Structural complexity by 2D intergrowth in Ca₁₂[Mn₁₉N₂₃] and Ca₁₃₃[Mn₂₁₆N₂₆₀]

The new Mn–rich alkaline earth nitridomanganates Ca₁₂[Mn₁₉N₂₃] and Ca₁₃₃[Mn₂₁₆N₂₆₀] were obtained by a gas-solid reaction of Ca₃N₂ and Mn with N₂ at 1273 K and 1223 K, respectively. These phases represent the first examples of layered nitridomanganates and possess crystal structures with extended 2D networks of chemically bonded Mn atoms containing similar building blocks but of different levels of structural complexity. Furthermore, Ca₁₃₃[Mn₂₁₆N₂₆₆] is the first representative of complex intermetallic structures with preferably covalent (two- and four-centre) bonding. 

These semiconducting phases order antiferromagnetically and show a Curie-Weiss-type paramagnetic behaviour above their Néel temperatures. Bonding analysis as well as magnetic susceptibility and electron spin resonance measurements revealed that only a fraction of Mn atoms in both structures carries a localized magnetic moment, while for most Mn species the magnetism is quenched due to metal-metal bond formation. The displayed localized magnetism in Ca₁₂[Mn₁₉N₂₃] and Ca₁₃₃[Mn₂₁₆N₂₆₀] originates from the manganese atoms not involved in metal-metal bond formation (green triangles) and is characterized by a large orbital contribution, untypical for most 3d-elements. Magnetic moments of the remaining Mn species are quenched, since their d-electrons are utilized for chemical bonding between these metal atoms.

PH / CPfS