research article mechanochemical preparation of cobalt nanoparticles...

Research ArticleMechanochemical Preparation of Cobalt Nanoparticles througha Novel Intramolecular Reaction in Cobalt(II) Complexes

Seyed Abolghasem Kahani and Massumeh Khedmati

Department of Inorganic Chemistry Faculty of Chemistry University of Kashan Kashan 87317-51167 Iran

Correspondence should be addressed to Seyed Abolghasem Kahani kahanikashanuacir

Received 29 August 2014 Accepted 2 November 2014

Academic Editor Nageh K Allam

Copyright copy 2015 S A Kahani and M Khedmati This is an open access article distributed under the Creative CommonsAttribution License which permits unrestricted use distribution and reproduction in any medium provided the original work isproperly cited

A novel solid state reaction involving a series of cobalt(II) hydrazine-azides has been used to prepare metallic cobalt nanoparticlesThe reactions of [Co(N

2H4)(N3)2] [Co(N

2H4)2(N3)2] and [Co(N

2H4)(N3)Cl]sdotH

2O via NaOH KOH as reactants were carried out

in the solid state These complexes undergo an intramolecular two-electron oxidation-reduction reaction at room temperatureproducing metallic cobalt nanoparticles (Co1ndashCo6) The aforementioned complexes contain cobalt(II) that is an oxidizing agentand also hydrazine ligand as a reducing agent Other products produced include sodium azide and ammonia gas The cobaltmetal nanoparticles were characterized using X-ray powder diffraction (XRD) scanning electronmicroscopy (SEM) and vibratingsample magnetometer (VSM) The synthesized cobalt nanoparticles have similar morphologies however their particle sizedistributions are different

1 Introduction

Among the ferromagnetic elements Co nanoparticles havea wide range of applications in catalysis optoelectronicsmagnetic recording media and rechargeable batteries [1ndash3] Many interesting properties were observed when mag-netic metal particles were being prepared in nanoscale Forexample as particle size decreases the surface-to-volumeratio increases and properties which depend on this ratiochange Thus nanoparticles show many unusual chemicaland physical properties compared to bulk particles [4] Inan elaboration of this kind of approach various methodshave been developed for the synthesis of metal nanoparticlesincluding vapor liquid and solid state processing routes[5 6] In the literature the top-down and the bottom-up approaches are used to synthesize nanoparticles [7]The mechanochemical synthesis is an interdisciplinary newapproach between the top-down and bottom-up approaches[8]The idea of performing reactions directly between solidsexcluding the dissolving stage is attractive to chemistsbecause reactions in aqueous solution undergo side reactions[9] Mechanochemistry refers to reactions that are inducedby mechanical processes milling or grinding The synthesis

of nanocrystalline materials by mechanical milling mechan-ical alloying and mechanochemical processing has beenstudied [10] On the other hand the study of coordinationmechanochemical redox reactions is still in its infancy [11 12]The chemistry of coordination compounds is a wide area ofinorganic chemistry and an enormous number of reactionsare known to occur in these compounds [13] The numer-ous types of reactions including ligand exchange reactionsisomerization reactions redox reactions and reactions ofcoordinated ligands have been reported in the solid state [14]The electronic interactions between metal and ligands play aprominent role in the intramolecular reactions [15] Conse-quently intramolecular electron transfer involving metal andligands takes place between coupled redox centers In manycases ligand to metal charge transfer excitation is associatedwith the reduction of the metal and oxidation of the ligandbut in some cases the ligand serves as the source of thereducing agent [16] Hydrazine is such a compound andthe preparation of many complexes is based on it [17] Theextensive coordination chemistry of hydrazine is evidencefor this type of reaction [18] Transition metal complexeshave several unique features in reactionsThemost importantone is the pattern of electron transfer [19] So far there

Hindawi Publishing CorporationJournal of NanomaterialsVolume 2015 Article ID 246254 8 pageshttpdxdoiorg1011552015246254

2 Journal of Nanomaterials

are no reports in the field of mechanochemical reductionof cobalt(II) complexes to metallic cobalt nanoparticles inany literature In undertaking this project [Co(N

2H4)(N3)2]

[Co(N2H4)2(N3)2] and [Co(N

2H4)(N3)Cl]sdotH

2O complexes

are used for the preparation of cobalt nanoparticles in thesolid state Results show that an electron is transferred fromligand to metal and an intramolecular oxidation reductionreaction has occurred A new preparation method of nickelnanoparticles in the solid state at room temperature has beenreported [20] Here this newmethod is extended to cobalt(II)complexesThese researches join the topics of the intramolec-ular reaction metals mechanochemistry nanoscience andcoordination chemistry Using coordination compounds asreactants in the preparation of metallic nanoparticles createsa new area of research in coordination chemistry

2 Experimental

21 Starting Materials All chemical reagents used in thisexperiment were pure grade and used without furtherpurification Cobalt sulfate heptahydrate cobalt chloridehexahydrate sodium azide hydrazinemonohydrate solutionsodium hydroxide and potassium hydroxide were purchasedfromMerckThewater used throughout this workwas doublydistilled water

22 Synthesis of [Co(N2H4)(N3)2] Complex Using hydrazine(N2H4) as a cobridge with azide a honeycomb lay-

ered cobalt(II) coordination polymer [Co(N2H4)(N3)2] is

obtained as followsAn aqueous solution (10mL) of hydrazine sulfate (013 g

10mmol) and CoSO4sdot7H2O (028 g 10mmol) was heated at

93∘C for 10min and then quickly mixed with a hot aqueoussolution (15mL) of excessive NaN

