Design and synthesis of new luminescent coordination networks of sql topology showing the highest degrees of interpenetration

Abstract

A new β-diketone ligand of nanometric length (HL), whose crystal structure shows a distance of 23 Å between two peripheral nitrile groups, has been employed with silver(I) to assemble 2D sql coordination networks (CNs) showing the highest degree of interpenetration (Z) reported so far of 7- and 8-fold. Reacting HL with silver triflate and nitrate allowed isolation and characterization of the new compounds [Ag(HL)₂](CF₃SO₃) (1) and [Ag(HL)₂](NO₃)·3H₂O (2) in which only nitrile groups coordinate to tetrahedral silver atoms. X-ray diffraction analyses show the presence in both compounds of similar sql networks whose large rhombic windows (Ag⋯Ag edge length of more than 26 Å) allow Z values of 7 and 8 for 1 and 2, respectively. Among the two species, the different degree of interpenetration is correlated to the conformational steric hindrance of the ligand rather than the size of the rhombic windows, and it is ultimately a consequence of the nature of the counterions. A Cambridge Structural Database (CSD) screening by ToposPro software shows that 1 and 2 are unique and, to the best of our knowledge, have the highest Z among interpenetrated sql 2D coordination networks (753 structures, for which the highest Z value is 5). The topologies of entanglement in the two structures have also been analysed and identified by their extended ring net (ERN) as the new patterns 28L1 for 1 and 32L1 for 2. We propose a correlation between Z and the diagonal length of the 4-rings by comparing 1 and 2 with 168 further structures showing the same type of interpenetration. Finally, the two CNs show interesting emissive properties at room temperature that are related to their different degrees of interpenetration.