Chiang Mai J. Sci. 2013; 40(4) 625

Chiang Mai J. Sci. 2013; 40(4) : 625-635http://it.science.cmu.ac.th/ejournal/Contributed Paper

Synthesis, Characterization and AntibacterialEvaluation of Some Mixed-metal Mixed-ligandComplexesMohammad N. Uddin*, Didarul A. Chowdhury and Jahowa IslamDepartment of Chemistry, University of Chittagong, Chittagong-4331, Bangladesh.*Author for correspondence; e-mail: nasircu72@gmail.com

Received: 26 November 2012Accepted: 20 February 2013

ABSTRACTAttempt has been taken to prepare and study some of the mixed metal complexes

using varied ligand systems. Investigation of the spectral properties (like IR, UV), magneticsusceptibility, conductance values of the prepared complexes helped to the characterizationof their structural features. The mixed metal complexes have been found to be of the type[MLx][MLy] where, M = Cu, Cd, Ni, Co, Zn and M= Hg, Lx = ethylenediamine, aniline,NH3and Ly = I

, SCN-. Antibacterial activities of some of the prepared complexes were studied.

Keywords: Mixed-metal complexes, antibacterial activities, ethylenediamine

1. INTRODUCTIONNumerous heterobimetallic and

homobimetallic complexes have beenprepared in which metals are linked byunsaturated or saturated ligands. Alsothat, mixed metal complexes shows someexceptional structural behavior. A seriesof heterobinuclear, thiocyanato-bridgedcomplexes of macrocyclic ligands ofcopper(II) and nickel(II) have beencharacterized by variable-temperaturemagnetic susceptibility (1.72–300 K)by Tomkiewics et al.[1]. Xiang et al. [2]prepared [Zn(bipy)3][Zn(SCN)4] complexand characterized by X-ray diffractionanalysis. Pryma et al. [3] have synthesizedthree heterometallic Cu/Cd complexes, (1)[Cu(en)2CdBr4].dmso, (2) [Cu(en)2CdI4].dmfand (3) [{Cu(en)2}3Cd(NCS)6](NCS)2.

Ohba et al. [4] synthesized the polymericcomplex [Ni(en)2]3[Fe(CN)6]2.2H2O (en =

ethylenediamine) bridged by cyanideligands between Ni(II) (S=2) and Fe(III)(S=1/2). [Ni(en)2]3[Fe(CN)6]2.2H2O [4]and [Ni(pn)2][Fe(CN)6]ClO4.2H2O [5](pn = 1,2-diaminopropane) have chain and2D sheet structure. Whereas complex[Ni(tren)]3[Fe(CN)6]2.6H2O (tren = tris(2-aminoethyl)amine) characterized to have a3D structure consisting of -Fe-CN-Ni-NC-Fe-CN- chains [6].

Langenberg et al. [7] studied structuraland magnetic properties of the pentanuclearcomplexes [(Ni(bpm)2)3(Fe(CN)6)2].7H2O(bpm = bis(1-pyrazolyl)methane) and[(Ni(bpy)2)3(Fe(CN)6)2].7H2O (bpy = 2,2i-bipyridine). Kou et al. [8] studiedferromagnetic complex [Cu(en)]3[Fe(CN)6]2.3H2O. Suzuki et al. [9] preparedand characterized double complex salts[Cu(en/tn)2]2[Fe(CN)6].nH2O (tn = 1, 3

626 Chiang Mai J. Sci. 2013; 40(4)

diaminopropane) and cyanide-bridgedcomplexes, [{Cu(dien/dpt)}2(NC)2Fe(CN)4].4H2O (dpt = dipropylenetriamine). Zouet al. [10] studied crystal structure andmagnetic properties of trinuclear complex[(Cu(tren))2Fe(CN)6]. 12H2O. Xiang et al.[11] prepared [NiL1]3[Cr(CN)6]2.18H2Ofrom the reaction of K3[Cr(CN)6] and[NiL1](ClO4)2 in water medium [ where,L1= 3,10-bis (2-hydroxyethyl)-1,3,5,8,10,12-hexaazacyclotetradecane].

