research article solution studies on co(ii), ni(ii),...

Research ArticleSolution Studies on Co(II) Ni(II) Cu(II)and Zn(II) Complexes of Hexamethylenetetramine inAqueous and Non-Aqueous Solvents

Awawou G Paboudam12 Christian Geacuterard2 Aminou Mohamadou2 Moise O Agwara1

Mariam A Conde3 and Peter T Ndifon1

1 Department of Inorganic Chemistry Faculty of Science University of Yaounde I PO Box 812 Yaounde Cameroon2 Institut de Chimie Moleculaire de Reims (ICMR) UMR CNRS 7312 Universite de Reims Champagne-ArdenneMoulin de la Housse BP 1039 51687 Reims Cedex 2 France

3 Departement de Chimie Faculte des Sciences Universite de Douala Douala Cameroon

Correspondence should be addressed to Aminou Mohamadou aminoumohamadouuniv-reimsfr andPeter T Ndifon pndifonyahoocom

Received 27 August 2013 Revised 16 December 2013 Accepted 17 December 2013 Published 3 March 2014

Academic Editor Alfonso Castineiras

Copyright copy 2014 Awawou G Paboudam et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

Potentiometric studies in aqueous medium and spectrophotometric study in non-aqueous medium were used to understand thebehavior of hexamethylenetetramine (HMTA) complexes The protometric studies of HMTA enabled us to confirm that only onebasic site of this ligand is protonated in acidic medium and this ligand is decomposed in acidic medium In aqueous mediumonly hexa-aqua complexes in which HMTA is present in the second coordination sphere forming H-bonds with hydrogen atoms ofcoordinated anduncoordinatedwatermolecules are obtained In non-aqueous solventsHMTAcoordinates tometal ions displayingdiversity in the structures of the resulting complexes in which HMTA can either be monodentate bridged bidentate tridentate ortetradentate

1 Introduction

Hexamethylenetetramine (HMTA) is a heterocyclic ligandwith four nitrogen donor atoms having three rings mergedin a chair conformation as shown in Figure 1

HMTA can therefore form various metal complexes pos-sessing interesting structural features and applications [1ndash5]Hexamethylenetetramine as a ligand can bind either in amonodentate manner to a metal [6 7] acting as bridg-ing ligand linking two three or four metals [8ndash11] orbind to metal-containing species through the formation ofhydrogen bonding [5 12ndash16] The combination of both co-valent and hydrogen bonding in certain complexes of hex-amethylenetetramine leads to the formation of three-di-mensional structures that easily decompose by thermaltreatment to give thin films of metal oxides [15 16]

The formation of covalently bonded and hydrogen-bondedcompounds of hexamethylenetetramine is influenced by sev-eral factors such as the nature of the solvent steric hindranceof the counter ion and the pH of the solution [17]

Whenwater is used as the solvent during synthesismetal-aqua complexes are obtained which bind to HMTA throughH-bonds forming ionic species [18] When non-aqueoussolvents are used for synthesis metal-HMTA covalent speciesare formed [10 15] Recently we reported the isolationof metal-HMTA covalently bonded species isolated fromethanol [19] Metal-H

2O-HMTA ionic species involving H-

bonds isolated from ethanolwater mixture have also beenreported [5 12ndash16 20]

We report here the results of the study on the influence ofsolvent on the electronic and structural properties of metal-HMTA complexes in aqueous and non-aqueous solvents

Hindawi Publishing CorporationInternational Journal of Inorganic ChemistryVolume 2014 Article ID 397132 9 pageshttpdxdoiorg1011552014397132

2 International Journal of Inorganic Chemistry

N

N

N

NN

N

N

NH2C

C

H2C

CH2 CH2

CH2

H2Cage-like structure

Figure 1 Structure of hexamethylenetetramine

2 Experimental

21 Chemicals All solvents were purified by conventionalprocedures [21] and distilled prior to use All the chemicalscommercially available (Aldrich) and metallic salts (Fluka)were used as supplied without further purification

22 Physical Measurements

221 Protometry Stock solutions of metal nitrates wereprepared from commercially available reagents (Fluka) ofthe highest purity (gt99) and were used without furtherpurificationTheir concentrations were determined by EDTAtitration at pH = 10 using murexide as an indicator forNi2+ and PAN [1-(2-pyridyl-azo)-2-naphtol] for Cu2+ Ionicstrength was kept constant (I = 01) by the addition ofpotassium nitrate (Fluka) of the highest purity (gt99 ) Thesolutions of carbonate-free titrating base KOH 01molsdotLminus1were prepared from standardized 1molsdotLminus1 solutions (Pro-labo)

Protometric titrations were performed with a Metrohm665 Dosimat and a Metrohm 654 pH meter The combinedglass electrode was standardized with nitric acid 10minus2molsdotLminus1(pH = 200) and the slope determined from a refinement oftitration curves of acetic acid solutions All measurementswere performed at 20∘C under a nitrogen stream Titrationcurves were fitted with the refining program PROTAF [2223] The solutions of both ligands used for the determinationof the protonation and complexation constants were titratedwith KOH 01molL Their concentrations ranged from 5 times10minus3 to 10minus2molsdotLminus1 and the ratios 119862L119862M from 1 to 4The equilibrium constants were determined by fitting the

titration curves into the least squares refinement PROTAFsoftware [22 23] The PROTAF software allows the calcula-tion of the formation constants of the protonated or hydroxylcomplex species containing one or several metal cations(maximum of three) and one or several ligands (maximum ofthree) The overall formation constants 120573mlh (1) correspondsto equilibria of the type (charges are omitted)

mM + lL + hH 999445999468 MmLlHh 120573mlh =[MmLlHh]

[M]m[L]l[H]h(1)

12

11

10

9

8

7

6

5

4

3

2

1

0

minus1 minus08 minus06 minus04 minus02 0 02 04

HMTA (fresh)HMTA (7 days)

pH

Eq OHminus

Figure 2 Titration curve of HMTA ligand by KOH (119862L =10minus2molsdotLminus1 and 119862OH = 01molsdotLminus1) HMTA solution freshlyprepared in acidic medium and HMTA solution one week after itspreparation in acidic medium

222 Spectrophotometry In order to show the complex-ation of HMTA to metal ions in non-aqueous mediuma spectrophotometric study was carried out in a mixtureof ethanoldimethylformamide Jobrsquos continuous variationmethod [24] was used to study the coordination of the metalions to HMTA and to determine the stoichiometry of themetal complexes formed

Equimolar solutions (01molsdotLminus1) of metal chloride(CoCl

2 NiCl

2 and CuCl

2) and HMTA ligand were prepared

in a mixture of ethanoldimethylformamide in 65 35 (v v)DMF is used to avoid precipitation of formed complexes Afixed volume of each metal is placed in a series of beakersa volume of ligand is added progressively into these beakersin a manner that the ligandmetal (LM2+) ratio ranges from0 to 4 Spectrophotometric titrations were carried out inquartz cells of 1 cm pathlength using Shimadzu UV-2401-PCspectrophotometer equipped with a TCC-240A temperaturecontrolled cell holder

3 Results and Discussion

31 Protometric Study This study involves the titration of anaqueous solution of 10minus2molsdotLminus1 HMTA to which was addeda solution of 4times10minus2molsdotLminus1 of HNO

