When synthesizing the versatile precursors (NMe4)[Ni(CF3)3(MeCN)] we recently encountered the problem that marked amounts of C2F5 were incorporated instead of CF3 under the chosen reaction conditions forming mixed-ligand nickelates [Ni(CF3)x(C2F5)y(MeCN)]− (x + y = 3). We studied the three products with y = 0, 1, or 2, using 19F nuclear magnetic resonance (NMR) spectroscopy and single-crystal X-ray diffraction. We were able to trace the reaction mechanism and solve the problem by modifying the experimental conditions.