Morphological Control of Aurophilic Chains of Gold(I) Dithiolate Dimers With Alkali and Alkali Earth Cations

The synthesis, characterization, X-ray structures, and luminescence of a series of coordination polymers containing Group 1 and 2 metal cations with anionic gold(I) iso-maleonitriledithiolate units ([Au₂(i-mnt)₂]²⁻; {Au₂[S₂C = C(CN)₂]₂}²⁻) are described. Crystals of M(DMF)₆[Au₂(i-mnt)₂] (M = Mg, Ca, Ba) contain 1-D aurophilic chains of [Au₂(i-mnt)₂]²⁻ units. For M = Mg and Ca, the cations are DMF-saturated while for the M = Ba analogue a more complex network structure is formed whereby the N-cyano moieties from [Au₂(i-mnt)₂]²⁻ bind to a dinuclear Ba(II) cluster with bound DMF units; the M = Sr system forms a related hydrate with similar dinuclear Sr(II) units which lie pendant to but not bridging the aurophilic chains. Crystals of the related Group 1-based materials, of the form M₂(DMF)n[Au₂(i-mnt)₂] (M = Li, n = 6; K, n = 4; Cs, n = 3), also contain 1-D aurophilic chains, from which the N-cyano moieties of the i-mnt bind to the Group 1 metal centers; the lithium cations cap the N-cyano moieties, while potassium and cesium cations bridge the chains via more complex dinuclear [K₂(DMF)₄]²⁺ and [Cs₄(DMF)₆]⁴⁺ clusters respectively. The emission maxima, ranging from 570 - 670 nm are influenced by the intra- and intermolecular Au─Au distances as well as a combination of the Au─Au─Au angles and intra-ring torsion in the [Au₂(i-mnt)₂]²⁻ units. The structural data illustrates a preference for N-cyano and cluster formation in the Group 1 and larger Group 2 metal centers and indicates a clear interplay between the obtained structural morphology and the size and charge of the cation.