Synthesis and spectroscopic characterisation of cobalt(III) and nickel(II) complexes with 5-methyl-3-formylpyrazole-N(4)-dibutylthiosemicarbazone (HMPzNBu2): X-ray crystallography of [Co(MPzNBu2)2]NO3·H2O (I) and [Ni(HMPzNBu2)2](ClO4)2 (II)

New cobalt(III) and nickel(II) complexes of 5-methyl-3-formylpyrazole-N(4)-dibutylthiosemicarbazone (HMPzNBu2), [Co(MPzNBu2)2]X·H2O and [Ni(HMPzNBu2)2]X2 (X=Cl, Br, ClO4, BF4 and NO3), respectively, have been synthesised and physico-chemically characterised by magnetic measurements (polycrystalline state), 1H NMR [for Co(III) complexes], electronic and IR spectra. The reported species are all cationic complexes, behaving as 1:1 [for Co(III) complexes] and 1:2 [for Ni(II) complexes] electrolytes in MeOH. Electronic spectral features of the diamagnetic Co(III) and paramagnetic Ni(II) species classify them as six-coordinate distorted octahedral ones. IR spectra (4000–200 cm−1) indicate a monoprotic tridentate (NNS) function of HMPzNBu2 coordinating to the central Co(III) via the pyrazolyl (tertiary) ring nitrogen, azomethine nitrogen and thiolato sulfur atom; while for the Ni(II) complexes, HMPzNBu2 behaves as neutral NNS tridentate, bonding to Ni(II) through the pyrazolyl iminic nitrogen, azomethine nitrogen and thioketo sulfur. 1H NMR data (in DMSO-d6 at 300 MHz) for the uncomplexed ligand and those of its Co(III) complexes are commensurate with the propositions of bonding sites envisaged from IR data. X-ray crystallographic data of I (P<f>1¯</f>, triclinic) and of II (C2/c, monoclinic) have authenticated CoN4S2 and NiN4S2 octahedral coordination, respectively; in both I and II; the pair of coordinating ligands are nearly orthogonal to each other with the difference that while in I, the pair of ligands are monodeprotonated, in II, the same pair of ligands are neutral. [Copyright &y& Elsevier]