Infrared Study of Metal Chelates of Bisacetylacetoneethylenediimine

Chem. , 1955, 59 (10), pp 998–1004. DOI: 10.1021/j150532a002. Publication Date: October 1955. ACS Legacy Archive. Note: In lieu of an abstract, this...
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998

KPIHEITJENO AND ARTHURE. MARTELL

Vol. 59

INFRARED STUDY OF METAL CHELATES OF BISACETYLACETOKEETHYLENEDIIMINE AND RELATED COMPOUNDS1 BY KEIHEIU E N OAND ~ ~ ARTHUR E. MART ELL^^ Contribution f r o m the Chemical Laboratories of Clark University, Worcester, Mass. Received February 1, 1966

Infrared allsorption frequencies from 4000 to 400 cm. - 1 are reported for bisacetylacetone-ethylenediimine, bisacetylacetone-1,2-propylenediimine, bisbenzoylacetone-ethylenediimine, bisbeneoylacetone-l,2-propylenediimine, bisbenzoylacetone-1,3-propvlenediimine,bistrifluoroucetylacetone-ethylenediimine, and many of the corresponding Cu(II), Ni(II), Co(1I) and Ptl(I1) chelate compounds. Frequencies are assigned in most cases to bond or group vibrations, and shifts of frequencies resulting froni replwement of enolic hydrogen of ligand by metal ions are discussed. Three bands in the frequency range 580430 cm. -1 are tentatively assigned to vibrations of covalent metal-ligand bonds.

Since the discovery by Tsumaki3 of the oxygen- were obtained by the latter technique. The significant spectral lines found for the compoundR studied are reported carrying property of bissalicylaldehyde-ethylenedi- in Tables I1 and 111,together with the assignments that were imine-Co(II), this substance and similar metal possible in each case. chelate compounds have been investigated exteiisively as models of the naturally occurring oxyTABLE I gen carrying compounds. However, a systematic study of the infrared absorption spectra of these compounds has not been reported. This paper is the first of a series dealing with an infrared study of the structures of metal chelates resembling both the synthetic and natural oxygen carriers. The work reported here is restricted to nineteen compounds \ related to bisacetylacetone-ethylenediimine, and It' which differ from the synthetic oxygen carriers R R' R" n mainly in the absence of the aromatic ring. 1 BisacetylncetoneThe ligands chosen for this investigation-bisaceethyleiietliiiiiiiie".h.' CH, CHI H 1 tylacetone-ethylenediimine, bisncetylacetone-1,22 Bisacet!ll:icetoiie-I ,2propylenediimine, bisbenzoylacetone-ethylenedipi~o~j~leiietliiiiiiiie imine! bisbenzoylacetone-l,2-propylenediimine, 3 Bisbenzoylaoetonebisbenzoylacetone-1,3-propylenediimine and hisethy1t.iiediiniiiie" trifluoroacetylacetone-ethylenediimine-form lieu4 Bisl~eiizo~lacetone-1~2tral, tetradentate chelates of the trailsition metals. I)rop~leiiediiniiiie CsHb CH3 CH3 I The metals chosen for investigation, Co(II), Ni5 BisI~euzoylacetoiie-1,3(11))Cu(I1) and Pd(II), are known to form square~)t,n~)~leiietlii~iiiiie CoH, CH3 H 2 planar coordinatioii compounds and were selec,ted G Bi.itt~iRuot~o:~cetyla~etoriein order to provide a series of related metal chelet,Ii!.IciietIiiiiiiiie"" CH3 CFa H 1 ates having analogous struct'ures, no residual " .4. Conil~es :uid C. Conil)es, Cottrpl. Teiid., 108, 1252 charges, and having 110 coordinated groups Ixyo11d (1850). N i ( I I ) , CuIII) nntl Pd(I1) chelntes rrported hy the four provided by the ligand. G. l[oi,g;Ln ~ i i t l .J. Sniitli, J . Choti. Soc., 918 (102G). Experimental Part The composition nnd structures of the ligands employed in tjhis inveRtigat,ion are summarized in Table I . Tlir preparation of t,liese compounds will be reported elxeivliere.4 As indicated by the foot,notes to Tnble I , most of t h e x ligands and m e h l chelstes have not been reported previously. The infrared ahsorption spectra were mensui,ed with thp aid of R Perltin-Elmer Model 21 double Imm recoidiitg infrared spectrophotometer. Sodium chlor,itle optics \vei'e w e d in the region from 4000 to G50 cm-', nntl n n i n k r changenble potnssium hromitle piism nssenhly wns sulwtituted for mensureinents i n the region From 050 to 400 c m . - l . Infrared absorption in carbon tett*nchloride or chloroform wns investigated as a function of concentrat,ion for some compounds solul)le in these solvents. No significnnt were found ovcr the spectix obtained hy t,he pota I,i.oinitle pellet, mc.thotl. Tlicivfnre all the spectra q i o r t w l

