Formation of azacrown complexes of Tin(IV): crystal and molecular structure of [H2L]2[SnCl5(H2O)]2·H2O·MeCN (HL = 1,4,7,10,13-pentaoxa-16-azacyclooctadecane)

Abstract

Reaction of SnCl₄ and aza-18-crown-6 (1,4,7,10,13-pentaoxa-16-azacyclooctadecane, HL) provides the white solid SnCl₃L 1 with elimination of HCl. Analytical and spectroscopic characterisation of 1 points to a structure in which a SnCl₃ unit is bonded to the deprotonated nitrogen atom and the two adjacent oxygen atoms of the azacrown. Partial hydrolysis of 1 during an attempted recrystallisation in acetonitrile, gave colourless crystals of the ionic compound [H₂L]₂[SnCl₅(H₂O)]₂·H₂O·MeCN 2 the structure of which was determined by X-ray diffraction: monoclinic, space group C2/m, a= 40.15(2), b= 12.231(6), c= 10.019(7)Å, β= 104.05(5)°, Z= 4. Two independent azacrown molecules are both protonated. Molecule 1 has the solvate water molecule located centrally over the ring cavity, held by three strong O–H_water⋯ O_ring 2.793 and O_water⋯ H–N_ring 2.690 Å hydrogen bonds; molecule 2 behaves as a second-sphere ligand to two separate six-co-ordinate [SnCl₅(H₂O)]^– anions positioned on opposite sides of the ring. The co-ordinated H₂O molecules are located over the centre of the azacrown ligand and are involved in hydrogen bonding to the nitrogen and oxygen atoms of the ring.