Synthetic and structural studies of tin(IV) complexes of crown ethers

Abstract

Fourteen inorganic tin(IV) and organotin(IV) complexes of crown ethers (L), of general formulae SnX₄·L·2H₂O, SnCl₄·L·4H₂O·nCHCl₃(n= 0 or 1), (SnR₂X₂)_n·L·2H₂O (n= 1 or 2), and (SnPh₃X)₂·L·2H₂O, have been synthesised. The structure and bonding in these adducts are discussed in terms of their i.r. and ¹¹⁹Sn Mössbauer spectroscopic data. These suggest co-ordination to the tin either by one or more of the polyether O atoms, or by the water molecules of hydration (the crown ether acting as a second-sphere ligand). The latter structure is confirmed by a single-crystal X-ray determination of Sn(OH₂)₂Cl₄·18-crown-6·2H₂O·CHCl₃. The crystals are monoclinic, space group P2₁/n, with a= 10.315(6), b= 13.630(8), c= 20.649(13)Å, and β= 94.68(5)°. The structure was solved using multisolution direct methods and refined by least squares to R= 0.062 (R′= 0.068) for 3 142 observed diffractometer data. The water molecules within the octahedral Sn(OH₂)₂Cl₄ units are found to be cis to each other and are involved in an extensive hydrogen-bonding scheme. The latter links together the 18-crown-6 molecules, unco-ordinated water molecules, and Sn(OH₂)₂Cl₄ octahedra, to give hydrogen-bonded chains which run parallel to the b axis.