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

Abstract Three new symmetrical binuclear diorganotin(IV) complexes with the symmetrical bis-tridentate Schiff base, N , N -bis(4-oxo-4-phenylbutan-2-ylidene)oxalohydrazide, (R 2 Sn) 2 [Ph–C(O) CH–C(Me) N–N C(O)–C(O) N–N C(Me)–CH C(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, 1 H, 13 C, 15 N and 119 Sn 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 ( 119 Sn) 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 1 J ( 119 Sn, 13 C) for Ia , 1b and Ic are found to be 135.6°, 133.85° and 135.0° respectively. From the 2 J ( 119 Sn, 1 H) 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 (H 4 L) 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.