3and 01molsdotLminus1 KNO

3

by a 01molsdotLminus1 KOHThis titration was repeated after 7 daysand the results obtained are represented in Figure 2

Figure 2 shows that HMTA deteriorates in acidicmedium In the presence of HNO

3 HMTA dissociates

progressively and is transformed into other productsprobably ammonia and formaldehyde [25]

In order to avoid the degradation of HMTA prepared inacidicmedium a solution of 97610minus3molsdotLminus1 ofHMTA (pre-pared without adding the nitric acid) was titrated directlyusing 5 times 10minus2molsdotLminus1 nitric acid in 01molsdotLminus1 KNO

3medi-

umThe neutralization curve (Figure 3) of this ligand shows adecrease in pH corresponding to the protonation of one basicsite of the ligand

International Journal of Inorganic Chemistry 3

8

7

6

5

4

3

2

1

0

0 01 02 03 04 05 06 07 08 09 1

pH

VHNO3

Figure 3 Titration curve of the ligand HMTA (119862L = 976 times10minus3molsdotLminus1) with HNO

35 times 10

minus2molsdotLminus1

8

7

6

5

4

3

2

0 02 04 06 08 1 12 14 16

HMTAHMTACuHMTAZn

HMTACoHMTANi

pH

Vacid

Figure 4 Titration curves of the HMTA ligand alone and of theHMTA-M2+ systems with HNO

35 times 10

minus2molsdotLminus1 (M = Co Ni Cuor Zn 119862M = 5 times 10minus3molsdotLminus1 and 119862L = 5 times 10

minus2molsdotLminus1 I = 01 T =25∘C)

The value of the deprotonation constant obtained is 489This value is close to the value of 559 reported in theliterature [26] indicating that only one of the four nitrogendonor atoms is protonated in water

32 Metal Complex in Solution The formation of metal-HMTA complexes is expected when metal cations are intro-duced and would lead to the modification of the acid-baseequilibrium compared to that of the ligand alone

In this respect aqueous solutions (5 times 10minus3molsdotLminus1) ofCo(II) Ni(II) Cu(II) and Zn(II) salts respectively wereprepared and placed in a thermo-regulated cell containinga solution of 10minus2 molsdotLminus1 of HMTA ligand (01 molsdotLminus1 ofKNO3medium) and themixture titratedwith a solution of 5times

10minus2molsdotLminus1 HNO

3 Different curves showing the variation

of the pH as a function of the volume of nitric acid for thedifferent systems studied are illustrated in Figure 4

In general the formation of a complex in solution entailsincrease in the acidity of the reaction medium (ligand +metal) compared to that of the ligand alone In this studythe neutralization of the HMTA-metal salt mixture shows adecrease in pH at equal volume of nitric acid solution anda displacement of equivalent volumes as those of the ligandThe titrations curves of the HMTA-metallic salt systems (M= Co Ni Cu or Zn) are perfectly superimposed onto thatof ligand within the pH range of our study This superpo-sition of the curves indicates that the complexation did notoccur In order to better visualize this non-complexation werepresented the curves of 119899H as a function of pH (Figure 5)where 119899H represents the average number of protons per moleof ligand (free orand coordinated ligand) The curve shouldenable the determination of the level of protonation of thevarious species within the pH range under consideration

The set of five curves for pH 35 to 55 correspond to thetitration of the free ligand and the four metal-ligand systemsThe curves are perfectly superimposed indicating that at thetime of the competition between the proton and the metalliccation to bind to the ligand only protonation of the ligandtakes place thus confirming that there is no complexation inaqueous medium This observation is in agreement with theobservation that in most syntheses of complexes with HMTAin aqueous medium the ligand does not coordinate directlyto the metal but it is found in the crystalline structure outof the coordination sphere stabilizing the crystal lattice byhydrogen bonds [14ndash18 27]

33 Spectrophotometric Study Potentiometric studies onHMTA showed that only one basic site is protonated inacidic medium and all attempts to get this ligand coordinatedto different metal ions in water failed There is thereforeno direct coordination in aqueous medium between HMTAand metal ions This spectrophotometric study using thecontinuous variation method was therefore carried out inorder to understand the behavior of HMTA in non-aqueoussolvent (ethanolDMF) and to study the influence of HMTAon the geometry of metal-HMTA species in non-aqueoussolvents

331 Copper(II)-HMTA System The electronic spectraobtained for the study of the copper(II)-HMTA system arepresented in Figure 6

The electronic spectra obtained for the study of thecopper(II)-HMTA system at various ratios 119877 = [HMTA][Cu2+] show a large dissymmetric band whose max-imum absorption is situated at 804 nm (120576 = 40 Lsdotmolminus1sdotcmminus1)for the species [Cu(DMF)6]2+ (Figure 6) This maximumabsorption displaces progressively with the addition of theHMTA ligand up to 772 nm (120576 = 64 Lsdotmolminus1sdotcmminus1) for 119877 =[HMTA][Cu2+] = 15

When R is in the range 15 to 25 the absorbance ispractically constant and decreases for R = 3 The variation of120582max on the electronic spectra whenHMTA ligand is added is


8 976543210

00

05

10

15

HMTAHMTACuHMTAZnHMTACo

HMTANi

pH

nH

Figure 5 The curves of 119899H versus pH for the M2+-HMTA systems(M = Cu Zn Co or Ni)

in agreement with the coordination of HMTA to the metalliccation

The curves in the visible spectra of the Cu2+-DMFsystems and Cu2+-HMTA-DMF are similar this indicatesthat the environment of the Cu2+cation is the same for thedifferent complex speciesThe electronic transition bands andthe molar extinction coefficient of the different complexesare in agreement with an octahedral coordination around theCu2+ ion [28]

A plot of the absorbance versus the ligandM2+ ratio Rat two wavelengths 120582 = 760 nm and 670 nm (Figure 7) revealcurves of the same shapes presenting maxima at the same RvaluesR= 15 andR= 35 showing the progressive fixing of theHMTA ligand on Cu2+ cation up to a maximum of 15 and 35and the reaction can be represented as follows (2)

[Cu(DMF)6]2+

+ 1 5 HMTA 997888rarr [Cu(HMTA)15(DMF)]2+

(2)

HMTA is a tetradentate ligand not being able to form achelate and we are therefore left with two possibilities for thestructure of this complex

A dinuclear copper(II) complex is obtained in whichevery Cu2+cation is bound to oneHMTA ligand and the thirdHMTA linked to the two metallic centers to give a structureof formula [Cu

2(HMTA)

3(DMF)

8]4+ (Figure 8) A similar

structure has been isolated with the cobalt metal in ethanolicmedium by Ndifon et al [19]

A polymer in which the central Cu2+ is bound to threemolecules of DMF and three HMTA with these last ligandsbeing linked to three other metallic centers could also beobtained (Figure 9) This structure can also be comparedto the cobalt coordination polymer synthesized in ethanolicmedium [19] The slight depressions observed at R = 2 and 3

14

12

1

08

06

04

02

0

500 600 700 800 900 1000 1100 1200

Abso

rban

ce

Wavelength

(a)

(b)(c)

(d)(e) (f)

(g)

(h)(i)

Figure 6 Variation of the electronic spectra of the Cu2+-HMTAsystem according to the ratio 119877 = [HMTA][Cu2+] (a) R = 0 (b)R = 05 (c) R = 1 (d) R = 15 (e) R = 2 (f) R = 25 (g) R = 3 (h) R =35 (i) R = 4

