Synthesis, Crystal Structure and Properties of Iron Bisdicyanamide (Fe[N(CN)2]2) and Iron Diammin Bisdicyanamide (Fe[NH3]2[N(CN)2]2)

The phase-pure syntheses of Fe(dca)2 and Fe(dca)2(NH3)2 have enabled comprehensive investigation of their structural and magnetic properties. Fe(dca)2 crystallizes in the orthorhombic space group Pnnm, with Fe2+ ions octahedrally coordinated by six dca ligands, forming a rutile-like 3D network. Temperature-dependent structural analysis reveals minor distortions and a slight unit cell volume contraction (~2.5 Å3) from 300 K to 25 K. Fe(dca)2(NH3)2 crystallizes in the monoclinic space group P21/c, featuring two axial ammonia ligands and dca-bridged Fe2+ ions forming layers. Magnetic susceptibility measurements of Fe(dca)2 reveal a ferrimagnetic transition at TC = 19.1 K, confirmed by SQUID data, Mößbauer spectroscopic measurements and low-temperature neutron diffraction. A magnetic hysteresis at 5 K indicates long-range cooperative magnetic ordering. ATR-IR spectroscopic measurements support the structural models and confirm the chemical composition of both compounds. TGA shows the thermal decomposition of Fe(dca)2.