Syamal, A

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13RESIDUAL PARAMAGNETISM OF COBALT IN SOME COBALT (III) COMPLEXESA . SYAM ALCmcMinAL Lauoiiatohy, Bubdw ak  ITn iversity , B u rb w an , I nbia  {Received December 18, 1907)ABSTRACT. Rocond order paramagnetic, term and electronicabsorp lion spectra of cobalt (III) iii fifteen octahedral cobalt (ITT) ooinj^ lexoK hove been measured by the Gouy nu^ thod and a UVTSPPX'JK. The observed values of residual piiramagnotisni are found to bo always lower than those calculated on the basis ofl igand field theory. Probable explana­tions for the observed discrepancy are i)rosented. The nature of the bonding in those com­plexes are also discussed.I N T it O D TJ 0 T I O NThe magnetic properties of spin-pairod cobaltic complexes have received rathoi little attention. The early works indicate that the observed susceptibilities of octahedral cobalt (III) complexes have a substantial contribution due to the second order paramagnetism term which is independent of temperature (Rostmbohm, 1919; Kernahan et al, 1955; Belova et al, 1955; BalUiausen et al^  1957; Kanokar et al, 1960). Ballhausen and Asmuson (1957) have shown that second order para­magnetism term is highly dependent upon the nature of the ligands and follows the spoctroohomical series very closely. The interest in the magnetic properties of cobalt (III) complexes has arose recently owing to tho recent development of the ligand field theory (Grifith et al, 1957).It is wellknown that oxidation from Co+  ^to Co+® results in tho increase of AE values and as a consequence tho spins are paired in an octahedral environment of 3#  cobalt (III) and cobaltic complexes are generally found to bo diamagnetic. But there still remains some contribution of the second order paramagnetism of tho cobalt atom. Grifith and Orgol (1957) were tho first to calculate theoretically, on the basis of ligand field theory, the amount of second order paramagnetism in octahedral spin-paired complexes of #  system. With an end in view to check the validity of Grifith and Orgel’s theory, we have measured tho room tempera­ture magnetic susceptibility as well as the electronic absorption spectra of some cobalt (IH) complexes. The preparation and characterisation of a large number of cobaltic complexes containing biguanide and l-amidmo-O-alkyluroa as the basic units have already been reported from this laboratory (Dutta et al, 1964, 1965, 1967). It may be mentioned here that this is the first report on the determination of second order paramagnetism term of cobalt (III) hetaroohelates.120Residual Paramagnetiam of GobvU 121X P K B I M E N T A LThe complexes were prepared according to the published procedures (Dutta et al, 1965; Dutta et a?., 1965, 1967; Ray et al,, 1938, 1940) and their purity was chocked by elemental analysis of metal and nitrogen.Magnetic susceptibility measurements in the state of powder were carried out by modified Gouy method. The forces on the samples were recorded by a single pan semimicro Mettler analytical balance reading upto fifth decimal place o f a gram. Copxier sulphate pentahydrate was used as the calibrant.Electronic absorption spectra in state of aqueous solution were recorded with the help of a Hilger-Watts Uvispock Spectrophotometer using one cm. cells.Chemicals used were all G.R.E. Merck vaiiety.K E 8 XT L TThe following diamagnetic corrections were utilised to calculate Xd •=  —10;N (open chain) — —5.56; N(ring) — —4.6;NO == —13.1; NO — -18 .9 ; Cl- =  20.1; 1“  =  44.6; S -  -1 5 ;  NHg == -1 7 .1 ; H O = :-12 .8 ; ophen — —105; dipy ——101.The observed x  calculated by the relation (van Vlock, 1932) :Xp + X d ^ X mwhere Xd =  diamagnetic susceptibility of the atoms,Xm =  molar susceptibility in C.G.S. unit.and X (calcd) was obtained by using observed K  values in equation 1). The results so obtained are included in table 1.D I S C U S S I O NResidual paramognotism can arise from either (i) second order paramagnetism or (ii) quenching of diamagnetism or both. Recent work of Proctor et al (1951) discards the quenching of diamagnetism factor as a possible source of residual paramagnetism. The diamangotism of the ligands is retained in the complex and is not quenched.According to the ligand field theory of Grifith and Orgel (1957) we may also calculate x  values from the relation :— 2 ^  r cA ^  ^  ^ .0 ^  “  3 bmC'J ‘ K  K ■ (1)where K  denotes the energy separation in wave number unit between the ground state (lAig) and the excited singlet state (% g) o f Osymmetiy cobalt (III) complexes.122 A. SyamalcSo^  C4H®  oiiD c6c6 a^s3SV *©o09s<D&Ic8 .2tj n o° r_T3 . o- o ^ 0M?5aH• " t  g  ioi *600dh- r -d  doo 00 Oid  d  dO O 05r-H r—( OO 05^  d05d0 5  0J© oCOCD <M |m4 <o CO QO o i (M 00 o CO© © © © © © © o O 00 © ©f-l rH f-( <N (N pH pHt - (M lO 30 O © (N l> o o o to (N 9CO CO »n i - 00 © t - 00 l> r - l'* ©pH rH rH l-H pH f—« pH pH rH pH pH pHOo © © to to ©to CO rH CO CO !