Indian Jnumal or Chemica l Techno logy Vo l. I 0. M;trch :wen. pp. I X0- 1 X.'i

Articles

Synthesis and characterization of poly(piperazinyl phosphorimine) and its metal complexes in aqueous medium

S K urnarcsa n & P Kannan ';'

Dcpartmetll or Chemistry. A nna Unive t·s ity. Chennai oOO 02.'i . India

l?eceit'£'ri21 Nmnn!Jer 2001: U'l'iserl receit'er/28 Nm'l'll liJer 2002: w-cepter/8 .lwnuu-v ?J!03

l'ol y( piperazinyl phosphoriminc) was prepared by Schotlen-lloumann method using phosphorus oxych loride a nd piperazine at room tempera ture. Polymer metal complexes were prepared in aqueous solutions using div:den t meta l sa lts viz. Cu(ll ), Ni(ll ), Mg(II ), Ca(II) and Cd(II ) with the polymer. Spectral evidences confirmed th e formation or the metal compll·xes. Thermogravimetri c analysis and differential scannin g calorimetry were emplo)'l'd to in vest igate the thermal stahility or the polymer and its metal complexes. The IR spec troscopy of the polymer and complexes suggests that metals could be co-ordinat ed through oxygen or Ute phosphorimine group and tertia ry nitrogen atom. The DRS, EPR and magnetic moments confirmed the complex formation and showed the geometry or the complexes. Sma ll a ngle XRD pattern shows that the polymer was a morphous, whereas the complexes were crysta lline. Energy dispersive X- ray crystallographic studies eon!irmed the metal incorpora tion in the polymer chain.

In recent years, po l y m~..:r-m c ta l comp lexes gained considerab le interes t owing to their attracti ve appli cati ons in eli versified fi elds such as cata lys is 1,

ex tracti on of meta ls including radi oacti ve elements2,

bio- inorganic chemistry\ water and was te water

treatmcnt4·5

, etc. Polymer-metal complex is co mposed of synthetic polymer and metal ions bound to the polymer li gand by a coordinate bond . The complexati on of meta l ions w ith polymer matri ces containing functi onal li gand results 111 superi or properti es compared with the simple compound counterparts. When metal ion was added to a so lution of polymer li gands such as polyacry li c ac id, PV A, polyethy leneiminc or polyv iny lpyridin e, a poly mer chelate was rapidly fonned6 Water so luble acry late fo r uptake of Cu(l l ) and M g(ll ) ions using their carbony l chelating sites were reportcd7

. It is obvious that organic polymer wh en complexecl with inorganic metal salt s result in an organic backbone functi onali zed with inorganic metal s, wh ich imparts both fl ex ibility clue to organic moiety and stability due to inorganic functi ons in the same polymeri c backbone. Si yam and Henn} synthes ized anionic,

ca ti onic and amphoteri c acry lamide p1dy mers by Utiliz ing the non-bonding lone pair nf c iL'L i rlltl S in the

* For correspondence: (E-mail : pakantwn (" ·' ;,l. ,ll lli v.edu : Fax: +9 1-44-2200660)

nitrogen atom for the complexat ion o f Cu(ll ) and

M g( ll ) metal ions.

The complex ing ability and effi ciency of

functio11alized polys tyrene w ith 2,2 '-dipy ri clyl amine with vari ous metal s was i 11 ves ti gateds. Kal i yap pan c l

I •>- 14 h . I I . . I I a . synt cs izcc t 1c sencs ot po ymcr meta complexes both in aqueous and non-aqueous mediu m for multifaceted appli cati ons. It is interes ting to note th at phosphoru s was al so used for the recovery of transition metal 1011 in th e form o f phosphine I. I 1' 1(' L. P N . . I I . 1ga11c s · · . 1 terature on - conl: ttn t ng c 1e at1ng polymers is scarce. Onl y a few reports for low molecu lar weight compounds contai ning P-N I I . . d . h ,. 17 I X G II c 1c at1ng Sites appeare 111 t e Iterature · . enera y

phosphoru s-nitrogen (P-N) bonds arc not liable to easy chemical attack and are found to be rcl:llive ly stabl e. These facts contributed to the interes t in the inves ti gati ons on li gand containing P-N bonds in polymer network . M etal-ion bindi ng charac ter isti cs 1'>

o f phosphorus con taining polymers prompted the au thors towards a renewed look into thi s domain of chelating polymers.