Bertini et al. [12] synthesized and studiedthe compounds K[Cu(en)2][Fe(CN)6]and [Cu(L)2]3[Fe(CN)6]2.H2O (L = (N-ethyl)ethylenediamine, = 4; L = (N-propyl)ethylenediamine, = 5). The structuresof the compounds of the type[Ni(1,1dmen)2]2 [Fe(CN)6]X.yH2O (1,1-dimen= 1, 1dimethylethylene diamine; = CF3SO3,y = 2; = BzO, y = 6; = N3, y = 4) weresolved [13]. Kundu et al. [14] studiedspectral and magnetic properties of thecomplexes [CuL2][L2Cu(CN) Fe(CN)5]2.H2O (L = piperazine, = 5, L = N-methylpiperazine, =6, L = N, N�-dimethylpiperazine, = 6).

The literature survey reveals that verylittle work has been done on the coordinationchemistry of mixed metal complexes.The present work has been an attempt toprepare and study some mixed metalcomplexes using varied ligand systems.Investigation of the spectral properties (likeIR, UV), magnetic susceptibility, conductancevalues of the prepared complexes helped tothe characterization of their structural features.Antibacterial activities of some of theprepared complexes were also studied.

2. MATERIALS AND METHODS2.1 Instrumentations

The analyses of the metal contents ofthe prepared complexes were obtained byAtomic Absorption Spectrophotometer

(model Thermo Scientific ICE-3000) fromB.C.S.I.R. Laboratory, Chittagong. TheInfrared spectra of the prepared complexeswere obtained by FTIR spectrophotometer(Model- 8900, Shimadzu, Japan) using KBras the matrix in the range 400-4000 cm-1 fromresearch laboratory of the Department ofChemistry, C.U.E.T., Chittagong. Electronicabsorption spectra were run on ShimadzuUV-Visible Recording Spectrophotometer(Model-1800) using 1 cm cells. An electrothermal melting point apparatus was usedfor the determination of the meltingor decomposition points of the complexes.Conductivity measurement was performedon a Philips Conductivity Meter (Model-HI9255). Determination of conductivity of anelectrolytic solution involves measuring ofthe electrical resistance of that solution ata particular temperature, usually 25C.Magnetic susceptibility values of some ofthe prepared complexes were determinedusing the Magnetic Susceptibility Balance,(Sherwood Scientific) from RajshahiUniversity and in the laboratory of ChittagongUniversity, Bangladesh.

2.2 ChemicalsEthylenediamine, aniline, methanol,

chloroform and N, N-dimethylformamide(DMF) were obtained from Aldrich ChemicalCompany Ltd. Ammonium nitrate andpotassium iodide were obtained from M|SMerak (Germany). Perchloric acid, nitric acid,sulphuric acid and ammonia were obtainedfrom BDH Chemicals Ltd. All chemicalsexcept solvent were used as received. Solventswere dried by standard methods and distilledunder an inert atmosphere.

2.3 Preparation of Mixed MetalComplexes

Preparation of [HgI4]2-or [Hg(SCN)4]

2-: 2mmol (0.54 g) of mercuric chloride (HgCl2)

Chiang Mai J. Sci. 2013; 40(4) 627

was dissolved in about 40 cm-3 of water. Thena slight excess of 10% KI or NH4SCN solutionwas added dropwise. A clear solution of[HgI4]

2- or [Hg(SCN)4]2- was formed.

Preparation of [M(en)3]2+: In another

beaker, 2 mmol (0.589 g) of metal sulphateor nitrate was dissolved in about 50 cm-3 ofwater. An excess amount of ethylenediaminewas added to it dropwise. A small amount(10-15 crystals) of ammonium nitrate andpotassium iodide (KI) or ammoniumthiocyanide (NH4SCN) was added. Themixture was heated to boil for about 2-3minutes. NH3 or aniline was used as ligandfor the preparation of [M(NH3)6]

2+ or

[M(aniline)6]2+, respectively.

Mixed Metal Complexes, [MLx][MLy]:Two solutions were mixed together in theirhot states. The mixture was stirred forsometimes and allowed to cool with frequentstirring. The precipitate was formed almostimmediately and the solid product wasfiltered off and washed with water, driedover calcium chloride.

Color, M.P. and percentage of yield andmetal contents of the prepared mixed metaland mixed ligand complexes are includedin table 1. Percentage of metal contents wasdetermined by AAS.

