Layered Transition Metal Nitroprussides - Their Preparation, Crystal Structure, and Magnetic Properties

Abstract

Divalent transition metal (T) nitroprussides form a series of insoluble coordination compounds, which generally crystallize in 3D frameworks, except for a layered (2D) phase of copper. In this contribution, the preparation of layered phases for T = Mn, Fe, Co, Ni, Zn, and Cd is reported. The incorporation of imidazole (Im) during their preparation by the precipitation method inhibits the coordination of the axial CN groups to the metal T, and layered (2D) structures of formula unit T(Im)2[Fe(CN)5NO] result. The metal T is found coordinated to the N end of the equatorial CN groups. Imidazole molecules occupy its axial coordination sites. In the interlayer region, imidazole molecules from neighboring layers interact through their dipole and quadrupole moments. The stacking of the aromatic rings from neighboring molecules deviates from the sandwich-type configuration, which in turn weakens the magnetic interactions between T2+ cations located in neighboring layers. Axial unbridged CN and NO groups play a steric hindrance role, thus causing a deviation from the sandwich configuration for the aromatic rings. This series of 2D transition metal nitroprussides can be exfoliated by using appropriate solvents, for example, 1-methyl-2-pyrrolidone.