Co(I1) chelnte reportPd by G . nIorgan and J . Smith, The st~i~uctiirnl proof of these compnutds ~ v i l lb~ g i v ~ ni n :I Iutet, I)ul)licat,ioii. e Ligand a i d C'u d i d : ~ t rI , P ~ O I , ~hyP ~R. L. Belfortl, A . E. R,Iart,ell i ~ n t l \ [ . Cn,lvirr * J n / ( t , l i ( f /o,l' I/mqariic c o i r / A'liclcm Chcmi.str!/, i n

ihr'd., 2034 (102R).

1) I'f'SS.

Discussion For conveiiie:ice the infrared absorptjion spectra of t>hecompouiitls inlrestigatecl have been divided into three regiotis, with the frequency ranges : 4000-2800 crn. -Il 1'700-900 em. --I and 900-400 em.-'. These three regioiis 1 \ 4 1 he discussed sepn8rately. 3200-2800 crn.-l Region.-The three possi tdc struct,ures of I)isacetylncetone-ethylenecliiniine are illust,rated by formulns I, I1 and 111. It is reasonnlile t80expect, hydrogen honding 1,et'veen hydroxyl hydrogen and imino nitrogen (I),or between imino hydrogen and carbonyl oxygen (11). Struct'iirc. 111 is t,he non-hydrogen-bonded form wit8h free carbonyl grorips. The infrared spectra of bisncet,ylncetone-et,hylenediimine, and of its Pd(II), Ni(I1) and Cu(I1) chelates are illustrated in Fig. 1.

40

I

I

t 2500

3000 :3500 i (cin.-l). Fig. 1.-Absorption spect rn of hisncetylncetone-et,hylenetliimiiie (a), and its Cu(I1) ( [ I ) , Ni(I1) (c), atid Ptl(I1) ((1) chehtes i t i 3000 c ~ n . -region. ~

\.

H,,6

CH.,

I \-

It, 1s apparent t>hatthe ligniitl has a h o a d ahsorpt#ioriband at; about, 3150 cm.-', wliich may be due to the stretching vibration of either ai1 0-H group in accorda,ncewith formula I or of a K-H groups of the type indicated by formula 11. This aasignment is strengthened by the disappearance of the hand in the metal chelates shown i n Fig. 1. E1.irlence for strong hydrogen bonding is found i n the broadening of the bmd, and the esteiit of the shift From the normal position (3730-3550 rm. --I for free 0-H and 3.1.00-3300 cm.-' for free N-H). .11though thew is 110 positive proof that this absorption is due to the vibration of the hydrogen-\)onded 0-H group in I, i t is the opinion of the mthors that this is the case, since the hydrogen-horlded N-H vibration is often too weak to be oliseriwl. Since this ligaiid does not ahsorh in the region around 1700 cm.-', as will be discussed later, it ca~inot,have a free carbonyl group. Hence 111 is eliminated aiid the ligand ii3 believed to lie a tautornettic equilihriiim mixturt: of structures I and 11. Absorption bands i n 3000-2500 em. --I which are observed hotjh in the ligand and in the chelates are assigned to (3-H stretching vibrations of CH, CH, and CI-1, groups. Since absorption bands of the other compounds investigated Iia1.e charact,eristics similar to those of bisacetylacetone-ethylenediimille, similar structures inr-oliring hydro~eii-l~oiidii~g are proposed for all ligands. It seems, therefore, that, the six-membewd ring systems containing hydrogen b o d s (sti~ucturesI and 11) are greatly stabilized by conjugated douhle bond systems, as in the case of P-diketones and salicylaldehyde.!' Because of valence-k~onded resorialice i n these ring systems, i t is nwessar,y that each ring have a planar structure. However, both hydrogen-bonded rings of the molecule cannot be iti the same plane because of tlie steric hindrance and electrost'atic repulsions of 0-H--N or 0-H-X (6) (a) R . S. Rnstiiussen, D. D. Tiinnieliff a n d I:. K. Bmttain, J . A m . C h r n i . Soc., 7'1, IOGS (194R); 71, 1073 (ISl49)' (I))31. T>itlmi, RW". Chpni. SIJ,,.J ~ I J ( L 26, ! ~38.; , (19521,