Table 1. Color, % of Yield, M.P., % of Metal contents of the prepared mixed metal andmixed ligand complexes.

*The mercury content of the complexes could not be determined

2.4 Evaluation of Bacterial ActivitiesFor the detection of antibacterial activities

and sensitivity spectrum analysis, the discdiffusion method by Bauer et al.[15,16] wasfollowed. Nutrient Agar (NA) was used asbasal medium for culture of test bacteria andN, N-dimethylformamide (DMF) was usedas a solvent to prepare the desired solution(1%) of the compounds initially.

Nutrient Agar (NA) medium was preparedusing the composition; Beef extract, Peptone,NaCl, Agar, Distilled water. 1000 mL ofdistilled water was taken in a beaker and then

15 gm of agar powder, 3 gm of beef extract,5 gm of peptone and 0.5 gm of NaCl wereadded slowly in that water and they weremixed thoroughly with a glass rod, heatedto boiling for 10 minutes. After 10 minutesof boiling, the medium was transferred in250 mL conical flasks at the rate of 200 mLper flask. The conical flask was closedwith the cotton plug and autoclaved at 121Cand 15 psi pressure for 15 minutes, thenculturing of different micro-organisms wasperformed.

Sensitivity spectrum analysis: Paper discs of

Complexes

[Zn(en)3][HgI4]

[Cd(en)3][HgI4]

[Ni(en)3][HgI4]

[Co(en)3][HgI4]

[Zn(NH3)6][HgI4]

[Ni(NH3)6][HgI4]

[Cd(Aniline)6][HgI4]

Color

Yellow

Yellow

White

Brown

Yellow

Green

Whitebrown

Yield(%)

95

95

95

90

95

95

90

M.P.(C)

198(d)

198(d)

200(d)

200(d)

200(d)

210(d)

210(d)

% ofMetal(Calc.)

7.83(6.86)9.10

(11.23)6.74

(6.20)6.15

(6.22)7.80

(7.47)6.95

(6.75)9.39

(8.15)

Complexes

[Cu(en)2][Hg(SCN)4]

[Cd(en)3][Hg(SCN)4]

[Ni((en)3][Hg(SCN)4]

[Zn(en)3][Hg(SCN)4]

[Zn(Aniline)6][Hg(SCN)4]

[Co(NH3)5Cl][Hg(SCN)4]

M.P.(C)

164-166

128-129

182-184

146-148

200(d)

200(d)

Color

Violet

White

Purple

White

White

Blue

Yield(%)

95

95

95

95

95

90

% ofMetal(Calc.)10.97

(10.31)16.84

(15.49)9.20

(8.73)10.21(9.64)6.87

(6.19)10.50(9.62)

628 Chiang Mai J. Sci. 2013; 40(4)

5 mm diameter were soaked with 10 mL from2% solution of test complexes. 0.2 mL ofthe suspension of test organism was taken insterilized glass Petri plates of 100 cm diameterand then the molted and cooled (45oC)NAmedium was poured at the rate of 10 mLper Petri plate and shaked gently. Then thediscs with test complexes were placed on theseeded agar plate. A control plate was alsomaintained in each case with solvent.The plates were kept firstly for 24 hours atlow temperature (4C) and the test complexdiffused from disc to the surroundingmedium by this time. The plates were thenincubated at 352C for growth of testorganisms and were observed at 24 hoursinterval for two days. The activity wasdetermined by measuring the diameter of thezone of inhibition in mm.

Test organisms: In the present study, toscreen the antibacterial activities of differentcomplexes, a variety of bacterial strains wereused as test organism. Bacterial strains werecollected from the microbiology laboratoryof the Department of Microbiology,University of Chittagong. Collected pathogensare listed as: Gram-positive, a) Bacillus cereusBTCC 19, Gram-negative, b) Salmonella typhiAE 14612, c) Eschericahia coli ATCC 25922.

A number of mixed-metal complexeshave been tested for antibacterial evaluation.

3. RESULTS AND DISCUSSIONMixed-metal mixed-ligand complexes

were prepared by using water as the solvent.Mixed metal complexes were prepared by thereaction of one metal complex with a differentmetal complex in molar ratio 1:1. All thecomplexes were obtained almost immediatelyafter mixing of the component metalcomplex solutions. During preparation of[Cd(aniline)6][HgI4], the [Cd(aniline)6]

2+

complex mixture was heated to dissolve theoily layer formed due to the presence of

aniline. After that, both solutions wereadded at hot state. Then the mixture washeated again for about one hour at lowtemperature. The precipitate formed wasseparated out by filtration and preserved ina desiccator.

