Knotted Network Consisting of 3-Threads and a Zwitterionic One-Dimensional Polymorphs of <i>trans</i>-3-(3-Pyridyl)acrylate of Cobalt and Nickel, M<sup>II</sup>(C<sub>8</sub>H<sub>6</sub>NO<sub>2</sub>)<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>
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We present the hydrothermal synthesis, characterization (IR, DT-TGA), single-crystal structures, and magnetic properties of two polymorphs of trans-3(3-pyridyl)acrylate of cobalt(II) and of nickel(II), MII(C8H6NO2)2(H2O)2. Hydrothermal reaction at 120 or 170 °C results exclusively in the different polymorphs. The infrared spectra and thermogravimetric analyses of the complexes are almost similar for the two polymorphs but show a difference between cobalt and nickel in energies of the vibrational modes and in the decomposition temperatures. The crystal structures of the two polymorphs are quite different; one crystallizes in a monoclinic space group and the other in a triclinic. This major difference is due to the different stereochemistry, cis or trans, of the coordination at the metal sites. When it is trans-MN2O4, it results in the monoclinic cell consisting of a 3D-network of metals bridged by the ligands through single bonds (M−N and M−O). There is threading of three sublattices up to 2a × 4b × 2c, at which point the three sublattices are knotted into one infinite framework. When it is cis-MN2O4, it results in the triclinic cell and consists of Zwitterionic linear chains of metals bridged by one single ligand via the pyridine and a bidentate carboxylate group and the other ligand is bonded only via the pyridine while its carboxylate end is free. All four compounds are paramagnetic with Weiss constants suggesting weak interactions.
