % from naphthyl group.

Hi gh intense transiti on at 380-425 nm may be as­signed to li gand centered (LC) transitions (HOMO~LUMO). The transit ions at 440-455 nm may be overlapped with dod bands, and metal-to-

li gand (MLCT) trans iti ons and those are correspond­ino to HOMO-I~LUMO and HOMO-I ~LUMO+1. o

Pure dod bands may appear at 630-640 nm.

Cyclic voltammclry

The redox property of the complexes was exam­ined by cycli c voltammet ry in the potential range +2.0 to -2.4 V verslls SCE. A representat ive voltam­mogram is shown in Fig. 2 and data are show n ill Table 4. The complexes display one quasireversibl e oxidation couple at - 1.45 V. The qU:.1sireversibility is exam ined from peak-to-peak separation, b.Ep z lOO mV . One elect ron nature of the coup le is exa mined 0 11

co mparing with current height of Fe(CN)()~-;Fe(CN )r,"" couple and Ip,,/I pc eq uals to 0.9- 1.0. On comparing with prev iously reported electrochemi stry of Co(l l) complexes l5

, we may assign that the ox ida ti on is clue to Co( lI )-centre in the complex . There are fou r qua­sireversible to irreversible reduction couples appear­ing at - - 0.6 V, - -0.95 V, - - 1.4 V and - I.60 V. The azo (N=N) group is a potential electro n transfer cen­ter U

.5

,C,. The azo function contri butes 46'/0 ancl 49 ';'o to form LUMO and LUMO+ I respectively. Thus. the red uctions may be assigned to I-N=N-)/ [-N- N-r, [-N-N-)"/[-N-N-J"".

This article reports the syn thesis and characteri za­tion of [Co(ex-NaiRh(N, hJ (ex-NaiR = l-alkyl-2-(naphthyl-a-azo) imiclazo les). One of the complexes has been characteri zed by single crysta l X-ray studi es . The complexes show hi gh poten ti al Co(l Il )/Co(lI ) redox couple alongwith azo reductions.

Supplementary material Crysta ll ographi c data for the structures have bee n

depos ited with the Cambridge Crysta ll ographic data cen ter, CCDC No. 25 1234 for [Co(ex-NaiEt)~( 1')21 (2b). Copies of this informati on may be obta ined free of charoe fro m the Director, CCDC, 12 Union Road. o Cambridge CB2, I EZ, UK (e- mai l:

2228 IND IAN J CHEM. SEC A. OCTOBER 2006

dcpos it @ccdc.ca ll1 .ac. uk or www: hllp ://www.ccdc. cam.ac.uk).

Acknowledgement Financi al support fro m the Department of Sc ience

and Technology, New Delhi is gratefu lly ack now l­edged.

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