3(13 g 20mmol) The

mixed purple solution was kept at 93∘C for 10min withoutdisturbance After slow cooling down to room temperature at5∘Ch dark-red column crystals were obtained The crystalswere filtered and washed with distilled water and ethanolrespectively and then dried in vacuo [21]

23 Synthesis of [Co(N2H4)2(N3)2] Complex Co(N3)2in

solution was obtained by reacting the cobalt(II) chloridewith sodium azide solution 1 2 Cobalt(II) azide molarratios CoCl

2sdot6H2O (480 g 20mmol) reacted with NaN

3

(260 g 40mmol) in 50mL water Stoichiometry amountsof hydrazine hydrate (240 g 40mmol) were added to theCo(N

3)2solution The solutions were continuously stirred

in an ice bath for 05 h The solid complex thus obtainedwas filtered and washed with dilute ethanol and dried overanhydrous calcium chloride [22]

24 Synthesis of [Co(N2H4)(N3)Cl]sdotH2O Complex Co(N3)Cl

in solution was obtained by reacting the cobalt(II) chlo-ride with sodium azide solution 1 1 molar ratios in 50mLwater Stoichiometry amounts of hydrazine hydrate (120 g20mmol)were added to theCo(N

3)Cl solutionThe solutions

were continuously stirred in an ice bath for 05 h The solidcomplex thus obtained was filtered and washed with diluteethanol and dried over anhydrous calcium chloride [22]

25 The Mechanochemical Synthesis of Cobalt NanoparticlesA mixture 0175 g (01mmole) of [Co(N

2H4)(N3)2] complex

and 05 g (125mmole) sodium hydroxide in excess wasloaded into a mortar pestle of 50mL capacityThe stoichiom-etry of reactions between cobalt(II) hydrazine complex andalkali bases (NaOH KOH) was 1 25 and grinding was car-ried out for 1 h For the purification process the product wastransferred to a beaker and washed The product (Co1) waswashedwithmethanol filtered anddried in a vacuumoven atroom temperature for a period of at least 24 h A similar pro-cedure for the preparation of Co2 from [Co(N

2H4)2(N3)2]

(0207 g 01mmole) and NaOH (05 g 125mmole) is car-ried out In the reaction between [Co(N

2H4)(N3)Cl]sdotH

2O

complex (0203 g 01mmole) and NaOH (05 g 125mmole)Co3 nanoparticles were produced In the preparation of Co4Co5 and Co6 the mole ratio is similar to Co1 Co2 andCo3 respectively However in the preparation of Co4 Co5and Co6 the alkaline reactant is KOH In the solid phasean intramolecular redox chemical reaction between ligandand central atom occurred and cobalt metal generated ((1)(2) and (3)) The following reactions take place at roomtemperature in the solid phase

[Co (N2H4) (N3)

2] +

5

2

NaOH

997888rarr

1

2

NH3+

5

2

NaN3+ Co + 52

H2O

(1)

[Co (N2H4)

2(N3)

2] +

5

2

NaOH

997888rarr

1

2

NH3+

5

2

NaN3+ Co + 52

H2O + N

2H4

(2)

[Co (N2H4) (N3)Cl] sdotH

2O + 52

NaOH

997888rarr

1

2

NH3+

3

2

NaN3+ Co + 72

H2O + NaCl

(3)

Similar reactions occurred in the presence of KOH asalkaline in solid state reactionDuring themilling of reactantsin the redox reactions ammonia gas is released andNaN

3was

produced Ammonia combines with hydrochloric acid andforms ammonium chloride Colorimetric testing can be usedto detectNaN

3[23] A drop of the filtered solution is placed in

the depression of a spot plate and treated with 1 or 2 drops ofdilute hydrochloric acid A drop of ferric chloride solution isadded and the spot plate gently heated A red color indicateshydrazoic acid and thus the presence of sodium azide in thesolution

26 Characterization of Materials The cobalt complex andcobalt powders were characterized by X-ray powder diffrac-tion (XRD) XRD measurements were performed using aPhilips Xrsquopert pro MPD diffractometer with Cu K120572 radiationin the range 2120579 from 10 to 80 at room temperature IR spectrawere obtained as KBr pellets in the range 4000 to 400 cmminus1using a Shimadzu FTIR spectrometer Scanning electronmicroscopy (Philips XL30ESEM) was used to character-ize cobalt nanoparticles A vibrating sample magnetometer

Journal of Nanomaterials 3

(VSM Meghnatis Daghigh Kavir Co) was used to evaluatethe magnetic parameters of cobalt nanoparticles

3 Results and Discussion

In the solid state [Co(N2H4)(N3)2] [Co(N

2H4)2(N3)2] and

[Co(N2H4)(N3)Cl]sdotH

2O undergo an intramolecular two-

electron oxidation reduction reaction These reactions underalkaline condition (NaOH KOH) lead to formation of cobaltmetal azide and ammonia Depending on the oxidizingagent pH and temperature hydrazine reacts in differentpathways In aqueous solution hydrazine reacts as onetwo or four electron oxidation paths and is converted to amixture of dinitrogen and ammonia azide and ammoniaandor only dinitrogen respectively The redox reactions ofhydrazine cobalt(II) complexes have several unique featuresthe most important of them being the patterns of electrontransfer from ligand to metal On the other hand thesemechanochemical reactions occurred at room temperatureand the final main product is metallic cobalt nanoparticlesIn this work the cobalt nanoparticles are prepared withdifferent shapes by using amechanochemical route Howeverwhen the cobalt complex as a reactant was used in aqueoussolution cobalt nanoparticles with different morphologieswere formed [24] The metallic cobalt nanoparticles werecharacterized using XRD IR VSM and SEM analysis

