Synthesis and Characterization of the Nitrogen-Centered Trigonal Prismatic Clusters [W6NCl18]n[minus] (n[equals]1-3)This research was funded by DOE Grant No. DE-FG03-01ER15257.

The extraordinarily rich chemistry of octahedral transition metal halide and chalcohalide clusters has begun to see use in a variety of applications, ranging from catalysis to chemical sensing. In facilitating the design of such cluster-based materials, new synthetic methods for adjusting the core electronic character by atom substitution and for exchanging the six outer terminal ligands are of considerable value. However, the prospect of utilizing a wholly different type of cluster unit arose very recently with the discovery of the molecular species [W6CCl18] n (n= 0–3). Instead of an octahedron, these clusters feature a carbon-centered W6 trigonal prism surrounded by twelve edge-bridging chloride anions and six radially extended terminal chloride ligands. Such units are also known to exist within the one-dimensional compounds A3Nb6SBr17 (A=K, Rb, Cs, and Tl), [4] suggesting that this trigonal-prism structure type may be quite pervasive. Noting that the electronic character of the centered, edgebridged octahedral clusters [Zr6ZCl18] n is highly dependent upon the interstitial atom Z, we attempted to replace the carbon atom in [W6CCl18] 2 with other atoms. Herein, we report the introduction of an interstitial nitrogen atom, which permits ready access to more electron-rich trigonal prismatic clusters. Synthesis of the molecular salt Na[W6NCl18] (1) parallels the low-temperature solid-state process employed for producing the original carbon-centered cluster phase, although with NaN3 used in place of CCl4. Elemental bismuth is known to be highly effective as a reducing agent in the formation of clusters such as [W6Cl14] 2 and [W6O12Cl12] 2 , and is thought to act here according to reaction (1). A stoichiometric