Coordination of isoniazid, an anti-tuberculosis (TB) drug with chromium, molybdenum, and tungsten metalcarbonyls

Isoniazid, an anti-tuberculosis (TB) drug has been coordinated with chromium, molybdenum, and tungsten metal carbonyls and three new zero-valent complexes fac-[M(CO)(3)(isoniazid)(3)] (M = Cr, Mo, and W; 4, 5, and 6) (isoniazid = 4-H2N-HNOCC5H4N) have-been synthesized. Reaction of the complex precursors fac-[M(CO)(3)(CH3CN)(3)] (M = Cr, Mo, and W; 1, 2, and 3) prepared 'in situ' with three equivalents of isoniazid in methanol at room temperature afforded high yields of isoniazid substituted metal carbonyl complexes 4, 5, and 6. The complexes have been characterized by elemental analyses, mass analysis, thermal analysis (TGA, EGA), FT-IR, UV/visible and H-1 NMR spectroscopic techniques and powder X-ray diffraction (XRD). The FF-IR (KBr and methanol solution) spectra of the complexes 4, 5, and 6 exhibit two bands corresponding to nu(CdropO) of metal carbonyl groups and nu(C=O) of coordinated isoniazid molecules. The bulky -CONHNH2 group of isoniazid molecules made more impact on the M-C bond strength of metal carbonyls and affects their fundamental modes of vibrations leading to the appearance of more number of nu(CdropO) bands. These steric effects are also reflected in the H-1 NMR spectral features of the complexes when considering the complexes as a whole, wherein the four protons on the pyridine ring of the coordinated isoniazid molecules resonate at different chemical shifts. All the three complexes exhibit similar XRD pattern suggesting similar geometry.