31 Analysis of Metallic Cobalt Nanoparticles CrystallinePhase According to the XRD pattern in the literature[Co(N

2H4)(N3)2] crystallizes in the orthorhombic system

and space group C2221 This complex is showed as acobridge with azide and hydrazine and honeycomb lay-ered cobalt(II) coordination polymer [21] However XRDpatterns and crystal structure of [Co(N

2H4)2(N3)2] and


2O have not been reported During

solid state reactions all complexes are converted to metalliccobalt thus all diffraction peaks related to complex patternsdisappeared In accordance with the diffraction pattern anal-yses it could be concluded that the nanoparticles preparedin this work were pure hcp cobalt The cobalt nanoparticleshave JCPDS card no 05-0727 and P63mmc space groupThemechanochemical reaction of cobalt(II) complex to metalliccobalt is accompanied by a change in the crystal structure Allthe diffraction peaks can be well indexed to hcp phase cobaltwith lattice constants of 119886

0= 25031 A 119888

0= 40605 A The

fundamental difference between crystalline and amorphoussolids is due to their X-ray diffraction patterns Howeverpoor crystallinity of the powder results in broad peaks in theX-ray pattern There are different lines broadening sourcessuch as crystallite size lattice strain anisotropic samplebroadening and faulting tending to produce different effectson the line profiles Here in the metallic cobalt patternthe background noise from fluoresced X-rays is increasedwhich is most problematic in powder diffraction (Figure 1)The choice of X-ray source in X-ray powder diffraction isdependent on the material that must be analyzed Someatoms absorb incident X-rays and fluoresce by the absorptionof X-rays which decreases the diffracted signal and alsothe fluoresced X-rays increase the background noise When

200

0

Cou

nts

Cou

nts

Cou

nts

Cou

nts

Cou

nts

Cou

nts

Cou

nts

Cou

nts

Cou

nts

Co(N2H4)2(N3)2

Co(1)

Co(2)

Co(3)

Co(4)

Co(5)

Co(6)

Co(N2H4)(N3)2

Co(N2H4)(N3)Cl

(002)(101)

(102)(100)

(110)

400

200

100

0

400

200

0

400

200

0

400

200

0

0

100

200

400

600

200

0

20 30 40 50 60 70

Position (2120579)

50

100

150

50

100

150

Figure 1 X-ray diffraction patterns of the Co(N2H4)(N3)2

Co(N2H4)2(N3)2 and Co(N

2H4)(N3)Cl and their products cobalt

metal nanoparticles (Co1ndashCo6) in hcp lattice


Co

Co(N2H4)(N3)2

Wavenumbers (cmminus1)

Tran

smitt

ance

()

3000 2000 1000

Co(N2H4)(N3)ClmiddotH2O

Co(N2H4)2(N3)2

Figure 2 IR spectra of Co(N2H4)(N3)2 Co(N

2H4)2(N3)2 and

Co(N2H4)(N3)Cl in the region 400ndash4000 cmminus1 and cobalt nanopar-

ticles (Co1ndashCo6) are produced and all the absorption bands disap-pear

copper radiation is employed the X-ray powder pattern ofcobalt nanoparticles demonstrates the effect of fluorescenceon the diffraction pattern [25] Therefore there is an uncer-tainty in the estimation of crystallite size from the full widthat half maximum (FWHM) of the diffraction peaks by theScherrer formula The pattern of X-ray diffraction showsthe crystalline structure of final products All the diffractionpeaks can be well indexed to the hexagonal phase of cobalt

32 Infrared Spectra of Complexes and Cobalt NanoparticlesVibration spectra of [Co(N

2H4)(N3)2] [Co(N

2H4)2(N3)2]

and [Co(N2H4)(N3)Cl]sdotH

2O show N

2H4and azido vibra-

tions frequencies (Figure 2) Hydrazine coordinates to aCo(II) as a bridging bidentate ligand showing bands (N-N) near 970 cmminus1 [26] Here the azido vibrations appear at2010ndash2050 1260ndash1350 and 610ndash670 cmminus1The antisymmetricand symmetric N

3

minus stretching absorption bands occur at2010ndash2050 cmminus1 and 1260ndash1350 respectively the deforma-tion stretching also was observed at 610ndash670 cmminus1 [27] Inthe chemical reaction the cobalt complexes are converted tocobalt metal nanoparticles (Co1ndashCo6) thus the absorptionbands due to ligands group in complexes disappeared and

Table 1 Magnetic parameters in cobalt metal nanoparticles thathave been measured at 298K

Sample 119867

119888(Oe) 119872

119903(emug) 119872

119878(emug)

Co1 39805 2019 13545Co2 34118 1549 9962Co3 38992 1533 8833Co4 47116 1172 6868Co5 39805 1948 11392Co6 23558 1548 11918

the metallic cobalt nanoparticles have no absorption bandsin medium IR

33 Magnetic Properties of Metallic Cobalt NanoparticlesCobalt nanoparticles were prepared from [Co(N

2H4)(N3)2]


2H4)(N3)Cl]sdotH

2Oby chemical

redox reaction in solid state The magnetic susceptibil-ity reveals paramagnetic and a week interaction betweencobalt(II) ions in the polynuclear complex [21] The conver-sion of cobalt(II) complexes to metallic cobalt can be accom-panied by a change in magnetization These molecular para-magnetic complexes are changed into ferromagnetic cobaltmetal nanoparticles (Figure 3) The saturation magnetization(119872119878) values of Co1 Co2 Co3 Co4 Co5 and Co6 at 298K

were 13545 9962 8833 6868 11392 and 11918 emugrespectively (Table 1) Here the cobalt nanoparticles have asaturationmagnetization less than that of the bulk cobaltThe119872

