Cationic ligands for Ag(I): Organometallic polymers versus unimolecular complexes

We have prepared and characterized two cationic ligands and their Ag(I) coordination compounds. For the bidentate ligand 2, 2,2-bis-pyridin-2-ylmethyl-2,3-dihydro-1H-isoindolium bromide, we obtained the organometallic polymer [AgL]x[CF3SO3]2x (4), and the unimolecular complex [AgL2][PF6]3 (5). Compound 4 exists as an organometallic linear polymer with triflate anions either bonded to Ag(I) or non-bonded and sandwiched between the polymer chains. Complex 5 is the only unimolecular example in this series due to the non-interaction of PF6- anions with Ag(I) or with the cationic portion of the ligand. In the case of the tridentate cationic ligand 3-(3-pyridin-2-yl-2-pyridin-2-ylmethy-propyl)-benzyl-triethylammonium bromide (3), two dimeric Ag(I) complexes are formed, [Ag2L2][CF3SO3]4 (6), and [Ag2(CH3CN2)2L2][PF6]4 (7). Both of these dimers have essentially similar structures, with a closed-shell Ag(I)⋯Ag(I) interaction of approximately 3.00 Å in both cases; the pyridyl moieties of the ligands are forced into an electronically unfavourable face-to-face arrangement. The coordination spheres of the Ag(I) cations are completed by CF3SO3- in the case of 6, and by CH3CN solvent in the case of 7. In the extended packing diagrams, the arrangements of 6 and 7 are driven by intermolecular π-stacking and cation–anion interactions.

Graphical abstractThe structures of several cationic nitrogen donor ligands, and their Ag(I) complexes, are presented. The ligands are cationic derivatives of bis(2-pyridylmethyl)amine (bpma) and the Ag(I) complexes are either monomeric, a linear chain polymer (dependent on counterion) or dimeric complexes with an Ag(I)⋯Ag(I) closed-shell interaction. The latter complexes maintain the closed-shell interaction despite the unfavourable electronic interactions of the ligand pyridyl groups.Figure optionsDownload full-size imageDownload as PowerPoint slide