Cobalt( ii )–pyrazine–chloride coordination polymers: synthesis, reactivity and magnetic properties

• Published in: CrystEngComm 2014-01, Vol.16 (45), p.10439-10444
• Main Authors: de Campos, Elvio Antonio, Silva, Nuno J. O., Shi, Fa-Nian, Rocha, João
• Format: Article
• Language: English
• Subjects: Angles (geometry); Bridges (structures); Chlorides; Ferromagnetism; Heating; Orbitals; Pyrazines; Unit cell
• ISSN: 1466-8033; 1466-8033
• DOI: 10.1039/C4CE01413H

The reaction of cobalt( ii ) chloride hexahydrate and pyrazine in a reduced amount of water under hydrothermal conditions affords [CoCl 2 pyz] n , which crystallises in an orthorhombic unit cell ( a = 12.0014, b = 7.1040, c = 3.5380 Å), space group Cmmm . Fourier transform infrared spectroscopy confirms the coordination of pyrazine to Co( ii ) in an octahedral geometry. This compound is thermally stable in air up to 320 °C and may also be obtained by the single-step decomposition of [CoCl 2 (pyz) 2 ] n at 190 °C, with an activation energy of 121 kJ mol −1 . [CoCl 2 pyz] n contains Co( ii ) chains bridged by two chloride ions making an angle of 92.21°, leading to orthogonal (d-p) orbitals and to one-dimensional ferromagnetic chains. In contrast, in [CoCl 2 (pyz) 2 ] n only pyrazine bridges the Co( ii ) ions, setting them apart and resulting in a purely paramagnetic system. Because the simple contact with a pyrazine vapour or aqueous pyrazine reintroduces this molecule into [CoCl 2 pyz] n , while heating [CoCl 2 (pyz) 2 ] n removes pyrazine affording [CoCl 2 pyz] n , the magnetic behaviour may be reversibly switched between the two states.