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)] (<b>L2</b>), was synthesized with terminal acryloyl functional groups to allow incorporation into copolymer gel actuators. NMR spectroscopy was used to show that <b>L2</b> adopted a horseshoe shape with transoid–transoid pym–hyz–py linkages. Metal complexation studies were performed with <b>L2</b> and salts of Pb­(II), Zn­(II), Cu­(II), and Ag­(I) ions in CH₃CN in a variety of metal to ligand ratios. Reacting <b>L2</b> 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 <b>L2</b> did not interact with the bound metal ions in solution. Seven of the linear complexes (<b>1</b>–<b>7</b>) were crystallized and analyzed by X-ray diffraction. Most of these complexes (<b>4</b>–<b>7</b>) also showed no coordination between the acryloyl arms and the metal ions; however, complexes <b>1</b>–<b>3</b> showed some interactions. Both of the acryloyl arms were coordinated to Pb­(II) ions in [Pb₂<b>L2</b>(SO₃CF₃)₄] (<b>1</b>), one through the carbonyl oxygen donor and the other through the alkoxy oxygen donor. One of the acryloyl arms of [Cu₂<b>L2</b>(CH₃CN)₃]­(SO₃CF₃)₄ (<b>2</b>) 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 [Pb₂<b>L2</b>(ClO₄)₄]·CH₃CN (<b>3</b>). Reaction of excess AgSO₃CF₃ with <b>L2</b> was repeated in CD₃NO₂, resulting in crystals of {[Ag₇(<b>L2</b>)₂(SO₃CF₃)₆(H₂O)₂] SO₃CF₃}_∞ (<b>8</b>), 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 <b>L2</b> or the core shape of the linear complexes