The First Mixed-Halide Zirconium Cluster Compounds: Zr6Cl1.6I10.4Be, Zr6Cl1.3I10.7B, and Zr6Cl11.5I1.5B. Matrix Effects and Halogen Substitution in Compact Network Structures

Abstract

Investigations of the effect of halogen size on structure stability have been conducted in well-reduced and heavily interbridged zirconium chloride-iodide cluster systems. The title compounds are obtained in good yields from reactions of Zr, ZrCl(4), ZrI(4), and B or Be in sealed Ta tubes for approximately 4 weeks at 850 degrees C. Single-crystal diffraction at room temperature established these as Zr(6)Cl(1.65(4))I(10.35(4))Be and Zr(6)Cl(1.27(3))I(10.73(3))B [R&thremacr;, Z = 3, a = 14.3508(8), 14.389(1) Å, c = 9.8777(9), 9.915(2) Å, respectively] and Zr(6)Cl(11.47(2))I(1.53(2))B [P4(2)/mnm, Z = 2, a = 12.030(1) Å, c = 7.4991(8) Å]. These are derivatives of the Zr(6)I(12)C and orthorhombic Zr(6)Cl(13)B structures, respectively, the latter containing unusual linear chains of clusters interbridged by Cl(i-i) that are in turn interconnected by three-bonded Cl(a-a-a) atoms. The random substitution of fractional Cl at specific I sites in the first two, and I for certain Cl in the third, was positionally resolved in all cases. The replacement always occurs at two-bonded X(i), so that single types of halogen are left in sites that interconnect clusters and generate the three-dimensional array. Structural changes seen in both structures are specifically related to relief of X.X crowding in the parent structure (matrix effects). Substitution of Cl for I(i) in the Zr(6)I(12)C type greatly reduces intercluster I.I repulsions and allows, among other things, a 0.20 Å (5.8%) reduction in Zr-I(a-i) intercluster bond lengths. Increased Cl.I repulsions caused by I substitution in orthorhombic Zr(6)Cl(13)B (Pnnm) convert the twisted chains and angular Cl(a-a-a) interchain bridges to planarity in tetragonal Zr(6)Cl(11.5)I(1.5)B. Phase widths found are 0 </= x </= 1.4 for Zr(6)Cl(x)()I(12)(-)(x)()Z (Z = B, Be) and 0 </= x </= 1.5 for Zr(6)Cl(13)(-)(x)()I(x)()B. The limit for iodine substitution in the chlorine-rich rhombohedral Zr(6)Cl(12)(-)(x)()I(x)()Be is about x = 2.5.