The relationship between ligand structures and their CoII and NiII complexes:: Synthesis and characterization of novel dimeric CoII/CoIII complexes of bis(thiosemicarbazone)

4,6-Diacetylresorcinol serves as a starting point for the generation of multidentate S/N/O or O/N/O symmetrical chelating agents by condensation with thiosemicarbazide or semicarbazide to yield the corresponding bis(thiosemicarbazone) H4L1 or bis(semicarbazone) H4L2, respectively. Reaction of H4L1 and H4L2 with M(NO3)(2) center dot 6H(2)O (M = Co or Ni) afforded dimeric complexes for H4L1 and binuclear complexes for H4L2, revealing the tendency of S to form bridges. The dimeric cobalt complexes of H4L1 are very interesting in that they contain Co-II/Co-III, side/side, low-spin octahedral coordinated Co-III-ions and high-spin square-planar coordinated Co-II-ions. These complexes have the general formula [(H2L1)(2)Co-2(H2O) (NO3)] center dot nEtOH. Arguments supporting these anomalous Co-II/ Co-III structures are based on a pronounced decrease in their magnetic moments, elemental and thermal analyses, visible and IR spectra, as well as their unreactivity towards organic bases such as 1,10-phenanthroline (phen), 2,2'-bipyridine (Bpy), N, N, N',N'-tetramethylethylenediamine (Tmen) and 8-hydroxyquinoline (oxine, Ox). The dimeric octahedral Ni-II complex [(H2L1)(2)Ni-2(H2O)(4)] center dot 3H(2)O showed higher reactivity towards phen and Bpy and formed adducts; [(HL1) Ni-2(B)(H2O)(5)] NO3 (B = phen or Bpy). In the presence of oxine, the dimeric brown paramagnetic octahedral complex [(H2L1)(2)Ni-2(H2O)(4)] center dot 3H(2)O was transformed to the dimeric brick- red diamagnetic square-planar complex [(H3L1)(2)Ni-2](NO3)(2). The latter showed dramatic behavior in its H-1 NMR spectrum in DMSO-d(6), which was explained on the basis of H+-transfer. By contrast, the binuclear Ni-II - H4L2 complex (11) showed higher reactivity towards phen, Bpy and oxine. These reactions afforded mixed dimeric complexes having the molar ratio 2 : 2 : 1 (Ni-II: H4L2 : base). The binuclear Co-II - H4L2 complex afforded an adduct with phen and trinuclear complexes with Bpy and oxine. All complexes were found to be unreactive towards Tmen. Structural characterization was achieved by elemental and thermal analyses, spectral data (electronic, IR, mass and H-1 NMR spectra) and conductivity and magnetic susceptibility measurements.