Layered Carbodiimides A2M(CN2)3 with Tetravalent Cations M = Sn, Zr, and Hf

The ternary carbodiimides Li2Sn(CN2)(3), Na2Sn(CN2)(3), Li2Zr(CN2)(3) and Li2Hf(CN2)(3) were synthesized and their crystal structures were solved and refined by means of powder X-ray diffraction [Li2Zr(CN2)(3) and Li2Hf(CN2)(3) crystallize in R (3) over barc, whereas Li2Sn(CN2)(3) and Na2Sn(CN2)(3) crystallize in Pnna]. All structures are characterized by alternating layers of carbodiimide units and metal atoms, although cations show distinct distributions within layers. All three lithium metal carbodiimides reveal partial occupations of Li+ and M4+ on opposite sites in the order of 10 % (at room temperature). This and the general structural assembly exhibit analogies to the corresponding ternary oxides A(2)MO(3). Furthermore, all A(2)Sn(CN2)(3) structures can be related to the hierarchical NiAs type structure by space group theory via group-subgroup relationship.