We report on the synthesis of the II-IV-N₂ semiconductors ZnSiN₂, MnSiN₂, and the Zn_1-xMn_xSiN₂ solid solutions by a one-step solid-state metathesis reaction. The successful syntheses were carried out by reacting the corresponding metal halides with stoichiometric amounts of silicon nitride and lithium azide in sealed tantalum ampoules. After washing out the reaction byproduct LiCl, powder X-ray diffraction patterns were indexed with orthorhombic space group Pna2₁. Single phase products were obtained without applying external pressure and at a moderate reaction temperature of 700 °C. The resulting ZnSiN₂ was found to consist of nano-sized grains and needle-shaped nano-crystals. With increasing manganese content in the Zn_1-xMn_xSiN₂ solid solution, we found the reaction product to be increasingly crystalline. Both the cell parameters and the bandgap values across the different compositions of the solid solutions change linearly. The sample Zn_0.95Mn_0.05SiN₂ synthesized by means of solid-state metathesis reaction is an intense red emitter with a broad emission maximum at λ_max ≈ 619 nm when excited with ultraviolet light after annealing the sample at a pressure of 6 GPa and a temperature of 1200 °C.