Nitrogen‐Rich Compounds of the Lanthanoids: The 5,5′‐Azobis[1H‐tetrazol‐1‐ides] of the Light Rare Earths (Ce, Pr, Nd, Sm, Eu, Gd)

On the occasion of Carl Auer von Welsbach 's 150th birthday in 2008, we investigated the 5,5′‐azobis[1 H ‐tetrazol‐1‐ides] (C 2 N ₁₀²⁻ ; (ZT) 2− ) of the light lanthanoids (Ln) cerium, praseodymium, neodymium, samarium, europium, and gadolinium. Their synthesis was performed by crystallization from aqueous solutions of disodium 5,5′‐azobis[1 H ‐tetrazol‐1‐ide] and the respective lanthanoid nitrate. All compounds are isotypic (triclinic space group P ‐1) and crystallize according to the general formula [Ln(H 2 O) 7 ] 2 (ZT) 3 ⋅10 H 2 O. The crystal structures of all compounds were determined. A distinct lanthanoid contraction could be established, clearly observable by the decrease in the bond lengths in the LnNO 7 polyhedra from the Ce to the Gd compound. Further, and in contrast to the previously published 5,5′‐azobis[1 H ‐tetrazol‐1‐ides] of the heavy yttric earths, the light Ln cations in this study are coordinated not only by H 2 O molecules but also by one (ZT) 2− anion. Further characterization was performed by vibrational (IR and Raman ) spectroscopy and elemental analysis.