Luminescence of tartrate bridged dinuclear 2,2'-bipyridine platinum(ii) complexes: emission color controlled by intra- and inter-molecular interactions in the solid state.

Novel dinuclear Pt complexes with a chiral (l-) and an achiral (meso-) tartrate [{Pt(bpy)}(μ-x-tart)] (bpy: 2,2'-bipyridine; tartH: tartrate; x = l (1), meso (2)) and with a racemic (dl-) tartrate [{Pt(bpy)}(μ-d-tart)][{Pt(bpy)}(μ-l-tart)] (3) were synthesized, and the influence of their stereochemistry on their molecular and crystal structures affecting their luminescence was discussed. Effects of the dinuclearity on the structures and luminescence were revealed by comparison with those of a novel racemic mononuclear complex [Pt(bpy)(d-tartH)][Pt(bpy)(l-tartH)] (4). The X-ray crystallography showed the crystallization of 1 in two polymorphs, namely monoclinic 3[1·6HO] (1α) and triclinic 2[1·6HO] (1β), and those of other complexes in monoclinic hydrate crystals 2·12.5HO, 3·4HO, and 4·HO. The chiral complexes in 1α, 1β, and 3·4HO showed clamshell-like structures with Pt-Pt and π-π interactions, while the achiral complex in 2·12.5HO displayed a twisted form without intramolecular interactions. The complexes in 1α were assembled in a right-handed helical arrangement through significant Pt-Pt interactions, and those in 1β and 3·4HO were stacked in one-dimensional columns through significant and slight π-π interactions, respectively. The complex in 2·12.5HO constructed an intermolecular dimer through Pt-Pt interactions with its adjacent complex. The crystal structure of 4·HO displayed a three-dimensional network architecture through π-π interactions and hydrogen bonding. These crystals exhibited luminescence depending on their molecular and crystal structures (λ nm = 535 (4·HO), 569 (3·4HO), 621 (2·12.5HO), 649 (1β), and 656 (1α)). The formations of intermolecular dimers and clamshell-like structures through Pt-Pt interactions in 2·12.5HO and in 3·4HO, respectively, lead to red-shifts in emissions compared to 4·HO, and further low-energy emissions of 1α and 1β were derived from the intermolecular Pt-Pt and π-π interactions, respectively.