The Ni(II) Complex of 2-Hydroxy-Pyridine-N-Oxide 2- Isothionate: Synthesis, Characterization, Biological Studies, and X-ray Crystal Structures Using (1) Cu Kα Data and (2) Synchrotron Data

C12H20N6NiO6S2 or NiL2(SCN)2](NH4)2.2H2O, where L is 2-hydroxy-pyridine-N-oxide, has been
prepared and characterized using elemental analyses, IR, UV and visible spectrometry, magnetic
moment measurements, thermal analyses and single crystal X-ray analyis. The results indicate that
the complex reacts as a bidentate ligand and is bound to the metal ion via the two oxygen atoms of
the ligand (HL). The activation energies, ΔE*, entropies ΔS*, enthalpies ΔH* and order of reactions
have been derived from differential thermo-gravimetric (DTA) curves. Based on inhibition zone
diameter measurements, the complex exhibited significant antibacterial activity against both
Staphylococcus aureus and Escherichia coli. It also exhibited significant antifungal activity against
Candida albicans, but no activity was found against Aspergillus flavus. The crystal structure of the
Ni(II) complex [C12 H20 N6 Ni O6 S2], Mr = 467.17, was determined from Cu Kα X-ray diffraction data, λ
= 1.54178 Å, at 100 K using direct methods. The crystals are monoclinic, space group P21/n with Z =
4 and a = 8.9893(2) Å, b = 17.6680(5) Å, c = 12.5665(3) Å, β = 108.609(1)°. In parallel with this study
corresponding results were derived for the crystal structure determined independently from
synchrotron X-ray diffraction data, λ = 0.61990 Å, at 100 K. The unit cell parameters derived in this
experiment are a = 9.000(2) Å, b = 17.700(4) Å, c = 12.590(3) Å, β = 108.61(3)°. Both studies show 4
O and 2 N atoms coordinating Ni in a distorted octahedral arrangement. Each of the Ni 2-hydroxypyridinium-
N-oxide moieties is highly planar and the S=C=N-Ni ligands are approximately linear. The
crystal structure is characterised by a number of strong hydrogen bonds.