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)=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, H-1, C-13, N-15 and Sn-119 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 delta(Sn-119) 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(Sn-119, C-13) for Ia, 1b and Ic are found to be 135.6 degrees, 133.85 degrees and 135.0 degrees respectively. From the (2)J(Sn-119, H-1) value, the Me-Sn-Me angle for Ib is found to be 130.46 degrees. 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. (C) 2013 Published by Elsevier B.V.