Intermolecular hydrogen-bonding in the solid-state structure of CpFe(CN)2(PTAH): Structural and spectral comparisons with its [K][CpFe(CN)2PTA] salt

The salt K[CpFe(CN)2PTA] (1) has been synthesized from the photolysis of K[CpFe(CN)2CO] and 1,3,5-triaza-7-phosphaadamantane (PTA) in methanol. Protonation of the salt by hydrogen ion exchange employing DOWEX 50 WX8-100 ion exchange resin yielded the complex CpFe(CN)2PTAH (2). The solid-state structures of both compounds have been determined by X-ray crystallography. Protonation was shown via ν(CN) and 31P-NMR to occur at one of the PTA nitrogens. Furthermore, it was found in the solid-state of the protonated structure that intermolecular hydrogen-bonding occurs between the cyanide nitrogen of one molecule and the PTA nitrogen of another molecule. The average FeCCN distance for 1 is 1.877(11) Å. FeCCN distances for complex 2 differ significantly at 1.839(12) and 1.940(12) Å, with the shorter bond length associated with the hydrogen-bonded CN group. Spectral (ν(CN) and 31P-NMR) characterization of the complexes and their potential use as precursors to double metal cyanide derivatives are reported.