Metallophilicity versus π–π Interactions: Ligand‐Unsupported Argentophilicity/Cuprophilicity in Oligomers‐of‐Dimers [M 2 L 2 ] n (M=Cu I or Ag I , L=tridentate ligand)

To verify whether attractive metallophilic interactions exist in the dimer‐of‐dimers [Cu 2 (ophen) 2 ] 2 (Hophen=1 H ‐[1,10]phenanthrolin‐2‐one) ( 1 ), we designed and synthesized a series of such [M 2 L 2 ] 2 structures by varying the d 10 metal and/or the ligand (M=Cu I or Ag I , L=ophen or obpy; Hobpy=1 H ‐[2,2′]bipyridinyl‐6‐one), and have successfully obtained three dimers‐of‐dimers: [Ag 2 (ophen) 2 ] 2 ⋅6 H 2 O ( 2 ), [Cu 2 (obpy) 2 ] 2 ( 3 ), and [Ag 2 (obpy) 2 ] 2 ⋅4.5 H 2 O⋅0.5 DMF ( 4 ). X‐ray analyses of these structures show that interdimer MM separations in [Ag 2 (ophen) 2 ] 2 (3.199 Å) are remarkably shorter than those in [Cu 2 (ophen) 2 ] 2 (3.595 Å). Shorter interdimer MM separations are found in the structures of [M 2 (obpy) 2 ] 2 (2.986 and 2.993 Å in [Cu 2 (obpy) 2 ] 2 , 3.037 to 3.093 Å in [Ag 2 (obpy) 2 ] 2 ), in which the π systems are smaller than in the complexes with the ophen ligand. Detailed structural comparison of these dimers‐of‐dimers indicates that the interdimer, face‐to‐face π–π interactions repulse rather than support the interdimer metal–metal attractive interactions. This study also yields qualitative comparison of the strengths between argentophilic, cuprophilic, and face‐to‐face π–π interactions. DFT calculations on the four dimers‐of‐dimers further support the above deduction. The structure of a trimer‐of‐dimers [Ag 2 (obpy) 2 ] 3 (AgAg 3.171 to 3.274 Å) is further evidence that the oligomerization of the [M 2 L 2 ] molecules is favored by stronger metallophilic and weaker face‐to‐face π–π interactions.