Indian Journal of Chemistry Vol. 45A, May 2006, pp. 11 26- 11 30 Synthesis, characterization, spectroscopic and electrochemical studies of new thioether ligated octahedral low-spin cobalt(II) complex: Oxidative cleavage of C-S bond Chandrama Ba s u. Santanu Chowdhury & Soma Mukherjee* Departme nt of Environmental Sc ie nce , University of Kal ya ni. Kal ya ni, Nadia 74 1 235. Wes t Bengal, India Email: so mmukh 445 @y ahoo.co.in Recei ved 24 October 2005: rel'ised 6 Februarv 2006 The reac ti on of coba lt (!! ) acetate tetra hydrate wi th dithiaalkyl s ubstituted aryl azo-oxime li gand HON=C(P h)N =N C 6 H 4 S(C H 2 hSCr,H"N=NC( Ph)=NOH (H 2 PhL). I, affords a thioether li gated oc tahedral low-s pin [Co 11 ( PhL)]. 2, (r( t 2 g\ 1 • S = / /2) w ith CoN 4 S 2 coo rdin a ti o n. The room tempe rature magnetic moment of so lid [Co 11 (PhL )] is 1. 88 /IIJ. Th e low-spi n co nfigura ti on is further authenti ca ted by it s e ig ht lin e EP R spec tra (g = 2.02, A = 3 1 C) in frozen acetonitrile (77 K). The co mpl ex di sp la ys a quasi-rever si ble (t:.£1' = 90 mY ) one-elec tron cyclic res pon se in acet onitrile at 0.08 V versus saturated calomel electr od e. The response is assigned to th e [Co 11 ( PhL)j/[Co 111 (PhL)t ox ida ti on. Moreov e r. the bivalent [Co 11 (PhL)], 2. undergoes an oxida ti ve cleavage of th e C-S bond to afford parent [Co 111 (PhL)C I0 4 j. 3, and transformed [Co 111 (P hL')( PhL" )]. co mplexes in th ei r tri va le nt state. In CDC I_ 1 • the splitting of the vinylic proton s of [Co 111 ( PhL' )(PhL")]. 4. appear s at 05.85 (dd ). 5.66 (del) and 5.58 (dd). respec ti vely (dd =doublet of doublet). A ll complexe s have been characterized w ith th e help of C. H. N anal ys is. FAB ma ss. cyclic voltammetry, spectr osco pi c techniques (UV- vis. 1 H NMR a nd EPR) and magne ti c stu die s. IPC Code: Int. C l 8 C07F 15/06 Control of the spin states of metal ions has attracted much attention in inorga ni c and biological che mi stry'- 6 . It has bee n of special interest to clarify how the spin states of metal ions can be contro ll ed by proper modulation of ligand frames. In th e crucial choice of companion sites that co ul d promote spin-pairing, we were guided by our early experience th at oximato-N coordination 7 - 12 is a remarkable tool for redox activation as well as to induce low spin characte r. It is well-known th at low-spin octahedral 1'-20 w cobalt( IT ) complexes are very scarce · . e report herein th e synthesis of a low spin octahedral cobalt(If) comple x with the hel p of acyclic hexadentate N, S ligand, 1. To the best of our knowledge, this demonstrates th e first example of thioether ligated low spin cobalt(ll) comple x of CoN 4 S 2 chromophoric class in the so li d state. Moreover, 1 undergoes an ox idative cleavage of C-S bond when it is reacted with a cobalt( TI ) acetate tetrahydrate to afford the parent and transformed trivalent complexes 3 and 4 respectively (Scheme I ) 21 . The C-S bond is also cleaved by alkali as found in cyclic thi oe ther li gands as well as with some non-cyclic ones 22 - 31 . Materials and Methods A Perkin-Elmer 2400 C elemental analyzer was us ed to collect microanalytical data (C, H, N) . Electrochemical measurements were performed un der nitrogen atmosphere using the Versastat ll PAR system. For spectroscopic/electrochemical studies, HPLC grade solvents were used. Com mercial tetraethyl ammoni um bromide was conve rted into pure tetraethyl a mmonium perchlorate as known alread/ 2 . 2-Aminothiophenol was obtained from Aldrich, USA. Other chemi ca ls and solvents were of analytical grade and used as received. Solution