The crystal and molecular structures of tetrachloro- tris(NN-diethylpropionamide)thorium(IV) and tetra-N-thiocyanatotetrakis(NN-dimethylpropionamide)thorium(IV)

Abstract

Amide complexes of thorium tetrachloride often adopt a different stoichiometry to those formed by the same ligand with uranium tetrachloride, a difference which can be ascribed to the smaller radius of the U(IV) centre as compared with that of Th(IV). For example, with the amide depa (=EtCONEt 2) the complexes 2UCl 4·5depa [1] and ThCl 4·3depa [2] are obtained. The former has been shown [1] to be ionic, [UCl 3(depa) 4] +[UCl 5(depa)] −, with the 7-coordinate uranium atom in the cation adopting the rather unusual bipyramidal geometry which had already been observed [3] in the neutral complex U(NCS) 4(dmiba) 3 (dmiba = Me 2CHCONMe 2. It was ▪ ▪ therefore of interest to determine the structure of ThCl 4·3depa in order to ascertain whether the coordination geometry was gain pentagonal bipyramidal, and also to investigate the structure of the probably 8-coordinate complex Th(NCS) 4·4dmpa (dmpa = EtCONMe 2) the preparation of which has also been reported recently [2]. Crystal Data ThCl 4·3depa ( 1) (ThC 21H 45Cl 4N 2O 3) M = 761.5, monoclinic P 2 1 n , a = 18.107(4), b = 10.347(2), c = 17.867(4) Å, β = 108.5(1)°, Z = 4,λ(MoK lga)0.71069 Å. 3126 reflections with I⩾ 2.5σ (I) use in the structure solution and refinement, R = 0.046, R w = Th(NCS) 4·4dmpa ( 2) (ThC 24H 44N 8O 4S 4) M = 821.0, monoclinic P 2 1 a , a = 22.759(6), b = 13.763(4), c = 11.910(3) Å. β = 91.4(1)°, Z = 4, λ(MoK α 0.71069 Å. 3729 reflections with I ⩾ 2.5σ(1) used in the structure solution and refinement, R = 0.049, R w = 0.053. The coordination geometry for ( 1) is pentagonal bipyramidal as shown in Fig. 1, with two chlorine atoms occupying the axial positions. This kind of geometry is common in seven-coordinate dioxouranium(VI) complexes, rather unusual for U(IV) compounds and the first example for that concentrating mononuclear Th(IV) derivatives. The ThCl axial bond distances (2.69 Å av.) are shorter respect to the ThCl equatorials (2.75 Å av.) as consequence of the different steric hindrance experienced by the anionic ligands. The coordination geometry for ( 2) (see Fig. 2) is nearly square antiprismatic. The substitution of the chlorine with the less hindering isothiocyanate ligand allows a higher coordination number around the thorium ion, while the changed of the neutral ligand does not seem of some effect. The ThN and ThO bond distances have the averaged values of 2.50 Å and 2.38 Å respectively.