Unique coordination of pyrazine in T[Ni(CN)4].2pyz with T=Mn, Zn, Cd

The materials under study, T[Ni(CN)4].2pyz with T=Mn, Zn, Cd, were prepared by separation of T[Ni(CN)4] layers in citrate aqueous solution to allow the intercalation of the pyrazine molecules. The obtained solids were characterized from chemical analyses, X-ray diffraction, infrared, Raman, thermogravimetry, UV-Vis, magnetic and adsorption data. Their crystal structure was solved from ab initio using direct methods and then refined by the Rietveld method. A unique coordination for pyrazine to metal centers at neighboring layers was observed. The pyrazine molecule is found forming a bridge between Ni and T atoms, quite different from the proposed structures for T=Fe, Ni where it remains coordinated to two T atoms to form a vertical pillar between neighboring layers. The coordination of pyrazine to both Ni and T atoms minimizes the material free volume and leads to form a hydrophobic framework. On heating the solids remain stable up to 140 deg. C. No CO2 and H2 adsorption was observed in the small free spaces of their frameworks. - Graphical abstract: Framework for T[Ni(CN)4].2pyz with T=Mn, Zn, Cd.