119878value of the bulk cobalt was about 1625 emug at 300K

It is known that the magnetization behavior of a magneticmaterial is highly size dependent Despite the endless numberof reports on magnetic studies of magnetic nanoparticlesthe influence of particle size on the magnetic propertieshas not been systematically studied [28] The metallic cobaltnanoparticles show magnetic parameters such as saturationmagnetization and coercivity that vary with particle sizeusually in a nonlinear fashion [29 30] It is envisaged thatthe application of Co nanoparticles can be expanded oncethe intrigue relationship between magnetic properties andparticle size of Co can be delineated The large magneticparticle contains mobile walls when the size of the particledecreases below a critical size the domain walls disappearand the particles become single domain Magnetic particlesin the nanometer-size range are necessarily single-magnetic-domain structures The critical size depends on the saturatedmagnetization anisotropy energy and exchange interactionbetween individual spins [31]

34 Analysis of Cobalt ParticlesMorphologies Figure 4 showsan SEM image of a typical cobalt particle prepared viaintramolecular chemical reductionMorphology of the cobaltnanoparticles was dependent on the complex structure asreactant The SEM of Co1 and Co2 show aggregated porestructure containing the nanosheets and nanosheet thicknessranging from 35 nm to 60 nm An aggregated spherical parti-cle without pore is observed in Co3 and Co4 and their parti-cle sizes are ranging from 50 nm to 80 nm The Co5 and Co6nanoparticles have pore structure containing the nanosheets


150

100

50

0

minus50

minus100

minus150

80

100

60

40

20

0

0

minus20

minus40

minus60

minus80

minus100

100

50

minus50

minus100

minus10000

minus8000

minus6000

minus4000

minus2000 0

2000

4000

6000

8000

10000

minus10000

minus8000

minus6000

minus4000

minus2000 0

2000

4000

6000

8000

10000

minus10000

minus8000

minus6000

minus4000

minus2000 0

2000

4000

6000

8000

10000

Applied field (Oe) Applied field (Oe)

Applied field (Oe)

Mag

netiz

atio

n (e

mu

g)

Mag

netiz

atio

n (e

mu

g)

Mag

netiz

atio

n (e

mu

g)

Co(1)Co(2)

Co(3)Co(4)

Co(6)Co(5)

Figure 3 Hysteresis loop and the saturation magnetizations of cobalt nanoparticles have been measured at 298K (Co1 = 13545 Co2 = 9962Co3 = 8833 Co4 = 6868 Co5 = 11392 and Co6 = 11918 emug) respectively

and nanosheet thickness ranging from 25 nm to 35 nmThe statistical analysis shows that Co1 Co2 Co5 and Co6nanoparticles have similar morphology whereas Co3 andCo4 nanoparticles have a different morphology The resultsshow that when polynuclear complex [Co(N

2H4)(N3)2] is

used in the reaction the product changes to aggregatedwithout pore and nanosheet cobalt nanoparticles How-ever when mononuclear complexes [Co(N

2H4)2(N3)2] and


2O are used the complex is converted

to an aggregated powder of Co1 Co2 Co5 and Co6 respec-tively On the other hand the results show that when alkalinemedia are changed from NaOH to KOH respectively themorphology of metallic cobalt nanoparticles has significantlychanged In the new solid state method an intramolecular

chemical reduction of the cobalt complex causes the forma-tion of particles in the nanoscale range Besides XRDpatternsand SEM micrographs of metallic cobalt phase formationare confirmed by using the energy-dispersive X-ray (EDX)data The EDX spectra acquired at low magnification of thepowders are shown in Figure 5 Energy-dispersive X-rayanalysis of these prepared cobalt nanoparticles show thatthey are all pure

4 Conclusions

The common method is used in the preparation of metalliccobalt nanoparticles which is the chemical reduction ofcobalt(II) salts by hydrazine in alcoholic solution at 60ndash70∘C


3)

Co(4

4

Co(

)

2HCo(NCo(N2H4)(N3)ClmiddotH2O


Co(1)

Co(2)

Co(5)

Co(6)

Co(N2H4)2(N3)2

Co(N2H4)2(N3)2

Co(N2H4)(N3)2

Co(N2H4)(N3)2

1120583m

1120583m

1120583m

+NaOH

+NaOH

+NaOH

+KOH

+KOH

+KOH

500nm

500nm

500nm

500nm

500nm

500nm

Figure 4 SEM showmorphologies and particle size distributions in metallic cobalt nanoparticles (Co1 and Co2) aggregated nanosheet withthickness 35ndash60 nm (Co3 and Co4) aggregated spherical particles with size 50ndash80 nm (Co5 and Co6) aggregated nanosheet with thickness25ndash35 nm

Journal of Nanomaterials 7(c

ps)

40

30

20

10

00 5 10 15 20

Energy (keV)

Co

Co

Co

Figure 5 Energy-dispersive X-ray spectrum of metallic cobaltnanoparticle that is prepared from Co(N

2H4)(N3)2complex

There are many substances that contributed in the reactionsand the high temperature causes many side reactions onmetallic nanoparticle Here we proposed a new method forthe preparation of cobalt nanoparticles in the solid stateat room temperature Besides being able to react at roomtemperature conditions the complex has both oxidizing andreducing properties In all aqueous preparation of metalliccobalt by hydrazine a 4eminus oxidation reduction pathway hasbeen reported but here we observed a new 2eminus oxidationreduction pathway in the solid state reaction This is anew methodology in the intramolecular reaction at roomtemperature Fine cobalt powders with a different morphol-ogy were prepared from cobalt(II) hydrazine complexes byintramolecular redox reaction in solid state Here dependingon the interaction between the metal ion and ligands aspecial cobalt(II) complex for intramolecular redox reactionis designed Therefore the coordination sphere of complexhas a profound effect on the intramolecular redox reactionThe results show that when complexes and alkalinemedia arechanged the morphology of metallic cobalt nanoparticles hassignificantly changed However the cobalt metal is producedfrom [Co(N

