Indian Jo Imal of Chemistry Vol. 45A, Jul y 2006, pp. 1638- 1642

Synthesis, spectroscopic (IR, electronic and FAB-Inass) and lnagnetic studies of SOlne mixed ligand cOlnplexes of chromium (III)

R K Dubey"-* , U K Dubey" & C M Mishrah

"Syntheti c Inorganic Metallo-Organic Research Laboratory. Deparlmelll of Chemistry, Uni versity o f Allahabad. All ahabad 2 11 002, India

hDeparlment of Chemi stry, R.J . College, M um ba i 400068, India

Ema il : raja lkoxy@yahoo.com.

Received 31 Octover 2005; revised 18 May 2006

Some ncw mi xed li gand co mplexes o f chromium (III ) of the type [Cr(LH LI)C1 ].2I-1 20 [where LI-I = SchilT bases (deri ved from the condensation of 2-aminopyri dine, 2-ami nophenol, o-tolud ine, p- tolud ine, aniline, 3-nit roaniline and anthranilic acid wit h salicylaldehyde/vanillin and substitu ted benzimidazole/be nzoxazole, or mereaptobcczimidazole; L=pyridine l have been sy nthesized by the interac ti ons o f chromium (III ) chl oride with corresponding li gand in 1:2 molar ratio in re tl uxing pyridine solution. The resulti ng products ha ve been characteri zed by element al analysis and spectra l as well as magnetic susceptibility measureme nts. Structures of the chromium (I II ) complexes are also proposed.

IPC Code: Inl. CI8 C07FII /OO

Chromiul11(lll ) complexes o f Schi ff bases and substituted benzi midazole/benzoxazole are o f g reat importance due to their bio logica l, pharmaco logical, cli nical and analy ti cal applicatio ns l

-J

. Chromium is considered to be an essenti a l trace e lement in experimental animals and probably in human be ings , where it is present in tri valent state4

. Bio logically, the metal acts as a cofac tor in the in iti ati on o f insulin acti on. Chromiu m(III ) ca n fo rm a te rnary complex between insulin -S and ti ssue insuli n receptor-SH , fac ilitat ing the initi al insuli n-ti ss ue inte rac ti o n. Chrom ium(I1I) complexes occurring in brewer, yeast and other foods, termed ' gl ucose tolerance fac tor ' have been fo und to possess outstanding bio logical activity . Therefore, a thoro ugh knowledge o f the coordi nation chemi stry of chromi um(lII ) mi xed ligand compl exes (invo lving di fferent donor ato ms) will be of much inte rest in e lucidating the struc ture­reac ti vity corre lati on of the said complexes.

Material and Methods All the used chemi cals and solvents were of A.R.

(BDH or Flub) g rade. So lvents were dried by the standard procedures). C hromium was determined by atomic abso rption spec troscopy, G BC-932 AA, and chlori de present in the co mpl exes was estimated by Yolhard's methoc( '. E lemental anal yses (C HN) were carried out on Herbaceous carlo Erba 1108 analys is at RS IC, C DRI Lucknow. IR (4000-200cm-l

) and

elec tronic spec tra were recorded on Perkin-Elmer grating and Pye-Unicam model 557/SP 8- 100 spectro photo meters. Magnetic susceptibility was measured o n Guoy-balance using Hg[Co(NCS)4) as standard. FAB-mass spectra of chromium(III ) co mplexes were recorded on JEOLS X 102/DA-6000 mass-spectrometer/data syste m using argon/xenon (6 kY, 10 mA) as the FAB-gas .

The Schiff bases (sapH, o-smab H, p -smabH , sabH , saphH , saaH and vaaH) were synthesized by reflu xing (for 4-5 h) a mix ture o f an equi molar amount of aldehydes (such as salicy la ldehyde and vanillin) with correspo nding amines (such as 2-aminopyridine, 0 -

to ludine, p-to ludine, aniline. 2-ani inopheno l, 3-nitropheno l and anthranillic ac id) in methano li c medium 0 11 water bath. The resulting products were further rec rys talli zed using THF/be ll zene mi xture, 2(o-hydroxyphenyl)-benzoxazole7 and 2-marcapto­benzimidazole were prepared by standard literature procedure. T he general struc tures o f the ligand are g iven in Fig. 1.

