Formation and crystal structures of a monomer–dimer pair of mono(cyclopentadienyl)calcium complexes, [C5(t-Bu)3H2]2CaI(THF)2 and {[C5(t-Bu)3H2]2CaI(THF)}2

The mono(cyclopentadienyl)calcium iodide complex [{(Cp3T)CaI(THF)x}n] (Cp3T=[C5(t-Bu)3H2]−) is generated from the 1:1 reaction of K[Cp3T] and CaI2 in THF. No redistribution into [(Cp3T)2Ca] and CaI2(THF)n is observed in THF solution. The mono(ring) compound crystallizes from THF as a monomer with a distorted piano stool geometry; the coordination environment around the calcium consists of a pentahapto [Cp3T]− ligand, an iodide, and two THF molecules. It is the first structurally authenticated monomeric mono(ring) halide complex of a heavy alkaline-earth metal. From a toluene–THF mixture, the mono(ring) complex crystallizes as an iodide-bridged dimer, with a pentahapto [Cp3T]− ligand and one terminal THF on each metal atom. The CaI and CaI′ distances are nearly equal at 3.087(2) and 3.101(2) Å.