lnJ i ~m Jou rnal or Chemistry Vol. 4)/\. Septcmher2006. pp. 1994- 1998

Cu K-absorpti on near edge studies on di ethylenetri amine mixed li gand co pper(! f) complexes in solid state and in aqueous solution

S K Joshi "·"', P K Sharma b, 8 D S hri v ~t s l ~ t v a ', I\ Mi shra " & K 8 Panclcya "

"Ph ysics Dcpa rttnen t. Government Post Graduate Arts and Sc ience College. R~lllam 4)7 00 I. lmkt Email : skjoshi_rltn @sancktrnct.in

h Ph ys ics Department. llo lkar Science Co ll ege . Indore 4)2 017. Ind ia ,. Schoo l o f Studies in Ph ys ics . Vikram Uni ve rsit y. Ujjai n45G 0 10. India

d School or Ph ysics. D./\. Un ive rsity. Indore 4)2 017. Ind ia ' Dept. ofChemisty. 1\. P.S. ni vc rsity. Rewa 486 003. India

Ncceii'NI 25 1\pri/ 2005: n 'l' i.lcd 22 Jun e 2006

The Cu K-absmption n c ~tr edge stntclurc studi es of some: coppcr( ll ) mi xed l igand compl exes arc I'C J' urtcd here. invo lving the primary li gand dicthy lcnet t·iaminc ( D ET A) and the secondary li gands imidazo le(l m). methy l i m i c~t /olc (M im) and ethy l imidazole ( Elm). The studies h~1 vc been made both in the so lid as we ll as in the aqu eous so luti on forms. The chemical shirt s o hi~Iin c cl li1 r Cu K-ahsorption edge suggest that the entry o r the secondary l igands into the cc·ordJn~ttion

sphere allcct s the chc tni c~tl shirt s onl y sli ghtly. Th e chemica l shi/.1 v~ tlu cs arc larger in th e so lid state as coJlipat"CCI 10 the correspond ing values in th e aqueous so luti on /·arm indi ca ting more ionic nature or the co mple xes in the so lid .• t ~I t e . r'urther in tiH.: solid slate. the re is 11o sp lilling of the K-~tbsorption edge. whne ~1 s in the aqueou s so lution J'onn the K -edge spl it s into K 1 and K2 edges showing th~11 the octahedral geomet ry in the so lid form gets dis torted in the solution form. T he rcLiti1·c order ol· ioniL·ity or the complexes in sol id form is ~tl t ered in solut ion form. which c111 he exp lained in terms o:· the change-, in th e geometry of thc comp lexes on di sso lution in 1\'~II e r.

IPC Code: Int. C l. x C07r- J/08: GO I N2:l /OO

Di cthy lcnctriaminc (DET A) ( I ) is a tridentate li gand with three nit rogen donors suitabl y situated to form two fi ve membered rings. It ca n form six coordinate oc tahed ral compl exes when present in 1:2 metal:ligand rat io. In I : I stoichiometry, the li gand fo rms three bonds w ith the metal ion leaving one pos iti on to be occup ied by an anion or a base (as available) to form a rom coordinate sys tem req u1r111g a geometry intermediate to planar or a tetrahedral ex treme

1•

Cu K -absorption studies on four dillcrent complexes of Cu(Il) with DETA have been carried out on solid compounds as well as on their aqueous solutions. The complexes included in the present study arc: lchloro

diethy lcnc triaminc copper ( II ) I ch loride. ICuCI • DETAI Cl (1 ): ldicthylcnctriamine imidazole copper

( ll ) lchloridc, !CuC12·DETA-lml (2); ld iethy lcnetri aminc

methyl i miclazole copper ( II ) I chloride.

!CuC12·DETA-Mlml (3 ): and. ldiethylcnetriamine ethy l

imidazole copper ( II ) I ch loride. !CuCI2·DETAElml (4).