groups. Consequently the actiid structure is helieired to be such that each riiig system is rotatitig about the axis of the C-C bond of ethyleuediimiiie, a proposition which is also confirmed by dipole 1110ment mensurernent..' HoiveT.er, i n the metal chclate compounds, hotli rings are fised in the same plane without steric Iiiiidrance hj. t'he centrnl metal atom as shown iii tlie formula 11.. This conchision coiicei*ningcoplsnnritj. of the metal c!relnt,e rings is fiirttiei- suppoited hy the tleinoiist~~~atioti t,hrough X-ray studies tlia8t t!ie ana,logoiis compound, ~~iss,zlicyla,ltlel~y~le-et h?-lei!rtliimiiie-(~o(IT is also coplaiiar.6 1700-900 cm.-' Region.-Thew is no significant alxorption band between 2800 and 1700 cni. - I , t,he first a,lwrptjion band being oliservetl aroutitl 1600 cm. - I ; lioi~ever,ma8nyal)sorptjion l)anrls a,i'c found i n 1700-900 c'm.--I yegion, whirh a.re slimmarized in Table 11aiitl IJI. If, as suggested xho\.e, t'he liga8tidsare tautomei,ic. mistures of structures I cznd 11, ol)ser\-ed infi~arecl alisorption spectix may lie coiisitleretl to be l h ~ result of t)he superposit'ion of spect'ra corrmpoiitliii,q to both struot,ures. Accordiiig to tlie tautoniei.ii4 forms I and I1 of the ligand, nnd structure I\' of' tlie metal c,helat,es, we ea11 expect st'rong absorptions in the double hontl 1-cgion correeponcliiig to C-C, C=N, and llydrogen-boli~ledC=C) stretching vibrations for the ligancl, and nhsorpt'ioris arising from C-C and C=N lmitls for tjhe metal ctielate compounds. Rowei'er, sincte these do~rtile bonds are conjugated, miti since we call expect, i'esonance in the ring systems involving hydrogen h o ~ ~ d ing, these double Iioiids have coiisiclerable siliglebond character and would ha,ve lower t h i tiornia,l frequencies. Thus it is fsiirly cei,tniii that thcx first absorption baiitl a t 11315-I600 em. - I , ~ v h i c l iis 211ivaj7s very strong a i d is fowid only ill the l i p i d s , iii can be assigned to a C=O st'retcliiyg i~ihi~a~tioii the hydrogen-bonded ring syst,ems.' ( G ) E. W. Hughes, (3. H. l 3 w k r l e w a n d A I . C:il!.in, O E h ~ S r - Z ' $ l , March 15. 1944. (7) (a) Fat, iiistnrire, tlie a h o r l ) t i o n Iintirl corwhi~onding to tile hydrogen-honded cerl)onyl gro111, is s l i i f t ~ dto 10:3!)-1AX? rtIi.-1 i r i t,lie conjitgrtted chelate s y s t e m of nceth.lacrtorw (,,f. ref. 51)). (1,) RrlIntny a n d Brnnoh have nlso assigned t h e clirlntrfl e n r l ~ o t ~ 311ti011 yl of p-(liketoiiPs t o t l i i s region, J . C'hcin. ,Sw.,44S7 (1!>,;4),

KEIHEIUENOA N D ARTHURE. MARTELL

1000

INFRARED

Ligand

1610vs 1582vs 1565m 1550m 1520s 1498m 1452s 1440s

1374s 13569

ABSORPTION SPECTRA

Compound 1 Metal chelate Cu Ni

1595s

1530s 1515s 1495m 1478m 1439m

OF

TABLE I1 COMPOUNDS 1, 2, 6,'

AND

Compound 2 Metal chelate Cu Ni

Pd

Ligand

1585s 156.5m

1593s 156im

1605vs 1583vs 1565m 155Ow

1604vs 1585m

1583vs 1567w

1527s 1517s

1515s 1504s

1517s

1507vs

1517vs

1465m 1460 -30mb

1466s 1455 -25Sb

1473m

1472s

1442m

1442s 1415s

1472s 1465s 1438s 1417s

1372m 1357ni 1318s

1372m 1343w 1311w

1368m 1343w 1315w

1417s

1409s

14085

1355m

1354ni

135Gm

THEIRR l E T A L

Vol. 50

CHELATE COhIPOUNUS

Compound 6 Metal chelate Ligand Cu

1614s 1611s 1582vs 1564m 15331x1 1513vw

Assignments

C=O

1580vw 1548vw

1

ls4Om 1470w

1440w

C=C &etching

C=N stretcliing

1513vw

1450w

1J

CH, and CHI deformations

1393w 1377w 1343vw

1376,

1282s

1 2 9 3 ~ s CF3 stt'et,ching

CHI deformntion

1290m 1286vs

1284vs 1283m 1276m

1283111

1276m

1265m

1197w

1143m

1237w

1239,

1211w

1207w

1156m 1 1 1 3 ~ 1 1 2 2 ~ 1118w

0-H

. . i n H I,onderl rings

0-H.

