Structures and NMR Solution Dynamics of Diorganotin Complexes with Bulky Quadridentate Salen- and Salphen-Type Schiff Bases (N2O2) Incorporating Diazenylpyridyl Side Arms

Abstract

A series of six complexes [n-Bu2Sn(L1)]⋅S (S=Benzene/toluene, mixed/partial) (1), [Ph2Sn(L1)]n⋅S (S=Benzene) (2), [Bz2Sn(L1)] (3), [n-Bu2Sn(L2)]n (4), [Ph2Sn(L2)] (5) and [Bz2Sn(L2)] (6) were synthesized using diorganotin(IV) oxide precursors and two new bis-Schiff bases containing N2O2 donor atoms. The Schiff bases, H2L1 and H2L2, were prepared by reacting ethane-1,2-diamine or benzene-1,2-diamine with 2-hydroxy-5-(pyridin-3-yldiazenyl)benzaldehyde in absolute ethanol. Compounds 1–6 were characterized by IR and NMR spectroscopies, as well as by solid-state single-crystal X-ray diffraction (except for 3 and 6). In all the complexes the bis-Schiff bases occupy the equatorial positions and the R groups are in axial sites. However, while 1 and 5 are discrete molecules where the tin atoms adopt distorted octahedral geometries, 2 and 4 are monoperiodic polymers with the metal cations in pentagonal bipyramidal environments. Although solid state crystallographic results revealed asymmetrical molecular configurations, solution NMR studies proved symmetric arrangements for all the compounds. Tin NMR spectroscopy confirmed that all complexes are six-coordinate in solution, despite variations in solid-state coordination. Further analysis using Hirshfeld surface and fingerprint plots provided insights into intermolecular interactions in compounds 1, 2, 4, and 5. This comprehensive study underscores the structural diversity and solution-state dynamics of organotin(IV) complexes synthesized using novel Schiff bases.