A novel paramagnetic coordination polymer, fabricated from Co(NCS)2 and 2-pyridinecarbaldehyde isonicotinoylhydrazone

Abstract

We report on a mixed cobalt(II)/cobalt(III) heteroleptic coordination polymer of the salt-like structure {[(CoIIIL2)2CoII(NCS)2][CoII(NCS)4]}n∙a(solvent) (1∙a(solvent)), obtained by a reaction of Co(NCS)2 with 2-pyridinecarbaldehyde isonicotinoylhydrazone (HL). Complex 1∙a(solvent) contains 15.52% of solvent molecules, which fits to six molecules of EtOH per one [(CoIIIL2)2CoII(NCS)2][CoII(NCS)4] species, and the structure of the crystals can be assigned to the {[(CoIIIL2)2CoII(NCS)2][CoII(NCS)4]}n∙6EtOH composition. 1∙a(solvent) was found to be stable after drying at 80 °C for several days, yielding a solvent-free complex 1. The FTIR data of both structures supports the complete loss of solvents after drying, while the general framework remains intact. As evident from the comparison of the experimental X-ray powder diffraction data of 1 with the calculated powder pattern generated from the single crystal X-ray data of 1∙a(solvent), the former complex partially loses its crystallinity; however, the experimental powder pattern resembles the calculated one. Thus, the overall structure of 1 is similar to that of 1∙a(solvent). The crystal structure of 1∙a(solvent) is constructed from the V-shaped (CoIIIL2)+ cations, where the metal ion is N4S2-coordinated by two L. These (CoIIIL2)+ cations are interlinked through CoII(NCS)2 molecules by coordination via free 4-pyridyl nitrogen atoms, yielding a 1D polymeric cationic chain {[(CoIIIL2)2CoII(NCS)2]2+}n, which are interlinked into a 3D framework through a bunch of bifurcated (N)C–S⋯π(2-Py) and linear (NN)C–H⋯O non-covalent interactions. Due to such 3D aggregation, a half of rhombohedral cells are filled by the interlayered [CoII(NCS)4]2– anions, while the other half of cells is free from non-volatile species and filled with volatile solvent molecules, yielding 1D tubular voids, which occupy about 17% of unit cell volume. Direct current variable-temperature magnetic susceptibility measurements on a polycrystalline sample of 1∙a(solvent) were carried out in the temperature range 1.8–300 K. The magnetic behaviour of 1∙a(solvent) indicates the presence of magnetic anisotropy of the CoII ions and/or very weak intermolecular exchange interactions. The surface and pore properties of 1 and HL were calculated by N2 adsorption at 77 K. In addition, CO2 adsorption properties of 1 and HL at different temperatures were determined. It was found that 1 increased both textural and CO2 adsorption properties.