A low temperature reversible phase transition for 1,1 '-bis-(ferrocenyldimethylsilyl)ferrocenylene, (eta(5)-FcSiMe(2)C(5)H(4))(2)Fe, an oligomeric model for silyleneferrocenylene polymers

We have reinvestigated the solid state structure of 1,1'-bis-(ferrocenyldim ethylsilyl)ferrocenylene, (eta (5)-FcSiMe(2)C(5)H(4))(2)Fe, Fc = (eta (5)-C 5H5)Fe(eta (5)-C5H4). Using a DSC technique we observed a reversible phase transition for this compound at 169(3)K with DeltaH = 1.1 kJ/mol, and Delta S = 6.54 J/mol K. A single crystal X-ray diffraction study has demonstrated that this phase change involves a transformation from a high temperature p hase, space group P2(1)/c, Z = 2, to a triclinic low temperature phase, spa ce group (P) over bar, Z = 4. The phase transition involves the loss of the molecular crystallographic center of symmetry and rotations about the term inal and central cyclopentadienyl ring pairs. The results are compared to t hose reported for ferrocene.