2H4)(N3)2] complex and has completely different

morphology than ones prepared from [Co(N2H4)2(N3)2] and


2O The advantages of this work for

preparing the metallic powders lie in variation on morphol-ogy the high yield and solid state reaction conditions Incomparison with the method of preparing cobalt powdersfrom cobalt(II) salts in aqueous solution the intramolecularredox reaction of cobalt(II) hydrazine complexes show ahigh purity of metal cobalt Therefore mechanochemicalintramolecular redox reaction is attractive and offers a newmethod in preparation of metallic cobalt nanoparticle

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgment

The authors are grateful to University of Kashan for support-ing this work by Grant no 2567368

References

[1] S P GubinMagnetic Nanoparticles Wiley 2009[2] S A Kahani and H Molaei ldquoCobalt(III) ammine complexes as

precursors in the synthesis of cobalt nanoparticlesrdquo Journal ofCoordination Chemistry vol 66 no 24 pp 4430ndash4440 2013

[3] J P Liu E FullertonOGutfleisch andD J SellmyerNanoscaleMagnetic Materials and Applications Springer 2009

[4] E Roduner Nanoscopic Materials Size-Dependent PhenomenaThe Royal Society of Chemistry 2007

[5] J A Blackman ldquoMetallic nanoparticlesrdquo in Handbook of MetalPhysics P Misra Ed Elsevier Amsterdam The Netherlands2009

[6] B L Cushing V L Kolesnichenko and C J OrsquoConnor ldquoRecentadvances in the liquid-phase syntheses of inorganic nano-particlesrdquo Chemical Reviews vol 104 no 9 pp 3893ndash39462004

[7] C Altavilla and E Ciliberto Inorganic Nanoparticles SynthesisApplications and Perspectives CRC Press 2011

[8] P Balaz Mechanochemistry in Nanoscience and Minerals Engi-neering Springer 2008

[9] S A Kahani and M Sabeti ldquoThe mechanochemical oxidationof thiocyanate to polythiocyanogen (SCN )

119899using peroxydisul-

phaterdquo Journal of Inorganic and Organometallic Polymers andMaterials vol 21 no 3 pp 458ndash464 2011

[10] M K Beyer and H Clausen-Schaumann ldquoMechanochemistrythemechanical activation of covalent bondsrdquoChemical Reviewsvol 105 no 8 pp 2921ndash2948 2005

[11] J E House Jr ldquoMechanistic considerations for anation reac-tions in the solid staterdquo Coordination Chemistry Reviews vol128 no 1-2 pp 175ndash191 1993

[12] E C ConstableMetals and Ligand ReactivityWiley-VCHNewYork NY USA 1996

[13] J F Fernandez-Bertran ldquoMechanochemistry an overviewrdquoPure and Applied Chemistry vol 71 no 4 pp 581ndash586 1999

[14] V V Boldyrev and K Tkacova ldquoMechanochemistry of solidspast present and prospectsrdquo Journal of Materials Synthesis andProcessing vol 8 no 3-4 pp 121ndash132 2000

[15] H Taube ldquoElectron transfer between metal complexes retro-spectiverdquo Science vol 226 no 4678 pp 1028ndash1036 1984

[16] M Anbar ldquoOxidation or reduction of ligands by metal ionsin unstable states of oxidationrdquo in Mechanisms of InorganicReactions vol 49 of Advances in Chemistry chapter 6 pp 126ndash152 American Chemical Society Washington DC USA 1965

[17] J R Dilworth ldquoThe coordination chemistry of substitutedhydrazinesrdquo Coordination Chemistry Reviews vol 21 no 1 pp29ndash62 1976

[18] B T Heaton C Jacob and P Page ldquoTransitionmetal complexescontaining hydrazine and substituted hydrazinesrdquoCoordinationChemistry Reviews vol 154 pp 193ndash229 1996

[19] E SchmidtHydrazine and Its DerivativesWiley NewYork NYUSA 1984

[20] SAKahani andMKhedmati ldquoThepreparation of nickel nano-particles through a novel solid-state intramolecular reactionof polynuclear nickel(II) complexrdquo Journal of NanoparticleResearch vol 16 no 8 pp 2544ndash2546 2014

[21] X-T Wang Z-M Wang and S Gao ldquoHoneycomb layerof cobalt(II) azide hydrazine showing weak ferromagnetismrdquoInorganic Chemistry vol 46 no 25 pp 10452ndash10454 2007


[22] K C Pati C Nesamani and V R P Verneker ldquoSynthesis andcharacterisation of metal hydrazine nitrate azide and perchlo-rate complexesrdquo Synthesis andReactivity in Inorganic andMetal-Organic Chemistry vol 12 pp 10452ndash10454 1982

[23] J Kurzawa K Janowicz and A Suszka ldquoStopped-flow kineticdetermination of thiocyanates and thiosulphates with the appli-cation of iodine-azide reactionrdquo Analytica Chimica Acta vol431 no 1 pp 149ndash155 2001

[24] W Gong H Li Z Zhao and J Chen ldquoUltrafine particles of FeCo and Ni ferromagnetic metalsrdquo Journal of Applied Physicsvol 69 pp 5119ndash5121 1991

[25] B D Cullity and S R Stock Elements of X-Ray DiffractionPrentice Hall 3rd edition 2001