. . in H bonded rings

1280m

1252m

1203m

. . in H bonded rings

1265s 1242vs

1252~

1222w 1205s 1187s 1130s 1118s

1223w

107%

113ow

1141w

lll3vw llO4vw

1112vw ll0Ow

1062vw 1045w

1074n 1052.1~

1014w 999w 9G7w 942111

10281n 1008w 080w 950w

1126s 1101w

C R &etching

J

C-0in H bonded rings 1070vw C-0in metal chelate rings

1137m

10181n 9771n 04Om 928w 848s

1068w 1039w 1025w 1013m 985vw

106Gw 1047w 103ow 10161n 992vw

944111

941111

7589 7383

1012111 072w

835s

788vw

1051vw

1087111

1087s

803vw

800V\V

77iw i50m

750s i351n

928111 850111 8:K?111 815111 742m 735111

1002vw 941\v

804m

877m 8G8m 8Glw

747111

747s

688111

687w

680w 670w 650w

G88m

G02w

009vw

C-H

deformation of double bonded Carboils in H bonded or m?t:il chelate rings

779m i73m 753w 72Xm

680w

1013vw

730m 628vw

658m .592vw

i

Metal-ligarid vihmtion

Oct., 1955

d1ETAL CHELATES OF

BISACETYLACETONEETHYLENEDDIIMINE1001

TABLE I1 (Continued) Cnllr~Joillld 1

Ligand

Cu

AZetal chelate Ni

Pd

554vw 522w

544w 515w 454m

418vw

Ligand

410vw

480m 419vw

477w 4GDln 419vw

Compound 2 Metal chelate Cu Ni

562vw 479w 454117

458w 418vw

a The number of compound refers to Table I, specified (e. g., between 1460 and 1430 cm.-l).

4lDvw

561vw

Compound 6 Metal chelate

Ligand

543w 530w 513vw

489w 473vw 418vw

Cu

528w 514w 455n1

433vw 420vw

Assignments

) Metal-ligand vibration

42Ovw

Definite absorption peak cannot be found; broad band in the range

TABLE 111 INFRARED ABSORPTION SPECTIM OF COMPOUNDS 3, 4,5 A N D THEIRMETALCHELATE COMPOUNDS Ligand

Compound 3 Metal chelate Ni

cu

Co

1490111 1474s 14G5ni

Compound 4 Metal chelate Ni

Cu

co

1GO5r,s

1003vs I58Gs 1577s 1547s 1522s

Ligand

1600s 1578s

1518vs l509vs 1488vs 1471s 14G28

l50liii 1568s 15501n 1 5 1 9 ~ s 1517s 1505s 140lvs 1400vs 1406s 1430s 1598s 1579s

1502~s 1570vs 1548s 1522s 1513m 1486m 1469~ 1436s

1597s 157-1111

1500s 1571111

1509vs 1485vs 1462vs

1508vs 1484s 346Ovs 1440s -35"

1440s

1590s 1558s 1511s 1500vs 1485vs 1453s 1436s

Compound 5 Metal chelate Cu

Ligand

Assignment3

IGOOvs

C=O.. . in H bonded rings C=C stretching and phenyl

1596vs 1585~s 1546vs 1525m -10" 1487vw 1470ni 1437s

1597s 15761n 1514vs 1507vs 1485,s 14G8vx 1440s

1

Phenyl CH3 and CH1 deformations

1444s 1431s 1383w 1341s

1432s

135Sm 1303w l%88111

1287s

1234111 117Gw

l24Ow 1233~ 1177w 1IC,Rv\r.

1240w 1231JV 1178~ I lC,lV\\

1432s 1417s 1365~ 1362m 1310w 1322s 1300~ 1287s

1238~ 1232w 117SIV 1158vw

L24Gin 1221\T 1 li5v\v

1422s

1417s

1368111 1367w 1 3 3 8 ~ 1337W

1208vw 1271w 1242111 12:351n 11T8v\\

1295vw

1406vs 1370m 1341w

1380~n 1320vs 1310s 1289s

1353m 132Gm 1308n1

12m 1251m 1225~ 1178~

1286111 12471n 1208vw 1 1 7 3 ~ Phenyl ~

11:31w 1127vw 1 1 2 0 ~ I117vw 1088vw 109lw

1065JIl 102iw

1073m 1030w 1015117

10751n 1020w 1020w

107-h 1027n. 1020\r

922h

802w

9OGw

004w

1087s

1242w 1232w 117Gvw

854w

1127w

1 1 3 7 ~ 1133w

119ow 1085~ I OG21n 1057w 1024111 1021w

1 0 9 3 ~ 1092w

1084w

1063w 1020w

1063w 1022w

1065m 1025w 098vw

007w

915w

913w

932w

876vw 853w 835vw

887vw 8G2vw

86Ovw

022vw

. in H bonded rings

0-H..

