Synthetic crystallography: synthon mimicry and tecton elaboration in metallate anion salts

The use of molecular tectons (building blocks) able to form cyano-based hydrogen bonded synthons (NH⋯NC) to synthesise a diverse range of crystal structures is described. Square planar dianionic metal complexes with 4 terminal cyano groups are shown to form salts with the dications [4,4′-H2bipy]2+ and [4,4′-H2bipip]2+ in which hydrogen bond networks of varying dimensionality are formed. The structures of new salts of these cations with [M(CN)4]2−, [M(SCN)4]2−, and [M(mnt)2]2− (M = Pt, and in one case Pd) are reported and compared with those of analogous [MCl4]2− and [M(dtox)2]2− salts. The consequences of the stereochemical preference of the cyano group for linear CN⋯H hydrogen bonding and the prospects for the elaboration of cyano-functionalised tectons to afford chemical and structural diversity in the structures synthesised are discussed.