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

Abstract

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.