Indian Journal of ChemistryVol. 22A, June 1983, pp. 527-528

Bis- & Tris-chelates of Cobalt with SomeIsonitrosoacetophenones

C NATARAJAN*t & A NAZEER HUSSAINDepartment of Inorganic Chemistry, Madurai Kamaraj'University,

Madurai 625021

Received 27 August 1982; revised and accepted 3 January 1983

Cobalt complexes of the type, ML2 .nH20[M =Co(II); L= anionof 4R-HINAP; HINAP = isonitrosoacetophenone; R = - H, - Me,-OMe, -CI, -Br and n=O, I], ML2.HL[M=Co(lI); HL=4-N02HINAP] and ML,[M =Co(IIJ) and HL =4-MeHINAP] havebeen prepared and characterized. The IR data suggest N - and 0-bondings of the oximino group in one and the same molecule of thecomplex, the exception being 4-N02 substituted complex wherebonding occurs through isonitroso nitrogen only. Substitution in thephenyl ring of the complexes produces shifts in V(C=0) which arerelated to the Hammett's substituent parameters. The magneticmoments observed for the cobalt(1I) complexes, except that of 4-N02 substituted complex, indicate distorted octahedral geometry.The PMR spectra of cobalt(III) chelates with 4-MeHINAP and 4-OMeHINAP suggest a cis octahedral structure for these complexes.

The ambidentate behaviour of isonitrosornono-ketonea':" has generated considerable interest in thestudy of their metal chelates. In the metal chelates ofthese ligands, both N- and 0- bondings of the oximinogroup in one and the same molecule of the complexhave been established using IR data. In the presence ofisonitroso compounds, in slightly alkaline mediumcobalt(II) readily undergoes oxidation by atmosphericoxygen3,4. However no systematic approach has beenmade to establish the bonding and stereochemistry ofbis- and tris-chelates of cobalt. We report herein a newset of cobalt(II) chelates of para-substitutedisonitrosoacetophenones (HINAP) and few tris-chelates of cobalt(III).

Coblat(II) acetate tetrahydrate used was of ARgrade. The ligands and their sodium salts wereprepared according to the reported procedures.

Preparation of chelates: General methodCobalt(II) complexes were prepared by adding an

aqueous solution of the sodium salt of the respectiveligand (2 mmol) with stirring to an aqueous solution ofthe metal salt (1 mmol). The precipitated orange-yellow complexes were suction filtered, washed freelywith water and dried over anhydrous calcium chloride.Yields were quantitative.

The orange-yellow cobalt(III) complex of 4-MeHINAP was prepared by adding a neutralized

[Present address: Extension Centre, Madurai Kamaraj University,St. John's College Campus, Palayamkottai 627002.

ethanolic solution of the ligand (2 or 3 mmol) withstirring to an aqueous solution of metal(II) acetate(I mmol). The precipitated complex was filtered,washed liberally with water, little ethanol (96%) andfinally recrystallized from ethanol; yield - 80%.

The complex Co(4-0MeINAPh was prepared asreported in the literature".

The water content of the complexes was determinedfrom mass loss on heating these between 100 and120°C.The room temperature magnetic moments weredetermined employing a Gouy balance withHg[Co(CNS}4] as calibrant. IR spectra were recordedin KBr on a Perkin-Elmer 577 spectrophotometer,PMR spectra in CDCI3 on a Perkin-Elmer R32 90MHz spectrometer with TMS as the internal referenceand electronic spectra in chloroform solution on aPerkin-Elmer 402 UV-VIS spectrophotometer.

The analytical results are consistent with theassigned formulae (Table I). The complexes are non-electrolytes in DMF (10 -3 M solutions) and themolecular weight of parent complex Co(INAP)2determined in benzene by cryoscopic method shows itto be monomeric. The ligand 4-N02HINAP gives ahighly paramagnetic (J1eff 5.4 B.M.) complex whosecomposition is compatible with 1:3 (metal-ligand)stoichiometry. The complex is insoluble in water andpartially soluble in organic solvents.

The IR spectra of the free ligands exhibit v(C=O)and v(NO) in the ranges 1642-1690and 922-1010 em -1respectively. The latter corresponds to NO stretch

Table I-Analytical and Magnetic Moment Data of theComplexes

Complex Found (Calc.) (%) Ilcff(B.M.)