in H bonded rings C-0in m e h l chelnte rings

C-0-

1I39w

1120w 1085w

CH, deformation

1295vw

1159v\v

80Rl11

1422vs

1093w 1082w 1070w 1 0 2 4 ~ Phenyl 999vw 973vw 919vw 894vw 883w 854vw

846m

804w

787\\

70 1 \v

1002

VOl.

59

TABLE I11 (Continued) Ligand

Coinpoiind 3 Metal chelate cu Ni

Compound 4 Metal chelate Ni

Co

Ligand

Cu

Co

753vs

737x3

735vs

746vs

728s

731s

%Gin

7431~

700s

696s G85m

G0ln

691s

701~ G85w G74w

090s

707m 693s 084111

707111 G92s (384x1

eoos GGDw 576w 567w

5Glw 535m

587m

5.57~

543vw

566w

5G4w

408vw

495w

4G5vw

480w

481~

419vw

118vw

418vw

Coiiipoiind B Metal chelate Cu

Ligand

743s 731s 708m 686m 67Gm

745111 732s 7081n 696m G861n

61Gvw 5G5w

Gl9vw

538w

1

.4ssigninents

) } Phenyl Phenyl

Metal-ligand vibration

504vw

478vw 460vw

451vw

451vw

417vw 419vw 418vw 419vu. Same as footnote b, Table 11.

458vw 418vu

Metal-ligand vibration 497vw

If the methyl group which is directly attached to the carbonyl carbon in structure 11, is replaced by the strongly negative group, such as trifluorocarhon, one would expect a decrease i n the polarizability of the carbonyl group, and a corresponding shift of the absorption band to the higher frequency. This seems to be the case in bistrifluoroacetylacetone-ethylenediimine (compound G) , for which hydrogen-bonded C=O absorption shifts to 1G14 em. - I , the highest carbonyl frequency observed for the compounds studied. The next strong absorption a t 1596-1580 em.-' in the ligands, which is usually accompanied by a weaker absorption of 1565-1560 ern.-', can he assigned to a C=C stretchiiig vibration in the hydrogen-bonded rings. In the case of benzoylacetoiie derivatives, the a,bsorptions due to skelet,al vibrations of phenyl rings are also expected i i i this region ; however, these absorptions may overlap each otJherand each absorption cannot be identified separately. The main ahsorption band at 1590-1580 cm.-' is usually shifted to a slightly higher frequency by metal chelation, while the second ahsorption band shifts to a lesser extent or is missing i n some compounds. The next set of fairly intense bands, which consists of two bands in most cases, can be assigned to C=K stretching vibration in the hydrogeii-bonded rings. These bands shift to a slightly higher frequency and become more intense by metal chelation. In trifluoroacetylacetone-ethylenediimine, the assigned C=N bands becomes very weak, while the bands due to hydrogen-bonded C=O and C=C bonds have the same intensities as mas observed for bisacetylacetone ethylenediimine. This indicates that the strong negativity of trifluorocarboil group probably stabilizes the carbouyl structure I1 rather than I,so that the contribution of C=N to the spectra becomes less than in lisacetylacetone compound. It is also probable that the hydrogen-bonded N-H deformation vibration in structure I1 absorbs

418vw

418vw

in these region; however the intensity of this band is usually too weak to be observed. Although one additional absorption band of intermediate intensity a t 1450-1445 cm. -' is found in the ligand, it is doubtful whether this band can be assigned to N-H def ormatioil, All benzoylacetone derivatives have a sharp absorption band of intermediate intensity a t 11901485 cm. - I , the frequency of which remains almost unchanged from ligand to metal chelate compounds. This band can be assigned, without doubt, to the skeletal vibration of phenyl ring. Weak absorption bands a t around 1176 and 1027 cm.-l in these compounds can also be assigned to vibrations of the monosubstituted phenyl ring. It is known that CH2 deformation gives rise to absorption a t around 1-165 cm.-' mid asymmetrical CHB deformations to absorption a t around 1450 em. Two absorption bands of varying intensities in this region, which are found in all of the compounds, can be assigned to these modes or vibration. Although the symmetrical deformation of hydrogen in the CHa group is known to give an absorption band in the range of 1385-1370 cm.-l, which is very stable in position,8 these compounds reported here do not always give clear absorption bands which can be assigned to this mode of vibration. The next fairly strong absorption band is ohserved a t 1290-1280 em.-' in all ligands except the trifluoro compound, which shows absorption a t 1242 em.-'. Since no band with comparable intensity can be found in this region in the metal chelate compounds, it is believed to be due to 0-H deformation vibration in hydrogen-bonded rings. Although it is known that alcohol gives rise to two bands in the region 1410-1050 cm.-', it is not, made clear which of these bands is due to C-0 stretching, and which corresponds to the 0-H deformation vibration. However, another absorptioii (8) L. J. Bellniny, "The Infrared Spectra of Coiiqilex h I o I e r i i l ? ~ . ' ' John Wiley and Sons, Ino., New York, N. Y.,1054. 1). 1'1.

