Primary and secondary coordination of crown ethers to scandium(III).: Synthesis, properties and structures of the reaction products of ScCl3(thf)3, ScCl3•6H2O and Sc(NO3)3•5H2O with crown ethers

The synthesis and spectroscopic characterisation of [ScCl(15-crown-5)(MeCN)][SbCl6](2),[ScCl2(18-crown-6)][FeCl4] and [ScCl2([15]aneS(2)O(3))][FeCl4]([15]aneS(2)O(3) = 1,4-dithia-7,10,13-trioxacyclopentadecane) are reported, the last containing the first example of thioether-scandium(III) coordination. The structure of [ScCl(15-crown-5)( MeCN)] [SbCl6](2) reveals a pentagonal bipyramidal cation with axial Cl and MeCN, whilst [ScCl2(18-crown-6)][FeCl4] is also pentagonal bipyramidal with axial Cl ligands. H-1 and Sc-45 NMR spectroscopies have been used to study the speciation in the ScCl3/18-crown-6 system in the presence of the Lewis acids SbCl5 and FeCl3 in anhydrous MeCN. Hydrolysis of any of the above complexes and of [Sc(12-crown-4)2](3+) (formed from ScCl3(thf)(3), crown and SbCl5), results in the formation of [ScCl3(H2O)(3)].crown,the solution NMR spectra of which show a common scandium species and uncomplexed crown ether. The structure of [ScCl3(H2O)(3)].18-crown-6 reveals a mer octahedral scandium species which is hydrogen bonded via the scandium-coordinated water to the 18-crown-6 (secondary coordination) leading to infinite chains. Similar complexes have been isolated directly from reaction of ScCl3.6H(2)O and the crown ethers in absolute ethanol, including [ScCl3(H2O)(3)](n).(crown) (n = 1 or 2, crown = 18-crown-6; n = 2, crown = 15-crown-5 or 12-crown-4). Hydrated scandium nitrate and the crown ethers react in ethanol solution to form a surprisingly diverse range of structural types containing the crown ethers hydrogen bonded to the scandium-aquo-nitrato or scandium-aquo-hydroxo-nitrato complexes. X-Ray crystal structures are reported for [Sc(H2O)(2)(NO3)(3)].(12-crown-4)(2), [Sc(H2O)(4)(NO3)(2)]NO3.15-crown-5 and [Sc-2(NO3)(2)(H2O)(6)(OH)(2)](NO3)(2).12-crown-4. However, in the related [Sc-2(NO3)(4)(H2O)(4)(OH)(2)][Na(12-crown-4)(2)](NO3).(H2O)(3) the hydrogen bonding occurs between the lattice water and the scandium dimer unit.