Influence of the counter ions and ligands on structures of silver(I) helicates with di-Schiff bases containing imidazole groups

Abstract

Five complexes, [Ag₆(bmimen)₅(MeCN)][CF₃SO₃]₆·H₂O 1, [Ag₇(bmimen)₆][ClO₄]₇·MeCN 2, [Ag₂(bmimen)₂][NO₃]₂· 0.5H₂O 3, [Ag₃(bmimpn)₂][CF₃SO₃]₃4 and [Ag₃(bmimpn)₂]_n[NO₃]_3n5, were obtained by self-assembly of AgX (X = CF₃SO₃⁻, ClO₄⁻ or NO₃⁻) with bmimen and bmimpn (bmimen = 1,2-bis[(1-methyl-2-imidazolyl)methyleneamino]ethane, bmimpn = 1,3-bis[(1-methyl-2-imidazolyl)methyleneamino]propane). X-Ray single-crystal diffraction shows that bmimen functions in three co-ordination fashions to bridge silver(I) atoms into hexa-, hepta-, and di-nuclear helicates in 1, 2, and 3, respectively. The bmimen ligand can serve in a usual bis(bidentate) fashion with each imidazole-imine bidentate entity chelating a Ag atom, thus bridging a pair of adjacent Ag atoms in 1, 2 and 3; it can also act in an unusual tridentate mode with a bidentate entity bridging a pair of adjacent Ag atoms and the imidazole group in another bidentate entity ligating the third Ag atom in 1, whereas it can also function in another unusual tetradentate mode with a bidentate entity chelating a Ag atom and another bidentate entity bridging another two Ag atoms in 2. On the other hand, bmimpn acts in two unusual tetradentate fashions to bridge Ag atoms into trinuclear and polymeric helicates in 4 and 5, respectively. The bmimpn ligand can ligate two Ag atoms, where the di-imine group chelates a Ag atom and two imidazole groups simultaneously bind another Ag atom; it can also ligate three Ag atoms in 5, in which the two imidazole groups simultaneously bind a Ag atom while each of the two imine groups ligates a Ag atom. The adjacent Ag⋯Ag separations in the cationic chains of 1, 2, 4 and 5 are ca. 3.0 Å, indicating weak metal–metal interaction, while those in the double helicates of 3 are larger (ca. 3.34 Å). The ¹H NMR spectra of 1, 2 and 3 in solution are virtually identical, as are those of 4 and 5.