Reaction of M(C ₅ Me ₅ ) ₂ (OEt ₂ ), M = Eu or Yb, with phenylacetylene; formation of mixed-valence Yb ₃ (C ₅ Me ₅ ) ₄ (µ-CCPh) ₄ and Eu ₂ (C ₅ Me ₅ ) ₂ (µ-CCPh) ₂ (tetrahydrofuran) ₄

Reaction of yb (C5Me5)2(OEt2) with PhCCH yields the mixed-valence complex Yb3(C5Me5)4(µ-CCPh)4 though Eu(C5Me5)2(OEt2) reacts with PhCCH to give the divalent complex Eu2(C5Me5)2(µ-CCPh)2(thf)4(thf = tetrahydrofuran)after crystallization from thf.