X-ray crys tallographic inves ti gati on of the complexes was al so carri ed out ex tens ively to ass ign the structure of the metal complexes. Energy dispersive X-ray crys tall ography method is already used to identify and study the crys tall ine propert ies or the metal alloys and th eir compos i tional analys is using th eir characteri sti c fluorescent peaks w ith the

Kuman:s:m & Kannan: Synthesis of poly(pipcrazinyl phosphorimine) ami it s metal comp lexes Articles

standard values20. The metal atoms in the pol ymer

chain have been identifi ed using energy di spersive X­ray crystallographic method. In continuation of

. k . I . ~ - 1 4 h k d I prevtous wor tn tltS area , t e present wor ea s with hitherto unreported synthesis and characteri zation of poly( pi perazi ny 1-phosphori mines) and it' s metal complexes , in aqueous med ium for effective remova l of metal ions from the wastewater streams.

Experimental Procedure

Materials Phosphorus oxychloride and dichloromethane were

purified before use21. Anhydrous piperazine

(Lancaster) and vari ous meta l sa l ts (Fiuka) were used as rece ived.

Syuthesis of poly(piperazinyl phosplwrimine) {Poly(PPI)]

Piperazine ( I mmol) was dissolved in aqueous sod ium hydroxide so luti on (30 mL, 4 N) with vigorous stirring. Phosphorus oxychloride ( I mmol) was dissolved in dry methylene chloride (20 mL) and added to the mixture in one lot. A dirty white precipitate formed wit hin five minutes was collected and dried in vacuum for 24 hat 75°C. The polymer is purified by titrating wi th luke warm DMSO. A bri ght white precipitate obtained was filtered

and dried in vacuum oven at 80°C overnight (Yie ld < go%).

Preparation f~{ poly(piperazinyl plwsplwrimine)­metal complexes

A series of polymer-metal complexes such as Cu(ll ), Ni(ll), Mg(ll) , Ca( ll ) and Cd( ll ) were prepared at room temperature in aqueous med ium w ith poly(piperazinyl phosphorimine). The typical procedure for the preparation of polymer meta l comp lex !Cu(ll) complex ] is as follows: Poly( PPI ) (2 mmol of repeatin g unit) was dissolved in distilled wate r (20 mL). A n aqueous so lution of copper sulphate (I mmol) in distilled water (20 mL) was added to the polymer solution in one lot with vigorous st irring. The polymer metal comp lex is fanned instantan eously after the addition o f metal salts. Stirring was cont inued for another one hour to complete the react ion. The precipitated polymer metal complex, was filtered, washed with water and dried in vacuum. A sim il ar procedure was adopted to prepare other metal complexes viz. Ni(ll), M g(l l ), Ca(ll) and Cd( II ).

Characterization and measurements The so lubility of the pol ymers was tes ted with

variou s solvents. The intrinsic viscosity measurements of the poly mer was made in Ubbelohde suspended level viscometer using water at 30°C. Fourier-transform infrared (FT -1 R) spectra of the polymers were recorded on a Nicolet Avtar 360 ESP

spectrophotometer using KBr pellets. The 1H and 1' C-NMR spectrum of pol ymer was recorded on a

Hitachi 300 MHz spectrometer 111 0 20 ustng tetramethylsilane (TMS) as the internal standard. Thermal transitions of the polymer and pol ymer metal complexes were determined on a Perk in-Elmer thermal analyzer DSC-7 with controller TAC 7/DX

under nitrogen atmosphere at a heatin g rate of 20°C/min. Thermogravimetric analyses were carr ied out on a M ett ler Toledo thermo-ba lance using 0.5 mg of sample at a heating rate o f 20°C min· 1 (argon atm