[26] D Nicholls and R Swindells ldquoHydrazine complexes ofnickel(II) chloriderdquo Journal of Inorganic and Nuclear Chemistryvol 30 no 8 pp 2211ndash2217 1968

[27] K Nakamoto Infrared and Raman Spectra of Inorganic andCoordination Compounds Part B JohnWiley amp Sons NewYorkNY USA 5th edition 1997

[28] B D Cullity and C D Graham Introduction to MagneticMaterials John Wiley amp Sons 2009

[29] G Herzer ldquoGrain size dependence of coercivity and perme-ability in nanocrystalline ferromagnetsrdquo IEEE Transactions onMagnetics vol 26 no 5 pp 1397ndash1402 1990

[30] G Herzer ldquoNanocrystalline soft magnetic alloysrdquo inHandbookof Magnetic Materials vol 10 North Holland Amsterdam TheNetherlands 1997

[31] G C Papaefthymiou ldquoNanoparticle magnetismrdquo Nano Todayvol 4 no 5 pp 438ndash447 2009

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MetallurgyJournal of


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MaterialsJournal of


Nano

materials


Journal ofNanomaterials


are no reports in the field of mechanochemical reductionof cobalt(II) complexes to metallic cobalt nanoparticles inany literature In undertaking this project [Co(N

2H4)(N3)2]


2H4)(N3)Cl]sdotH

2O complexes

are used for the preparation of cobalt nanoparticles in thesolid state Results show that an electron is transferred fromligand to metal and an intramolecular oxidation reductionreaction has occurred A new preparation method of nickelnanoparticles in the solid state at room temperature has beenreported [20] Here this newmethod is extended to cobalt(II)complexesThese researches join the topics of the intramolec-ular reaction metals mechanochemistry nanoscience andcoordination chemistry Using coordination compounds asreactants in the preparation of metallic nanoparticles createsa new area of research in coordination chemistry

2 Experimental

21 Starting Materials All chemical reagents used in thisexperiment were pure grade and used without furtherpurification Cobalt sulfate heptahydrate cobalt chloridehexahydrate sodium azide hydrazinemonohydrate solutionsodium hydroxide and potassium hydroxide were purchasedfromMerckThewater used throughout this workwas doublydistilled water

22 Synthesis of [Co(N2H4)(N3)2] Complex Using hydrazine(N2H4) as a cobridge with azide a honeycomb lay-

ered cobalt(II) coordination polymer [Co(N2H4)(N3)2] is

obtained as followsAn aqueous solution (10mL) of hydrazine sulfate (013 g

10mmol) and CoSO4sdot7H2O (028 g 10mmol) was heated at

93∘C for 10min and then quickly mixed with a hot aqueoussolution (15mL) of excessive NaN

3(13 g 20mmol) The

mixed purple solution was kept at 93∘C for 10min withoutdisturbance After slow cooling down to room temperature at5∘Ch dark-red column crystals were obtained The crystalswere filtered and washed with distilled water and ethanolrespectively and then dried in vacuo [21]

23 Synthesis of [Co(N2H4)2(N3)2] Complex Co(N3)2in

solution was obtained by reacting the cobalt(II) chloridewith sodium azide solution 1 2 Cobalt(II) azide molarratios CoCl

2sdot6H2O (480 g 20mmol) reacted with NaN

3

(260 g 40mmol) in 50mL water Stoichiometry amountsof hydrazine hydrate (240 g 40mmol) were added to theCo(N

3)2solution The solutions were continuously stirred

in an ice bath for 05 h The solid complex thus obtainedwas filtered and washed with dilute ethanol and dried overanhydrous calcium chloride [22]

24 Synthesis of [Co(N2H4)(N3)Cl]sdotH2O Complex Co(N3)Cl

in solution was obtained by reacting the cobalt(II) chlo-ride with sodium azide solution 1 1 molar ratios in 50mLwater Stoichiometry amounts of hydrazine hydrate (120 g20mmol)were added to theCo(N

3)Cl solutionThe solutions

were continuously stirred in an ice bath for 05 h The solidcomplex thus obtained was filtered and washed with diluteethanol and dried over anhydrous calcium chloride [22]

25 The Mechanochemical Synthesis of Cobalt NanoparticlesA mixture 0175 g (01mmole) of [Co(N

2H4)(N3)2] complex

and 05 g (125mmole) sodium hydroxide in excess wasloaded into a mortar pestle of 50mL capacityThe stoichiom-etry of reactions between cobalt(II) hydrazine complex andalkali bases (NaOH KOH) was 1 25 and grinding was car-ried out for 1 h For the purification process the product wastransferred to a beaker and washed The product (Co1) waswashedwithmethanol filtered anddried in a vacuumoven atroom temperature for a period of at least 24 h A similar pro-cedure for the preparation of Co2 from [Co(N

2H4)2(N3)2]

(0207 g 01mmole) and NaOH (05 g 125mmole) is car-ried out In the reaction between [Co(N

2H4)(N3)Cl]sdotH

2O

complex (0203 g 01mmole) and NaOH (05 g 125mmole)Co3 nanoparticles were produced In the preparation of Co4Co5 and Co6 the mole ratio is similar to Co1 Co2 andCo3 respectively However in the preparation of Co4 Co5and Co6 the alkaline reactant is KOH In the solid phasean intramolecular redox chemical reaction between ligandand central atom occurred and cobalt metal generated ((1)(2) and (3)) The following reactions take place at roomtemperature in the solid phase

[Co (N2H4) (N3)

2] +

5

2

NaOH

997888rarr

1

2

NH3+

5

2

NaN3+ Co + 52

H2O

(1)

