The structure of hexasodium bis[μ-(phosphato-O,O')-pyrophosphatothorate(IV)]

Crystals of Na6[Th(PO4)(P2O7)]2 are triclinic, space group P-1, with a = 8.734(2), b = 8.931(2), c = 6.468(1) A, α = 93.33(3), β = 108.29(4), γ = 110.10(4)0, U = 442.0 A3, Dsub(m) = 4.264, Dsub(c) = 4.281 Mg m-3. The structure was refined to R = 0.040 for 2475 observed reflexions [I > 2sigma(I)]. A binuclear unit of Th polyhedra with a double bridge of two phosphato O atoms occurs in the structure. The Th atom exhibits ninefold coordination in the shape of a tricapped trigonal prism. Th-O distances range from 2.309(8) to 2.785(7) A. The pyrophosphato group is non-linear with P-O-P 129.4(4)0. The terminal P-O bonds range from 1.424(7) to 1.559(7) A. Bridging P-O distances are 1.621(8) and 1.630(8) A. The O-P-O bond angles are in the range 103.3(4) to 117.5(4)0. In the discrete PO4 tetrahedron P-O bond lengths vary from 1.475(7) to 1.577(7) A and O-P-O bond angles from 102.0(4) to 116.1(4)0. The polyhedra around Na form a three-dimensional network. The dimers of Th polyhedra fit in the holes among the Na polyhedra forming an extremely close-packed structure. (Auth.)