Structural and spectral studies of diorganotin(IV) complexes containing bis-tridentate N,N-bis(4-oxo-4-phenylbutan-2-ylidene)oxalohydrazide ligand

Three new symmetrical binuclear diorganotin(IV) complexes with the symmetrical bis-tridentate Schiff base, N,N-bis(4-oxo-4-phenylbutan-2-ylidene)oxalohydrazide, (R2Sn)2[Ph–C(O)double bond; length as m-dashCH–C(Me)double bond; length as m-dashN–Ndouble bond; length as m-dashC(O)–C(O)double bond; length as m-dashN–Ndouble bond; length as m-dashC(Me)–CHdouble bond; length as m-dashC(O)−Ph] (R = Ph: Ia; R = Me: Ib; R = n-Bu: Ic) have been synthesized by reaction with corresponding diorganotin(IV) dichloride at room temperature in methanol in presence of triethylamine. The complexes have been characterized by elemental analyses, IR, 1H, 13C, 15N and 119Sn NMR spectroscopy. Two dimensional H,H-COSY, NOESY, H,C-COSY, gs(gradient selected)-HMQC and gs-HMBC techniques were applied in order to assign proton and carbon chemical shifts unambiguously. The δ(119Sn) values for the complexes Ia–Ic are −320.1, −181.9 and −150.7 ppm respectively, indicating pentacoordinated tin centres. The C–Sn–C angles calculated from 1J(119Sn, 13C) for Ia, 1b and Ic are found to be 135.6°, 133.85° and 135.0° respectively. From the 2J(119Sn, 1H) value, the Me–Sn–Me angle for Ib is found to be 130.46°. From NMR spectra a distorted trigonal-bipyramidal geometry at each tin centre is proposed. The structures of the complexes have been confirmed by single crystal X-ray diffraction analysis of one representative compound Ia. The ligand, N,N-bis(4-oxo-4-phenylbutan-2-ylidene)oxalohydrazide (H4L) coordinates to the metal centre in enolate form via the phenolic O, imino N and enolic O atoms. The X-ray structure indicates that the coordination geometry of tin atoms are intermediate between trigonal bipyramid and a square pyramid. The oxygen atoms are in axial positions while the imino nitrogen atom of the ligand and two phenyl groups occupy the equatorial sites.