[Co (N2H4)

2(N3)

2] +

5

2

NaOH

997888rarr

1

2

NH3+

5

2

NaN3+ Co + 52

H2O + N

2H4

(2)

[Co (N2H4) (N3)Cl] sdotH

2O + 52

NaOH

997888rarr

1

2

NH3+

3

2

NaN3+ Co + 72

H2O + NaCl

(3)

Similar reactions occurred in the presence of KOH asalkaline in solid state reactionDuring themilling of reactantsin the redox reactions ammonia gas is released andNaN

3was

produced Ammonia combines with hydrochloric acid andforms ammonium chloride Colorimetric testing can be usedto detectNaN

3[23] A drop of the filtered solution is placed in

the depression of a spot plate and treated with 1 or 2 drops ofdilute hydrochloric acid A drop of ferric chloride solution isadded and the spot plate gently heated A red color indicateshydrazoic acid and thus the presence of sodium azide in thesolution

26 Characterization of Materials The cobalt complex andcobalt powders were characterized by X-ray powder diffrac-tion (XRD) XRD measurements were performed using aPhilips Xrsquopert pro MPD diffractometer with Cu K120572 radiationin the range 2120579 from 10 to 80 at room temperature IR spectrawere obtained as KBr pellets in the range 4000 to 400 cmminus1using a Shimadzu FTIR spectrometer Scanning electronmicroscopy (Philips XL30ESEM) was used to character-ize cobalt nanoparticles A vibrating sample magnetometer





2H4)2(N3)2] and







2H4)2(N3)2] and




0= 25031 A 119888

0= 40605 A The


200

0

Cou

nts

Cou

nts

Cou

nts

Cou

nts

Cou

nts

Cou

nts

Cou

nts

Cou

nts

Cou

nts

Co(N2H4)2(N3)2

Co(1)

Co(2)

Co(3)

Co(4)

Co(5)

Co(6)

Co(N2H4)(N3)2

Co(N2H4)(N3)Cl

(002)(101)

(102)(100)

(110)

400

200

100

0

400

200

0

400

200

0

400

200

0

0

100

200

400

600

200

0

20 30 40 50 60 70

Position (2120579)

50

100

150

50

100

150






Co

Co(N2H4)(N3)2


Tran

smitt

ance

()

3000 2000 1000


Co(N2H4)2(N3)2


2H4)2(N3)2 and





2H4)(N3)2] [Co(N

2H4)2(N3)2]


2O show N

2H4and azido vibra-


3



Sample 119867

119888(Oe) 119872

119903(emug) 119872

119878(emug)

Co1 39805 2019 13545Co2 34118 1549 9962Co3 38992 1533 8833Co4 47116 1172 6868Co5 39805 1948 11392Co6 23558 1548 11918



2H4)(N3)2]


2H4)(N3)Cl]sdotH

2Oby chemical







150

100

50

0

minus50

minus100

minus150

80

100

60

40

20

0

0

minus20

minus40

minus60

minus80

minus100

100

50

minus50

minus100

minus10000

minus8000

minus6000

minus4000

minus2000 0

2000

4000

6000

8000

10000

minus10000

minus8000

minus6000

minus4000

minus2000 0

2000

4000

6000

8000

10000

minus10000

minus8000

minus6000

minus4000

minus2000 0

2000

4000

6000

8000

10000


Applied field (Oe)

Mag

netiz

atio

n (e

mu

g)

Mag

netiz

atio

n (e

mu

g)

Mag

netiz

atio

n (e

mu

g)

Co(1)Co(2)

Co(3)Co(4)

Co(6)Co(5)



2H4)(N3)2] is


2H4)2(N3)2] and





4 Conclusions



3)

Co(4

4

Co(

)



Co(1)

Co(2)

Co(5)

Co(6)

Co(N2H4)2(N3)2

Co(N2H4)2(N3)2

Co(N2H4)(N3)2

Co(N2H4)(N3)2

1120583m

1120583m

1120583m

+NaOH

+NaOH

+NaOH

+KOH

+KOH

+KOH

500nm

500nm

500nm

500nm

500nm

500nm



ps)

40

30

20

10

00 5 10 15 20

Energy (keV)

Co

Co

Co


2H4)(N3)2complex









Acknowledgment


References










































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials







2H4)2(N3)2] and







2H4)2(N3)2] and




0= 25031 A 119888

0= 40605 A The


200

0

Cou

nts

Cou

nts

Cou

nts

Cou

nts

Cou

nts

Cou

nts

Cou

nts

Cou

nts

Cou

nts

Co(N2H4)2(N3)2

Co(1)

Co(2)

Co(3)

Co(4)

Co(5)

Co(6)

Co(N2H4)(N3)2

Co(N2H4)(N3)Cl

(002)(101)

(102)(100)

(110)

400

200

100

0

400

200

0

400

200

0

400

200

0

0

100

200

400

600

200

0

20 30 40 50 60 70

Position (2120579)

50

100

150

50

100

150






Co

Co(N2H4)(N3)2


Tran

smitt

ance

()

3000 2000 1000


Co(N2H4)2(N3)2


2H4)2(N3)2 and





2H4)(N3)2] [Co(N

2H4)2(N3)2]


2O show N

2H4and azido vibra-


3



Sample 119867

119888(Oe) 119872

119903(emug) 119872

119878(emug)

Co1 39805 2019 13545Co2 34118 1549 9962Co3 38992 1533 8833Co4 47116 1172 6868Co5 39805 1948 11392Co6 23558 1548 11918



2H4)(N3)2]