Oct., 1955

RJETAL

CHEL.4TER O F

BISACETYLACETONEETHYLENEDIIMIN B!

1003

band at around 1160 cm.-l is fairly stable in posi- acetone derivatives. Since each six-membered ring tion from one ligand to the other, and is therefore system of the ligands can rotate freely to some assigned to the C-0 stretching vibration, Although extent about the axis of the C-C bond of alkylene the intensity of this band is not so t,troiig, and is bridge, i t is expected that the ligand will have ahvery weak in bisbenzoylacetone-ethyleiiediimine, sorptions which w e due to such skeletal deformathe frequency is shifted to the lower values by metal tion of the alkylenediimine bridge. However, the chelation. 'I'his shift may be due to the increased energy corresponding t o the frequency range under mass of metals attached to oxygen, as well as to a discussion is protiably t800high to warrant assignment t o these modes of vibration. Thus these weakening of the C-0 linkage. In the trifiuoro compound, 0-H deformation and bands are not assigned to any definite mode of viC-0 stretching vibrations are assigned to the nb- bration at present, time. sorptions at 12-12 and 1078 em. --I, respectively, The absorptions due to metal-oxygen and metalboth being shifted in the direction opposite to that nitrogen bibrntioiis are also expect,ed in this region. which mould be expected as a result of the induc- Some absorptJionsresulting from metal-oxygen vibrations in metallic acetylacetonates were observed tive influence of the trifluoromethyl group. Carbon-fluorine stretching vibrations &reknown at 700-GOO em.-' by Morgan9 and more extensively to give rise to very strong bands i n the 1400-1000 by I,ecomte.lo Also the nature of bonding between cm.-l region. By comparing the spectra of bis- the metal and oxygen of t,hese compounds was found cetylacetone-ethylenediimine, bistrifluoroacetylace- by magnetic moment measurements1' to be essentone-ethylenediimine and its Cu(I1) chelate, along t,ially ionic. OH the other hand, the metal-oxygen with bisacetylacetone-Cu(I1) and bistrifluoroace- and metal--nitrogen bonds in the bisacetylacetonetylacetone-Cu(II), the following fiJve stroiig ab- etliylenediimiiie chelates are believed to be essensorption bands, which are fairly stab'e in position, tin'lly coralent hecause of the great difference of the can be assigned to C-F stretching vibrations; 1282, ultraviolet a.nd Iisible ahsorption spectra between 1222, 1187, 1130 and 1118 cm.-l for the ligand and the lignitd and its metal chelate and 1293, 1223, 178, 1147 and 112G for the Ca- z'ilsobissalic~laltleliyde-etli~~lenediimiiie-~i~I1) -Co(IT), i\diich have a similar skeletal structure, (11) chelate. 900400 cm. Region.-The main absorption were found by magnetic. moment measurements to bands in tJhitsregion &cur at 780-650 em.-' in the have covalent nietal.-ligniid bonds.'l The relaspectra of both the ligands and the metal chelate t'ionship between the polarity of the coordin at'ion compountls. There are also lignnci ahsorpt,ion bond and the boiid streiigtii has been st.ated by bands of intermediate intensities around 840 Cottrell and S i ~ t t o nto~involve ~ a decrease ill the em. -I, and aeveral characteristic absorption bands covalent contribution to the bond strength with of weak or intermediate intensitJiesin the spectra of increasing polaiity u p to a certain difference in pothe metal chelate compounds. larity, as W R pointed out by Waleh. Tliere~i~fter. Bisacetylacetone-ethylenediiniine and bisacetyl- n,ccording to Pauliiig, incrcasing polarity should acetone-l,2-propylenediimine as well :LS their metal increa,se the ionic contribution to bond strength. chelate compoiiiids, give very sharp absorption AltJhough there are maiiy uncertainties i n applying bands of intermediate intensities at around '750 and these ideas to the c!ielate compounds under discus740 em. - l nliich shift slightly with metal chelation. sion, it seems that the more covalent metal-ligand Bistrifluoroacetylacetone-ethylenediiniine adso gives hoiitls in bisnret-\.lacetone-etli.