Uranium eight-coordinate complexes

One such oxygen containing ligand includes acetylacetonate (acac for short), that can form an eight coordinate complex of the form U(acac). Thiol ligands have long been known for use with uranium, too. 

Sohd uranium—phosphate complexes have been reported for the IV and VI oxidation states, as well as for compounds containing mixed oxidation states of U(IV) and U(VI). Only a few sohd state stmctures of U(IV) phosphates have been reported, including the metaphosphate U(P03)4, the pyrophosphate U(P202), and the orthophosphate, CaU(PO4)2. The crystal stmcture of orthorhombic CaU(POis similar to anhydrite (194). Compounds of the general formula MU2(PO4)3 have been reported for M = Li, Na, and K, but could not be obtained with the larger Rb and Cs ions (195). In the sohd state, uranium(IV) forms the triclinic metaphosphate, U(P03)4. Each uranium atom is eight-coordinate with square antiprismatic UOg units bridged by... 

A rare ytterbium(III) complex [Yb(HB(pz)3)3] has an eight-coordinate bicapped trigonal prismatic structure (48) with two tridentate ligands and one bidentate ligand. The complex is stereochemi-cally rigid in solution. 1 A number of thorium and uranium complexes have been reported. These include [U(HB(pz)3)4], [U(H2B(pz)2)4], [U(HB(pz)3)2Cl2], and mono- and di-Cp metal-halogen complexes.49... 

In the addition mechanism, the coordination number of uranium is increased from six to seven, whereas in the substitution mechanism, there is no increase in the coordination number. The absence of any synergistic effect for uranium(IV) and thorium(IV),127 which give coordination-saturated complexes M(HA2)4 with organophosphoric acids in which the metal ions are eight coordinate, is in accord with the addition mechanism. 

Neutral complexes of the thiocyanate ligands can be isolated as Lewis base adducts. Thorium and uranium form tetra(hydrate) complexes An(NCS)4(H20)4. The compound U(NCS)4(piper-azine) has been reported. The neutral adducts Th(NCS)4(L)4 and U(NCS)4(L)3 (L = N,N-diisopropylpropionamide) have been structurally characterized. The smaller size of the uranium ion is reflected in the isolation of a seven-coordinate compound, while an eight-coordinate thorium compound is formed. If more sterically demanding carbamide ligands are employed (L = N,N-diisopropylbutyramide, L = 7V,VV-dicyclohexylacetamide), seven-coordinate thorium complexes, Th(NCS)4(L)3 and Th(NCS)2Cl2(L )3, can be isolated. " ... 

The uranium atom is eight-coordinate the linear uranyl group is equatorially surrounded by six oxygen atoms of the three bidentate carbonate groups. In the equatorial plane the radius of the complex ion amounts to 4.85 A, thus, it is one of the largest inorganic ions existing in sea water 119). 

K(pzTp) reacts with UCI4 in THF giving [UC lpzTph], which contains an eight-coordinated uranium center in a distorted square antiprismatic geometry. This complex reacts with sodium alkoxide,... 

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