New boron-centered mixed-halide zirconium cluster phases with a cubic structure: NaZr6Cl12-xI2+xB (x <= 6) and A(0.5)(II)Zr(6)(Cl,I)(14)B (A(II) = Ca, Sr, Ba)

The boron-centered mixed-halide zirconium cluster phases were obtained from reactions of appropriate amounts of NaCl or ACl(2) (with A = Ca, Sr, Ba), ZrCl4, ZrI4, Zr (powder), and elemental B in sealed tantalum containers at 800-850 degrees C. Single crystals of NaZr6Cl10.94(1)I3.06B and Sr0.5Zr6Cl1 1.34(2)I2.66B have been characterized by X-ray diffraction at room temperat ure (cubic, Pa(3) over bar, Z = 4, a = 1331.3(1) pm, and a = 1326.2(2) pm, respectively). The Zr-6 octahedra in these phases are centered by boron and three-dimensionally connected by exo-iodide atoms which bridge simultaneou sly three octahedra. Six out of the twelve inner chlorides (one symmetry in dependent site) which bridge the edges of each octahedron, but are not invo lved in inter-cluster bridging (according to AZr(6)I(6/2)(a-a-a)(Cl12-xIx)B -1), can be completely substituted by iodide. Such a substitution is not po ssible for the remaining six inner halides on the second symmetry independe nt site, because the larger iodide atom on this site would experience stron g repulsive forces from short anionic contacts. This gives the phase width of NaZr6Cl12-xI2+xB to x less than or equal to 6. The size of the voids tha t cover the cations A limits this structure to members with A = Na, Ca, Sr, and Ba. This structure type requires the existence of two differently size d halide types simultaneously.