Rational Design of Supramolecular Gridlike Layers and Zigzag Chains through a Unique Interplay of d¹⁰−d¹⁰ and π−π Stacking Interactions

Six new Cu(II)−M(I) complexes (M = Ag, Au) were synthesized to illustrate the role of the convolution of d10−d10 (aurophilic or argentophilic) and π−π stacking interactions in sustaining supramolecular solid-state architectures. Two types of supramolecular synthons are involved: a rectangular one, based on the aurophilic (argentophilic) interactions between the [M(CN)2]- spacers, and a linear one, relying upon π−π contacts between the aromatic ligands. The reactions between [Cu(acac)(BB)(H2O)](ClO4) complexes and K[M(CN)2] in a 2:1 molar ratio (BB = 2,2‘-bipyridine; 1,10-phenanthroline) lead to the following heterotrinuclear complexes: [{Cu(acac)(bipy)}2{Au(CN)2}](ClO4)·0.5CH3CN (1), [{Cu(acac)(bipy)}2{Ag(CN)2}](ClO4)·0.5CH3CN (2), [{Cu(acac)(phen)}2{Ag(CN)2}](ClO4) (3), and [{Cu(acac)(phen)}2{Au(CN)2}](ClO4) (4). The recrystallization of 4 from acetonitrile affords [{Cu(acac)(phen)}2{Au(CN)2}](ClO4)·0.5CH3CN (5), which is isomorphous with the compounds 1−3. By reacting [Cu(sal)(bipy)]ClO4 with K[Ag(CN)2] in a 1:1 molar ratio, a heterobinuclear complex, [{Cu(sal)(bipy)}{Ag(CN)2}] (6), is obtained (sal- is the anion of the salicylaldehyde). The copper(II) ions in compounds 1−6 exhibit a square-pyramidal geometry, with the apical position occupied by the nitrogen atom from the cyano bridge. As expected, the crystallographic investigation of compounds 1−3 and 5 reveals the formation of supramolecular grids resulting from the combination of the two supramolecular synthons. The M···M distances in these compounds are 1: 3.295(11) (Au···Au); 2: 3.2144(7) (Ag···Ag), 3: 3.2789(10) (Ag···Ag); 5: 3.389(7) (Au···Au) Å, while the distances associated with the π−π stackings vary between 3.3 and 3.6 Å. The crystal structure of 4 differs from that found in the other trinuclear complexes. It consists of supramolecular chains resulting from the aromatic interaction between the organic ligands attached to the copper ions, without the intervention of the d10−d10 interactions. The analysis of the packing diagram for compound 6 reveals supramolecular zigzag chains, resulting from the convolution of Ag···Ag [2.9708(5) Å] and π−π aromatic (3.27−3.55 Å) interactions.