Extended solid frameworks and their molecular cluster derivatives

A general method for the computer-assisted generation of polyhedra-based cluster structures is introduced in Chapter 1. The cluster family of interest is delimited, and its definitive structural elements are employed in the design of an infinitely extended parent solid. For computational facility, this polyhedra-based solid is transformed into a parallel graph representation consisting of a simple lattice of points and lines. Pieces of the lattice, corresponding to fragments of the parent solid, are generated by a recursive procedure, converted into ligated clusters, and their structures compiled in a database. Database structures are then subjected to four types of cluster rearrangement processes defined herein. The procedure is demonstrated for iron-sulfur clusters derived from an Fe$\sb2$S parent solid with the antifluorite structure; these are enumerated for formulae containing eight or fewer tetrahedral iron centers. Applications involving structural models employed during the crystallographic resolution of cluster-containing biomolecules and elucidation of laser ablated cluster ions are discussed in detail.

Chapter 2 describes a formalistic approach to the deconstruction of covalent metal-anion and cluster frameworks via incorporation of additional anions. Its utility is demonstrated by application to the tightly-bound cluster frameworks of three-dimensional $\rm Re\sb6S\sb8Cl\sb2$ and two-dimensional $\rm Re\sb6Se\sb8Cl\sb2$. The compact $\rm Re\sb2Q\sb2$ (Q = S, Se) interactions linking face-capped octahedral $\rm\lbrack Re\sb6Q\sb8\rbrack \sp{2+}$ cores in these phases are broken up by insertion of TlCl to afford two-dimensional $\rm\lbrack Re\sb6Se\sb8Cl\sb3\rbrack \sp{1-}$sheets, one-dimensional $\rm\lbrack Re\sb6Q\sb8Cl\sb4\rbrack \sp{2-}$ chains and, ultimately, isolated $\rm\lbrack Re\sb6Q\sb8Cl\sb6\rbrack \sp{4-}$-clusters. Cesium-containing analogues of the molecular phases provide previously unavailable access to the solution chemistry of the $\rm\lbrack Re\sb6S\sb8X\sb6\rbrack \sp{4-}$ (X = Cl, Br, I) and $\rm\lbrack Re\sb6Se\sb8I\sb6\rbrack \sp{4-}$ clusters.

Finally, a thorough examination of the solid state reaction between W(CO)$\sb6$ and iodine is undertaken in Chapter 3. Heating the reactants at 140$\sp\circ$C invokes the release of CO gas, whereupon nucleation proceeds to form triangular $\rm\lbrack W\sb3I\sb9\rbrack \sp{1-}$ clusters. Insoluble $\rm W\sb4I\sb{13},$ a molecular phase featuring tetrahedral $\rm\lbrack W\sb4I\sb{11}\rbrack \sp{1-}$units, crystallizes at 165$\sp\circ$C. Further heating to 200$\sp\circ$C produces a solid that dissolves in ethanol to afford square pyramidal $\rm\lbrack W\sb5I\sb{13}\rbrack \sp{1-}$ clusters. Nucleation terminates at 550$\sp\circ$C with the formation of one- $\rm(W\sb6I\sb{18})$ and two-dimensional $\rm (W\sb6I\sb{12}$ and $\rm W\sb6I\sb{18})$ solids built up from octahedral $\rm\lbrack W\sb6I\sb{14}\rbrack \sp{2-}$ cluster units. The temperature-dependent isolation of these clusters exposes a nucleation pathway in unprecedented structural detail.