Gold−Gold Interactions as Crystal Engineering Design Elements in Heterobimetallic Coordination Polymers

A series of coordination polymers containing Cu(II) and [Au(CN)2]- units has been prepared. Most of their structures incorporate attractive gold−gold interactions, thus illustrating that such “aurophilic” interactions can be powerful tools for increasing structural dimensionality in supramolecular systems. [Cu(tren)Au(CN)2][Au(CN)2] (1, tren = tris(2-ethylamino)amine) forms a cation/anion pair, which is weakly linked by hydrogen bonds but not by aurophilic interactions. [Cu(en)2Au(CN)2][Au(CN)2] (2-Au, en = ethylenediamine) is a 2-D system composed of a chain of [Au(CN)2]- anions and another chain of [(en)2Cu−NCAuCN]+ cations; short Au−Au bonds of 3.1405(2) Å connect the anions. This bond is shorter than that observed in the analogous silver(I) structure, 2-Ag. The average M−C bond lengths of 1.984(8) Å in 2-Au are significantly shorter than those found in 2-Ag, suggesting that Au(I) is smaller than Ag(I). Cu(dien)[Au(CN)2]2 (3, dien = diethylenetriamine) forms a 1-D chain of tetranuclear [Au(CN)2]- units that are bound to [Cu(dien)] centers. Aurophilic interactions of ca. 3.35 Å hold the tetramer together. Cu(tmeda)[Au(CN)2]2 (4, tmeda = N,N,N‘,N‘-tetramethylethylenediamine) forms a 3-D network by virtue of aurophilic interactions of 3.3450(10) and 3.5378(8) Å. Altering the Cu:Au stoichiometry yields Cu(tmeda)[Au(CN)2]1.5(ClO4)0.5 (5), which has an unusual 2-D rhombohedral layer structure (space group R32). Complex 5 is composed of three mutually interpenetrating Cu[Au(CN)2]1.5 networks which are interconnected by aurophilic interactions of 3.4018(7) and 3.5949(8) Å. Weak antiferromagnetic coupling is observed in 2 and 5.