Ramanujam, V. V.

Sivasankar, B.

English

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line but the absorption maxima obtained with2,4,6-collidine are not so prominent as obtainedwith other bases mentioned above.It is apparent from the spectral data that withthe bases like pyridine, ~- and y-pkoline, the cobalthydroxamates form octahedral" adducts as foundin the case of nickel hydroxamates earlier", But thecobalt hydroxamates unlike their nickel analogues!do not form octahedral adducts with the bases likea.-picoline, 2,4- and 2,6-lutidines, quinoline, anilineand 2,6-dimethylaniline. The electronic spectra+do not indicate any tendency on the part of cobalthydroxamates to add up two molecules of thesebases to furnish octahedral complexes. On theother hand, attainment of the octahedral stereo-chemistry by the mono-adducts of the cobalt hydro-xamates with the said bases by polymerisation, asobserved in the case of nickel(II) complexes,[Ni(R),..Bh, may be ruled out. This is because, ifsuch dimerisation occurs, one would expect anabsorption maximum between 1100 and 1150 nm.The formulae of the- isolated products, their ele-mental analyses, colour, decomposition point, mag-netic moment and molecular weight data are shownin Table 1. Mono-adducts result with bases cap-able of imparting steric hinderance while the otherbases furnish bis-adducts. No definite compoundcould, however, be isolated from 2,6-lutidine. Mag-netic moments of the bis-adducts are normals forany octahedral cobalt(II) complex but the mono-adducts have slightly lower values (Table 1) whichare consistent with the penta-coordination ' of thecentral atom. The experimentally determined mole-cular weights of these adducts reveal the monomericstructure in all the cases except for Co(R1);t·Colliand CO(Ra)2.Colli where the experimental mole-cular weights in benzene are much higher than thevalues calculated for monomers. It seems thatthese are octahedral unlike other 1 : 1 base adductsof cobalt hydroxamates. In solution, however, itseems that these compounds exhibit an equilibriumbetween the monomeric five-coordinated speciesand the dimeric octahedral species. Therefore,the other mono-adducts are definitely five-coordi-nated species and do not dimerise to attain the octa-hedral stereochemistry as observed in the case ofthe corresponding nickel(II) complexes'. Cryoscopicdata point out that there is a slight dissociation ofthe base adducts in benzene solution.In all the adducts, the ."C=O (carbonyl) remainsalmost at the same position as observed in the parentmetal hydroxamates suggesting that the five-mem-bered chelate rings do not open up after the additionof the base molecules. Infrared spectral studiesfurther reveal that both the bases are coordinatedto the central atom since in case of bis-adductsthere is a single ."N-H band for the piperidine adductsand a single ."C=N band for the other base ad ducts.References1. BHA1'TACHARYYA, B. C.• BHOWAL. S. K. & BASAK. G.,Indian J. Chem., 20A (1981), 145.2. BHA1'TACHARYYA. B. C.• BHOWAL. S. K. & BASAK. G.,Indian J. Chem .• 14A (1976), 354.NOTES3. DUNN. T. M .• cited in Modern coordination chemistry.edited by J. Lewis & R. G. Wilkins (Interscienee,New York). 1960. 290.4. WO?D. J. S., cited. in Progress in inorganic chemistry.edited by S. J. Lippard (Interscience, New York) 16(1972), 310,339. •5. FWC;lIS, B. N .