(Sr9N1.33(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, CN35-, representing the true nitridocarbonate ion as the nitrogen analogue of the (oxido)carbonate ion CO32-, were obtained from essentially pressureless sodium flux synthesis. CN35- ions in (Sr9N1.33(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 CN35- ion in both compounds is coordinated by three-capped trigonal prisms of Sr. (Sr9N1.33(8))(SrIn3)[CN3] shows fully trigonal planar D3h symmetry, but slightly distorted to nonplanar C3v symmetry is seen in Sr4(Sr6N)2[In4][CN3]4 due to noncentrosymmetric coordination. C-N distances in the CN35- ion arrive at longer than typical C-O distances in the CO32- 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.