Uranium(IV) and thorium(IV) halide and pseudohalide complexes with substituted amide and urea ligands

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Thorium(IV) and uranium(IV) halide and pseudohalide derivatives form complexes with variable stoichiometry with differently substituted amide and urea ligands. This is related either to the bulk of the anionic or/and of the neutral ligands. The compounds here reported are ThBr 4(MeCON( i-Pr) 2) 2 (I), Th(NCS) 4(MeCON( i-Pr) 2) 4·CH 2Cl 2 (II), ThBr 4((Et) 2NCON(Et) 2) 2 (III), ThCl 4(PhMeNCONPhMe) 3 (IV) and U(NCS) 4(EtCON( i-Pr) 2) 3 (V). Crystal data show that the coordination geometry around thorium in (I) and (III) is trans octahedral while in (II) it is dodecahedral with the N atoms of the NCS groups occupying the dodecahedral B sites and the neutral ligand O atoms the A sites. The different hindrance of bromine in (I) with respect to isothiocyanate in (II) allows in (II) the coordination of four neutral ligands instead of two as has been found in (I). In (IV) the coordination polyhedron about the seven coordinate thorium ion is a pentagonal bipyramid with two chlorine atoms in the axial positions as in tetrachloro tris( N, N-diethylpropionamide) thorium(IV). A similar coordination geometry around uranium(IV) has been found in (V) where two N atoms from the (NCS) are in the axial positions ligands while in the diisopropylacetamide derivative (dipa) U(NCS) 4(dipa) 4 the coordination polyhedron is a regular dodecahedron. The hindrance of the additional methyl group present in the diisopropylpropionamide ligand causes a reduction in the coordination number around uranium from eight to seven.