The complex [Cd(Aniline)6][Hg(SCN)4]was formed immediately. To avoidpossibility of decomposition of [Hg(SCN)4]to some blackness of HgS, heat was avoidedduring preparation of the complexes[Cd(en)3][Hg(SCN)4], [Zn(en)3][Hg(SCN)4]and [Co(NH3)5Cl][Hg(SCN)4].

All the complexes are insoluble inchloroform. Some of them are moderatelysoluble in methanol. All complexes are highlysoluble in DMF except [Co(en)3] [Hg(SCN)4].This complex is moderately soluble in DMF.The metal analysis data indicate formation ofthe desired complexes with 1:1 metal ratioof the complex cation and the complex anion.

Primarily, the complexes werecharacterized qualitatively by the followingprocedure:

A little amount of the preparedcomplex was taken in a test tube. Thenconcentrated nitric acid (HNO3) was addedto the sample and gently warmed on a waterbath for the decomposition.

The presence of Cu, Cd, Ni, Co orZn with mercury was determined by passingH2S gas to the acidified solution. The blackprecipitate formed indicated the presence ofHg. Then the filtrate solutions were treatedby adding NH4OH and H2S. The whiteprecipitate formed indicated the presence ofZn, black precipitate formed for Ni andyellow precipitate formed for Cd. Cu andCo in mercury containing complexes weredetermined by formation of brown and bluecolors, respectively with the addition ofpotassium ferrocyanide.

Chiang Mai J. Sci. 2013; 40(4) 629

3.1 Infra-red SpectraTentative infrared spectral bands of

some mixed metal complexes in table 2.Representative IR spectrum of [Cd(Aniline)6][HgI4] is shown in figure 1. The bands3320-3295, 2990-2965 and 1600-1585 cm-1are assigned to N-H, C-H, C-C, respectivelyfor mixed metal complexes by Pryma andHamza et al.[3,17]. The bands appearing at1315-1400 cm-1 (specially the highest frequencyones near 1400 cm-1) have been assigned toC-N mode. Dobrzanska et al.[18]

haveprepared some mixed metal complexes whereCaN frequency was observed at 2130-2060cm-1. Pryma and Cernak et al.[3,19]have assigned a band near 2095 cm-1 and2136 cm-1 to CaN for copper-cadmium andcopper-palladium mixed metal complexes.Rao and Tomkiewicz et al. [1,20] also havedescribed the location of the C=N bonds inthe approximate same region in several mixedmetal complexes containing CN groups. Onthe basis of these studies, the band observedfor the present complexes in the regions

of 1200-1000, 1520-1600, 1360-1401,2000-2250 cm-1 have been assigned as dueto C-C, C=C, C-N and CaN, respectively.In addition frequency near 690-820 cm-1 hasbeen assigned to c-s for the preparedcomplexes [21].

Appearance of strong CaN bands in theregions 2020-2096 and 2100 cm-1 in thepresent complexes is a good indication ofM-SCN-M coordination of the thiocyanategroup. Navarro et al. [22] using normalcoordination analysis have assigned thebands for Hg-I frequency at 155 cm

-1.No Hg-I stretching frequency could bedetected in the present study since IR spectrumcould not be run below 400 cm-1. El-ajailyet al. [23,24] have prepared and investigatednew Schiff base complexes of Cr(II), Pb(II)and TiO(IV) and observed new bands at444-540 cm-1 attributed to M-N vibrations.The bands of prepared complexes appearingat 444-540 cm-1 have been assigned to M-Nvibrations [25].

