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]aneS2O3)] [FeCl4]([15]aneS2O3= 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. 1H and 45Sc 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 ScCl3·6H2O 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 [Sc2(NO3)2(H2O)6(OH)2](NO3)2·12-crown-4. However, in the related [Sc2(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.