Abso

rban

ce

14

12

1

08

06

04

02

0

0 05 1 15 2 25 3 35 4 45

Ratio HMTACu2+

120582 = 760nm

120582 = 670nm

Figure 7 Variation of the absorbance A with HMTACu 2+ ratio R

NN

NN

Cu

Cu

D

D

D

D D

D

N

N

N

N

N

NN

N

D

D

Figure 8 Dinuclear complex [Cu2(HMTA)

3(DMF)

8]4+ with D =

DMF

probably represent the fixation of 2 or 3 HMTA moleculesrespectively forming unstable intermediate species which arestabilized as more HMTA molecules are fixed

When 150 le R lt 25 the absorbance varies very slightlywith R the curve suggests the formation of metal-HMTAspecies

When R = 2 the absorbance decreases and two HMTAligands coordinate on the metal ion giving a mononuclearstructure (3)

[Cu(DMF)6]2+

+ 2HMTA 997888rarr [Cu(HMTA)2(DMF)

4]2+

(3)


NN

NN

Cu

Cu

Cu

Cu

D

D

N N

N N

N

N

N

N

D

Figure 9 Polymer complex [Cu(HMTA)15(DMF)

3]2+ with D =

DMF

NN

NN

Cu

D

D

N N

N N

N

N

N

N

D

Figure 10 Mononuclear complex [Cu(HMTA)3(DMF)

3]2+ with D

= DMF

500 600 700 800 900 1000 1100 1200

Abso

rban

ce

Wavelength

(a)

(b)(c)

(d)(e)

(f)(g)016

012

008

004

0

Figure 11 Variation of the electronic spectra of the Ni2+-HMTAsystem with 119877 = [HMTA][Ni2+] (a) R = 0 (b) R = 05 (c) R =15 (d) R = 2 (e) R = 25 (f) R = 3 and (g) R = 35 R = 4

When R = 25 the absorbance increases slightly as thecoordination of five HMTA ligands on two metal ions issuggested giving a dimer with an HMTA forming a bridge

When R = 3 the absorbance decreases and the value ofthe R ratio indicates the coordination of three ligands onthe metal ion (4) to probably give a structure similar to themononuclear structures described by Bai et al [6] for nickeland by Shang et al [29] for cobalt

[Cu(DMF)6]2+


3]2+

or [Cu(HMTA)15(DMF)

119899]2+

+ 1 5 HMTA

997888rarr [Cu(HMTA)3(DMF)

3]2+

(4)

The steric hindrance of the HMTA ligand prevents theformation of a coordination polymer possessing six HMTAligands around every metallic cation

At 119877 ge 3 the absorbance A increases very slowlyjustifying the complete formation of the complex[Cu(HMTA)

3(DMF)

3]2+ (Figure 10)

332 Nickel(II)-HMTA System The electronic spectra of the[Ni(DMF)

6]2+ species and Ni2+-HMTA-DMF are similar

These spectra (Figure 11) show the presence of two bandswith 120582max at 670 nm presenting a shoulder around 730 nmand 120582max at 1175 nm in the near infrared These bands withweak molar extinction coefficients [Ni(DMF)

6]2+ 8 lt 120576 lt

11 Lsdotmolminus1sdotcmminus1 and [Ni(HMTA)119898(DMF)

119899]2+ 10 lt 120576 lt

15 Lsdotmolminus1sdotcmminus1 are characteristic of an octahedral en-vironment around the Ni2+ ion [30] The third transition isprobably masked by the metal-ligand charge transfer bandThe presence of a shoulder at 730 nm in the second bandcharacterizes the distortion of the octahedral structure

The progressive addition of the HMTA ligand is char-acterized by a slight displacement of the first maximum ofabout 5 nm toward the strong energy and the displacementof this band is less noticed as absorbance increases Theseobservations are in agreement with the coordination of theN-donor atoms of HMTA ligand to the Ni2+ cation

A plot of absorbance versus R at 120582 = 670 nm and 120582= 720 nm (Figure 12) reveals two curves of similar shapethat increase with R with a slight drop at 05 and 35representing the fixing of 05 and 35 HMTA ligand on Ni2+ion respectively

When R = 05 the complex can be considered as be-ing dinuclear [Ni

2(HMTA)(DMF)

10]4+ (5) with the ligand

HMTA linking two Ni2+ centers as illustrated in Figure 13

[Ni(DMF)6]2+

+ 05 HMTA

997888rarr [Ni(HMTA)05(DMF)

5]2+

or 2[Ni (DMF)6]2+

+HMTA

997888rarr [Ni2(HMTA) (DMF)

10]4+

(5)


0 05 1 15 2 25 3 35 4 45

120582 = 730nm

120582 = 670nm

Ratio HMTANi2+

017

015

013

011

009

007

Abso

rban

ce

Figure 12 Variation of the absorbance A as a function of theratio 119877 = [HMTA][Ni2+]

NN

NN

Ni Ni

D

D

D

D D

D

DD

D

D

Figure 13 Dinuclear complex [Ni2(HMTA)(DMF)

10]4+ with D =

DMF

NN

NN

Ni Ni

D

D

D

D

NN

NN

N

N

N

N

NN N

NN

N

N

N

NN

NN

N

N

NN

Figure 14 Dinuclear complex [Ni2(HMTA)

7(DMF)

4]4+ with D =

DMF

Similar structures with cobalt which include[Co(HMTA)

2(H2O)Co(H

2O)6] and [Co

2(N3)4(HMTA)(H

2O)]

have been reported [9 31]When R = 35 the complex can be considered as

dinuclear or polymeric compound The dinuclear complex[Ni2(HMTA)

7(DMF)

4]4+ (6) has oneHMTAmolecule bridg-

ing two nickel centres (Figure 14) Each nickel centre ishexacoordinated involving three monodentate HMTA andtwomolecules of DMF Carlucci et al [32] did isolate a similarstructure with the silver(I)

2[Ni (DMF)6]2+

+ 7 HMTA 997888rarr [Ni2(HMTA)

7(DMF)

4]4+

or [Ni(HMTA)05(DMF)

5]2+


7(DMF)

4]4+ (6)

The polymeric compound [(DMF)(HMTA)2Ni(HMTA)

15]2+119899

(7) in which two ligands are bound to the central nickel(II)and the three others carrying the Ni2+ ion and the three other

neighbouring Ni2+ ion in which a molecule of DMF com-pletes the octahedral environment around every nickel(II) isobtained (Figure 15)

n[Ni (DMF)6]2+

+ 35HMTA 997888rarr [(DMF) (HMTA)2Ni2(HMTA)

15]2+

119899

or n [Ni(HMTA)05(DMF)

5]2+


15]2+119899

(7)

333 Cobalt(II)-HMTA System As in the nickel(II) com-pounds the spectra of the [Co(DMF)

6]2+ and Co2+-HMTA-

DMF species are similar These spectra (Figure 16) show thepresence of a band at 520 nmwith a slight shoulder at 490 nmand a second peak in the near infrared around 1050 nm Theshapes of this band as well as the values of molar extinctioncoefficient confirm an octahedral environment around theCo2+ ion in these compounds

Contrary to the observation in Cu2+ and Ni2+ the pro-gressive addition of the HMTA ligand leads to a slight vari-ation of the absorbance of the Co(II) complex formed up toR = 2 after which the addition of HMTA has little effect onthe electronic spectra

