Phase Transition of a Dicyanamide with Rutile‐like Structure: Syntheses and Crystal Structures of α‐ and β‐Cd[N(CN) 2 ] 2

Cadmium dicyanamide Cd[N(CN) 2 ] 2 was synthesized through aqueous ion exchange at room temperature. A reversible phase transition was detected by in situ X‐ray powder diffractometry above 55 °C. The crystal structures of both phases were determined by X‐ray powder diffraction (β‐Cd[N(CN) 2 ] 2 : T = 22 °C, a = 621.60(3), b = 748.76(4), c = 770.21(5) pm, β = 91.784(3)°, P 2 1 /n (no. 14), Z = 2, wR p = 0.063, R p = 0.050, R F = 0.059; α‐Cd[N(CN) 2 ] 2 : T = 150 °C, a = 624.62(5), b = 752.92(6), c = 768.30(7) pm, Pnnm (no. 58), Z = 2, wR p = 0.083, R p = 0.064, R F = 0.087). Both polymorphs consist of Cd 2+ and bent planar [N(CN) 2 ] — ions. α‐Cd[N(CN) 2 ] 2 crystallizes analogously to rutile and is isotypic with M II [N(CN) 2 ] 2 (M = Mg, Cr, Mn, Co, Ni, Cu). The monoclinic low‐temperature polymorph β‐Cd[N(CN) 2 ] 2 is closely related to that of the orthorhombic high‐temperature polymorph α‐Cd[N(CN) 2 ] 2 by a translationengleiche transition of index 2.