Synthesis of complexes

The chromium(JII) complexes o f the type [Cr(L)2)( L 1)CI ).2H20 were prepared by reacting a mi xture of chromium(lll ) chloride hexahydrate with correspo nding ligands (LH) in 1:2 molar rati o in freshly dis till ed boi ling pyridine , immedi ate ly fo llowed by additio n of zinc du st. T he mi xture was

DUBEY e/ (/1.: STUDIES OF SOME MIX ED LIG AND COMPLEXES OF CHROMIUM (III ) 1639

H k Y

@-6 = N--\Q;-Z O-H

Where X = H (sablI); CH)(o-smabH); Y=NO,(snabH); Z=CH)(p-smabH)

Where X = COOH(saaU); OJ-I(saphl l); C-X replaced by N(sapIl)

refluxed for -2 h and then filtered while hot and the filtrate was allowed to attain room temperature. The filtrate was treated with few mL of water, stirred thoroughly and filtered to obtain chromium(II1) complexes. All the sy nthetic and analytical details are g iven in Table 1. The synthesis and structures of the representati ve complexes are given in Fig. 2.

©()-o©()-o N 0-11 0-11

(Hopbz) (Hopbox)

Fig. I - Structure of the ligands

Results and Discussion The new mi xed ligand complexes have been

sy nthesized by the reacti on of CrCl,.6H20 with corresponding ligand (LH) in pyridine and the

Table I - Sy nthetic, analytical and magnetic data of the va ri ous mi xed li gand complexes of chromiulll(lII ) containing Schifr bases and substi luted benzi Illidazole/benzoxazole

S. Reactants (g, mmol) Product Found (Calcd) (%) ~l cff

No. (g, % yield) C H N Cr CI (BM )

CrCl , 6 H20 + sapH [Cr(sapl1(py)C I].2H 20 (1) 57.80 4. 18 11 .36 8.6 1 5.80 3.89 (1.708, 6.4 )(2.54, 12.8) (2 .365g, 6 1.85) (58.33) (4.55) (11.72) (8.70) (5 .93)

2 CrCI, .6H20+ o-smab [Cr(o-smabh(py)C I]. 2H10 (2) 63. 13 5.58 6.87 8.22 5.43 3.79 (1.332, 5.0)(2.112, 10.0) (2.439g, 78 .33) (63.60) (5.33) (6.74) (8.34) (5 .68)

3 CrCI, 6H 2O+p-smabH [Cr(p-smabh(py)C1].2H20 (3) 63.36 5.20 6.70 8.26 5.33 3.70 ( 1.646, 6.2)(2.6 1 I, 12.4) (3 .068g, 79.7 1) (63.60) (5.33) (6.74) (8.34) (5.68)

4 CrCI.1 6H20+ sabH [Cr(sabl1(py )Cl].2H20j (4) 63.10 4.44 6.8 1 8.65 5.76 3.90 (0.943,3.538)( 1.396,7 .077) (1.335g, 63.43) (62.56) (4.9 1) (7.06) (8.74) (5.95)

5 CrCI .1 .6H20+ saphH [Cr(saphh(py)Cl].2H10 (5) 60.1 8 4.90 6.29 8. 15 5.49 3.85 (0.957,3.59)( 1.532,7. 18) ( 1.492g, 66.28) (59.37) (4.66) (6.70) (8.29) (5.65)

6 CrCI, 6H 20 + snab H [Cr(snabh(py)CI]. 2H20 (6) 54.75 4. 18 10.84 7.45 5.09 3.61 (0.932,3.50) ( 1.695,7.0) (1.56 Ig. 65. 15) (54.34) (3.97) (10.22) (7.59) (5. 17)

7 CrCl J .6H20+ saaH [Cr(saah(py)CI].2H20 (7) 58.73 4.65 6.60 7.56 5.05 3.72 (0.253 , 0.95) (0.458, 1.9) (0.4 107g, 63.39) (58.02) (4.27) (6. 15) (7.6 1) (5.1 9)

