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), ['' Bu2SnL2(OH2)](2) (2), ['' Bu2SnL1](3)center dot 0.5C(3)H(6)O (3), ['' Bu2SnL3](3)center dot 0.5C(6)H(6) (4) and [Ph2SnL3](n)center dot 0.5C(6)H(6) (5) (L = carboxylic acid residue, i.e., 2- { [(E)- I -(2-oxyaryl)alkylidene] amino I 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 2- { [(E)- 1 -(2-oxyphenyl)ethylidene] amino I 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-(OSn)-Sn-... bridges involving the carboxylic acid 0 atom of the ligand and a long (SnO)-O-... distance of 3.174(2) angstrom 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['' Bu2SnL1](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 angstrom; Sn-O(endo): 2.96 angstrom) 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 ['' Bu2SnL3](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 (SnO)-O-... interaction (3.491(2) angstrom) involving the exocyclic 0 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 0 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 Sn-119 NMR chemical shift data. Compounds 1-6 were also studied using ESI-MS and their positive- and negative-ions mass fragmentation patterns are discussed. (c) 2005 Elsevier B.V. All rights reserved.