A plot of the absorbance versus R at 120582 = 520 nmand 485 nm respectively (Figure 17) shows two curves ofidentical shapes with maxima at R = 1 and 2

When R = 1 only one HMTA ligand is coordinatedto the Co2+cation and the structures in Figures 18 and 19are expected and the complex can be a mononuclear witha single HMTA coordinated and the hexacoordination iscompleted by five molecules of DMF Bai et al [6] and Shanget al [29] isolated compounds with similar structures withnickel ([Ni(NCS)

2(C6H12N4)(CH4O)2(H2O)]) and cobalt

([Co(NCS)2(C6H12N4)(CH4O)2(H2O)]) where an HMTA

ligand is coordinated to the central metal


NN

NN

NN

NN

NN

NN

D N

NN

N

N N

N N

NiNi

Ni

Ni

D

D

D

Figure 15 Polymer complex [(DMF)(HMTA)2Ni(HMTA)

15]2+119899

with D = DMF

04

03

02

01

0

500400300 600 700 800 900 1000 1100

Abso

rban

ce

Wavelength

(a)

(b)

(c)

(d)

Figure 16 Variation of the electronic spectra of the Co2+-HMTAsystem with 119877 = [HMTA][Co2+] (a) R = 0 (b) R = 05 (c) R = 15and (d) R = 2minus4

A polynuclear complex [Co(HMTA)(DMF)4]2+ in which

the Co2+ ion is coordinated to two HMTA ligands havingtwo other neighbouring cobalt(II) ions and four moleculesof DMF which complete the hexacoordination (Figure 19)can also be obtained This structure is similar to the cobaltcoordination polymer isolated from an ethanol solutionwhere the octahedral coordination is completed by twomolecules of water [19]

When the ratio R = 2 two HMTA ligands are linked tocobalt(II) as shown by the structures in Figures 20 21 and 22

4 Conclusion

Our goal was to study the effect of aqueous and non-aqueousmedia on the coordination of hexamethylenetetramine tometal ions We used both protometric and spectrophotomet-ricmethodsThe protometric studies of theHMTA ligand hasenabled us to confirm that only one basic site is protonatedin acidic medium and this ligand is decomposed in acidic

0 05 1 15 2 25 3 35 4 45

120582 = 480nm

120582 = 520nm

Abso

rban

ce

Ratio HMTACo2+

045

04

035

03

025

02

Figure 17 Variation of the absorbance A as a function of theratio 119877 = [HMTA][Co2+]

NN

NN

Co

D

D

D

D

D

Figure 18 Monomer complex [Co(HMTA)(DMF)4]2+ with D =

DMF

NN

NN

Co

Co

D

D

D

D D

D

N

N

N

N

NN

N

N

D

D

Figure 19 Polymeric complex [Co(HMTA)(DMF)4]2+ with D =

DMF

NN

NN

Co

D

D

NN

N

N

D

D

Figure 20 Monomer complex [Co(HMTA)2(DMF)

4]2+ with D =

DMF

NN

NN Co

NN

NN

NN

NN

DD

CoCo

D D

D D

Figure 21 Polymer complex [Co(HMTA)2(DMF)

2]2+ with D =

DMF


N N

N N

Co

N N

N N

NN

NN

D

NNN

N

Co

Co

DD

D D

Co

D D

D

Co

D D


4]2+ with D =

DMF

medium In aqueous medium HMTA ligand does not coor-dinate directly to the metal ions but rather through the H-bonded species In non aqueous solvents HMTA coordinatestometal ions displaying diversity in the resulting structures inwhichHMTAcan either bemonodentate bridged tridentateor tetradentate

Conflict of Interests

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

Acknowledgments

Theauthors thank theGovernment of Cameroon for financialsupport through the research mobility fund program (AGP)and the Fonds drsquoAppuis a la Recherche (MOA and PTN)

References

[1] K S Patel and M O Agwara ldquoHexamethlenetetraamine com-plexes of divalent metal sulphatesrdquo Nigerian Journal of Sciencevol 24 article 57 1990

[2] M O Agwara P T Ndifon and M K Ndikontar ldquoPhysic-ochemecal studies of some hexamethylenetetramine metal(II)complexesrdquo Bulletin of the Chemical Society of Ethiopia vol 18no 2 pp 143ndash148 2004

[3] O S Polezhaeva N V Yaroshinskaya and V K Ivanov ldquoFor-mation mechanism of nanocrystalline ceria in aqueous solu-tions of cerium(III) nitrate and hexamethylenetetraminerdquo Inor-ganic Materials vol 44 no 1 pp 51ndash57 2008

[4] X J Yao Y W Xuan and W Wu ldquoHexaaquazinc(II) dichlo-ride bis(hexamethylenetetramine) tetrahydraterdquoActa Crystallo-graphica vol E64 Article ID m 1132 2008

[5] L L Zhan J Y Xin W Wen and X Ya Wen ldquoHexaaquocop-per(II)dichloride bis (hexamethylenetetramine) tetrahydraterdquoActa Crystallographica vol E64 Article ID m1024 2008

[6] Y Bai W-L Shang F Zhong X-J Pan and X-F NiuldquoAqua(hexamethylenetetramine-120581N)bis(methanol)bis(thiocy-anato-120581N)nickel(II)rdquo Acta Crystallographica vol E63 ArticleID m2628 2007

[7] S Wei-Li B Yan M Chao-Zhong and L Zhi-Min ldquoAqua(hex-amethylenetetramine-120581N)bis(methanol-120581O)bis(thiocyanato-120581N)cobalt(II)rdquo Acta Crystallographica vol E64 pp m1184ndashm1185 2008

[8] I S Ahuja C L Yadav and S Tripathi ldquoCoordination polymersof some uranyl salts involving 4 4-bipyridyl 4 4-bipyridyl NN-dioxide 13-bis (4-pyridyl) propane and hexamethylenete-traminerdquo Asian Journal of Chemistry vol 1 pp 195ndash207 1989

[9] M K Ammar T Jouini and A Driss ldquoSynthesis and struc-tural characterization of dihexamethylenetetraminetetraaquo-cobalt(II) hexaaquocobalt(II) sulfate hexahydraterdquo Journal ofChemical Crystallography vol 30 no 4 pp 265ndash268 2000

[10] A Ray J Chakraborty B Samanta et al ldquoTwo new hydrother-mally synthesised hexamine bridged L-M-L type coordinationpolymers characterisation and magneto-structural correla-tionrdquo Inorganica Chimica Acta vol 361 no 7 pp 1850ndash18602008

[11] Y Chen Y-L Wang S-M Ying and S-L Cai ldquoPoly[di-1205832-chlorido-1205834-hexa-methyl-ene-tetra-mine-bis-[chlorido(methanol-120581O)-cadmium(II)]rdquo Acta Crystallographica SectionE vol 63 no 11 Article ID m2751 2007

[12] T Trzesowska and R Kruszynski ldquoThe synthesis crystal struc-ture and thermal studies of a mixed-ligand 110-phenanthrolineand hexamethylenetetramine complex of lanthanum nitrateInsight into coordination sphere geometry changes of lan-thanide(III) 110-phenanthroline complexesrdquo Transition MetalChemistry vol 32 no 5 pp 625ndash633 2007

