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 [{(Cp-3T)CaI(THF)(x)}(n)] (Cp-3T = [C-5(t-Bu)(3)H-2](-)) is generated from the 1:1 reaction of K[Cp-3T] and CaI2 in THF. No redistribution into [(Cp-3T)(2)Ca] 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 [Cp-3T](-) 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 [Cp-3T](-) 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) Angstrom. (C) 2001 Elsevier Science B.V. All rights reserved.