Influence of Terminal Acryloyl Arms on the Coordination Chemistry of a Ditopic Pyrimidine–Hydrazone Ligand: Comparison of Pb(II), Zn(II), Cu(II), and Ag(I) Complexes

A new ditopic pyrimidine–hydrazone ligand, 6-hydroxymethylacryloyl-2-pyridinecarboxaldehyde, 2,2′-[2,2′-(2-methyl-4,6-pyrimidinediyl)­bis­(1-methylhydrazone)] (L2), was synthesized with terminal acryloyl functional groups to allow incorporation into copolymer gel actuators. NMR spectroscopy was used to show that L2 adopted a horseshoe shape with transoid–transoid pym–hyz–py linkages. Metal complexation studies were performed with L2 and salts of Pb­(II), Zn­(II), Cu­(II), and Ag­(I) ions in CH₃CN in a variety of metal to ligand ratios. Reacting L2 with an excess amount of any of the metal ions resulted in linear complexes where the pym–hyz–py linkages were rotated to a cisoid–cisoid conformation. NMR spectroscopy showed that the acryloyl arms of L2 did not interact with the bound metal ions in solution. Seven of the linear complexes (1–7) were crystallized and analyzed by X-ray diffraction. Most of these complexes (4–7) also showed no coordination between the acryloyl arms and the metal ions; however, complexes 1–3 showed some interactions. Both of the acryloyl arms were coordinated to Pb­(II) ions in [Pb₂L2(SO₃CF₃)₄] (1), one through the carbonyl oxygen donor and the other through the alkoxy oxygen donor. One of the acryloyl arms of [Cu₂L2(CH₃CN)₃]­(SO₃CF₃)₄ (2) was coordinated to one of the Cu­(II) ions through the carbonyl oxygen donor. There appeared to be a weak association between the alkoxy donors of the acryloyl arms and the Pb­(II) ions of [Pb₂L2(ClO₄)₄]·CH₃CN (3). Reaction of excess AgSO₃CF₃ with L2 was repeated in CD₃NO₂, resulting in crystals of {[Ag₇(L2)₂(SO₃CF₃)₆(H₂O)₂] SO₃CF₃}_∞ (8), the polymeric structure of which resulted from coordination between the carbonyl donors of the acryloyl arms and the Ag­(I) ions. In all cases the coordination and steric effects of the acryloyl arms did not inhibit isomerization of the pym–hyz bonds of L2 or the core shape of the linear complexes.