[13] X-L Li D-Z Niu and Z-S Lu ldquoTetraaquabis(thiocyanato-kN)cobalt(II) hexamethylenetetramine (12) cocrystalrdquo ActaCrystallographica Section E vol 63 no 10 Article ID m24782007

[14] P Dagur D Chopra A S Prakash T N Guru Rowand M S Hegde ldquoSynthesis characterization and struc-ture of [Ni(H

2O)6]2(Cr2O7)2(hmta)4sdot2H

2O (hmta=hexameth-

ylene-tetramine) a novelmetal organic-inorganic hybridrdquo Jour-nal of Crystal Growth vol 275 no 1-2 pp e2043ndashe2047 2005

[15] S Banerjee A R Choudhury T N Guru Row S Chaudhuriand A Ghosh ldquoThree-dimensional supramolecular H-bondingnetwork in the compounds containing hexamethylenete-tramine and aquated Ni(II) or Cd(II) saltsrdquo Polyhedron vol 26no 1 pp 24ndash32 2007

[16] G Singh B P Baranwal I P S kapoor D Kumar C P Singhand R Frohlich ldquoSome transition metal nitrate complexeswith hexamethylenetetraminerdquo Journal ofThermal Analysis andCalorimetry vol 91 no 3 pp 971ndash977 2008

[17] PAfanasiev SChouzierTivadoretal lsquolsquoNickel andcobalt hexam-ethylentetraminecomplexes (NO

3)2Me(H

2O)6(HMTA)

2sdot4H2O

(Me=Co2+Ni2+) new molecular precursors for the preparationof metal dispersionsrdquo Inorganic Chemistry vol 47 no 7 pp2303ndash2311 2008

[18] P A Chernasvskii P V Afanasrsquoev G V Pankina and N SPerov ldquoFormation of Co nanoparticles in the process of thermaldecomposition of the cobalt complex with hexamethylenete-tramine (NO

3)2Co(H

2O)6(HMTA)

2sdot4(H2O)rdquo Russian Journal

of Physical Chemistry A Focus on Chemistry vol 82 no 13 pp2176ndash2181 2008

[19] P T Ndifon M O Agwara A G Paboudam et al ldquoSynthesischaracterisation and crystal structure of a cobalt(II)- hex-amethylenetetramine coordination polymerrdquo Transition MetalChemistry vol 34 no 7 pp 745ndash750 2009

[20] M O Agwara P T Ndifon M D Yufanyi et al ldquoSynthesischaracterization and crystal structure of anH-bondednickel(II)


hexamethylenetretramine complexrdquo Rasayan Journal of Chem-istry vol 13 pp 207ndash213 2010

[21] D Perrin W L F Armarego and R D Perrin Purificationof Laboratory Chemicals Pergamon Oxford UK 3rd edition1988

[22] R Fournaise and C Petitfaux ldquoEtude de la formation des com-plexes en solution aqueuse-III Nouvelle methode drsquoaffinementdes constantes de stabilite des complexes et des autres parame-tres des titrages protometriquesrdquoTalanta vol 34 no 4 pp 385ndash395 1987

[23] R Fournaise andC Petitfaux ldquoComputerized analysis of poten-tiometric data obtained without any previous standardizationand used without any intermediary change into another valuesrdquoAnalusis vol 18 no 4 pp 242ndash249 1990

[24] P Job ldquoFormation and stability of inorganic complexes insolutionrdquo Annali di Chimica Applicata vol 9 pp 113ndash203 1928

[25] V M Kostyuchenko G A Kiryukhina G I Mordvinovaand A S Lapin ldquoStudy of the condensation products of thealkylphenols with hexamethylenetetraminerdquo Polymer ScienceUSSR vol 26 no 5 pp 1003ndash1012 1984

[26] A G Brolo M L A Temperini and S M L AgostinholdquoCopper dissolution in bromide medium in the absence andpresence of hexamethylenetetramine (HMTA)rdquo ElectrochimicaActa vol 44 no 4 pp 559ndash571 1998

[27] X Yawen W Wen and L Shujing ldquoSynthesis and crystallo-graphic characterization of a six coordinate Cu(II) complexbased on hexamethylenetetramine ligandrdquoCrystal Research andTechnology vol 44 no 1 pp 127ndash130 2009

[28] J O Jensen ldquoVibrational frequencies and structural determina-tions of hexamethylenetetraaminerdquo Spectrochimica Acta A vol58 no 7 pp 1347ndash1364 2002

[29] W L Shang B Yan M Chao-Zhong and Z M LildquoAqua(hexamethylenetetramine-120581N)bis(methanol-120581O)bis(thiocyanato-120581N)cobalt(II)rdquo Acta Crystallographica vol E 64pp m 1184ndashm1185 2008

[30] D L Sutton Electronic Spectra of Transition Metal ComplexesMcGraw-Hill London UK 1968

[31] F A Mautner L Ohrstrom B Sodin and R Vicente ldquoNewtopology in azide-bridged cobalt(11) complexes the weak ferro-magnet [Co

2(N3)4(HexamethylenetetramineKH

2O)]119899rdquo Inor-

ganic Chemistry vol 48 no 13 pp 6280ndash6286 2009[32] L Carlucci G Ciani D M Proserpio and A Seroni ldquoA novel

3D three-connected cubic network containing [Ag6(hmt)

6]6+

hexagonal units (hmt = Hexamethylenetetramine)rdquo InorganicChemistry vol 36 no 9 pp 1736ndash1737 1997

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy


Carbohydrate Chemistry

International Journal of


Journal of

Chemistry


Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of


Chromatography Research International


Applied ChemistryJournal of



Theoretical ChemistryJournal of


Journal of

Spectroscopy

Analytical ChemistryInternational Journal of


Journal of


Quantum Chemistry


Organic Chemistry International

ElectrochemistryInternational Journal of



CatalystsJournal of


N

N

N

NN

N

N

NH2C

C

H2C

CH2 CH2

CH2

H2Cage-like structure

Figure 1 Structure of hexamethylenetetramine

2 Experimental

21 Chemicals All solvents were purified by conventionalprocedures [21] and distilled prior to use All the chemicalscommercially available (Aldrich) and metallic salts (Fluka)were used as supplied without further purification

22 Physical Measurements

221 Protometry Stock solutions of metal nitrates wereprepared from commercially available reagents (Fluka) ofthe highest purity (gt99) and were used without furtherpurificationTheir concentrations were determined by EDTAtitration at pH = 10 using murexide as an indicator forNi2+ and PAN [1-(2-pyridyl-azo)-2-naphtol] for Cu2+ Ionicstrength was kept constant (I = 01) by the addition ofpotassium nitrate (Fluka) of the highest purity (gt99 ) Thesolutions of carbonate-free titrating base KOH 01molsdotLminus1were prepared from standardized 1molsdotLminus1 solutions (Pro-labo)

Protometric titrations were performed with a Metrohm665 Dosimat and a Metrohm 654 pH meter The combinedglass electrode was standardized with nitric acid 10minus2molsdotLminus1(pH = 200) and the slope determined from a refinement oftitration curves of acetic acid solutions All measurementswere performed at 20∘C under a nitrogen stream Titrationcurves were fitted with the refining program PROTAF [2223] The solutions of both ligands used for the determinationof the protonation and complexation constants were titratedwith KOH 01molL Their concentrations ranged from 5 times10minus3 to 10minus2molsdotLminus1 and the ratios 119862L119862M from 1 to 4The equilibrium constants were determined by fitting the

titration curves into the least squares refinement PROTAFsoftware [22 23] The PROTAF software allows the calcula-tion of the formation constants of the protonated or hydroxylcomplex species containing one or several metal cations(maximum of three) and one or several ligands (maximum ofthree) The overall formation constants 120573mlh (1) correspondsto equilibria of the type (charges are omitted)

mM + lL + hH 999445999468 MmLlHh 120573mlh =[MmLlHh]