Imidazo le is a mo lec ule o r bio logi cal importance. It is contained in the structure or several organi c

compounds and se rves as li gand to the meta l ions in a number o r compounds and complc ."< ,.::s

1. It is we ll

know n ~·' that X-ray absorpti on spec traum i s ve ry sensiti ve to the physico-c hemica l cond iti ons o r the <tbsorbing atom and conveys useful i nl'orm ~tti o n <tbout the elec tronic structure, e!Tccti ve cha rge o r the cent ral atom. chemica l bonding, etc. Foll o·w ing the X -ra y <tbsorpti on edge, there appears a ~. tru c t u rc on it s higher energy side, whic h is kn own as the X-r<t y absorpti on f'ine structure (XAFS). Tl;e fine structure ncar the edge cove ring the energy ratt .~e up to nc trl y 50 cV is called X-ray absorption nct r edge structure (XA NES). The structure ex tending over several hundred elec tron vo lts above 50 e V . beyond the XANES region is called ex tended X-· ray ~tbso rpti o n

fin e structure (EXAFS). XANES is a powe rfu l tec hni que for the stud y or compl exes and y ields use ful st ructu ral inf ormati on

4-6

. and has been used during the preseL. studi es .

Matcl'ials and Methods X-ra y absorpti on spec tra were recorded on a

laboratory XAFS spectrometer consisting o f <t -W em

JOS HI cl ol. CU K-AI3SORPTION STUDIES ON SOrvi E CO PPER(II ) M IXED LIGAND COM PLEXES 199)

H, H,

I I

~-N-H, ~-N-H, H -C I H -C I

• - Cu- Cl Cl ' - Cu -1m

H,-C I H,-C I

- N- H, C - N- H,

Cl

I I

H, H,

( I ) (2 )

H, H,

I I

~-N - H, ~;N-H, H -C I H-C I

' - Cu- Mlm Cl ' - Cu- Elm

H,-C I H,-C I -N-H, C-N-H,

Cl

I I

H, H,

( 3) (4 )

bent crys tal spec trograph having ( 20 I ) refl ec tin g planes of muscovilc mica as ana lyser and a scaled Ri ch-Sc iferl tungsten target X -ray tube operat ed at 17kV and 60 mA. The spectra were recorded photographi ca ll y and the intensity record s were taken on a Cad -Ze iss microphotometer coupled w ith a recorder. A t least nine independent measurements were taken for a sample and the results presented here arc an average of such measurements. The resoluti on

o f the spec tromete r (),/d),) was better than I 000 and the dispersion was about 0.6 pm/mm on the

photographi c film in the second order. WLcx2 and

WL0-l emi ss ion lines were used as reference lines to es tab li sh the wavelength sc al e. The error in the measurements were of the order of ±0.3 cV. Ot her detail s arc given in an ear li er communicati on7

T he comp lexes have also been studied in aqueous so luti on form. The absorpti on sc reens of the samples in soluti on form we re prepared using the pcrspex

sheet of dimensions 5 em x 5 em x . 0.5 em w ith a circular hole of 1.5 em diameter at its center for fillino the so lulion. One side was covered w ith cc ll ophan~ tape and then so luti on was fi ll ed inside the hole. Then other side was closed w ith a piece of ce ll ophane tape so that no air bubb le is left inside the so luti on. Thi s

Vi' :!::: c: :J

.ci ... cu c:

:.:=, (l) 0 c: cu .0 ... 0 Cll .0 <(

0

3 (Aq. Solu tion)

2 (Aq . Soluti on) 1 (Aq. So luti ol'l)

100

Energy (eV)

1 (Solid) 4 (So lid)

200

f ig. I - Ncar edge structu re ~It the K-ahsorption edge of co pper in Cu(ll ) co mpl exes with DET;\ in so lid ~111d solution l·lmm.

frame o f perspex was fi xed on the aluminum holde r and placed in front of the w indow of the X-ray tube. The aqueous so luti on was prepa red by taking 20-30 mg powdered sa mple di ssol ved in doub le di still ed wa ter. Sometimes, so luti on was hea ted up to

50°C for di sso lving the powder into water. For preparing the complexes. aqueous so luti ons of

CuC iz- 21-!p. DETA and the imidazo lcs we re mi xed in

equi molar rati o (0.00 1 mol each) and the soluti on was left in air for evaporation. Dark blue crys talline so li d. thu s obtained. was washed w ith small ~1moun1 o f co ld

wa ter and dried in an elec tri c oven at 80°C. /\ II the compounds gave sa ti sfactory elemental anal ys is.