Table 2. Infrared spectral bands of some mixed metal complexes.Complexes

[Cd(en)3][Hg(SCN)4]

[Ni(en)3][Hg(SCN)4]

[Cu(en)2][Hg(SCN)4]

[Zn(en)3][HgI4]

[Cd(en)3][HgI4]

[Ni(en)3][HgI4]

[Cd(Aniline)6][Hg(SCN)4]

[Zn(en)3][Hg(SCN)4]

[Cd(Aniline)6][HgI4]

N-H3157(w)3265(ms)3277(s)

3331(ms)3309(w)

3261(w)

3257(w)

3253(ms)3336(s)3275(m)3331(w)3298(w)

C-C997(m

1049(m)999(s)

1020(m)1031(m)1087(s)1006(w)1274(m)1020(ms)1055(ms)1095(w)1124(m)1006(s)

1058(ms)1001(m)1103(s)1489(s)

1570(ms)

C=C

1582(ms)1600(s)

1330(w)1450(w)

C-N1317(w)1448(m)1365(w)1452(s)1388(m)1454(vs)1369(w)1460(w)1325(ms)1456(m)1315(w)1390(m)1340(w)1352(w)1319(m)1365(w)

CaN(cyanide)2102(s)

2154(ms)2079(vs)2104(s)2096(w)2065(w)

2113(ms)2071(sh)2119(w)2160(w)

C-S709(m)740(w)711(m)731(w)694(m)

690(vs)819(ms)711(m)785(ms)

S-CaN596(s)663(s)601(w)

557(s)690(s)653(m)

420(w)435(w)

M-N430(s)474(w)446(w)503(s)439(m)532(m)472(w)507(w)462(ms)594(w)491(ms)578(m)449(s)462(s)445(s)459(s)690(s)

* vs = very strong; s = strong; ms = medium strong; m = medium; w = weak; vw = veryweak; sh = shoulder.

630 Chiang Mai J. Sci. 2013; 40(4)

3.2 Electronic SpectraThe UV-vis spectroscopy is a simple but

powerful tool for the interpretation ofchemical bonds and structure of most chelates.Because of the insolubility of the presentlyprepared complexes in common organicsolvents, the spectra of the preparedcomplexes were run in dimethylformamide.The bands at around 530 nm in the visibleregion for the prepared complexes can be

assigned to d-d transition. The peaks observedbelow 350 nm are assumed as due to n and n transitions.Figure 2 shows the electronic Spectra of[Ni(en)3][Hg(SCN)4] (lower) and [Cu(en)2][Hg(SCN)4](upper). And the peaks observedat 983 nm may be assumed as due to thepresence of mercury tetraiodide or mercurytetrathiocyanate.

Figure 1. IR spectrum of compound, [Cd(Aniline)6 ][HgI4].

Figure 2. The proposed structure of the complex, [Cu(en)2][HgI4].

Chiang Mai J. Sci. 2013; 40(4) 631

3.3 Magnetic MeasurementsFrom the experimental values of

magnetic measurements of some of theprepared complexes, it is found that magneticmoments of some of the mixed metalcomplexes are lower than the expectedtheoretical spin only values. The possiblereason of such lower magnetic moment maybe due to some antiferromagnetic interactionsin the mixed metal complex. The exchangeinteractions seem to be super exchange typeand most likely through the thiocyanatoor the iodo groups as shown by figure 2resemblance to the crystal structure of[Cu(en)2CdI4] [3]. However, weak bonds andlonger bond lengths may hide or preventpossibility of exchange interactions.

3.4 Molar ConductanceUsing N, N-dimethylformamide (DMF)

as the solvent the solutions of the complexes(of the order of 10-3 M) were used forconductivity measurements. The molarconductance values of the presently preparedcomplexes are shown in table 2. Theconductance values of 105-53 ohm-1cm2mol-1 in DMF solutions corresponding to 1:1electrolytes6 strongly support proposedformulation of the prepared complexes. Thissuggests +2 oxidation states of the metal ionspresent in such complexes.

The electronic spectral, magnetic andconductivity data for the mixed metalcomplexes are given in table 3.

Table 3. The electronic spectral data, magnetic data and conductivity data for the mixed metalcomplexes.