[M]m[L]l[H]h(1)

12

11

10

9

8

7

6

5

4

3

2

1

0

minus1 minus08 minus06 minus04 minus02 0 02 04

HMTA (fresh)HMTA (7 days)

pH

Eq OHminus

Figure 2 Titration curve of HMTA ligand by KOH (119862L =10minus2molsdotLminus1 and 119862OH = 01molsdotLminus1) HMTA solution freshlyprepared in acidic medium and HMTA solution one week after itspreparation in acidic medium

222 Spectrophotometry In order to show the complex-ation of HMTA to metal ions in non-aqueous mediuma spectrophotometric study was carried out in a mixtureof ethanoldimethylformamide Jobrsquos continuous variationmethod [24] was used to study the coordination of the metalions to HMTA and to determine the stoichiometry of themetal complexes formed

Equimolar solutions (01molsdotLminus1) of metal chloride(CoCl

2 NiCl

2 and CuCl

2) and HMTA ligand were prepared

in a mixture of ethanoldimethylformamide in 65 35 (v v)DMF is used to avoid precipitation of formed complexes Afixed volume of each metal is placed in a series of beakersa volume of ligand is added progressively into these beakersin a manner that the ligandmetal (LM2+) ratio ranges from0 to 4 Spectrophotometric titrations were carried out inquartz cells of 1 cm pathlength using Shimadzu UV-2401-PCspectrophotometer equipped with a TCC-240A temperaturecontrolled cell holder

3 Results and Discussion

31 Protometric Study This study involves the titration of anaqueous solution of 10minus2molsdotLminus1 HMTA to which was addeda solution of 4times10minus2molsdotLminus1 of HNO

3and 01molsdotLminus1 KNO

3

by a 01molsdotLminus1 KOHThis titration was repeated after 7 daysand the results obtained are represented in Figure 2

Figure 2 shows that HMTA deteriorates in acidicmedium In the presence of HNO

3 HMTA dissociates

progressively and is transformed into other productsprobably ammonia and formaldehyde [25]

In order to avoid the degradation of HMTA prepared inacidicmedium a solution of 97610minus3molsdotLminus1 ofHMTA (pre-pared without adding the nitric acid) was titrated directlyusing 5 times 10minus2molsdotLminus1 nitric acid in 01molsdotLminus1 KNO

3medi-

umThe neutralization curve (Figure 3) of this ligand shows adecrease in pH corresponding to the protonation of one basicsite of the ligand


8

7

6

5

4

3

2

1

0

0 01 02 03 04 05 06 07 08 09 1

pH

VHNO3


35 times 10


8

7

6

5

4

3

2

0 02 04 06 08 1 12 14 16

HMTAHMTACuHMTAZn

HMTACoHMTANi

pH

Vacid


35 times 10
















8 976543210

00

05

10

15


HMTANi

pH

nH





[Cu(DMF)6]2+


(2)



2(HMTA)

3(DMF)




14

12

1

08

06

04

02

0

500 600 700 800 900 1000 1100 1200

Abso

rban

ce

Wavelength

(a)

(b)(c)

(d)(e) (f)

(g)

(h)(i)


Abso

rban

ce

14

12

1

08

06

04

02

0

0 05 1 15 2 25 3 35 4 45

Ratio HMTACu2+

120582 = 760nm

120582 = 670nm


NN

NN

Cu

Cu

D

D

D

D D

D

N

N

N

N

N

NN

N

D

D


3(DMF)

8]4+ with D =

DMF




[Cu(DMF)6]2+


4]2+

(3)


NN

NN

Cu

Cu

Cu

Cu

D

D

N N

N N

N

N

N

N

D


3]2+ with D =

DMF

NN

NN

Cu

D

D

N N

N N

N

N

N

N

D


3]2+ with D

= DMF

500 600 700 800 900 1000 1100 1200

Abso

rban

ce

Wavelength

(a)

(b)(c)

(d)(e)

(f)(g)016

012

008

004

0




[Cu(DMF)6]2+


3]2+

or [Cu(HMTA)15(DMF)

119899]2+

+ 1 5 HMTA


3]2+

(4)



3(DMF)

3]2+ (Figure 10)




6]2+ 8 lt 120576 lt


119899]2+ 10 lt 120576 lt





2(HMTA)(DMF)



[Ni(DMF)6]2+

+ 05 HMTA


5]2+

or 2[Ni (DMF)6]2+

+HMTA


10]4+

(5)


0 05 1 15 2 25 3 35 4 45

120582 = 730nm

120582 = 670nm

Ratio HMTANi2+

017

015

013

011

009

007

Abso

rban

ce


NN

NN

Ni Ni

D

D

D

D D

D

DD

D

D


10]4+ with D =

DMF

NN

NN

Ni Ni

D

D

D

D

NN

NN

N

N

N

N

NN N

NN

N

N

N

NN

NN

N

N

NN


7(DMF)

4]4+ with D =

DMF


2(H2O)Co(H

2O)6] and [Co

2(N3)4(HMTA)(H

2O)]



7(DMF)



2[Ni (DMF)6]2+


7(DMF)

4]4+

or [Ni(HMTA)05(DMF)

5]2+


7(DMF)

4]4+ (6)


15]2+119899



n[Ni (DMF)6]2+


15]2+

119899


5]2+


15]2+119899

(7)


6]2+ and Co2+-HMTA-









NN

NN

NN

NN

NN

NN

D N

NN

N

N N

N N

NiNi

Ni

Ni

D

D

D


15]2+119899

with D = DMF

04

03

02

01

0

500400300 600 700 800 900 1000 1100

Abso

rban

ce

Wavelength

(a)

(b)

(c)

(d)





4 Conclusion


0 05 1 15 2 25 3 35 4 45

120582 = 480nm

120582 = 520nm

Abso

rban

ce

Ratio HMTACo2+

045

04

035

03

025

02


NN

NN

Co

D

D

D

D

D


DMF

NN

NN

Co

Co

D

D

D

D D

D

N

N

N

N

NN

N

N

D

D


DMF

NN

NN

Co

D

D

NN

N

N

D

D


4]2+ with D =

DMF

NN

NN Co

NN

NN

NN

NN

DD

CoCo

D D

D D


2]2+ with D =

DMF


N N

N N

Co

N N

N N

NN

NN

D

NNN

N

Co

Co

DD

D D

Co

D D

D

Co

D D


4]2+ with D =

DMF




Acknowledgments


References
















2O (hmta=hexameth-





3)2Me(H

2O)6(HMTA)

2sdot4H2O



3)2Co(H

2O)6(HMTA)






















6]6+











Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


8

7

6

5

4

3

2

1

0

0 01 02 03 04 05 06 07 08 09 1

pH

VHNO3


35 times 10


8

7

6

5

4

3

2

0 02 04 06 08 1 12 14 16

HMTAHMTACuHMTAZn

HMTACoHMTANi

pH

Vacid


35 times 10
















8 976543210

00

05

10

15


HMTANi

pH

nH





[Cu(DMF)6]2+


(2)



