Structural diversity of organotin(IV) complexes self-assembled from hydroxamic acid and mono- or dialkyltin salts

Three hydroxamic acid ligands (HL1 = acetohydroxamic acid; HL2 = benzohydroxamic acid; HL3 = N–phenylbenzohydroxamic acid), have been used to synthesize series of mono- or dialkyltin(IV) complexes, which include (i) the carboxyl acid hybrid five-coordinated dialkyltin complexes (C4H9)2SnL1L4 (1), [(CH3)2SnL2L5]·0.5C6H6 (2), (HL4 = acetic acid; HL5 = benzoic acid); (ii) the six-coordinated mono-n-butyltin complexes (C4H9)SnL1·Cl2·H2O (3), (C4H9)SnL2·Cl2·H2O (4), [(C4H9)SnL3·Cl2·H2O]·H2O (5), [(C4H9Sn)2(L3)2·Cl2·(OCH3)2] (6); and (iii) the alkali metal-mingled seven-coordinated mono-n-butyltin complexes [(C4H9Sn)3L2Na]+·Cl−·(CH3CH2)2O (7), [(C4H9Sn)3L2K]+·Cl−·CH2Cl2 (8). All complexes were characterized by elemental analyses, IR, 1H, 13C, 119Sn NMR and X-ray single crystal diffraction. In these complexes, hydroxamic acids present bidentate coordination modes with the carbonyl O atom and the hydroxyl O atom binding to tin center. In complexes 1–6, each tin atom is coordinated by one hydroxamic acid ligand. However, in complexes 7 and 8, tin atom is surrounded by three hydroxamic acid ligands, and all hydroxyl O atoms of the ligands also bind to the alkali metal center (Na or K). This kind of organotin(IV) framework containing one alkali metal is found for the first time. Furthermore, the supramolecular structures of 1, 3, 4 and 6 have been found to consist of 1D linear molecular chains formed by intermolecular N–H···X or C–H···X (X = O, N or Cl) hydrogen bonds. For complex 2, an interesting macrocyclic tetramer has been built by the intermolecular N–H···O hydrogen bonds. Fascinatingly, two unique symmetric dimeric structures are recognized in complexes 7 and 8, which is individually bridged by intermolecular N–H···Cl and N–H···O hydrogen bonds. In addition, for 8, the dimeric cycles have been further connected into a 1D supramolecular chain.