Figure I shows the X-ray K-absorpti on edges or Cu( ll) complexes w ith DETA ligand s in so lid ~1nd

so luti on forms.

Results and Discussion Tab les I and 2 contain X -ra y K-absorpti on data on

DETA complexes in so lid and aqueous so luti on. respec ti ve ly. The val ue 8980.3 cV is the value of

1996 IN D IAN J C II EM. SI:C /\. SU'T[ivi i3ER 2006

----------------~~~~-=~~~~--~~--~--~~--------~--~~~-------

T:thl c I - Chc tn ic:il shi fls ol' K -: thsu rption cugc ol' coppn complexes in so lid rorm

Comp lex

Copper tnct:il

I 2 3 -+

),K CU'' C "' (±0.005 ptll )

138. 0(>3

I 37.89 I I 37.90 I

1:\7 .90-+ 137.907

/ :·K cugc

(± 0 3cV)

8!JS0.3 899 I 5 8990.8 8990.7 8990 .'i

/:'/\ Chemical shirt 1'1 C Shi n or princ ipal ahswplion maximum K

(cV) (cV) (cV)

9001.2 9008.8 11.2 20. 3 9000.-+ 10 ) 20.2 8999.7 I 0-+ I 9.5

9000 -+ 10.2 20.1

T able 2- Chemica l shifl s o r K-:thsmptinn cugc o r copper compl exes in :tq uco us so luti on

Complex 1·~-.: edge / :'K cugc /:'/\ Shi l't ol"princ ipal ahsDq·•tionmaximum

(±0.005p111 ) (± 0 3cV) (cV) (cV) (cV)

I 37 'J<J .\ 898-+ .8 8998.0 -+ ) 17.7

137.97 1 8986.3 8992.5 2 6.0 12.:: 137.972 8986.2 900U J 5.9 :no 137.96') 89SCL-+ 8996 1 I 6 I I .~ .S

; ------------~~~------~~~------~~~----------~-~------------------~~--

copper metal K -absorpti on edge obtained by us and thi s value is the same as reponed earli e r~ . This va lue has been used in the present in vesti gati on for the es ti mation o r chem ica l shift s and shil't in the principal ;1 bsorpti on ma x ima in Table I and Tabl e 2.

A s stated earli er. DET/\ is a tridentate li gand fonning idea l two fi ve membered rings w ith a metal ion. A four coordinate structure is readil y attained w ith an ani on or unidentate base attached to the metal ion al ong w ith the li gand. In the comp lexes under stutl y. the ani on m;ty be a chl orin e atom. and uni dentalc ba se may be imidazok or a substituted imidazo le as the case may be.

The chemi cal shirt tJ. CK or the K-absorption edge

rnay be defined as the energy difl'c rence fJ.EK = ~:_· .. (compound ) - EK (meta I). The complex (1 ) shows chemical shirt v;tlue of 11.2 eV in so lid stale. In the imidazole ;tdduct (C uC I ~ DET/\· Im) where ch loride in the coordinati on sphere is rep laecd by an imidazo le ntolecule. the chemica l shift value is lowered to 10.5 eV. A s a li gand imidazo le is much higher in the spec tmc hemical series as compared to chloride. thi s demands an increase in the elec tm n density at the central metal ion resulting into a decrease 111 the pos iti ve ch;trge on the metal ion and hence 111 the chemical shi l't value.

