Studies of the reaction system [ScCl3(thf)3]–SbCl5–L (thf = tetrahydrofuran, L = 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane): unexpected formation and crystal structure of [H2L]Cl2·ScCl3(H2O)3·3H2O

Abstract

The reaction system [ScCl₃(thf)₃]–SbCl₅–cryptand 222 (L)(thf = tetrahydrofuran, cryptand 222 = 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane) has been studied as a possible route to scandium(III)–cryptate complexation. The compound [H₂L]Cl₂·ScCl₃(H₂O)₃·3H₂O 1 was isolated as yellow crystals. Microanalytical and spectroscopic (IR, ¹H) data and a crystal-structure determination provided complete identification of 1. Crystals are monoclinic, space group C2/c with a= 29.008(14), b= 8.369(7), c= 26.356(14)Å, β= 94.6(1)° and Z= 8. The molecular structure consists of discrete [H₂L]²⁺ cations, two accompanying chloride anions, a molecule of [ScCl₃(H₂O)₃] and three water molecules trapped in the lattice. The diprotonated di-endo cryptand cation binds two protons within the intramolecular cavity with an N ⋯ N separation of 6.34(4)Å. The encapsulated protons are covalently bound to the nitrogen atoms and each NH centre is involved in weak intracavity hydrogen-bonding interactions with the three adjacent oxygen atoms [N ⋯ O 2.84(2)(two), 2.83(2)Å and 2.74(2), 2.71(2), 2.72(2)Å]. The structure of the molecular adduct [ScCl₃(H₂O)₃] shows a central six-co-ordinate scandium atom with a near-idealised mer-octahedral geometry [mean Sc–Cl 2.417(7), mean Sc–O 2.122(14)Å].