23- and 27-Membered Macrocyclic Diorganotin(IV) Bis-dithiocarbamates: Synthesis, Spectroscopic Characterization, DFT Calculations, and Physicochemical Analysis as Anion Receptors

Four secondary diamines with aromatic spacer groups derived from α,α′-dibromo-p-xylene and 4,4′-bis(chloromethyl)-1,1′-biphenyl have been transformed into bis-dithiocarbamate ligands and each combined with dimethyl-, di-n-butyl-, and diphenyltin(IV) dichloride to yield a total of 12 mononuclear diorganotin(IV) bis-dithiocarbamate complexes with six-coordinate metal coordination geometries and either 23- or 27-membered macrocyclic structures. The products were fully characterized by IR and NMR (¹H,¹³C,¹¹⁹Sn) spectroscopy and high-resolution ESI⁺-TOF mass spectrometry. A representative selection of the macrocyclic complexes was further examined by DFT computational studies and the relative binding energies of the cis and trans isomers of the different diorganotin complexes were calculated and compared. Additionally, four possible conformations of the trans isomers were analyzed. With the purpose of examining whether the complexes can be applied to the recognition of anions, five macrocycles were selected based on criteria that allowed the influence of the aromatic spacer group, the N substituent of the dithiocarbamate ligand, and the organic groups attached to the metal center on the recognition properties to be explored. Among the NMe₄⁺X^–salts (X^–= F^–, Cl^–, Br^–, I^–, NO₃^–, HSO₄^–, and CH₃COO^–) examined, the diorganotin complexes were sensitive to fluoride and carboxylate anions.