Reductive trapping of [(OC₅W-W(CO)₅]²⁻ in a mixed-valent Smᴵᴵ/ᴵᴵᴵ calix[4]pyrrolide sandwich

Reduction of tungsten hexacarbonyl by the divalent samarium(II) complex [Sm-2(N4Et8)(thf)(4)] ((N4Et8)(4-) = meso-octaethylcalix[4]pyrrolide) in toluene at ambient temperature gave the remarkable heteronuclear mixed-valent samarium(II/III)/ tungsten complex [{(thf)(2)Sm-II(N4Et8)Sm-III(thf)}(2){(mu-OC)(2)W-2(CO)(8)}], which features the trapping of a rare [W-2-(CO)(10)](2-) anion with an unsupported W-W bond