80 mL!min). The magneti c moments were measured by the

Variable Susceptible M easuremenr methods (VSM). The diffusion reflec tan ce spectra (8000-26000 cm.1

)

were measured on Karl-Zeiss vsu-28

spectrophotometer. The EPR analyses were carri ed out at room temperature on a Varian

spectrophotometer. X-ray diffraction pattern of the

polymer was recorded with a Ri gaku DMAX Ill with nickel filter using Cu Ka radiation of wavelength

1.542A. Energy dispersive X-ray diffraction experiments were performed on cmploy i ng a Rotating anode X-ray generator (Ri gaku. 12 KW) operating at SOk VandiOOmA.

Quantitative estimation of the metal ions using Atomic Absorbence Spectroscopy

In the model effl uent treatment, clliciency of the polymer was tested and Atomic Absorbence Spectroscopy (AAS) was used to measure the residual metal ion concentration. Initiall y I 00 ppm (mg/L) of the metal ion concentration so lutions were prepared for Cu(ll), Ni(ll) and Cd( ll ). 100 mL of 100 ppm metal sa lt so lution was taken for the treatment. Then two mole equi valents of the polymer were added to that so lution as ten milli gram increments. This mixture was stirred fo r 30 min. A t the end of the reaction , the polymer metal comp lexes were filtered and the remaining metal ion concentration in the filtrate was measured by AAS . Quantitative es timation of the metal s was carri ed ou t ustng AAS (Perkin-Elmer model 2830).

181

Articles

Resu lts and Discussion A new poly(PPI) was syn thesized by Schotten­

Bou mann meth od. Thi s poly mer is so luble in water and inso luble in all other organic so l vent s. The po lymer metal complexes were obtained in aqueous medium without adjusting the pH. The po lychelates were inso luble in all organic so l vents. The intrin sic

viscos ity 1111 was obtained by ex trapo lating ll sp/C to zero concentrati on. The intrinsic viscos ity of the po ly( PPI ) was found to be 0. 18 elL g-1

• The result reveals th at the polymer is of moderately hi gh molecular weight material.

Representati ve IR spectra of poly(PPI) and poly mer metal complexes are shown in Fig. I . The infrared spectrum of polymer shows absorpti on around 2980-2925 cnf 1 corresponds to methy lene stretching vibra ti ons . The P=O and P-N-C (a lirhat ic) stretchings appeared around 1300 cm-1 and around 960 cm-1

respecti ve ly which supports the formation of polymer. The absorpti on bands around 1266 and 1384 cm-1

show the presence o f aliphatic C-N stretching in the pol ymer. In the case of polymer metal complexes, there is a shift o f P=O stretching, towards lower frequency indica ting the invo lvement o f oxygen of P=O group in co-ord inati on. The P- in the polymer undergoes shift towards higher/ lower frequency in the po lymer-metal complex sugges ti ve of the nitrogen li gand in vo lved in co-ordinati on. The band around 5SO cm-1 corresponds to metal -oxygen vibrati on, which supports the fo rmati on of polymer-metal complexes.

The 1H NMR spectrum of poly(PPI) shows a broad singlet at 2.5 8 clue to - NH group, which confirms that the polymer is ended with piperazine ring. A

broad tripl et centered at 3.2 8 corresponds to the methylene groups in piperazine rings. 13C NMR

spec trum of the polymer shows a broad signa l at 45 8 which is clue to th e methylene carbons in the piperazine ring, as shown in Fig. 2. 31 P NMR of the polymer shows a singlet at 1.17R 8, which confirms the phosphorus incorporati on in the chain .

