Solvent Direction of Molecular Architectures in Group 1 Metal Pentacyanocyclopentadienides



A series of group 1 metal salts of the pentacyanocyclopentadienide anion [Cp(CN)5] (1) have been crystallised from two distinct solvent systems and the structures of the resulting species investigated by single-crystal X-ray diffraction. The structural results show that the bonding mode of 1 and the architecture of the resulting lattice is subtly influenced by the alkali metal and the presence of coordination or lattice solvation. The crystallisation of Na[1] from propan-2-ol/n-pentane produces an open clathrate-type structure of hexagonal type HS-I composed of fullerene-like units in which 1 behaves as a planar five-fold symmetric node with solvent-filled lattice voids. In contrast, crystallisation of the sodium, potassium, rubidium and caesium salts from the same solvent system results in highly condensed, unsolvated phases in which 1 adopts a variety of non-planar coordination modes involving four or five of the CN groups. When crystallised from nitromethane/diethyl ether, the potassium, rubidium and caesium complexes form solvated arrangements with coordinated MeNO2 that contain helical subunits.