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) 22-; Au2S2C = C (CN) 222-) are described. Crystals of M (DMF) 6Au2 (i-mnt) 2 (M = Mg, Ca, Ba) contain 1-D aurophilic chains of Au2 (i-mnt) 22- 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) 22- 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) nAu2 (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) 42+ and Cs4 (DMF) 64+ 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) 22- 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.
Pells et al. (Sat,) studied this question.