Structural characterization of two solid state forms of the complex bis(1,1'-bis(diphenylphosphino)ferrocene) rhodium(I) tetraphenylborate.

This paper describes a work aimed at determining the molecular structure of a rhodium(I) complex along an experimental track in which a conventional X-ray single crystal structural analysis was accidentally preceded by a powder X-ray diffractometric investigation. The complex [Rh(dppf)(2)]BPh(4) (dppf=1,1'-bis(diphenylphosphino)ferrocene) was obtained from dichloroethane in two crystalline forms, hereafter referred to as alpha and beta, which are different in colour and in the content of lattice-entrapped solvent. Conventional and synchrotron powder wide angle X-ray diffractometry (WAXS), FT-IR, P-31 and H-1 NMR spectroscopy demonstrate that alpha and beta are dimorphic forms of the same molecular entity. The observed WAXS spectrum of the alpha form was computationally fitted (R=11.3%) with that calculated for [Rh(dppf)(2)]BPh(4), upon assuming that the molecular geometry of the title complex was identical to that of the already determined iridium analogue, i.e. square-planar with a pronounced tetrahedral distortion. X-ray single crystal structural analysis confirmed this conclusion. FT-IR, DSC and TG analyses have also been employed for a solid state characterization of the two species.