Complexes

[Cd(en)3][Hg(SCN)4][Ni(en)3][Hg(SCN)4][Cu(en)2][Hg(SCN)4]

[Zn(en)3][HgI4][Cd(en)3][HgI4]

[Zn(Aniline)6][Hg(SCN)4][Co(NH3)5Cl][Hg(SCN)4]

[Ni(en)3][HgI4][Ni(NH3)6][HgI4][Co(en)3][HgI4]

[Ni(en)3][Hg(SCN)4][Zn(NH3)6][HgI4][Cu(NH3)6][HgI4]

[Cd(Aniline)6][Hg(SCN)4][Zn(en)3][Hg(SCN)4]

Medium

DMFDMFDMFDMFDMFDMFDMFDMFDMFDMF

Spectral bands

983,533,507,459,433,393,355,341,273982,533,510,483,460,433,393,355,341

983,556,533,518,484,460,433,393,341,278983,533,507,483,460,433,393,328,305

983,533,510,483,460,433,393983,533,507,483,459,433,393

982,533,510,483,460,433,393,276982(sh),533,510,483,459,433,392982(sh),533,508,483,459,433, 392

983,533,507,482,459,433,392

eff(B.M)

2.12

3.692.642.274.21

Molar Conductivitym, ohm

-1cm2mol-1105

166.285.496.6123.4101.483.468.479.8131.891.691.682.452.8

3.5 Effect on the Bacterial GrowthIn the present work, some of the

prepared mixed-metal complexes as shownin table 4 were selected for antibacterialactivity against three human pathogenicbacteria. The evaluation results of the inhibitionzone due to the effect of compounds arepresented in figure 3. figure 4 shows Zoneof inhibition against Salmonella typhi bycomplexes J9, J10, J11 and J12. It is found that,except J15, all compounds are comparativelymore effective against Eschericahia coli. The

tested complexes are generally quite effectiveagainst Salmonella typhi and Bacillus cereus. Theenhanced activity as shown in figure 3 of thecomplexes can be explained in terms ofchelation theory13. Although chelation is notthe only criteria for antibacterial activity, someimportant factor such as nature of the metalion, metal ion coordinating site, hydrophilicity,hypophilicity and presence of coligands mayhave considerable influence on the antibacterialactivity. The chelate complexes may deactivatevarious cellular enzymes which play vital role

632 Chiang Mai J. Sci. 2013; 40(4)

in various metabolic pathways of thesemicroorganisms. Other factors such assolubility, conductivity and dipole momentaffected by the presence of metal ions, maybe the reasons for the increased biological

activities of the metal complexes. Thereforethe antibacterial activity of the metalcomplexes cannot be ascribed to chelationalone but it’s an intricate blend of all of theabove contributions.

Table 4. Identification no. and name of the inorganic synthetic compounds.

Figure 3. Evaluation results of the synthetic compounds against the test organism (Bacteria).

Bacillus cereus19--12241927----27241329--24--

Salmonella typhi2114--31272121212825262592012

Eschericahia coli282425353028242429282427132212

IdentificationNo.J1J2J3J4J5J6J7J8J9J10J11J12J13J14J15

Name of the complex

[Cd(en)3][Hg(SCN)4][Ni(en)3][Hg(SCN)4][Cu(en)2][Hg(SCN)4]

[Zn(en)3][HgI4][Cd(en)3][HgI4]

[Zn(NH3)6][HgI4][Zn(Aniline)6][Hg(SCN)4][Co(NH3)5Cl][Hg(SCN)4]

[Ni(en)3][HgI4][Ni(NH3)6][HgI4][Co(en)3][HgI4]

[Cu(NH3)6][HgI4][Cd(Aniline)6][Hg(SCN)4]

[Zn(en)3][Hg(SCN)4][Cd(Aniline)6][HgI4]

Zone of inhibition in diameter (mm)

Chiang Mai J. Sci. 2013; 40(4) 633

Figure 4. Inhibition zone against Salmonella typhi by complexes of J9, J10, J11, J12.

4. CONCLUSIONThe mixed metal complexes have been

found to be of the type [MLx][MLy] where,M = Cu, Cd, Ni, Co, Zn and M= Hg, Lx =ethylenediamine, aniline, NH3 and Ly = I

-.The infrared spectra and metal analysis dataindicate the formation of such complexes.Conductivity measurements indicate theirelectrolytic nature and +2 oxidation state ofthe metal ions present in such complexes.The magnetic measurements indicate some ofthe complexes to show antiferromagneticinteractions. The exchange interactions seemto be super exchange type and most likelythrough the iodo groups3 giving the molecularstructure as figure 2. The high yield of thecomplexes indicates good possibilities of theiranalytical uses to determine metal contents ofsome related compounds. Further works arerequired to exploit and ascertain suchpossibilities.

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