Self-assembly of diorganotin(IV) 2-{[(E)-1-(2-oxyaryl)alkylidene]amino}acetates: An investigation of structures by X-ray diffraction, solution and solid-state tin NMR, and electrospray ionization MS

The diorganotin(IV) compounds, [Me2SnL2(OH2)]2 (1), [nBu2SnL2(OH2)]2 (2), [nBu2SnL1]3 · 0.5C3H6O (3), [nBu2SnL3]3 · 0.5C6H6 (4) and [Ph2SnL3]n · 0.5C6H6 (5) (L = carboxylic acid residue, i.e., 2-{[(E)-1-(2-oxyaryl)alkylidene]amino}acetate), were synthesized by treating the appropriate diorganotin(IV) dichloride with the potassium salt of the ligand in anhydrous methanol.The reaction of Ph2SnL2 (L = 2-{[(E)-1-(2-oxyphenyl)ethylidene]amino}acetate) with 1,10-phenanthroline (Phen) yielded a 1:1 adduct of composition, [Ph2SnL2(Phen)] (6).The crystal structures of 1–6 were determined.The crystal of 1 is composed of centrosymmetric dimers of the basic Me2SnL2(OH2) moiety, where the two Sn-centres are linked by two asymmetric Sn–O⋯Sn bridges involving the carboxylic acid O atom of the ligand and a long Sn⋯O distance of 3.174(2) Å.The dimers are further linked into columns by hydrogen bonds.The coordination geometry about the Sn atom is a distorted pentagonal bipyramid with the two methyl groups in axial positions.The structure of 2 is similar.The same Sn atom coordination geometry is observed in compound 3, which is a cyclic trinuclear[nBu2SnL1]3 compound. Each Sn atom is coordinated by the phenoxide O atom, one carboxylate O atom and the imino N atom from one ligand and both the exo- and endo-carboxylate O atoms (mean Sn–O(exo): 2.35 Å; Sn–O(endo): 2.96 Å) from an adjacent ligand to form the equatorial plane, while the two butyl groups occupy axial positions. Compound 4 was found to crystallize in two polymorphic forms. The Sn-complex in both forms has a trinuclear [nBu2SnL3]3 structural motif similar to that found in 3. In compound 5, distorted trigonal bipyramidal Ph2SnL3 units are linked into polymeric cis-bridged chains by a weak Sn⋯O interaction (3.491(2) Å) involving the exocyclic O atom of the tridentate ligand of a neighboring Sn-complex unit. This interaction completes a highly distorted octahedron about the Sn atom, where the weakly coordinated exocyclic O atom and one phenyl group are trans to one another. In contrast, a monomeric distorted pentagonal bipyramidal geometry is found for adduct 6 where the Sn-phenyl groups occupy the axial positions. The solution and solid-state structures are compared by using 119Sn NMR chemical shift data. Compounds 1–6 were also studied using ESI-MS and their positive- and negative-ions mass fragmentation patterns are discussed.