In the quasibinary system Ta2O5/Ta3N5 we prepared a new oxide nitride phase, Ta3O6N, by the reaction of 1T–TaS2 with water-saturated ammonia gas. The determination of the unit cell metric and the crystal structure indicated that Ta3O6N is structurally related to the TiNb2O7-type. Quantum-chemical calculations on DFT level were used to rank the relative stabilities of possible N/O distributions and to provide a plausible structural model of the ground state with a minimum in the total energy. In agreement with Paulings 2nd rule, nitrogen ions prefer sites with high coordination numbers.