Synthesis and characterization of nickel-, palladium- and platinum(II) complexes of three o,o′-dihydroxydiarylazo dyes: Determination of the coordination geometry of this comprehensive series of tridentate diaryl dye complexes by combining results from NMR and X-ray experiments with theoretical ab initio calculations

The syntheses of the square-planar platinum(II) complexes [Pt(L)(tba)] (L = 5,5′-dichloro-2,2′-dihydroxyazobenzenate (dhab), (5-chloro-2-hydroxyphenylazo)-3-oxo-N-phenylbutanamidate (hpab) or (5-chloro-2-hydroxyphenylazo)-2-naphtholate (hpan) and (tba) = tributylamine) is reported, together with those of the complete set of analogous complexes [M(L)(py)] (M = nickel(II), palladium(II), platinum(II) and (py) = pyridine). The coordinating nitrogen has been assigned to the azo-nitrogen attached to the 5-chloro-2-hydroxyphenyl substituent in both [Ni(hpab)(py)] and [Pt(hpan)(tba)] by single crystal X-ray diffraction methods. It has been established that complexes with different group 10 metals are iso-structural by isomorphology of the crystals as determined by X-ray powder diffraction studies on the complexes containing pyridine in the fourth coordination site. Furthermore, we present a method to determine the coordination geometry by comparison of calculated 13C chemical shifts for possible coordination modes optimized by ab initio methods with experimentally measured 13C chemical shifts.