Effect of anion on Ag(i) meso-helical chains formed with 4,4′-dipyridyl ketone: solvent versus anion bridging and anion effects on the strength of ligand binding

Abstract

The synthesis and characterisation by IR spectroscopy and elemental analysis of ten new Ag(I)–L complexes are described. Of these complexes, nine are characterised by single crystal X-ray diffraction: {[Ag(L)](CF₃SO₃)·1/2H₂O}_∞ (1), {[Ag(L)](ClO₄)·1/2H₂O}_∞ (2), {[Ag₂(L)₂(CH₃CN)](ClO₄)₂·2CH₃CN·H₂O}_∞ (3), {[Ag₂(L)₂(CH₃CN)₂](ClO₄)₂·CH₃CN}_∞ (4), {[Ag₂(L)₂(CH₃CN)₂](PF₆)₂·2CH₃CN}_∞ (5), {[Ag(L)₂](CF₃SO₃)·1/2H₂O}_∞ (6), {[Ag(L)₂](BF₄)}_∞ (7), {[Ag(L)₂](PF₆)}_∞ (8) and {[Ag(L)₂](PF₆)·2CH₃CN}_∞ (9). The primary structures of 1–6 were meso-helical one-dimensional (1D) polymers, while 7 was a helical 1D polymer and 8 and 9 were (4,4) networks. Complexes 1–5 possessed 1 : 1 metal-to-ligand (M : L) ratios, while complexes 6–9 possessed 1 : 2 M : L ratios. The meso-helical chains of complexes 1 and 2 were di-μ-bridged at the Ag(I) nodes by the counteranions CF₃SO₃⁻ and ClO₄⁻, respectively, while the meso-helical chains of complexes 3–5 were di-μ-bridged at the Ag(I) nodes by the CH₃CN molecules. The effect of counteranions and solvent molecules on delicate anion–Ag, π–π-stacking and argentophilic interactions was studied through complexes 1–5. The 1D chains of complexes 6 and 7 possessed monodentate L ligand side arms. The uncoordinated N-donors of these side arms were inclined towards the Ag(I) centre of the adjacent chains and demonstrated narrower Ag–N_py–Cg_(pyridyl) angles. In the case of complexes 8 and 9, wider Ag–N_py–Cg_(pyridyl) angles and stronger N⋯Ag interactions resulted in (4,4) nets. The effects of the size and the nature of the counteranions on the topology were studied through complexes 6–9.