2(HMTA)

3(DMF)




14

12

1

08

06

04

02

0

500 600 700 800 900 1000 1100 1200

Abso

rban

ce

Wavelength

(a)

(b)(c)

(d)(e) (f)

(g)

(h)(i)


Abso

rban

ce

14

12

1

08

06

04

02

0

0 05 1 15 2 25 3 35 4 45

Ratio HMTACu2+

120582 = 760nm

120582 = 670nm


NN

NN

Cu

Cu

D

D

D

D D

D

N

N

N

N

N

NN

N

D

D


3(DMF)

8]4+ with D =

DMF




[Cu(DMF)6]2+


4]2+

(3)


NN

NN

Cu

Cu

Cu

Cu

D

D

N N

N N

N

N

N

N

D


3]2+ with D =

DMF

NN

NN

Cu

D

D

N N

N N

N

N

N

N

D


3]2+ with D

= DMF

500 600 700 800 900 1000 1100 1200

Abso

rban

ce

Wavelength

(a)

(b)(c)

(d)(e)

(f)(g)016

012

008

004

0




[Cu(DMF)6]2+


3]2+

or [Cu(HMTA)15(DMF)

119899]2+

+ 1 5 HMTA


3]2+

(4)



3(DMF)

3]2+ (Figure 10)




6]2+ 8 lt 120576 lt


119899]2+ 10 lt 120576 lt





2(HMTA)(DMF)



[Ni(DMF)6]2+

+ 05 HMTA


5]2+

or 2[Ni (DMF)6]2+

+HMTA


10]4+

(5)


0 05 1 15 2 25 3 35 4 45

120582 = 730nm

120582 = 670nm

Ratio HMTANi2+

017

015

013

011

009

007

Abso

rban

ce


NN

NN

Ni Ni

D

D

D

D D

D

DD

D

D


10]4+ with D =

DMF

NN

NN

Ni Ni

D

D

D

D

NN

NN

N

N

N

N

NN N

NN

N

N

N

NN

NN

N

N

NN


7(DMF)

4]4+ with D =

DMF


2(H2O)Co(H

2O)6] and [Co

2(N3)4(HMTA)(H

2O)]



7(DMF)



2[Ni (DMF)6]2+


7(DMF)

4]4+

or [Ni(HMTA)05(DMF)

5]2+


7(DMF)

4]4+ (6)


15]2+119899



n[Ni (DMF)6]2+


15]2+

119899


5]2+


15]2+119899

(7)


6]2+ and Co2+-HMTA-









NN

NN

NN

NN

NN

NN

D N

NN

N

N N

N N

NiNi

Ni

Ni

D

D

D


15]2+119899

with D = DMF

04

03

02

01

0

500400300 600 700 800 900 1000 1100

Abso

rban

ce

Wavelength

(a)

(b)

(c)

(d)





4 Conclusion


0 05 1 15 2 25 3 35 4 45

120582 = 480nm

120582 = 520nm

Abso

rban

ce

Ratio HMTACo2+

045

04

035

03

025

02


NN

NN

Co

D

D

D

D

D


DMF

NN

NN

Co

Co

D

D

D

D D

D

N

N

N

N

NN

N

N

D

D


DMF

NN

NN

Co

D

D

NN

N

N

D

D


4]2+ with D =

DMF

NN

NN Co

NN

NN

NN

NN

DD

CoCo

D D

D D


2]2+ with D =

DMF


N N

N N

Co

N N

N N

NN

NN

D

NNN

N

Co

Co

DD

D D

Co

D D

D

Co

D D


4]2+ with D =

DMF




Acknowledgments


References
















2O (hmta=hexameth-





3)2Me(H

2O)6(HMTA)

2sdot4H2O



3)2Co(H

2O)6(HMTA)






















6]6+











Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


8 976543210

00

05

10

15


HMTANi

pH

nH





[Cu(DMF)6]2+


(2)



2(HMTA)

3(DMF)




14

12

1

08

06

04

02

0

500 600 700 800 900 1000 1100 1200

Abso

rban

ce

Wavelength

(a)

(b)(c)

(d)(e) (f)

(g)

(h)(i)


Abso

rban

ce

14

12

1

08

06

04

02

0

0 05 1 15 2 25 3 35 4 45

Ratio HMTACu2+

120582 = 760nm

120582 = 670nm


NN

NN

Cu

Cu

D

D

D

D D

D

N

N

N

N

N

NN

N

D

D


3(DMF)

8]4+ with D =

DMF




[Cu(DMF)6]2+


4]2+

(3)


NN

NN

Cu

Cu

Cu

Cu

D

D

N N

N N

N

N

N

N

D


3]2+ with D =

DMF

NN

NN

Cu

D

D

N N

N N

N

N

N

N

D


3]2+ with D

= DMF

500 600 700 800 900 1000 1100 1200

Abso

rban

ce

Wavelength

(a)

(b)(c)

(d)(e)

(f)(g)016

012

008

004

0




[Cu(DMF)6]2+


3]2+

or [Cu(HMTA)15(DMF)

119899]2+

+ 1 5 HMTA


3]2+

(4)



3(DMF)

3]2+ (Figure 10)




6]2+ 8 lt 120576 lt


119899]2+ 10 lt 120576 lt





2(HMTA)(DMF)



[Ni(DMF)6]2+

+ 05 HMTA


5]2+

or 2[Ni (DMF)6]2+

+HMTA


10]4+

(5)


0 05 1 15 2 25 3 35 4 45

120582 = 730nm

120582 = 670nm

Ratio HMTANi2+

017

015

013

011

009

007

Abso

rban

ce


NN

NN

Ni Ni

D

D

D

D D

D

DD

D

D


10]4+ with D =

DMF

NN

NN

Ni Ni

D

D

D

D

NN

NN

N

N

N

N

NN N

NN

N

N

N

NN

NN

N

N

NN


7(DMF)

4]4+ with D =

DMF


2(H2O)Co(H

2O)6] and [Co

2(N3)4(HMTA)(H

2O)]



7(DMF)



2[Ni (DMF)6]2+


7(DMF)

4]4+

or [Ni(HMTA)05(DMF)

5]2+


7(DMF)

4]4+ (6)


15]2+119899



n[Ni (DMF)6]2+


15]2+

119899


5]2+


15]2+119899

(7)


6]2+ and Co2+-HMTA-









NN

NN

NN

NN

NN

NN

D N

NN

N

N N

N N

NiNi

Ni

Ni

D

D

D


15]2+119899

with D = DMF

04

03

02

01

0

500400300 600 700 800 900 1000 1100

Abso

rban

ce

Wavelength

(a)

(b)

(c)

(d)





4 Conclusion


0 05 1 15 2 25 3 35 4 45

120582 = 480nm

120582 = 520nm

Abso

rban

ce

Ratio HMTACo2+

045

04

035

03

025

02


NN

NN

Co

D

D

D

D

D


DMF

NN

NN

Co

Co

D

D

D

D D

D

N

N

N

N

NN

N

N

D

D


DMF

NN

NN

Co

D

D

NN

N

N

D

D


4]2+ with D =

DMF

NN

NN Co

NN

NN

NN

NN

DD

CoCo

D D

D D


2]2+ with D =

DMF


N N

N N

Co

N N

N N

NN

NN

D

NNN

N

Co

Co

DD

D D

Co

D D

D

Co

D D


4]2+ with D =

DMF




Acknowledgments


References
















2O (hmta=hexameth-





3)2Me(H

2O)6(HMTA)