• cited in Modern coordination chemistry.edited by J. LeWIS & R. G. Wilkins (lnterscienceNew York), 1960, 429.Complexes of Cobalt(II) with Schiff Bases Derivedfrom Salicylaldehyde & Some Amino AcidsV. V. RAMANUJAM* & B. SIVASANKARDepartment of Inorganic Chemistry. University of MadrasA. C College of Technology Campus. Madras 600 025 •Received 2 August 1980; revised and accepted 22 November 1980Complexes of cobalt(II) with schiff bases derlved from salicylal-dehyde and the amino acids, DL-2-aminobutyric acid, t-valfne,~-alanine, 3-aminobntyric acid, 4-aminobutyric acid and L-methionine have been synthesised and characterised. Magneticand spectral data indicate the complexes to be octahedral.THOUGH sch~ff ba~e complexes of cobalt(II).hav~ .been wIdel~ investigated with regard totheir ability to function as oxygen carriers'>? thereis no repo~t of such studies with complexes df schiffbases derived from amino acids. Most of theoxygen active complexes are square-planar and inthe pr~sence of mono~entate ligands acquire square-pyranudal configuration. In view of this a study ofthe stereochemical aspects of the schiff base com-plexes of cobalt(II) involving bidentate and triden-tate amino acids is considered worthwhile. Theamin? acids employed were DL-2-aminobutyric acid,t-valine, ,B-alamne, 3- and 4-aminobutyric acids andt-methionine.. The schiff base complexes were prepared by react-mg cobalt(I~) acetate with the preformed schiffbase. A mixture of the appropriate amino acid(0.01 mol) dissolved in the minimum amount ofwater and an aq. alcoholic solution of salicylaldehyde(0.01 mol) was heated to _500 over a water-bath.An aq. solution .of cobalt (~I) acetate (0.01 mol)was added dropwise to the schiff base under nitrogenatm<?sphere and th~ solid product which separatedo~t III about 15 mm collected, washed successivelyWith water, ethyl alcohol and ether and dried overanhydrous calcium chloride in vacuo.The schiff base complexes involving bidentateamino acids have been prepared both under nitrogenatmosphere as well as under atmospheric conditionsand under both the conditions the same productshave been isolated. However, schiff base com-plexes of cobalt (II) involving tridentate aminoacids. ?ould not be prepared under atmosphericconditions, Though several tridentate aminoa~i~s. like seri,ne, asparagine, aspartic acid,histidine, glutamine, glutamic acid and methioninewere used in the preparation of schiff base com-plexes, only those involving methionine, asparagine749INDIAN J. CHEM., VOL. 20A, JULY 1981and glutamine could be isolated under nitrogenatmosphere. In the other cases addition of cobalt/H)acetate to the preformed schiff base resulted in adark brown solution and no solid could be isolated.The dark brown complexes of asparagine and glut-amine schiff bases obtained under nitrogen atmos-phere were insoluble in water and common organicsolvents. These could not be fully characterisedas the analytical data are found to be inconsistent.It is possible that partial or total oxidation ofcobalt(II) had occurred.Schiff base complexes of cobalt (II) derived frombidentate amino acids are brown in colour and areinsoluble in water and common organic solventslike alcohol, acetone, benzene and chloroform.They are partly soluble in coordinating solvents likedimethylformamide, dimethyl sulphoxide and pyri-dine. The N-salicylidene-4-aminobutyrate comp-lexes are totally insclu ble in any of the solvents.The analytical data on the complexes of bidentateamino acid schiff bases and t-rnethionine schiffbase correspond to a stoichiometric compositionof Co(SB).2H~O (Table 1). The infrared spectraof these complexes show the following character-istic bands : 3250 which may be assigned to thepresence of water molecules, 1650 (vC=N) and 1600(vas COO-) superimposed on the phenyl ring absorp-tion and ,....,1400 cm? (vsCOO-).Thermogravimetric analyses of the complexesindicate the presence of two water molecules percobalt atom, which are lost around 180°C showingclearly that they are coordinated to the metal.Conductance measurements (3-5 ohm'< cm'' mol-l)in methanol of the schiff base complexes derivedfrom bidentate <x-amino acids and the tridentateL-methionine indicate that they are non-electrolytes,in accord with the expectation of a neutral