M C HCo(INAP), 17.55 54.52 3.73 3.44

(16.59) (54.10) (3.41)Co(4-MeINAP),. H2O 15.66 53.98 4.112 3.28

(14.69) (53.87) (4.52)Co(4-0MeINAP)2· H2O 14.72 49.23 4.42 3.31

(13.60) (49.89) (4.19)Co(4-CIINAP),.H2O 13.61 43.87 2:25 3.37

(13.33) (43.46) (2.74)Co(4-BrINAP),.H2O 11.51 36.45 2.52 3.64

(11.10) (36.19) (2.28)Co(4-MeINAP), 11.02 59.98 4.02 dia

(10.80) (59.45) (4.44)Co(4-N02INAP), . 10.00 45.89 2.83 5.424-N02HINAP (9.22) (45.08) (2.52)

Metals were estimated as oxides

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INDIAN J. CHEM., VOL. 22A, JUNE 1983

absorption of simple oximes'' and hence the Iigandsexist chiefly in the oxime form. In contrast, the sodium

-?~~ -NC::=0 /0 ----,\

I -, "C-H/V> }/C==N 'o~C

H/ 6 'tR'-.' 19

R= -H, -CH3 ,-OCH3 ,-Cl, - Br

salts of the ligands show a decrease in V(C =0) with aconcomitant increase in v(NO) indicative ofcoordination through carbonyl oxygen and oximinooxygen. The increase in v(NO) may be attributed to thecontribution from the resonance forms". The cobaltcomplexes register still lower values for V(C = 0)reflecting greater perturbation by the metal. Further itis noticed that NO group exhibits two stretches, one athigher frequency (1232-1240 ern -I) and the other atlower frequency (1175-1188 ern I). The lowerfrequency absorption is due to the NO groupcoordinating through oxygen as in the sodium saltwhereas the higher frequency band may be assigned tothe N coordinated NO stretch I. Hence an asymmetricstructure (I) involving N - and 0 - bondings of theoximino group in one and the same molecule has beenassigned. The 4-NOzHINAP complex, however,exhibits only one vNO at 1232 ern -I characteristic ofN - bonding of the oximino group only. In all theabove cases, V(C = N) is also found to decrease, but thedecrease is marked in the case of 4-NOzHINAPcomplex where bonding occurs through nitrogen only.

In all the hydrates the v(OH) appears in the range3440-3480 cm -I but no b(OH). This observation alongwith the fact that water is expelled on heating (110-20°)indicates the presence of lattice-held water.

Infrared spectra also indicate that V(C= 0) isaffected by substitution in the phenyl moiety of theparent ligand. In the metal chelates there are both (J-and n-interactions and V(C = 0) decreases in the orderOMe ~ Me > H > CI > Br > NOz and this sequence isconsistent with the Hammett's (J values (OMe, -0.27;Me, -0.17; H, 0; Br, 0.23; Cl, 0.23; N02, 0.78). Theelectron-releasing substituents -OMe and - Me tendto increase the electron density on the oxygen of the C=0 thereby facilitating strong (J but poor n-interaction. The reverse is true in the case of electron-attracting substituents. The large negative shiftobserved in the 4-N02HINAP complex is indicative of

528

back bonding. Useful information about n-bondingcould not be obtained from v(Co-O) since it has gotsignificant contribution from v(Co - N) in this region3.

0-...... 0"""ON, \ ,-NO ON". I "NO( "co' ( '·Co.'\ /: "'0 0/ f "'NOo o~../ 6.../

For the same substituent in the benzene ring, except-NOz and -OMe, v(C=O) varies as Co>Ni?Cu,indicating extensive delocalization of electrons fromthe highly populated d-orbitals of copper into n*orbitals of the ligand. This order is in keeping withIrving-Williams order of stabilities.

In the solid state the planar cobaltrl l) bis-chelatesmay have distorted octahedral geometry 7, theadditional coordination being achieved through theoxygen atoms above and below the plane, leading tolowering of magnetic moment (3.25-3.65 B.M.).

Cobalt(II!) complexes are diamagnetic and showtwo stretches for NO group.

The complexes of 4-MeHINAP and 4-0MeHINAPare unsymmetrical type and hence, they are expected toform cis\2) and Irans\3) octahedral complexes. TheCH3 and OCH3 signals in the PMR spectra of thecobalt(III) tris-chelates appear as single peaksrespectively at 62.42 and 3.88. This indicates that thethree ligands are magnetically equivalent suggesting acis structure for them.

No d-dbands can be observed for either cobalt(II) orcobaltfl llj ':":" which are suspected to be obscured bythe high-intensity charge transfer transition observedin the region 24,875-28,250 ern -I. The M -> L chargetransfer bands observed for cobalt(II) chelates are wellbelow the CT regions of copper(II) and nickel(II)chelates reported earlier 1 , indicating that the former ismore readily oxidizable than either copper(lI) ornickel(II). The complexes show two bands in the region32050-40250 em -I corresponding to n-n* transition.

We thank the CSIR, New Delhi for the award of asenior research fellowship to one of us (ANH).

References1 Natarajan C & Nazeer Hussain A, Indian J Chern, 20A (1981) 307.2 Natarajan C & Nazeer Hussain A, Trans Met Chern, 7 (1982) 252.3 Pathak P L & Haldar B C, J Indian chern Sac, 49 (1972) 745.4 Matsumoto C & Shima K, Chern Abstr, 67 (1967) 58963r.5 Welcher F J. Organic analytical reagent, Vol. 3 (Van Nostrand,

New York), 1955, 275.6 Hadzi D, J chem Sac, (1956) 2725.7 Carlin R L, Trans Met Chern, 1 (1965) I.8 Haldar B C. J Indian chern Sac, LI (1974) 224.