>• © d I> © © d00 CO © © pH <N © l > © ©<N <N pH (N pH i—H pH pH <M <N pH<M 00 '»44 $  ®  $  M  ^  'O  Oo >0 © to(M CO O i © c t to © d o iO CO © CO 'Ht -Ht © CM ©pH pH <N© © © ©©  o CO O'! O ©  o ©  o ©  o t -  © <M o2 8<M O to  o t -  o lO © o  o ©  o ©  o ©<M O o  o o  o o  o o  o PH o o  o ©o  d o  o o  o o  c d  o o  o o  o d  d o1 H 1 II 1 II 1 -1 ' 1 M 1 II i l - i ' 1 HI H-l<M05s i  2 g  p §  « s. O •—' o ooo0 3o o o O o o o © © © 8© o oo o o o o © o © © © to ©© oi o ©^ © 1- ot oi © >o ©^o ' p^ pH o" d © ©*' d c f pH pH doi oi (N CJ Ol OI Cl <N Cl Cl Cl Clow”U5COoCQwbOsalOS  GoCQaa§ -wbootS>»a'T iwbOo5 ?>odwwbOm PD noc»wbo(3 ^ 5 a a 5 aa< 200)05(D>§o>aH i iS ^®ns f i l■ t n i£ 0-0 aS3 O .. §aa « Q ^I  i l  l!' S  2>:S. O  *-< (N CO »o03 ^ rH fH iH-SlE a “I I  l i t "2 | | gI h B I« «* #Residual Paramagnetism of Cohult 123TJie obBervod values for residual paramagnetism are found to be always lower than tlxoae calculated theoretically. This discrepancy probably reflects bountling ef­fects on the susceptibility of those complexes. Uncertainties in the calculation of diamagnetic susceptibility of tho atoms Cu»nnot be overlooked too.Orbital reduction factor, Jc was calculated from the ratio ^ ((>b8.)/;Y )and is recorded in table 1. TIio results indicate that k varies from 0.7 to 1.0 in close agreement with tho work of Ballhausen et al (1057).According to Grifith and Orgol (1957), the error in calculating x values sliouid bo within 20%, but in our cast) the ^Tror is about 30%. This is presumably duo to uncertainties in the calculation of diamagnetic susceptibility of the atoms. Thus this study cleaily reflects the validity of Grifith and Orgofs theoretical treatment of ligand field theory.Magnetic susceptibility measurements indiiiato tliat tho complexes are essentially diamagnetic. Hence the <;omjyiexes are octahedral and are formed involving tho use of d'^ s'p^  hylxrid orbitals for bonding. I f the complexes would liave boon formed utilising hybrid orbitals, a moment value corresponding to two unpaired electrons sliould have boon recorded. Furtliermoro, biguanidos, l-amidino-O-alkylureas, ortho-phon-anthrolino, 2-2'-dipyridyl, othylenodiamine etc. are strong field ligands and formation of high spin complexes are precluded. The inner orbital nature of tho complexes has also been demonstrated from their spectral characteristic. All tho complexes exhibit two ligand field bands corres­ponding to the transitions, ^Aj^  and ^T2g-> ^Aj^  typical of octahedralcobalt (III) comploxes (Busch, 19fi0; Cotton et al, 1962).A C K  N O W  L K D O M K N T SThe author is indebted to Professor A. Mookherjee and Dr. R. L. Dutta for ko(!in interest in the work and for constant oncouragoinent. He wishes to express his sincerest thanks and gratitude to Professor S. K. Siddhanta for the necessary facilities. Thanks are also due to Mr. S. P. Chachra for some help in tho preparation of tho manuscript.li E F K K E N C K SBallhttuiijen, C, J. and AsmuKen, K. W., 1957, Acta, Chevi. Scand, 11, 479.Belova, L. ei al,„ 1955, Neorg. Khim. Ahad. N a vl\  S .S M .B ,, 30, 109.Busch, D. H., 1960, Cohalt, Roinhold Publishing Oorporatioii, p-124.Cotton, F. A. and Wilkinson, O., 1962, Advanced Inorganic Chemistry, Intersrionce Publishers, Inc., Now York, p-729.Dutta, R. L. and Syamal, A., 1965, J. Inorg, NncL Chem„, 27, 2447 ;1967, J , In d , Chem, Soc,, (in press).Dutta, R. L., et al., 1964, Science and Culture, 80, 549.J. In d , Chem. Soo., 1967, 44, 832, 842, 863.124 A.Orifit}), J. S. and Orgel, L. B., 1957, Tram. Faraday Soc., 60, 601.Koniahan, .T. L. and Sieuko, M. J., 1955, J. Armr. Chem. Soc., 77, 1978.Kanokar, C. R. and Nipanknr, S. V. 1966, J. Ind. Chem. Soc., 48, 397.Proctor, W. G. and Yu, F. 0. 1951, P/iy«. Revs., 81, 20.Kay, 1*. and Dutt, N. K,., 1939, J. Ind. Chem. Soc., 16, 621;1941, J. 7. d. Chem. Soc., 18, 289.Kosenbohm, E., 1919, Z. 2Jhyaik. Chem., 98, 693.VankVlock, 1932, .7 Ac Theory of hleclr’ic and Magnetic Susceptibilities, Oxford University I’rosB, Loudon.

Residual Paramagnetism of Cobalt in Some Cobalt (III) Complexes

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Residual Paramagnetism of Cobalt in Some Cobalt (III) Complexes

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