2H4)(N3)Cl]sdotH

2Oby chemical







150

100

50

0

minus50

minus100

minus150

80

100

60

40

20

0

0

minus20

minus40

minus60

minus80

minus100

100

50

minus50

minus100

minus10000

minus8000

minus6000

minus4000

minus2000 0

2000

4000

6000

8000

10000

minus10000

minus8000

minus6000

minus4000

minus2000 0

2000

4000

6000

8000

10000

minus10000

minus8000

minus6000

minus4000

minus2000 0

2000

4000

6000

8000

10000


Applied field (Oe)

Mag

netiz

atio

n (e

mu

g)

Mag

netiz

atio

n (e

mu

g)

Mag

netiz

atio

n (e

mu

g)

Co(1)Co(2)

Co(3)Co(4)

Co(6)Co(5)



2H4)(N3)2] is


2H4)2(N3)2] and





4 Conclusions



3)

Co(4

4

Co(

)



Co(1)

Co(2)

Co(5)

Co(6)

Co(N2H4)2(N3)2

Co(N2H4)2(N3)2

Co(N2H4)(N3)2

Co(N2H4)(N3)2

1120583m

1120583m

1120583m

+NaOH

+NaOH

+NaOH

+KOH

+KOH

+KOH

500nm

500nm

500nm

500nm

500nm

500nm



ps)

40

30

20

10

00 5 10 15 20

Energy (keV)

Co

Co

Co


2H4)(N3)2complex









Acknowledgment


References










































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




Co

Co(N2H4)(N3)2


Tran

smitt

ance

()

3000 2000 1000


Co(N2H4)2(N3)2


2H4)2(N3)2 and





2H4)(N3)2] [Co(N

2H4)2(N3)2]


2O show N

2H4and azido vibra-


3



Sample 119867

119888(Oe) 119872

119903(emug) 119872

119878(emug)

Co1 39805 2019 13545Co2 34118 1549 9962Co3 38992 1533 8833Co4 47116 1172 6868Co5 39805 1948 11392Co6 23558 1548 11918



2H4)(N3)2]


2H4)(N3)Cl]sdotH

2Oby chemical







150

100

50

0

minus50

minus100

minus150

80

100

60

40

20

0

0

minus20

minus40

minus60

minus80

minus100

100

50

minus50

minus100

minus10000

minus8000

minus6000

minus4000

minus2000 0

2000

4000

6000

8000

10000

minus10000

minus8000

minus6000

minus4000

minus2000 0

2000

4000

6000

8000

10000

minus10000

minus8000

minus6000

minus4000

minus2000 0

2000

4000

6000

8000

10000


Applied field (Oe)

Mag

netiz

atio

n (e

mu

g)

Mag

netiz

atio

n (e

mu

g)

Mag

netiz

atio

n (e

mu

g)

Co(1)Co(2)

Co(3)Co(4)

Co(6)Co(5)



2H4)(N3)2] is


2H4)2(N3)2] and





4 Conclusions



3)

Co(4

4

Co(

)



Co(1)

Co(2)

Co(5)

Co(6)

Co(N2H4)2(N3)2

Co(N2H4)2(N3)2

Co(N2H4)(N3)2

Co(N2H4)(N3)2

1120583m

1120583m

1120583m

+NaOH

+NaOH

+NaOH

+KOH

+KOH

+KOH

500nm

500nm

500nm

500nm

500nm

500nm



ps)

40

30

20

10

00 5 10 15 20

Energy (keV)

Co

Co

Co


2H4)(N3)2complex









Acknowledgment


References










































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




150

100

50

0

minus50

minus100

minus150

80

100

60

40

20

0

0

minus20

minus40

minus60

minus80

minus100

100

50

minus50

minus100

minus10000

minus8000

minus6000

minus4000

minus2000 0

2000

4000

6000

8000

10000

minus10000

minus8000

minus6000

minus4000

minus2000 0

2000

4000

6000

8000

10000

minus10000

minus8000

minus6000

minus4000

minus2000 0

2000

4000

6000

8000

10000


Applied field (Oe)

Mag

netiz

atio

n (e

mu

g)

Mag

netiz

atio

n (e

mu

g)

Mag

netiz

atio

n (e

mu

g)

Co(1)Co(2)

Co(3)Co(4)

Co(6)Co(5)



2H4)(N3)2] is


2H4)2(N3)2] and





4 Conclusions



3)

Co(4

4

Co(

)



Co(1)

Co(2)

Co(5)

Co(6)

Co(N2H4)2(N3)2

Co(N2H4)2(N3)2

Co(N2H4)(N3)2

Co(N2H4)(N3)2

1120583m

1120583m

1120583m

+NaOH

+NaOH

+NaOH

+KOH

+KOH

+KOH

500nm

500nm

500nm

500nm

500nm

500nm



ps)

40

30

20

10

00 5 10 15 20

Energy (keV)

Co

Co

Co


2H4)(N3)2complex









Acknowledgment


References










































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




3)

Co(4

4

Co(

)



Co(1)

Co(2)

Co(5)

Co(6)

Co(N2H4)2(N3)2

Co(N2H4)2(N3)2

Co(N2H4)(N3)2

Co(N2H4)(N3)2

1120583m

1120583m

1120583m

+NaOH

+NaOH

+NaOH

+KOH

+KOH

+KOH

500nm

500nm

500nm

500nm

500nm

500nm



ps)

40

30

20

10

00 5 10 15 20

Energy (keV)

Co

Co

Co


2H4)(N3)2complex









Acknowledgment


References










































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




ps)

40

30

20

10

00 5 10 15 20

Energy (keV)

Co

Co

Co


2H4)(N3)2complex









Acknowledgment


References










































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials





















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



research article mechanochemical preparation of cobalt nanoparticles...

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