The acetonitriletriide anion C₂N^3–, the fully deprotonated form of acetonitrile, is stabilized in a pure alkaline earth metal environment in Sr₄N[CN₂][C₂N]. The heterogeneous reaction of graphite and elemental nitrogen (from decomposed NaN₃) with Sr₂N at 1020 K yields for the first time a phase that contains the two triatomic anions acetonitriletriide C₂N^3– and carbodiimide CN₂^2– side by side. Further synthetic routes were likewise successfully tested, including a sodium free approach (Sr₂N + C) and the use of NaCN as carbon and nitrogen source. The monoclinic crystal structure is derived from powder and single-crystal X-ray diffraction data (P2₁/c, a = 397.74(1) pm, b = 1411.72(3) pm, c = 692.57(1) pm, β = 103.57(1)°, Z = 2). The existence of both anions in Sr₄N[CN₂][C₂N] is further confirmed by IR and Raman spectroscopy. With its novel 1-D chain structure of edge-sharing NSr₆ octahedra, the material also enriches the structural variety of ternary alkaline earth metal nitrides.