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

Two novel ternary air-stable transition-metal carbodiimides, MnHf(NCN) and FeHf(NCN), were synthesized via solid-state metathesis using either ZnNCN or NaNCN as the carbodiimide source and the corresponding binary metal chlorides. These two phases are the first examples of transition-metal carbodiimides with an (NCN) composition, akin to ubiquitous O perovskite oxides. The crystal structure of MnHf(NCN) was determined and refined from powder X-ray diffraction (XRD) data in the non-centrosymmetric space group 622 allowing for chirality, the assignment of which is supported by second-harmonic generation (SHG) measurements. FeHf(NCN) was found to crystallize isotypically, and the presence of iron(II) in a high spin state was confirmed by Fe Mößbauer spectroscopy. The structures are revealed to be NiAs-derived and can be described as a hexagonal stack of NCN anions with metal cations occupying 2/3 of the octahedral voids. Both IR spectroscopic measurements and DFT calculations agree that the NCN unit is a bent carbodiimide with 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 centers, likely due to the dilution of Mn over the octahedral sites or perhaps even due to some degree of magnetic frustration. The optical and electrochemical properties of MnHf(NCN) were then studied, revealing a wide band gap of 3.04 eV and p-type behavior.