Balundgi, R. H.

Chakravorty, A.

Raghavendra, B. S.

English

NOPR

CommunicationsNew Binuclear NickeJ(II) SpeciesB. S. RAGHAVENDRA. R. H. BALUNDGI & A. CHAKRAVORTYDepartment cf Chemistry. Indian Institute of TechnologyKanpnr 208016Received 19 A "gust 1976By reacting trimeric bis(acetylacetonato)nickel(II)with some tridentate Schiff base ltgands, new dl-nuclear mixed ligand species have been obtained. Aprobable structural model for such species is pro-posed.TRIMERIC bisjace.ylaceonaojnickelrl l), Ni3(acac}, has fused oc: ahedral Ni06 coordinationspheres'. The dinuclear fragment Ni2(acac)4 is co-ordinatively unsaturated and yields adductss suchas Ni2(acac)4(pyridine) in which ihe nickel(II) isagain octahedral, One may expect that speciesof type Ni2(acachT (T = tridentate monoanionieligand) wi hoc' ahedral nickel (II) should exist.It has indeed been possible to isolate such speciesusing the tridentate ligand Hsal nR2 (Ia).The Schiff base (La) was prepared by hcatir.gto reflux (0·5 hr) salicylaldehyde and the aminein equimolar proportions in ethanol. The solventWaS removed on a rotary evaporator. The Schiffbase (0·1 mole) and Ni3(acac)6 (0·07 mole) were takenin 75 ml toluene. The reaction mixture was heatedto reflux for 1 hr. The green solution was thenfiltered and cooled. Hexane was added to initiatecrystallization where needed. The green complexwas obtained in 50% yield. (Even when twice theabove amount of Schiff base was used in the prepa-ration the product isolated remained the same.)Analytical and molecular weight data (Table 1)establish the composition Nil(acac).(saltnR1).All the complexes show an IR band (Table 2) inthe region 1620-1630 crrr" assigned to vC = N of theSchiff base moiety. There are two strong bandsat ~1590 and ~1510 ern? which are due to thecombination of vC=C and vC=O of acacs withadditional contributions from aromatic vibrationsof the Schiff base. The complexes are fully para-magnetic (Table 2). Their ligand field spectra(Table 2) are closely akin to that' of Nia(acac)8' Onthe basis of model-building it is proposed that theNi2(acac)s(saltnRII) has the structure (II) in whichonly acac occupy bridging position.0" ,)--:0(, .....«ss> II ,"'(\ !I I I \ •I , I(J-,.. .... : "JoI .•••••..•.••••.,I 0 'N ,--0olo.n= 3HsOltnR1Ib.n=2H sol~nR2II/ IIITABLE 1 .. - CHARACTERIZATION AND MOLECULAR WEIGHT DATACompound m.p. Calc. (%) (Found) Mol. wl(a)(0C) --..~'-..~-------,-.-.--------~-~--------- ----------C H N Ni Calc. FoundNii(acac)3(salt nMe.) 201 52·30 /)·18 4·52 18·93 620 565(52'28) (6,08) (4-17) (18'97)~ i, (acac),(saltnEt 2) 1.'il 53·75 6'53 4·32 18·12(54,25) (6'50) (HI) (18·31)Ni.(acac )3(saltn Ell.) 160 56·28 7·15 3·97 16·67 704 675(56'30) (6,96) (4,06) (16'58)(a) Molecular weights were determined cryoscopically in purified dry benzene.CompoundTABLE 2·- PHYSICAL DATA(a)In. bands (cm-1)(h) Magnetic moment per Ni(BM){c) Electronic spectrain benzeneld)vC=N vC::-:O+',C-:-.C Solid Solution+'Jaromatic (chloroform)Ni.(acac).(sa1tn:\re2) 1623 1591; 1508 3·22 3·21 8550 (9); 15750 (11)Ni2(acac),(saltnEt2) 1627 1591; 1509 3·22 3·20 8550 (10); 15750 (14)Ni2(acac),(salt nBu.) 1628 1593; 1508 3·24 3·26 8550 (10); 15385 (13)(a\ All the data given in the table were recorded at room temperature (25-27"C).(0) IR spectra were recorded on a Perkin-Elmer 521 recording spectrophotometer.(e) Magnetic moments were measured using a scnsit ivc COllY balance.(d) Electronic spectra were recorded on a Cary model-I q recording spectrophotometer. Band positions are in crrr+:extinction coefficients per Ni (given in parentheses) arc in litre mol " crrr '.785INDIAN J. CHEM. VOL. 14A, OCTOBER 1976We note that the reaction of Nja(acac)e withligand (Ib) yields mononuclear pentacoordinatedNi(acac)(salenR.) which readily+forms octahedraladducts (III) with monodentate donorss, No evi-dence for dinuclear species has been obtained '\\-iththis ligand. The difference in the behaviour of laand Ib can be rationalized on the basis of structure(II). In this structure the saltnRILIigar d occupiesthree facial positions of an octahedron. The flexible-(CH.k chain makes this possibles, On the otherhand salenRI can only span meridional positions?