The two cobalt(III) complex salts [(CH 3 ) 4 N][trans-Co(NH 3 ) 2 (NO 2 ) 4 ] (I) and [(C 2 H 5 ) 4 N][trans-Co(NH 3 ) 2 (NO 2 ) 4 ] (II) have been synthesized in high yields by reacting equimolar quantities of [(CH 3 ) 4 N]Br and [(C 2 H 5 ) 4 N]Cl with K[trans-Co(NH 3 ) 2 (NO 2 ) 4 ], respectively in aqueous medium at room temperature. The salt I crystallized with monoclinic space group P 2 1 /m having cell dimensions aZ6.1926(7), bZ18.248(3), cZ 6.2335(6) A ห, bZ90.078(7)8, VZ704.41(16) A ห3, ZZ2, RZ0.0868 and the salt II crystallized with monoclinic space group P 2 1 /c having cell dimensions aZ10.2635(18), bZ9.0480(15), cZ9.752(2) A ห, bZ104.493(12)8, VZ876.8(3) A ห3, ZZ2, RZ0.0408. X-ray structure determination revealed the presence of discrete ions, [(CH 3 ) 4 N] C and [trans-Co(NH 3 ) 2 (NO 2 ) 4 ] K in I and [(C 2 H 5 ) 4 N] C and [trans-Co(NH 3 ) 2 (NO 2 ) 4 ] K in II. In the anion, the central metal atom cobalt(III) is octahedrally surrounded in trans geometry. The crystal lattice is stabilized by electrostatic forces of attractions and hydrogen bonding interactions in I. These are the first X-ray structures of salts containing the tetralkylammonium cations and the anion [trans-Co(NH 3 ) 2 (NO 2 ) 4 ] K . The packing diagrams show a layered structures in the two salts.