~lenediimine-mets,l similar absorption bands at 779 and 773 cm.-'. chelates will be stronger than ionic met,al-ligand While two hands are a81waysobserwd in the lig- lmnds i l l wstal chelates of acet8ylacetoiie. ands, one of these bmds is missiiig in some met'al YOWretuniiiig to the experimental results, we chelate compounds. These absorpiions are as- can assigil t,he followiiig; three baiids, at GS8, 609 signed to C-'H out-of-plane deformation vibr a t'1011s. a i d .is0 em. --I, to the met,nl-specific allsorpt,ions of The C-H out-of-plane deformations in analogous bisacet~p!ncetotie-et~lirrleiiediimii~e-Ni(II). These compounds of the type R'RNC=CHC!Hnare in the bands shift slightly with the kind of metals cliegeiiein,l frequency range of 840-800 cin. -I, which is Inted: i n t'lie Cii(1I) chelate to a slightly lower fre30-60 cm. -I higher than the values assigned ill the quency, nntl in the Pd(I1) clieln,tjeto a slightly present iiivestigation. However, the nroinat,ic na- higher frequency. Similar I)niicls ohserretl in the ture of the six-membered rings including hydrogen iuetnl cheln,tesof the other ligaiids are s110n.u i n the boiidiiig in t,he ligands, and of the same ring system Tables I1 and 111. These metal--ligand absorption including the metal ion in the metal chelate com- Ijatids nre iiwally iiot very strong, and ill some pounds, is believed to be the reason for the shift of compouiids it is possible that they are overlapped these bands from their normal positioii . (0) IT. LIorgnn, LT. S. .4to1nio Eiievgy Coiitiriission. 1919; .Al3CD. The compounds which have phenyl groups give 12G.50. J. Lecorlite, Di.rc. Fni~nrla!iSoc., 9 , 108 (1050); C . D u ~ n l R , . rise to sliaiy absorptions a t arouiid 750 and G90 F r (10) w t n a n n niid J. L e r o l i i t r . B i d / . sac. c I L Z ' ~F. r n n r e , 10G ( 1 ! 2 5 2 ) . cm.-', both of ivliich occur as doublets or triplets in (11) A. E. hlaitell atid fir. Calvin. "Clietiiistty G f the RIetal C l i e h t r cei%nin cases. These bands are assigned to C-H Cotniiounil.i," Pwntire-IInll. Inr.. Keiv York, N. Y . , 1952, 1 1 . 211. out-of-plane deformation of the phenyl i4iig. ( 1 2 ) Kltraviolet n n J visible nhsor~itiotrspectra will be veliortcrl i l l In all ligands additional absorption bands are a later I>iiblicatioii. oliserved i n the range of 850-800 cm.--I. These are (13) T. L. Cottrcll and L. E. Stitton, Proc. Rn7I. ,Sor. ( T , o u d o , t ) , more intense i n bisacetyla,cetone-ethylenediimine,8 2 0 7 , 49 (1951). (14) .4. D. Wvulsli, J . Chc,n. Soc., 308 (1948). -1 ,2-propylenediimine, and bistrifluciro:2cet3rlace(15) L. l'auling, "Tlie Nature of tile C'liriiiicnl Rot~cl," CotmcIl tone-etliyleiic~cliimiiie, and less st)rong i n lienzopl- T T i i i v t m i t v Prcan, Itliaca, N. Y.. 194;. 11. 4 %

1001

S.E. S.EL WAKKAD, H. A. R r m A N D I. G . EFL~ID

by other strong absorptions, such as those resulting from C-H deformation of the phenyl ring. It is interesting to note that the observed metal-ligand bands are spread over a wide frequency region, while the metal specific bands of bisacetylacetone metal chelates are observed in the range of 700-GOO cm.-l.lo If metal-specific absorptions of both types of compounds are due to the similar mode of metalligand vibrations, we could expect the absorptions of bisacetylacetone-ethylenediimine metal chelates to occur in a higher frequency region than those of bisacetylacetone metal chelates, since the covalent metal-ligand bonds of the former compounds have the higher bond energies. At present, however, it is difficult to compare the absorption bands of these compounds, because there are many modes of vibration, such as metal-oxygen and -nitrogen stretching, in-plane and out-of-plane deformation vibrations, all of which result in change of dipole moment, and hence are responsible for infrared absorptions. In general, the order of decreasing frequency of bands of each set of metal-specific absorptions in the