com-plex formed by dianionic ligands with a dipositivemetal ion.The electronic spectra of ex-amino acids andL-methionine schiff base complexes in dimethylsulphoxide show three absorption bands similar tooctahedral complexes of cobalt (H). The low energyabsorption band around 9500cm-1 has been assignedto to the transition 4T1g (F)~4T2g (F), a shoulder at15500 to 4Tlg(F)~ 4A2g transition and the bandin the region 19000-19500 cm-l to the transition4T1g (F) ~ 4TV (P)Diffuse reflectance spectra of the solid complexesalso show bands similar to those observed in solu-tion, except the weak intensity band at 15500 cm='.This indicates that the metal atom retains theoctahedral geometry in both the phases. Thediffuse reflectance spectra of cobalt(II) schiff basecomplexes derived from ~- and r-amino acidsare similar to those of Nssalicylidene-u-amino acidcomplexes indicating the similarity in geometries.In the case of L-methionine schiff base complex ofCo(H), apparently the thioether group is not in-volved in coordination.Magnetic susceptibility measurements indicatethe schiff base complexes derived from <X-, ~- andr-amino acids to be paramagnetic with momentsranging from 4.85 to 4.95 B. M., and these are inagreement with the predicted values for octahedralcomplexes involving three unpaired electrons.An octahedral configuration around the centralmetal ion is indicated from spectral and magneticdata. Since only five coordination sites arefilled, three by the schiff base and two by watermolecules, the plausible explanation is that thecomplexes are at least dimeric if not polymeric. Itis also observed that even a strong coordinatingsolvent like DMSO (solvent used for recording elec-tronic spectra) is unable to coordinate with themetal atom increasing the coordination numberto six in a mononuclear set up.Molecular weight measurements could not beundertaken because of the insolubility of the com-plexes in suitable solvents. This insolubility alsoindicates polymeric nature of the species. However,the dimeric structure proposed by Theriot et aU>TABLE I-ANALYTICAL DATA ON COBALT (U)-SCHIFF BASE COMPLEXESCobalt Complex % Metal % Carbon % Hydrogen % Nitrogen Decompo-sitionCalc. Exptl. Calc. Exptl Calc. Exptl Calc. Exptl temp."°CSalicylidene-z-arninobutyrate-Zl-Ijf) 19.50 19.20 43.68 43.20 5.62 5.40 4.63 4.70 310Salicylidene-valinate-2H.O 18.64 18.50 45.54 44.3 5.37 5.10 4.43 4.25 285Salicyclidene-B -alaninate-2HlO 20.45 20.50 41.64 42.5 4.81 5.20 4.85 4.80 295Salicylidene-3-aminobutyrate-ZffO 19.50 19.30 43.68 44.00 5.62 5.10 4.63 4.40 295Salicylidene-d-aminobutyrate-Zl-l-O 19.50 19.30 43.68 43.10 5.62 5.50 4.63 4.80 275Salicylidene-methioninate-Zl-isO 16.92 17.10 41.35 40.6 4.90 5.10 4.02 3.80 280·From TGA studies.750for Nesalicylidene-e-amino acid complexes ofcobalt(II) appears to be applicable in the case ofthe present complexes involving schiff bases derivedfrom (l-, ~- and y-amino acids. The experimentaldata are also in agreement with a dimeric structure.References1. BARLELEW, C. H. & CALVIN, M., J. Am. ehem, sse., 68(1946), 2251.2. BRUCKNER, S., CALLIGARRIS, M., NARDIN, G. &RANDACCIO,L., Acta Crystallogr. (Sect. B), 25 (1969), 1611.3. SCHAEFER, W. P. & MARSH, R. E, Acta Crystal/ogr. (SectB), 25 (1969), 1615.4 JONES, R. D., SUMMERVILLE, D. A. & BASOLO, F., Chem.Revs., 79 (979), 139.5. CARLISLE, G. O. & THERIOT, L. J., J. inorg . nucl. Chem.,35 (1913),2093.Mixed Chelate Complexes of Manganese(III)B. PRADHAN & D. V. RAMANA RAo*Department of Chemistry, Regional Engineering College,Rourkela 769008Received 14 August 1980; revised and accepted 16 December 1980Five mixed chelate complexes of manganese(III}, viz. Mn(tsc).(acac), Mn(tsc).(pyca), Mn(tsc).{et.dtc), Mn(acac).