8 CrCI.1 .6H20+ vaa H [Cr(vaah(py)C I] .2H20 (8) 56.85 4.27 5.07 6.79 4.59 3.88 (1.25,4 .7)(2 .55,9.4) (2.35g, 67.3 1) (56.56) (4.47) (5.65) (6.99) (4.77)

9 CrCl J 6 H20 + Hopbox [Cr(opbox)(pyhCl].2 H20 (9) 59.03 4.25 6.94 8.23 5.58 3.77 (0.588,2 .206)(0.93 1, 4.4 1 ) (0.82 Ig, 59.79) (59.80) (4.04) (6.74) (8.35) (5.69)

10 CrCIJ 6H 20 + mbzH [Cr( mbzh(py)Cl].2 H10 (10) 45.99 3.39 13. 17 10.06 6.92 3.78 (1.263,4.74)( 1.424,9.48) (0. 1.835g, 77.32) (45.55) (3.82) (13.97) (10.37) (7.07)

Table 2 - Electronic spec tral data of mixed complexes of chrom ium (Ill ) contain ing Schifr bases and substituted benzimidazo le/benzox azole

Complexes Transition (cm· l) 10 Dq (cm· l

) B (cm· l) f)J5

"A2g~ 4 T2g (F) 4A2g~ "T2g (F) 4A2g~ 4TIg (P)

15337 22077 342 10 15337 695 0.67 2 162 15 23252 35714 16215 705 0.68 3 16060 225 10 36 10 1 16060 7 10 0.,68 4 16793 22449 363 13 16793 645 0:62 5 16290 22977 35 120 16290 630 0.61 6 16750 23800 36 190 16750 675 0.65 '7 155pO 22200 34600 15500 696 0.67 8 16360 22647 34496 16360 553 0.53 9 15836 22227 34600 15836 645 0.62 10 ' 17210 23996 374 15 1721 0 670 0.65

1640 IND IAN J CIIEM. SEC A. JULY 2006

1 @-L~z

O-H

CrCI3.6H20 j(i) Hot pyridine 1 : 2 (ii) - 19. Zinc ddust

(i ii) t:,. -3h

[where X = II for (sab); CH) for (o-smab);

Y=N02 for (snab); Z=CH) for (p-smab)]

Fig. 2 - Syllth s is a lld s truc ture o f th e Cr(l ll ) complexes w ith Sc hilT bases

react ion products of the co mplexes thus formcd are represented by the equati on:

CrCh.6H,O+LII hot pyridine) [Cr(LhCL')CI].2H20 . - - I g zinc dust

where Lli = salicylidene-2-aminopy ridine (s~lpII),

sa li cy lidene-2- methyl-l-aminobcnzcnc (o-smabII ), sa li cy lidene-4-methyl-l-amino-bcnzcne (p. smabH), sa li cy lidcne- I-aminobenzenc (sabll) , Salicyliclcne 2-ami nophenol (sa phIl), Sal icy lidcnc-3-n i troani Ii ne (s nabH), salicy lidene-anthranili c acid (saaIl ), Vanilidene-anthranilic acid (vaaH ), 2-(o-hydroxy­phenyl)-benzoxazole (Hopbox) and 2-marcaptoben­zimidazo lc (mbzH).

These complexes are non-hygroscopic, air stable and grcen coloured :s_olid , and purity of the complcxes are checked by TLC..They are so luble in hot pyridine, DMSO and DMF, big ' insoluble in .ether, benzene and chloroform . The complexes are lIiernlally stable and do not melt or decomposed up' io 250°C. Molar conductance of thc complexes (in DMSO) reveals

Fig.:> -- Proposed struc ture of the Cr(lI.I) co mplexes

thei r non electro lyti c natures. The sy nthetic and analytical data of thc complexes Lire collected in Tablcs I and 2. Elemcn tal analysis valucs arc in close agrccmcnt wi th the valucs calculated for molecu lar formula assigned to th csc complexes, which is further supported by the FAB-mass studies of represcntati ve co mplexcs .

It is assumed, on the basis of establishcd facts that bonding takes place through '0 ' atom, after dcprotonation of 011 group prcsent in the ligands and coordinati on via 'N' of azomethyne group in all these li ga nds except in the case of mcrcaptobcnzimidazole, whcre mode of coordination is 'S' atom. Gcncral st ructures of the representati ve complexes are shown in Fig. 3.

lR spectral studies

The IR spectra of the li gand showed bands in the range 1655-1 628 cm-I which are attributed to V C=N

band which is shifted to lower frequency region 16 18-1595 cm-I in all the chromium(lll) complexes (Table 3) indicating that bonding is taking place I I I I . - oj l il 1' 1 t lroLl g 1 t le azomet line nitrogen' . le vc-o

(phenolic) stretching frequencics of the li g<'lIlds were observed at 1728-1 259 cm-I in thc free ligands which get shifted in highcr rcgion 1265-1 290 cm-I. It is indicati ve of bonding through phenolic oxygen II. The broad band appearing at - 1030 cm-I in the spectrum of the li gand has been ass igned to -OCH, group. A broad band observed at -3300 is indicati ve of NH group present in imidazole rings . This peak is almost unchanged in co mplex 10. However, VC=N mode (imidazolc-tertiary-nitrogen) occurring at -1610 cm-I

in the complexes indicated the coordi nation of li gand to chromium via their imidazo]e-tertiary-nitrogenI2.13

The infrared spcctra of all the complexes (1-10) showed the pyridine ring vibrations at -3450 cm-I (s) and -1050 cm-I (m). These bands also support coordination of pyridine mo lec Lllcs l~ . A broad band was observed in the complexes in the range -3450 em-I, which is not present in the li ga nd spectrum, due

DUBEY el!ll. STUDIES OF SOME MIXED LIGAND COM PL EXES OF CH ROMIUM (III ) 164 1

Tab le 3 - Charncteri stic IR rrequencies (em-I ) of mixed ligand complexes oi" ehroll1iull1 ( III) cOlllaining Schiffbases and substituted benzil11idazo le/benzoxazo le

Complexes VCr-N VCr-O VCr-S v 1("-0) Vc ~ :-.:

Phenolic

560 442 1276 1602

2 55 8 463 1278 159 7

3 552 460 128 1 160X

4 545 45H 1280 1596

5 539 445 1289 1595

6 577 456 1775 1617

7 542 459 16R6

8 55 1 447 1603

9 558 453 1279 1605

10 585 402 1599

to VOH of latticc water moleculcs ls prcsent in all thesc co mpounds sy nthes izcd dur ing thc prescnt sourcc of inves tiga ti ons. This band is supportcd by an addi ti ona l band appearing in the range 840-730 em-I , which aga in confirms thc prescnce of lattice held water mo lecules l6 in these complexes.

The complexes also showed medium to strong intensity bands in the region 570-535 cm· l, 46 1-440 cm- I and 402 cm· 1 which ca n bc attributed to V( Cr. N), v(Cr.O), and V(Cr- S), bands respec ti vc lyl 7

Electron ic spectra l studies

The electroni c absorption spectra of all th e chromium(lll ) complexes were measured in DMSO. These spcctra are quite similar to onc another and may be in terpreted on the basis of an oc lahedral environment around chromium(l I I) tn these complexes. The complexes showed threc bands - 16200 cm-I, - 22500 cm-; and - 32400 cm-; in the regIons. Thesc bands ca n be assigned to 4A2g~4T2g(F)(VI)' 4A 2g~4T2g( f)(V2 ) and 4A 2g ~ 4Tl g(P) (V3) transitions respectively in the order of increasing encrgy, Various ligand field parameters have bcen eva luated for the Cr(I ll ) co mplexes. Thc va lu e of first spin-allowed transiti on (VI) at - 16200 CI11 ·

1 is directl y taken as 10 Dq. The va lue of Racah para mcter (8),

vcoo- V-OClI .1 Ve ~ 1'1 v:\°2 1'011 Pyri dine

14491s) 3-100 I 0671~ 1 ) R5X

14791s) 3-1-13 104°(1 )) X3R

146Xls) 3-12 8 10(5111) H2O

14501s) 3-122 103411.1) X27

1472(s) 3·nO 104°1\1 ) H2O

14651s) 1330(s) 3-14 7 10471,11) X27

1396 1452(5) 3-12-1 1034(11) X3 6

1350 2825 1460(5) 3-1 72 105H(11) X40

14 XO(s) 3-145 1040(1 1) H16

1400(s) 3445 I 075(~ 1 ) H-Il

ca n be calcu lated by the eq uat ion of Undcrhill and 8i liing lX 8 = (V3 + V2 - 30 Dq)/ I 5.

