Formation of Disilver(I) Metallacycle and One-Dimensional Polymeric Chain from the Same Mononuclear Building Block: Assembly Mechanism upon Crystallization

Reaction of a flexible bis-bidentate ligand 1,4-bis(8-thioquinolyl)butane (C4TQ) with silver(I) salts afforded five complexes, namely, [Ag2(C4TQ)2](CF3SO3)2 (1), {[Ag(C4TQ)](CF3SO3)}n·0.5nCH3CN (2), [Ag2(C4TQ)2](ClO4)2 (3), {[Ag(C4TQ)](ClO4)}n (4), and {[Ag(C4TQ)(CH3CN)](ClO4)}n (5), of which 1 and 3 show dimeric M2L2 metallacycles while 2 and 4 show polymeric MnLn chains. The acetonitrile (MeCN) molecule in complex 2 is located in the crystal lattice without coordination to the Ag(I) ion. Therefore, two pairs of isomerized structures that retain the same compositions, [Ag2(C4TQ)2](CF3SO3)2 vs {[Ag(C4TQ)](CF3SO3)}n in complexes 1 and 2, as well as [Ag2(C4TQ)2](ClO4)2 vs {[Ag(C4TQ)](ClO4)}n in complexes 3 and 4, respectively, can be identified and regarded as ring-opening isomers. 1H NMR and electrospray ionization mass spectrometry studies in solution suggested that the cyclic and infinite structures were assembled from the same monomeric ML building blocks, which crystallized in different forms by dimerization or polymerization during the crystallization. The complex 5 also formed an infinite chain, but the MeCN molecule participated in coordination, indicating that the solvent and/or anion molecules may play a significant role in the assembly process. X-ray diffraction measurements and density functional theory calculations have been performed to track the structural conversion and elucidate the assembly mechanism.