Molecular tectonics and supramolecular chirality: rational design of hybrid 1-D and 2-D H-bonded molecular networks based on bis-amidinium dication and metal cyanide anions

Abstract

Using the bis-amidinium dication 1 bearing four acidic protons disposed in a divergent fashion and capable of chelating, through H-bonds, metal cyanide anions, neutral 1- and 2-D hybrid networks were generated. Whereas in the presence of M(CN)₄²⁻ (M = Ni(II), Pd(II) and Pt(II)), 1-D H-bonded networks are formed through a double dihapto mode of H-bonding between the dication and the dianion, in the case of M(CN)₆⁴⁻ (M = Fe(II) and Ru(II)), 2-D networks based on the interconnection by the dication 1 of 1-D networks analogous to those formed in the case of [M(CN)₄]²⁻ mentioned above are obtained. Interestingly, in the case of [M(CN)₆]³⁻ (M = Cr(III)), again a 2-D H-bonded network is formed through the formation of three dihapto modes of H-bonding between the dication and the trianion. Due to this dihapto or chelate mode of H-bonding, a supramolecular chirality of the Δ′ and Λ′ type is generated within the second coordination sphere of the metallic centres. The packing of the achiral 2-D networks thus obtained leads to channels which are occupied by water molecules forming polymeric H-bonded chains.