(pyca)and Mn(acac)(pyca)., where tscH = thiosemicarbazide, acacH =acetylacetone, pycaH = picolinic acid, et.dtc = diethyldithio-carbamate, have been isolated. The thiosemicarbazido complexeshave been obtained on oxidation of manganese(ll) by air in alkalinemedium whereas the other two mixed chelates have been obtainedfrom manganese(IlI) compounds by substitution reactions. Thecompounds have been characterized on the basis oftheir elementalanalyses, molecular "Weight, molar conductance, magnetic sus-ceptibility, infrared and electronic spectral data.THE 3+ oxidation state of manganese has beenwell-characterized by the preparation of a num-ber of anionic, cationic and neutral complexes and agood number of mixed chelate and mixed ligandcomplexes':". The complexes were generally ob-tained starting from the manganese(III) compounds.in the present investigation besides the usual methodfor isolating Mn(III) complexes, a method involvingNOTESoxidation of divalent to trivalent manganese in thepresence of ligands has been used.(i) Preparation of Mn(tsc).iacac), Mn(tsch(pyca)and Mn(tscMet~dtc) -Ethanolic solutions of manga-nese(II) chloride, acetylacetone/picolinic acid/sodiumsalt of diethyldithiocarbamic acid and thiosemicar-bazide in 1 : 1 : 2 molar ratio were reacted. Ethano-lie sodium hydroxide solution was added to it tillfaintly alkaline and then air was bubbled through theresulting solution for one hour when the colourlesssolution darkened and the compounds separated out.These were filtered, washed with ethanol, ether anddried in vacuo.(ii) Preparation of Mn(acacMpyca) - Tris (acetyl-acetonato)manganese(III), Mn(acac)a, in chloro-form and picolinic acid in ethanol were refluxed in1 : 1 molar ratio for one hour. The volume wasreduced to one-third by suction and the contents keptovernight when the compound separated out. It wasfiltered, washed with ethanol, ether and dried invacuo.(iii) Preparation of Mn(acac)(pyca)2 - Tris (acetyl-acetonato)manganese(III), Mn/acacj., in chloro-form and picolinic acid in ethanol were mixed in 1 : 2molar ratio and refluxed for 15 min when the com-pound separated out. It was filtered, washed withethanol, ether and dried in vacuo.Elemental analyses (Table 1) carried out by stan-dard methods were consistent with the formulationsof the compounds. The molar conductances for,..., 10-3M solutions of the complexes in nitro benzene mediumrange between 2.1 and 2.9 m ho em" mole=' indicatingthe non-electrolytic nature of the compounds.The magnetic moment values (determined usingGouy method) of 4.92-5.08 B.M. (Table 1 ) indicatethe presence of four unpaired electrons correspondingto high-spin manganese(III) state with 5Eg groundterm. The molecular weight measurements (Rastmethod using camphor) indicate that the compoundsare monomeric.Thiosemicarbazide exists in the tautomeric forms(I)and (Il) and can act as a neutral or charged chelatinggroup'.Haines and Sun" have reported that in thiosemi-carbazido complex, the band at 1049 cm? for freethiosemicarbazide becomes very weak and a newstrong band appears at 9W crrr", Such features canTABLE 1 - ANALYSES, COLOUR, MELTING POINTS, MAGNETIC SUSCEPTIBILITY AND MOLECULAR WElOHTs DATA OF MIXED CHELATEMANGANESE(III) CoMPLEXESm.p. Found (Calc.) % !Lerr Mol. wtCompound Colour (0C) (B.M.) foundMn S (calc.)Mn(tsc).(acac) Chocolate >300 16.04 18.70 5.05 356.2(16.44) (19.19) (335.9)Mn(tsch(pyca) Grey >300 15.11 17.43 5.0<' 338.1(15.38) 07.95) (357.2)Mn(tsc).(et.dtc) Greyish-brown >300 14.43 33.01 4.93 369.8(14.32) (33.43) (357.2)Mn(acac).(pyca) Grey 150 14.43 4.92 349.0(14.63) (375.2)Mn(acacnpyca), Pink 160 13.74 5.08 437.1• (13.79) (398.2)751

Complexes of Cobalt(II) with Schiff Bases Derived from Salicylaldehyde & Some Amino Acids

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Complexes of Cobalt(II) with Schiff Bases Derived from Salicylaldehyde & Some Amino Acids

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