The observed value (620± 100) of the Raca h inter­elec troni c repul sion parameter (8) was compared against the va lue (J 030 cm· l) fo r the free Cr" ion, which indicates considerabl e covalent character of the metal-ligand bonds in these derivati ves with the cova lency factor W35 for sp in all owed transitions) varyin g in the range (0.6±0. 1). Phys ica l state data of chromium(Ill ) complexes are provided in Table 4.

Mag neti c studies

The observed room temperature magnetic moment va lu es l9 (Tab le I) for chromium(lll ) complexes, sy nthesized during the present course of in ves ti gations, are obta ined in the range 3.61-3.90 8M , consistent with thc th eoreti ca l spi n only va lue

' + 3 (Pcl'r= 3.87 BM) for Ct·-' 'd' system.

FAil-mass spectral studies

The f AB-mass" spectrum of the comp lexes, such as [Cr(saph(py)C l. ]2 1-1 20 1 and [Cr(saaH py)C l.]. 21-1 20 7, ex hibited prominent molec ular ion peaks at lIl /z = 561 and 647 , co rrespo nds to the fo rmul a I and 7, whi ch suggests thc monomeric nature of the complexes, It is important to mention herc that the

1642 INDI AN J CHEM , SEC A, JULY 2006

Table 4 - Mi xcd li gand complexcs of chromium (III) containing Schi IT bascs and substitutcd bcnzimidazole/bcnzoxazole

Complcxcs Physica l statc Mc lting poi nt (0C)

Light grecn 300(a) 2 Dark green 270(a) 3 Green 300(b) 4 Light green 320(b) 5 Brown 330(b) 6 Brown 3 I I (a)

7 Whiti sh green 310(b) 8 Dark green 330(b) 9 Y cllowish brown 325 10 Sky blue 300(b)

a = dccomposed b = neithcr mclt nor dccomposed

+ [N2Cr)

m/z = 80.5 .

t-CH ·

[C29H27Nl04CrCIJ ~ [C29112JN ~2CrC ~+ mJz ~ 561(monomcr)

. !-C!" [CHNzC r] t [C29H2JN~02Cr] t mlz = 93.5 rnJz = 525.5

I- CH· 1-CsHl: 9

[CzHzN1Crt [C24Hl SN401Cr] mlz = J 06.5 mlz = 446.5

i-C6H40" " 1- Cs~N" [CSIIGN pcr] '~ C&H.O· [CI4HION20 2Crt .:.fcJ::Wi [C'9H'4N]0 2Cr]1 mIl = 198.5 m/z = 290.5 mlz - 368.5

FAB-l11ass fra gmentation panern of [Cr(sap)1(Py)CI] .2I'hO Scheme 1

[C3JH29N20~CrCO ~ [C))112lN 20 6CrC11 + + [er)

miz = 52.5 mlz = 647 (monomer)

1-C,HlO· 1- Cl "

[C,I-lsOer) t [CJ3H2.1N206Cr) • m/r.= 157.5 ml1;= 661.5

1-ClllsO· . • 1-CsH; + - C7 i-l50 2N [C H NO C ]t C7H50 2N

[C, 4I-1 lO02Crl .. 21 IS! 4 r. [C2&H2~N206Cr)

mh = 262.5 mlz = 397.5 n,!z ~ 532.5

FAO-mass fragmentation pattern of (Cr(saaMpy)CI].2HzO

Scheme 2

presence of H20 molecules 111 all complexes suggested by elemental analysis as we ll as infrared

spectral studies were in the form o f lattice water molecules not as coordinated H20 molecules. Other important peaks were observed nn dicating fragmentation of the ligand from complexes by the formation of radi ca l cations which are represented in Schemes I and 2.

Acknowledgement Th e authors are grateful to RSIC, IlT, Mumbai, for

providing FTIR and magnetic facility. C DR] is also acknowledged fo r elemental analys is and FAB-mass spectral stud ies.

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