Upon changing imidazole to substituted imidazo les. one would expec t a funhcr dec rease in the chemical shift value. M ethy l and ethy l are elec tron rek asing groups. and they would . therefore, cause relati ve ly higher elec tron densit y on the donor atom and hence on the centra l metal ion. One would expect. therefore. a dec rease in the chemica l shift va lue in go ing !'rom CuCI2·DETA· Im to CuCI 2·DETA-Mim/

E lm. The present data , howeve r. do not show ;t

signil'i ca nt decrease in chemical shi l l value for the substituted imidazole deri vati ves as compared to the imidazo le deri vati ves . It can be ex pla ined by the non­ri gidity o f the tetrahedral arrangemen t o f the li ga nds amund the central copper ion. The energy leve ls in the !'our coordinate square planar - tetrahedral sys tems arc highl y dependent on the nature a:KI bulk of the attached li gand. Rep lacement o f imidazo le in the four comd inatc structmcs by substituted in1idazo lc has to be viewed not onl y from ind ucti ve c iTcc t considerati ons but al so !'rom the poss ible change in geometri ca l parameters. leading to al te rna ti ons in the energy leve ls. Similar chemi ca l sh tft values l'or methy l imidazo le and eth y l imidazok; de ri vati ves arc in line w ith identi ca l protonati on con ~ t a nl values o f the two li gands1

.

A mong CuCI2 (l igand) type co lllpl excs. the chemical shirt s have nearly the same va lues as seen from Table I. Thi s indicates that metely a change in the chain length o r l igands has littl e cllcc t Oil the chemical shift va lue. The chemi ca l shi l'l value o l' the first comp lex is 11.2 eV and is s i g ni ~i c anll y large as compared to other complexes. As i ~ we ll kn own. change in the va lue of chemical shil't depends upon the ionicity, and hence one can kn o' " the order or ionic ity from the order o f chcmicd shifts in the complexes. The order from the chemicil shi It is: 1 > 2 > 3 > 4. Thi s sequence show:; that the ion icit y should al so dec rease in thi s ordcr'1-

11

In the present in ves ti gations, all the four complexes studi ed ha ve valency +2. The observed changes in the chemical shift values w ill , therefore. depend on the relat ive ionic character o f the comp lexes. Larger

.J OS HI £'1 a/. CU K- /\ 13 SORPTION STUDIES ON SOME COPP[R (II ) M IX[D LI GAN D COM PLEX[S 1997

chemical shift s show that the complexes arc more ionic in character and small chemica l shifts show the complexes arc less ioni c. The ionic character o f the Cu( ll ) complexes can. thu s. be in fe rred from the present study .

The order o f chemical shirt va lues o f all the rom complexes in aqueous so luti on form is: 4 > 2 - 3 > 1. The order o f chemical shift values o f the present complexes is same to that ofpK values wit h respect to

i midazo lcs 1 }: E lm 2': lm 2': M lm.

The increase in chemical shift in substituted imidazo lcs may be due to increase in basicity o f imidazolcs . The order o f the chemical shift value in aqueous soluti on form is just oppos ite to that repon ed for the complexes in so lid form. It is c lear from the present stud y that the ionic it y is more in solid samp les than that in the liquid (aqueous solution form). A s the chemical shift values arc more ror so lids as compared to those for soluti on: ioni city (which is dependent on chemi cal shift ) shows a decrease in so lution fonn. Further. in so luti on form. the cfTcc t o f di ssolut ion in w;~ t c r is di!Tcrcnt for difkrcnt li ga nds. ;~nd hence. the order or ionic ity is reve rsed in c ;~ sc of aqueous so luti ons. Thi s shows th ~ 1t the complexes in so lid form ~ 1rc more ionic than the complexes in aqueous so luti on form. as reported by carl icr workers for other

11 sampl es · .

T~tbl cs I and 2 show that there is a considera ble dec rease in the chemical shift v;~lu c o f IC'uC I·DETAI C' I in go ing from so lid ( 11.2 cV) to so luti on (4.5 cV ) f orm. i.e. a diflcrcncc o f 6.7 cV. Howeve r. for the remaining three sampl es . i.e. for the samp les in which substitut ed imidazolcs are used ~1 s

secondary li ga nds. thi s dillcrcncc between chemical shirt s in the so lid and so luti on forms comes ou t to be 4.5. 4.5 and -+ . 1 cV . respecti ve ly for imidzao lc. methy l imidazo le and eth y l imidazo le. Thu s. the contribution o f the secondary li gands to the di sso luti on crrcct in soluti on form is nearl y similar.