The magnetic moment. eli ffu se refl ectance and EPR spectral data (Fig. 3) are presented in Table I. The results reveal that the structure of Cu( ll ) complex is square planar, whereas Ni ( ll ) is oc tahedral. Ca( ll ), Cd( ll ) and Mg(II) metal complexes are having tetrahedral geometry and showing diamagnetic charac t e r~" . The TGA traces of poly(PPI) and polychelates data are g1ven in Tab le 2. Thermogravimetric analys is has been clone in the nitrogen atmosphere. The poly( PPI ) is stable up to

I R2

"' u c 0

E

"' c 0

1--

4000

Indian J. Chcm . Techno!.. March 200]

2000 5 00

Wavenumb er ( cm- 1)

Fig. 1- Rcprcscntali vc IR spectra of: (a) poly(PPI) (b) pol y( PPI)­i( ll ) (c) po ly( PPI)-Cu( ll ) (cl ) poly(PI' I )-Ca(ll ) (c) poly( PPI)­

M g( ll ) (I) pol y( I'PI )-Ccl( ll )

50 45 40 35 ppm

Fig. 2-uC-NMR spcc1rum ofpo ly(PPI )

200°C and commences degrad ing th ereafter. A close look over the TGA thermograms suggest that all the polychelates lose about 37% of their weight in the temperature range of 570-600°C. The Cu( ll ) comrlexcs are found to be more stab le on being

Kumaresan & Kannan: Sy nthes is of po ly(p iperaz iny l phospho rimine) and its meta l complexes Articles

Ta ble !- Magne ti c mo ment. d iffuse re fl ec tance and EPR spectra l data fo r po lymer-meta l complexes

Polymer-metal Co mplex

Magneti c mo ment (13 M)

Diffuse re fl ectance data ES R Geo metry

Elect ronic transitio ns (c m-1

)

Assignment 0 11 e

" _[_ 0

Po ly PPI -N i 3.2 9840.1 5700

Po ly PPI -Cu 1.76 I 5700.25260

~ B , g-~ A, g

charge transfe r 3A~c( F)-3T""( F ) 3A ~:(F)-3T 1: (F) 3A 2: (F)- 1T 1: (P)

2.25

2.43

2.14

2. 13

Oc tahedral

Sq uare Planar

Poly PPI -Ccl Po ly PPI -Mg Po ly PPI -Ca

Dia magnet ic Diamagneti c Diamag ne ti c

Tet r;1 heel ra I Teii-<Jhedral Te tra hedral

Table 2- Tg ancl TGA a n ;~ lys is o f poly( PPI ) ancl it s meta l comp lexes

Materia l 7 ~ 10% 17%

a) poly( PPI ) 46 200 290

b) po ly( PPI-C u) 65 2 10

c) po ly( PPI -Ni) (iQ 165

cl ) poly(PPI -Ca) 58 160

e) poly( PPI -Mg) ss 2 10

f) po ly( PPI -Ccl) so 225

a b c

:1000 4 0 00 2000 0 <1000 2000 0

M agnetic gauss

Fig. 3-EPR s pectr:~ of (a) poly( PPI )-C u(l l)( b) poly( PPI )- Ni (ll ) and(c) po ly( PPI)-Cd( ll )

280

285

300

305

300

co mpared with other co mpl exes. The glass transiti on temperature (Tg) of the polymer and polychelates are li sted in Table 2. The diffe rence in transition may be asc ribed to the crys tallinity of the polymer metal complexes and it is in accordance with the X-ray di ffracti on studies.

X-ray diffracti on study of the polymer and it 's metal co mpl exes show that poly( PPI ) is amorphous in nature, whereas the polymer-metal co mpl exes are crys talline. Thi s may be clue to inherent crystalline nature of the metals incorporated in the polymer backbone. Representati ve energy di spersive X-ray di ffrac tion patt ern for polymer metal [Cu(ll ), Ni (ll) , and Cd(ll )] co mplexes is show n in Fi g. 4. EDXRD studies of the polymer metal compl exes gave flu orescent peaks of their corresponding energy fo r Ni(ll ), Cu(ll ) and Ccl(ll ) as 7.6, 8.2 and 23.3 KeY

"' 0. 0

20%

325

280

320

3 15

330

325

400

~ 200 ., c:

23 %

360

300

345

330

350

340

a ( b

' I II I[ II (I ,, ,, [I

I' ,, ,,

I I I

I \ ,,

30%

380

330

400

360

390

390

37%

570

l'iOO

595

550

575

585

c

l 'I I. ' I / , ' I I . . I I . . I I . . \

! \ ! \ ! . -~ I I I \

I I\ i \ 0~--- '-~.

~) \ / \ __

-~-~ - ~-..r---~· ··\.

6 8 10 22 24 2 6

Ener gy ( keY)

Fig . 4- ED RD palle rn (a) po ly( PPI )- i(l l) (b) po ly( PPI)--C u(ll ) (c ) po ly(PPI)-Ccl( ll )

respectively. The above res ults confirm the incorporation of the metal into the polymer.

To ascertain the efficiency of the polymer, the model efflu ent treatment study was conducted and the res idual metal ion concentrati on was measured by AAS . The concentration of th e metal ions (in pp m) after treatment is plotted against the weight of the polymer and is given in the Fi g. 5.

The res ults reveal that the metal ion concentrati on decreases with increase in the polymer dosage. The Cu(ll ) metal ions concentrati on beco mes zero when

Articles lndi ;l ll J. Ch<:1n. 1\:chnol., 1VL1rch 2(!0:\

1\ ~ NaOII HN NH + CI-~-CI

\__/ Cl

M = CL Cu , Ccl, Mg. Ni

Sch<:1ne 1- Sy nth.:sis of poly mer and it s metal complcx<:s

'"".

1

-+=- cadm!um : --- Copper ,

-..- Nrck_el )

ooo 002 oo4 oo6 oon o 10 0.12 a 14 a 16 0.10 0 20

Weigh ! nf !he pn ly lllc r (g)

fi g. 'i - Efkct or po ly lller O il Cd( ll ). Cu( ll ) ; lllcl Ni( ll ) ion C<lllCe ll!r;l!ion

the pol y mer we ight is 200 mg. In th e case o f nickel ion concentrations. it needs II 0 mg of the j)lll y mcr to bri ng the zero eoncen trati on. 13ut cadmiu m ion requires on ly C10 mg of the polymer to bring the zero concent rati on. Studies on M g( ll ) and Ca( ll ) were not carri ed ou t clue to non-avail ab ility of facil i ti es for their es timati on in ow laborat ory. The change in the po ly mer dosage req uired to bring the metal ion concentrati on zero is g i ven in Fig. 5. It is noti ced from the AAS st udi es. that the metal-to-ligand rati o in th e meta l compl exes is I :2. Two mole equivalents of the pol y mer arc requi red tn take one mo le equi va lent of th e metal ions. The above ev idences suggest th at the chelation of meta l ions may poss ibly be occurring

I R4

between two groups from difl"crcnt po ly meric chains as shown in Scheme I.

Conclusions Pol y(p ipcraziny l phosphorimine) w:1s prepared and

complcxcd w ith Cu( ll ), N i( ll ), Cd( ll ). Mg( ll ) and C t( ll ) metals in neutra l aqueous medium successfully. The polymer and it s comp lexes were anal yzed and confirmed by variou s spectra l methods. The th erma l st abilit y or the pol y mers was ana lyzed by TGA and DSC techniques. The energy dispersive X- ray diffraction anal ys is confirmed the meta l incorporation in pol y mer backbone. The polymer was trea ted wit h model effl uen t and th e elli cicncy or the poly mer w as tes ted using th e AAS quantit :tti vc ly .

Acknowledgen1ent The authors gratefull y acknowledge the Mini stry of

Env ironment and Fores ts (ME&Fl, New Del hi, for fin ancial support.

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Er/11. 12 ( l tJ74) 1243. 7 Siy;1111 T & Henna E. M(lcmnw/f?et!. i\ 31 ( I 'N-l ) 3-l'J.

Kumares;m & Kar111an: Synthesis o r poly(pipcraziny l phosphorimine) and its metal complexes Articles

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I R Hideki Oota. Wuhiao Duan & Ki yoshi Sawada . .I Chem Soc Dolton Tmns ( 1999) .\07'i.

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2 1 Perrin D D & Armarcgn W L F. Purificotinn o( l ,tdmmtnrr Chemimls. third edition (Pergamon Press. U K). 19XX.

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