Compounds with the Electron-Rich [W6Cl18]2− Cluster Anion

Abstract

Cluster compounds of the general formula A2[W6Cl18] containing singly charged A cations (A = K, Rb, Ag, Tl, NH4, N(C2H5)4, N(n-C3N7)4, N(n-C4H9)4) and [W6Cl18]2− anions have been synthesized. Compounds were obtained by W6Cl18 reduction using methanol and the corresponding metal or (alkyl-)ammonium salts. The use of CoCp2 as reducing agent in inert solvents such as tetrahydrofurane also leads to the ionic compound (Co(C5H5)2)2[W6Cl18]. All compounds described here evidence the existence of octahedral clusters of the M6X12 type with 20 cluster electrons occupying metal centered states, thus exceeding the conventional number of 16 electrons for this cluster type. Electrospray ionization (ESI) mass spectra were recorded for the neutral compound W6Cl18 and for the ionic salts K2[W6Cl18], Cs2[W6Cl18], and (Co(C5H5)2)2[W6Cl18], showing that the cluster W6Cl18 unit in these compounds is preserved in solution. The base peak in the ESI spectra for all compounds corresponds to the [W6Cl18]2− anion, so that neutral W6Cl18 is prone to undergo a two electron reduction process. This result is confirmed by cyclic voltametry experiments, which makes of W6Cl18 a very clean mild oxidizing agent. The preparation of the complete series of ionic A2[W6Cl18] (A = K, Cs, CoCp2) clusters allows to systematically investigate their structural trends as function of the distinctive cations, which is the main focus of the present work.