(Sr₉N_1.33(8))(SrIn₃)[CN₃] and Sr₄(Sr₆N)₂[In₄][CN₃]₄: Two Fully Deprotonated Guanidinates Accessible from Pressureless Sodium Flux Synthesis

Two novel compounds featuring the fully deprotonated guanidinate ion, CN₃^5-, representing the true nitridocarbonate ion as the nitrogen analogue of the (oxido)carbonate ion CO₃^2-, were obtained from essentially pressureless sodium flux synthesis. CN₃^5- ions in (Sr₉N_1.33(8))(SrIn₃)[CN₃] and Sr₄(Sr₆N)₂[In₄][CN₃]₄ are embedded in frameworks of strontium nitride next to the indide In₄- and In₃-units. The CN₃^5- ion in both compounds is coordinated by three-capped trigonal prisms of Sr. (Sr₉N_1.33(8))(SrIn₃)[CN₃] shows fully trigonal planar <i>D</i>_3<i>h</i> symmetry, but slightly distorted to nonplanar <i>C</i>_3<i>v</i> symmetry is seen in Sr₄(Sr₆N)₂[In₄][CN₃]₄ due to noncentrosymmetric coordination. C-N distances in the CN₃^5- ion arrive at longer than typical C-O distances in the CO₃^2- ion, fully consistent with expectations. Density functional theory (DFT) calculations also suggest pseudomolecular features of CN₃-, In₄-, and In₃-entities. The CN₃-entity is formed via an electron-rich multicenter bonding mechanism, as evidenced by multicenter COBI, whereas multicenter COBI suggested that In₄- and In₃-entities are formed through an electron-deficient manner.