Crystal Engineering of Rare Earth Amides: ³_∞[Tb(Im)₃]@NH₃, a Homoleptic 3D Network Exhibiting Strong Luminescence

Abstract

The solvent-free reaction of terbium metal with an imidazole melt (C3H4N2, ImH) yields single-crystalline [Tb(Im)3]@NH3 (Im- = C3H3N2-, imidazolate anion) and hydrogen. Both N atoms of the imidazolate rings coordinate η1 to terbium cations, thereby forming a homoleptic three-dimensional network. The Tb3+ ions exhibit complete nitrogen coordination, resulting in trigonal prisms as coordination polyhedra and C.N. = 6. The network contains cavities large enough to take up NH3 molecules, the latter formed by the partial decomposition reaction of the amine ligand in the melt reaction. Ammonia can be removed thermally or over time without decomposition of the network. Unsubstituted imidazole can thus be utilized for crystal engineering and the formation of rare earth amide network structures. The compound exhibits an amazingly strong green emission. The emission spectrum shows the typical Tb3+ f−f transitions; additionally, an efficient ligand → Tb3+ energy transfer is observed.