Cation and anion diversity in [M(dithiooxalate)2]2- salts: structure robustness in crystal synthesis.

A series of crystalline salts based on the [M(dto)2]2− (dto = 1,2-dithiooxalate, M = Ni, Pt, Cu) dianion with hydrogen-bond donor cations have been synthesised following a molecular tectonics approach. The chelating M(dto)⋯HN supramolecular synthon has been exploited in a systematic study of its robustness. The effects of competition between hydrogen-bond acceptors, of the shape and functionality of the cations and of varying the metal in the anion are discussed. The preparation and structural characterisation of the new crystalline phases [4,4′-H2bipy][Pt(dto)2] (2), [HNC5H4CO2H-4]2[Pt(dto)2] (5), [HNC5H4CO2H-3]2[Pt(dto)2] (6), [HNC5H4CH2CO2H-4]2[Ni(dto)2] (7), [HNC5H4CH2CO2H-3]2[Ni(dto)2] (8), [HNC5H4CONH2-4]2[Ni(dto)2] (9), [HNC5H4CHNOH-4]2[Ni(dto)2] (10), [HNC5H4CHNOH-3]2[Ni(dto)2] (11), [4,4′-H2bipip][Ni(dto)2] (12), [H2NC5H9CO2H-4]2[Pt(dto)2] (14), [H2NC5H9CO2H-4]2[Cu(dto)2] (15), [H2NC5H9CO2H-3]2[Ni(dto)2][H2O]2 (16), [H2NC5H9CO2H-3]2[Pt(dto)2][H2O]2 (17), [H2NC5H9CO2H-3]2[Cu(dto)2][H2O]2 (18), [H(Me)NC5H9CO2H-4]2[Ni(dto)2][H2O]2 (20) is reported. The charge-assisted NH⋯dto synthon is formed in each of compounds 1–20, and is apparently much more robust than the conventional synthons used (such as the carboxylic acid dimer), which have a much lower rate of occurrence. The NH⋯dto synthon may be generalised to 3- and 4-pyridinium species and 3- and 4-piperidinium derivatives. In the latter cases branching of the hydrogen-bond networks through the NH2 groups arises. The robustness of the NH⋯dto synthon allows structures of the form [NH cation]2[M(dto)2] to be regarded as being formed by the packing of neutral supermolecules. Cases of isomorphism (as in 16–18) and latent polymorphism (e.g. in 4 and 6) are noted.