Self-Assembly of Dialkyltin(IV) Moieties and Aromatic Dicarboxylates to Complexes with a Polymeric or a Discrete Trinuclear Macrocyclic Structure in the Solid State and a Mixture of Fast Interchanging Cyclooligomeric Structures in Solution

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Abstract
It is well-known that the structures of trialkyltin(IV) carboxylates can be either monomeric, polymeric, or cyclooligomeric in the solid state. In contrast, all dialkyltin(IV) dicarboxylates characterized so far in the solid state have monomeric or polymeric structures, however, for some cases it has been proposed that their solution-state structure is cyclooligomeric. In order to generate more information on this subject, dimethyl- and di-n-butyltin(IV) complexes with phthalic and isophthalic acid have been prepared and analyzed both in solution and in the solid state. The solid-state structures of the two dialkyltin(IV) phthalates examined herein contain polymeric molecular chains, however, with supramolecular Sn···O‘ interactions, which result in the generation of cyclooligomeric units. This provides evidence for the presence of discrete cyclooligomeric structures in solution, which are involved in fast dynamic exchange equilibria as evidenced by 1H, 13C, and 119Sn NMR spectroscopy. In the case of the two dialkyltin(IV) isophthalate complexes studied herein (R = Me, n-Bu), only the di-n-butyltin derivative is soluble and NMR spectroscopy as well as FAB+ spectrometry indicates the formation of cyclic dinuclear, trinuclear, and/or tetranuclear species in solution, which may be involved also in fast dynamic exchange equilibria. In the solid state, however, discrete cyclotrinuclear units can be identified, in which the 24-membered macrocyclic cavity is almost completely planar, having six oxygen atoms directed into its interior and six Sn−n-butyl groups approximately perpendicular to the molecular plane. The diameter of the cyclic cavity can be described by the transannular O···O distances that vary from 7.68 to 7.84 Å, being large enough for the introduction of linear alkyl groups. This can be demonstrated by the supramolecular structure of this compound, which contains a new type of bis[2]pseudorotaxane formed between two molecules through mutual threading via two of the Sn−butyl groups. Such a supramolecular entity has been unknown so far, since the usual composition of bis[2]pseudorotaxanes is the trimolecular combination of a macrocyclic ring system with two threads.