COMPREHENSIVE TUNGSTEN-IODINE CLUSTER CHEMISTRY - ISOLATED INTERMEDIATES IN THE SOLID-STATE NUCLEATION OF [W6I14](2-)

The solid state reaction between W(CO)(6) and iodine provides a convenient entry to a realm of tungsten-iodine cluster chemistry inaccessible via direct reaction of the elements. A thorough examination of this reaction system has been undertaken, revealing unprecedented structural information on a nucleation process that culminates with the formation of the face-capped octahedral cluster [W6I14](2-). Heating the reactants at 140 degrees C invokes the release of CO gas, whereupon nucleation proceeds to form an amorphous black mixture (Phase A) containing trinuclear [W3I9](1-) clusters, whose structure consists of a metal-metal bonded W-3 triangle elaborated with six edge-bridging and three vertex-capping iodides. Insoluble W4I13, a molecular phase featuring tetrahedral [W4I11](1-) clusters dimerized through two bridging triiodide units, crystallizes when Phase A is heated at 165 degrees C. Further heating Phase A to 200 degrees C produces an amorphous solid (Phase B) that dissolves in ethanol to afford pentanuclear [W5I13](1-) clusters, with a square-pyramidal geometry closely related to that of [W6I14](2-) through formal removal of a [WI](1-) moiety. Reaction with Zn reduces [W5I13](1-) to [W5I13](2-), which then undergoes terminal ligand displacement when reacted with Ag(CF3SO3) to form [W5I8(CF3SO3)(5)](2-). Crystals of W5I16 are encountered when Phase A is heated to 250 degrees C; their structure is characterized by one-dimensional chains composed of [W5I13](1-) units linked by triiodide bridges. Heating Phase A at 300 degrees C in the presence of CsI yields a mixture of phases including CsW5CI16, containing the [W-5(C)I-13](1-) carbide cluster in which the base of square-pyramidal [W5I13](1-) is capped by a carbon atom (presumably originating from residual CO in Phase A). Cluster nucleation terminates at 550 degrees C with the formation of one- (W6I18) and two-dimensional (W6I12 and W6I16) solids built up from octahedral [W6I14](2-) cluster units, depending on the amount of iodine accompanying Phase B as a reactant. Incorporating KI in this reaction generates the dimensionally reduced product, which completely dissolves in ethanol and is precipitated as molecular (BU4N)(2)[W6I14] in good overall yield (30% based on W(CO)(6)). Treatment of the latter with Ag(CF3SO3) produces [W6I8(CF3SO3)(6)](2-), providing access to the ligand substitution chemistry of the [W6I8](4+) core. The temperature-dependent isolation of the preceding binary tungsten iodides demonstrates the following reaction sequence, based upon which a specific nucleation pathway is proposed: [W3I9](1-) --> [W4I11](1-) --> [W5I13](1-) --> [W6I14](2-).