Complexation of triorganotin derivatives of [18]crown-6-and [15]crown-5-(benzo-4-carboxylate) with alkali thiocyanates

Investigations of the simultaneous complexation of tri-n-butyltin and triph enyltin derivatives of [18]crown-6-or [15]crown-5-(benzo-4-carboxylate) by the anion and cation from NaSCN or KSCN are reported. The crystal structure of [Na+ subset of [15]crown-5-{C6H3-4-COOSn(C6H5)(3)NCS}(-)], 4 (.) NaSCN, displays an unusual zwitterionic nature with one intramolecular charge sep aration characterized by an Na-Sn distance of 9.29(1) Angstrom, and several intermolecular charge separations, the shortest being 5.48(1) Angstrom. Si milar distances (9.70(2), 9.28(2), intramolecular; 5.40(2) and 5.41(2) Angs trom, shortest intermolecular) are observed in the more complicated structu re of the corresponding [18]crown-6(benzo-4-carboxylate) derivative, 3 (.) NaSCN, with two independent molecules in the asymmetric unit. For the trin- butyltin analogues 1 and 2, complex equilibria were observed in acetone and unraveled by variable temperature C-13, Sn-117, and Na-23 NMR studies. The ir complexes with KSCN and NaSCN undergo decomposition in acetone solution, as evidenced by the transformation of [K+ subset of [18]crown-6-{C6H3-4-CO OSn(nBu)(3)NCS}(-)], into tri-n-butyltin isothiocyanate and a novel dimeric potassium [18]crown-6-(benzo-4-carboxylate), the structure of which was el ucidated by X-ray diffraction analysis.