T'ol. 69

metal chelates of a given ligand is: Pd > Ni and Co > Cu. On the other hand, the stability of complexes of these bivalent metal ioiis usually follows the order Pd > Cu > Ni > The relationship between the metal-ligand stretching force coilstant and the metal-ligand bond strength, which is a measure of the stability of complexes, might be expected to lead one to predict Pd > Cu > Ni > Co as the order of decreasing frequency.I7 However the greater mass of Pd might also be espected t,o shift its absorption frequencies to lower values. The irregularity of the Cu-ligand frequencies reported indicates that the absorptions may arise from a complicated, rather than a simple mode of vibration. For all the metals investigated, it is possible that other factors, such as resonance effects involving the d-orbitals of the metal ion, may also influence the metal-ligand vibrations. (16) D. P. Mellor and L. Rlaley, Nature, 159, 370 (1947); 161, 4313 (1948). (17) Bellainy and Branch recently rei>orted the lineal relatioiisliiii hetween the stability of salicylaldehyde metal ellelates and the shift of the ohrlute onrbonyl freqiieiicy in 11300 eiii.-1 region. However, n o attempt has been made i n lower freqiiency region, J . Clrern. S o c . , 4491 (1954).

THE ELECTROCHEMICAL BEHAVIOR OF THE TUYGSTEN ELECTRODE AND THE NATURE OF THE DIFFERENT OXIDES OF THE METAL RY S.E. S.EL WAKKAD, H. A. RIZICAND I. G. EBAID Department of Chemislry, Faculty of Science, Cairo University, Cairo, Egypt, and J o h n Harrison Laboratory of Chemisti,y, University of Pennsylvania, Philadelphia, P a . Received February 7 , 1855

The limited results previously reported on the behavior of the tungsten electrode in solutions of different pH values are conflicting. This is clarified here by calculating the potentials of the different oxides of tungsten and comparing them with the experimental results. It is found that the behavior of the tungsten electrode depends upon whether i t is massive or i n the powdered form. From this study it has been found possible to define clearly the pH range over which the tungsten electrode can function properly as an indicator electrode for hydrogen ion activity. The anodic oxidation of tungsten a t very low current density is studied and the nature of the different oxides of tungsten which are a p t to be formed on t h e electrode surface has been revealed. From all these studies it is shown that the tungsten electrode is far better than t h e antimony electrode as an indicator electrode for the hydrogen ion activity since u. calibration curve can stand for much longer period without any of the appreciable drift characteristic of the antimony electrode.

Quite recently the electrochemical behavior of the potentials of the different osides of tungsten are calantimony electrode mas studied by El Wakkncli~2 culated and compared with the esperimental results. and the factors which govern the electrode behavior It is shojvn that the behavior of t!ie tungsteil elerwere defined. The present investigation deals with tarodedepends upon whether it is i n the massixre or the tungsten electrode which has been the subject in the powdered form. From this study it has been found possible to define clearly the pH range over of a limited amount of experimental ~ v o r k . ~The -~ results obtained by different workers are conflicting which the tungsten electrode can function properly and the pH range over which the electrode can give as a n indicator electrode for the hydrogen ion sct8i\-correct measurements for the hydrogen ion activity ity. The anodic osida.tion of tungsten a t very low as well as the time during which a calibration curve current density is studied and the nature of the difcan give satisfactory values are obscure. The pre- ferent oxides of tungsten which can be formed on cise determination of these factors is complicated the surface of the electrode has been revealed. not only for the different types of osides given by From these studies it is concluded that this electungsten but also by the great variety of com- trode in it,s behavior as an indicator electrode for pounds with bases given by these osides, especially the hydrogen ion activity is far better than the anthe trioxide. In this investigation, howeirer, the timony electrode. A calibration ci1r.i.e in case of the tungsten electrode can stand for a much longer (1) S. E. 9. El Wakkad, J . Cham. Soc., 2894 (1950). period without the c1inracterist)icdrift of the anti(2) S. E. S. El Wakkad and A. Hickling, THISJOURNAL, 57, 203 (1953). mony electrode. (3) J. E. Baylis, Ind. E n g . Chem., 16, 852 (1023). Experimental (4) H. C. Parker, $bid., 17, 737 (1925). I. The Tungsten Electrodes.-Tlic tiingsteti Plrc(ro(lcs (6) A . L. Holven, ibzd., 21, 905 (1429). (6) H. T. 9. Britton and E. N. Dodd, J. C k e m . Soc., 82r) (lr)'31).

nwd wwp of the folloiviirg typcs: