Tailoring Structural Diversity in Dimethyltin Carboxylates by the pH-Controlled Hydrothermal Approach

The study presents a rational synthesis of new dimethyltin carboxylates, Me₂Sn(H₂btec) (1), Me₂Sn(btec)_0.5(2), [Me₂Sn(H₂O)₂(btec)_0.5]·H₂O (3), and [{Me₂SnOSn(OH)Me₂}(Me₂SnOH)(btec)_0.5]·H₂O (4), derived from tetratopic 1,2,4,5-benzenetetracarboxylic acid (H₄btec). The method relies upon hydrothermal reaction (130 °C, 72 h) of dimethyltin dichloride and H₄btec under optimized pH (2 < pH < 8) conditions that allow control over dimethyltin speciation in aqueous medium as well as degree of deprotonation of the tetrafuntional carboxylic acid. The formation of a three-dimensional assembly in 1 is assisted by the bridging bidentate (μ₂) mode of the carboxylate and O-H···O hydrogen bonds involving -COOH groups. The structure represents a unique example of the diorganotin framework derived from a partially deprotonated polyfuntional carboxylic acid. The structure of 2 adopts a three-dimensional motif wherein each pair of μ₂-carboxylate groups (designated by C1 and C4) of the tetraanionic ligand form different spatial arrangements. For 3, the formation of one-dimensional motif with eight-coordinated tin atoms is assisted by the anisobidentate character of the carboxylate groups. The structure of 4 includes linear chains comprised of [Me₂Sn(μ₂-OH)]₂ and the carboxylate ligand which extend to a layered motif with symmetrically substituted ladder-like distannoxanes acting as linkers. The underlying nets of 1, 2, and 4 exhibit sqc11, scu(sqc170), and sql topologies, respectively. Notably, these assemblies are extremely robust and show no sign of degradation upon exposure to neutral as well as weakly acidic/basic aqueous medium for 7 days.