(as in III) due to relative shortness of the -(CHlLkchain. It cannot span facially.Financial assistance given by Department ofAtomic Energy, Government of India, is gratefullyacknowledged.References1. BULLEN, G. J., ~-SON, R. & PAULjNG, P., [norg. cu«,4 (1965), 456.2. GRADDON, D. P., Coord. Chem, Reu., 4 (1969), 1.3. NAKAMOTO, K., Infrared spectra of inorganic and co-ordination compounds (Wiley-Interscience, New York),1970, 247. .e-/4. JORGENSEN, C. K, Actst:thern. scand., 9 (1955), 1362.5. BALUNDGI, R. H. &--CHAKRAVORTY, A., Lnorg, Chim,Acta, 8 (1974), 261.6. DI VAIRA, M. & ORIOLI, P. L., Inorg. cu»; 5 (1967),490.7. SACCONI, L., O)HOLI, P. L. & DI VAIRA, M., j. Am. chem,Soc., 87 (1"f65) , ~; ORIOLI, P. L., DI VAIRA, M. ~SACCONI, L., j. Am. chem, Soc., 88 (1966), 4381';TEWARI, R., SRIVASTAVA, R. c., BALUNDGI, R. H. &CHAKRAVORTY, A., I norg, nucl, Chern. Lett., 9 (1973),583.Chemical Oscillations inMn2+-catalysed Belousov-ZhabotinskiiReaction in Orthophosphoric Acid MediumK. PRASAD*, G. S. P. VERMA, A. PRASAD & V. B. DHARDepartment of Chemistry, Ranchi University, Ranchi 834008Received 22 April 1976; accepted 19 June 1976The occurrence of Belousov-Zhabotinskii reactionin orthophosphortc acid medium is reported for thefirst ttme, The existence of two alternate mechanismsfor the observed chemical oscillations in this systemis suggested.OSCILLATORY reaction between potassium bro-mate, malonic acid, and cercus/eerie ion insulphuric acid medium has received considerableattentionv". In this reaction malonic acid may bereplaced by a number of organic substances contain-ing active methylene group which can be easilybrominated by enol mechanism? The catalyst, thecerous/ceric ion, can also be replaced by a numberof metal ions capable of existing in two valencestates differing by one electron only and havingtheir Eo values between 0·9 and 1·6 (ref. 7). How-ever, no alternative to sulphuric acid medium forthis reaction has, as yet, been reported. In thispaper we report our observations on chemicaloscillations in orthophosphoric acid medium. Thework is all the more significant in view of chemicaloscillations found in biological systems containingenough of phosphate group.Potassium bromate (Baker analysed), manganoussulphate (S, Merck/GR), malonic acid (Riedel,extrapure) and orthophosphoric acid (E. Merck/GR) were used as such.Procedure - The reaction was followed potentio-metrically using bright Pt wire as indicator elec-trode and SCE as reference. Potassium chloridewas found to inhibit oscillations and so a very dilutesolution of RCI (0'002J\lI) was taken in the calomelelectrode. The two half cells were connected withthe help of potassium sulphate agar agar bridge.The e.m.f. of the system was determined usingdirect reading potentiometer (Titrieautomat,ILMLABOR, GDH.). To a solution containingorthophosphoric acid, malonic acid and manganoussulphate equilibrated at 35° ± 0.1°, was added asolution of potassium bromate alw equilibrated atthis temperature. The bright Pt indicator electrodewas inserted in the vesseland e.m.f. recordedat vary-ing time intervals. The results are plotted in Fig. 1.The oscillation in the present system is found tobe qualitatively different from that found in sul-phuric acid medium. The total oscillatory state ofthe system can be divided into three parts (Fig. 1),The oscillatory states from A to B and from C to Dare similar to that found in Belousov-Zhabotinskiireaction system in sulphuric acid medium. Thesestates are characterized by a slight increase in timeperiod with time.The state from B to C is unique. It shows alter-nate long and short periods, L1, 51; Ls, 51; ...•..•..Lb 5;, suggesting that the system has two alternatecyclic routes by which it reaches the autocatalyticstate signalled by a sudden rise of e.m.f. of thesystem. The shorter time period is associated withshorter amplitude whereas the longer time period isassociated with longer amplitude. These amplitudescan be related to the difference between the upperand lower critical [bromide ion] limih,8,1I.Thus itseems that the two alternative routes are havingtwo pairs of critical [bromide ion] limits under twodifferent conditions. More work is required toelucidate this point.1!§Y~\}~J~~t};~~o 2 4 6 8 10 12 14 16 18 ) ,',c ?~ 26 28 30 32 34 36TIME IN MINUi ",SFig. 1 - Plot of e.m.f. against time at 35° ([Malonic acid] =0·032M, [KBr03]=0'044M, [MnSOJ=0'OOO8M and[HaP04]= 8'4N)*To whom correspondence regarding the paper may be made.786

New Binuclear Nickel(II) Species

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New Binuclear Nickel(II) Species

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