On the hi gher energy side o r the K-edge. there appears a pronounced absorpti on pc~tk ;~nd thi s is rckrrcd to as the principa l absorpti on m~t x imum. The shift o f the principal ~tb so rpti o n ma x imum in a compkx can he dcf'i ned ~ ~ s the energy d i !Terence bet ween the prin c ip;~l ~tbso rpti o n ma x imum (£ ") and the corresponding energy o r the metal edge £ "' . Thi s parameter is se nsiti ve to metal ion. Koul and P;~dalia 1 ~ h;~ vc reported that the values o f the shift or the prin c ip ~tl ;~bso rpti o n ma ximum in so li d form and al so so l uti on form for copper( II ) complexes I ic bet ween

17.7 and 22.0 cV . C'omp ~tri so n with the report ed values shows that all the sampl es under in ves ti g<~t i o n

possess ox idation s t<~t c (+2). The shift o f the main pc;~ k toward s high energy

side w ith i ncrcase in ox idation state h~t s been ex pl;~incd 15

in terms o f a simila r shift o f unocc upied 4JJ* (antibonding) orbital s. It has been argued th at ~ ~

more ox idi zed mct;~l forms a stronger bond w ith the li ga nd giv ing ri se to more stabl e bonding orbit al s. These antibonding o r b it ~ tl s arc. however. rai sed in energy due to stronger repul sive forces . and hence. the principal absorpti on max imum shift s towards the high energy side.

The shift o f principa l absorp ti on ma x imum for Cu( II) complexes i 11 ;~q ucous so luti on form shows less v ;~lu cs as compared to va lues reported for comp lexes in so lid form . From thi s. it can be inferred th <1t the complexes in so li d form show more ioni c c h~tra c t e r as compared to the compl exes in aqueous so luti on form.

T he splitting o f the main edge occ urs due to admi xed (3d--+s-.fJJ ) s l~tt c s . The K 1 edge is ass igned to

tran siti on l s~(3d-4s). while the K :- edge to tr~lllsitiun

l s~4p state. W e h;~ vc not observed an y splitting of the m;~in edge in the case o f Cu( ll ) comp lexes. The non-splitting beha viour can be ex pbincd fo ll o\l'ing Dey and Agarw~tl 11'. Accordin g to them. on compound rorm<lti on usuall y the interacti on di stance inn eases and dchybridi zati on sets in . As a result. -+s band becomes narrower and no more ~tdmi xcs w ith the 3d bane!. The Is elect ron now has to mi ss the 3d b~llld

and 4s band s before it find s an empty .fJJ s t ~ tt c. The net result is that the kink K 1 (sp litting) di s~tppca rs <tnd we get on ly one main edge. The complexes in aq ueous so luti on form show splitting in the K­~tb sorp ti o n edges . Thi s is in line w ith the di stoncd oc tahedral geometry o r the complexes in the so lut ion form.

Conclusion It has been shown here that the entry o r the

secondary li gands into the coordinati on sphere all cc ts the chemical shirt s o f K-absorpti on edge or Cu( ll ) centra l metal ion in the di cthy lcnctriaminc mi xed­li gand copper complexes onl y sli ghtl y . Funhcr. on the ba sis o r X-ra y absorpti on chemi cal shirt s. it C lll he concluded that the so lid s ~tmpl cs of copper( II ) mi xed­li gand complexes arc more ionic in n<tturc as compared to the sampl es in so lut ion. The K­absorpti on edges do not show an y splitting in solid s t ~tt c suggest ing octahcd ra I gcomet ry . whereas in the

1998 INDI AN .I C II I::: M. SEC 1\ . SI:::PT[ M13ER 2006

soluti on state the K-edge split s into K 1 and K2 edges suggestin g a di storted octahedral geometry. The re lat ive order of the ionicity amongs t the studi ed sampl es h;ts been es tabli shed. The ox idation stat e 2+ or copper in all the samp les studi ed ha s al so been establi shed in the present investi gati ons. Earli er X-ra y ;tbsorpt ion spectroscopic studi es on copper

I 17-20 I I - ld I 1· I . 1· . samp es 1a ve a so ytc ec usc u 111 ormat ton.