2sdot4H2O



3)2Co(H

2O)6(HMTA)






















6]6+











Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


NN

NN

Cu

Cu

Cu

Cu

D

D

N N

N N

N

N

N

N

D


3]2+ with D =

DMF

NN

NN

Cu

D

D

N N

N N

N

N

N

N

D


3]2+ with D

= DMF

500 600 700 800 900 1000 1100 1200

Abso

rban

ce

Wavelength

(a)

(b)(c)

(d)(e)

(f)(g)016

012

008

004

0




[Cu(DMF)6]2+


3]2+

or [Cu(HMTA)15(DMF)

119899]2+

+ 1 5 HMTA


3]2+

(4)



3(DMF)

3]2+ (Figure 10)




6]2+ 8 lt 120576 lt


119899]2+ 10 lt 120576 lt





2(HMTA)(DMF)



[Ni(DMF)6]2+

+ 05 HMTA


5]2+

or 2[Ni (DMF)6]2+

+HMTA


10]4+

(5)


0 05 1 15 2 25 3 35 4 45

120582 = 730nm

120582 = 670nm

Ratio HMTANi2+

017

015

013

011

009

007

Abso

rban

ce


NN

NN

Ni Ni

D

D

D

D D

D

DD

D

D


10]4+ with D =

DMF

NN

NN

Ni Ni

D

D

D

D

NN

NN

N

N

N

N

NN N

NN

N

N

N

NN

NN

N

N

NN


7(DMF)

4]4+ with D =

DMF


2(H2O)Co(H

2O)6] and [Co

2(N3)4(HMTA)(H

2O)]



7(DMF)



2[Ni (DMF)6]2+


7(DMF)

4]4+

or [Ni(HMTA)05(DMF)

5]2+


7(DMF)

4]4+ (6)


15]2+119899



n[Ni (DMF)6]2+


15]2+

119899


5]2+


15]2+119899

(7)


6]2+ and Co2+-HMTA-









NN

NN

NN

NN

NN

NN

D N

NN

N

N N

N N

NiNi

Ni

Ni

D

D

D


15]2+119899

with D = DMF

04

03

02

01

0

500400300 600 700 800 900 1000 1100

Abso

rban

ce

Wavelength

(a)

(b)

(c)

(d)





4 Conclusion


0 05 1 15 2 25 3 35 4 45

120582 = 480nm

120582 = 520nm

Abso

rban

ce

Ratio HMTACo2+

045

04

035

03

025

02


NN

NN

Co

D

D

D

D

D


DMF

NN

NN

Co

Co

D

D

D

D D

D

N

N

N

N

NN

N

N

D

D


DMF

NN

NN

Co

D

D

NN

N

N

D

D


4]2+ with D =

DMF

NN

NN Co

NN

NN

NN

NN

DD

CoCo

D D

D D


2]2+ with D =

DMF


N N

N N

Co

N N

N N

NN

NN

D

NNN

N

Co

Co

DD

D D

Co

D D

D

Co

D D


4]2+ with D =

DMF




Acknowledgments


References
















2O (hmta=hexameth-





3)2Me(H

2O)6(HMTA)

2sdot4H2O



3)2Co(H

2O)6(HMTA)






















6]6+











Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


0 05 1 15 2 25 3 35 4 45

120582 = 730nm

120582 = 670nm

Ratio HMTANi2+

017

015

013

011

009

007

Abso

rban

ce


NN

NN

Ni Ni

D

D

D

D D

D

DD

D

D


10]4+ with D =

DMF

NN

NN

Ni Ni

D

D

D

D

NN

NN

N

N

N

N

NN N

NN

N

N

N

NN

NN

N

N

NN


7(DMF)

4]4+ with D =

DMF


2(H2O)Co(H

2O)6] and [Co

2(N3)4(HMTA)(H

2O)]



7(DMF)



2[Ni (DMF)6]2+


7(DMF)

4]4+

or [Ni(HMTA)05(DMF)

5]2+


7(DMF)

4]4+ (6)


15]2+119899



n[Ni (DMF)6]2+


15]2+

119899


5]2+


15]2+119899

(7)


6]2+ and Co2+-HMTA-









NN

NN

NN

NN

NN

NN

D N

NN

N

N N

N N

NiNi

Ni

Ni

D

D

D


15]2+119899

with D = DMF

04

03

02

01

0

500400300 600 700 800 900 1000 1100

Abso

rban

ce

Wavelength

(a)

(b)

(c)

(d)





4 Conclusion


0 05 1 15 2 25 3 35 4 45

120582 = 480nm

120582 = 520nm

Abso

rban

ce

Ratio HMTACo2+

045

04

035

03

025

02


NN

NN

Co

D

D

D

D

D


DMF

NN

NN

Co

Co

D

D

D

D D

D

N

N

N

N

NN

N

N

D

D


DMF

NN

NN

Co

D

D

NN

N

N

D

D


4]2+ with D =

DMF

NN

NN Co

NN

NN

NN

NN

DD

CoCo

D D

D D


2]2+ with D =

DMF


N N

N N

Co

N N

N N

NN

NN

D

NNN

N

Co

Co

DD

D D

Co

D D

D

Co

D D


4]2+ with D =

DMF




Acknowledgments


References
















2O (hmta=hexameth-





3)2Me(H

2O)6(HMTA)

2sdot4H2O



3)2Co(H

2O)6(HMTA)






















6]6+











Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


NN

NN

NN

NN

NN

NN

D N

NN

N

N N

N N

NiNi

Ni

Ni

D

D

D


15]2+119899

with D = DMF

04

03

02

01

0

500400300 600 700 800 900 1000 1100

Abso

rban

ce

Wavelength

(a)

(b)

(c)

(d)





4 Conclusion


0 05 1 15 2 25 3 35 4 45

120582 = 480nm

120582 = 520nm

Abso

rban

ce

Ratio HMTACo2+

045

04

035

03

025

02


NN

NN

Co

D

D

D

D

D


DMF

NN

NN

Co

Co

D

D

D

D D

D

N

N

N

N

NN

N

N

D

D


DMF

NN

NN

Co

D

D

NN

N

N

D

D


4]2+ with D =

DMF

NN

NN Co

NN

NN

NN

NN

DD

CoCo

D D

D D


2]2+ with D =

DMF


N N

N N

Co

N N

N N

NN

NN

D

NNN

N

Co

Co

DD

D D

Co

D D

D

Co

D D


4]2+ with D =

DMF




Acknowledgments


References
















2O (hmta=hexameth-





3)2Me(H

2O)6(HMTA)

2sdot4H2O



3)2Co(H

2O)6(HMTA)






















6]6+











Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


N N

N N

Co

N N

N N

NN

NN

D

NNN

N

Co

Co

DD

D D

Co

D D

D

Co

D D


4]2+ with D =

DMF




Acknowledgments


References
















2O (hmta=hexameth-





3)2Me(H

2O)6(HMTA)

2sdot4H2O



3)2Co(H

2O)6(HMTA)






















6]6+











Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


















6]6+











Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of










Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

research article solution studies on co(ii), ni(ii),...

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