Tetratopic pyrimidine–hydrazone ligands modified with terminal hydroxymethyl and acryloyl arms and their Pb(ii), Zn(ii), Cu(ii) and Ag(i) complexes

Abstract

The first tetratopic pyrimidine–hydrazone (pym–hyz) molecular strands containing terminal hydroxymethyl (L1) and acryloyl (L2) functional groups have been synthesised. L1 was produced by step-wise imine condensation reactions, starting with 6-hydroxymethyl-2-pyridinecarboxaldehyde. L2 was then synthesised through the treatment of L1 with acryloyl chloride. NMR spectroscopy and X-ray crystallography showed that the ligands adopted a helical shape, comprised of 1 and 1/3 helical turns. Both L1 and L2 uncoiled upon reaction with an excess amount of Pb(II), Zn(II) and Cu(II) ions, resulting in linear M₄LA₈ complexes (where M = Pb(II), Zn(II), or Cu(II); L = L1 or L2; and A = ClO₄⁻, SO₃CF₃⁻ or BF₄⁻). Horse-shoe shaped Pb₂LA₄ complexes were also formed by reacting Pb(II) ions with either L1 or L2 in a 2 : 1 metal to ligand ratio. The addition of Ag(I) ions to either L1 or L2 resulted in Ag₂L₂A₂ double helicates, which were stable in the presence of excess Ag(I). The Pb(II), Zn(II) and Ag(I) complexes were characterised by NMR spectroscopy, while UV-Vis spectroscopy was used to probe the Cu(II) complexes. In addition, X-ray crystallography was used to analyse the linear Pb₄L1A₈, horse-shoe shaped Pb₂L1(ClO₄)₄, twisted Cu₃L2(SO₃CF₃)₆, and double helicate Ag₂L1₂(SO₃CF₃)₂ complexes yielding the structures [Pb₄L1(ClO₄)₇(H₂O)]ClO₄·4CH₃NO₂ (1), [Pb₄L1(SO₃CF₃)₈]₂·6CH₃CN·H₂O (2), [Pb₂L1(ClO₄)₂(CH₃CN)(H₂O)](ClO₄)₂·2CH₃CN·C₄H₁₀O·H₂O (3), [Cu₃L2(SO₃CF₃)₃(CH₃CN)₂(H₂O)](SO₃CF₃)₃·2CH₃CN·H₂O (4) and [Ag₂L1₂](SO₃CF₃)₂·CH₃CN·H₂O (5), respectively.