Perovskite-Like Carbodiimides AB (NCN) 3 : Synthesis and Characterization of MnHf(NCN) 3 and FeHf(NCN) 3 .

Two novel ternary air-stable transition-metal carbodiimides, MnHf(NCN) ₃ and FeHf(NCN) ₃ , were synthesized via solid-state metathesis using either ZnNCN or Na ₂ NCN as the carbodiimide source and the corresponding binary metal chlorides. These two phases are the first examples of transition-metal carbodiimides with an AB (NCN) ₃ composition, akin to ubiquitous AB O ₃ perovskite oxides. The crystal structure of MnHf(NCN) ₃ was determined and refined from powder X-ray diffraction (XRD) data in the non-centrosymmetric space group P 6 ₃ 22 allowing for chirality, the assignment of which is supported by second-harmonic generation (SHG) measurements. FeHf(NCN) ₃ was found to crystallize isotypically, and the presence of iron(II) in a high spin state was confirmed by ⁵⁷ Fe Mößbauer spectroscopy. The structures are revealed to be NiAs-derived and can be described as a hexagonal stack of NCN ^2- anions with metal cations occupying 2/3 of the octahedral voids. Both IR spectroscopic measurements and DFT calculations agree that the NCN ^2- unit is a bent carbodiimide with C _{2 v} symmetry, necessary to account for the size difference present in such a vacancy-ordered structure. Magnetic studies reveal predominantly strong antiferromagnetic interactions but no long-range order between the paramagnetic Mn ²⁺ centers, likely due to the dilution of Mn ²⁺ over the octahedral sites or perhaps even due to some degree of magnetic frustration. The optical and electrochemical properties of MnHf(NCN) ₃ were then studied, revealing a wide band gap of 3.04 eV and p-type behavior.