Ack nowledgement Since re th;tnks arc due to Dr R N P;tte l. Department

of Chemi stry A.P.S. Uni versity. Rewa 486003. for use ful discuss ions.

Rcfet·enccs Pandey K 13 & l';t tc l R N. /111/ .I C/1£' 111. 20A ( I !J90) 602.

2 .J oshi S K. Sliri vast:t\'a 13 D. Dcs li pandc A P (cds) X-Nar Spec!m.ICOf!\' a/1{1 ; \ 1/ il't! 1\rem (Narosa Puhl is liin l! ll ou s~ . Ncw Dclhi). l0fJ 8. ~

\ K:tl:t rc R K. Joshi S K. Sli riv:Jstava BD. Pat e l R N. Pandcya K I\ & Mi , hra 1\ . X-m_1· Sf'ccllmll . .1 1 0 002 ) .127.

4 K:111 L S. Solomon D .1 . l'cn nn- ll :dlll .I E. ll mll!so n K 0 & Soloman [ I. .I 1\ 111 C/11' 11 1 Soc. I O!J ( I !J 87) 64.13. ~

:1 \V:tki t:J II. Ya m:Jgucli i T. Yns liid :1 N & Fuj iwa ra M . .If i ll ./

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6 f'urcnlid L R. Renner M W & Fujita E. F h \'s ico fl . 208. 20fJ ( lfJfJ) ) 73!J. .

7 Sliri vastav;J 13 D . .J oshi S K & Pandcya K 13. X -rm · Sf il'CirrJ/ 11.

27 ( I!J88) 127 . 8 Caucli oi s Y & Scnc mau d C. \l'(ll ·ei<' llg Jfl.,. oj' X-nn·

/ ·.'111iss io ll l . illcs o 11 d i \!Jsrllplio ll l ·.'dg cs 1 Pergamon PrL·ss. Ox r·o r·d) I !J 78.

fJ Aga rwa l 13 K & Verma L P . .I l ' hrs. C.l ( I !J 70) :1 .1 :1. 10 Nig:rm AN. Raj pul 0 P & Shri vasta v:r II D. X-mr .'ifwcllmll.

14 ( I 1)8:1 ) 1:\6.

II Shri vastava 13 D. Mishr:1 A. Joshi S K & 'vLllldl oi S 1~ . IIlli ./ Clit ll l . .l l i\ ( I fJfJ2 ) fJ 2fJ.

12 P:rt cl R N. Pandey II C . Pandey K 13 & i\1 ctk herj cc G N. f lit!

.I C 'ht'"'· .lS/\ ( I fJ!JfJ ) 8:10. 13 Mi shra A. Shr·ivasl:rv:t 13 D. Sharma P &:. Josh i S K. X- m 1·

Spt•cfmlll. 24 ( I fJfJ:l ) 240. 14 Koul P N & Pada lia 13 D. X -rar Spccllw ll. 22 ( lfJ 83) 12S. I :1 Glen G & Dodd C G . .I 1\pp / 1'/ ,n . .l!J ( l lJti ::> 1 ) 0, 72.

I (J Dey A K & Agarwal 13 K . .I C/1('111 1' /n·s . ~f) ( I !J 7.l) 13!J 7. 17 M ishra /\. Pandey D. Kekre P /\ . Dubey R K & Kumar ;\.

1\ sioll.l 1'/n ·s. 8 ( 10fJfJ ) 227. IS M ishra 1\ . 1':111dcy D. Dubey R . Kckrc P :\ & Kumar ,\ . X­

I'll.\' Spec/ m ill. 2!) (2000) 16 1. I 0 Mi shr·a A. Dubey R K. P:u1d cy D K & Sh ,-i ,·as t:rva 13D. /11(/ ./

l'hrs. 74/\ (2000 ) 17 1. 20 Mi sh ra /\. Dave M. Kh:H.l ikar P V & Jo ;l1i ,\ . A1io11 ./ !'h"''·

f) (2000) 41 fJ .