New Rare Earth Metal Complexes with Nitrogen‐Rich Ligands: 5,5′‐Bitetrazolate and 1,3‐Bis(tetrazol‐5‐yl)triazenate—On the Borderline between Coordination and the Formation of Salt‐Like Compounds

From the two nitrogen‐rich ligands BT 2− (BT=5,5′‐bitetrazole) and BTT 3− (BTT=1,3‐bis(1 H ‐tetrazol‐5‐yl)triazene), a series of novel rare earth metal complexes were synthesised. For the BT ligand, a vast number of these complexes could be structurally characterised by single‐crystal XRD, revealing structures ranging from discrete molecular aggregates to salt‐like compounds. The isomorphous complexes [La 2 (BT) 3 ] ⋅ 14 H 2 O ( 1 ) and [Ce 2 (BT) 3 ] ⋅ 14 H 2 O ( 2 ) reveal discrete molecules in which one BT 2− acts as a bridging ligand and two BT groups as chelating ligands. The complexes, [M(BT)(H 2 O) 7 ] 2 [BT] ⋅ x  H 2 O ( 3 – 5 ), (M=Nd ( 3 ), Sm ( 4 ), and Eu ( 5 )), are also isomorphous and consist of [M(BT)(H 2 O) 7 ] + ions in which only one BT 2− acts as a chelate ligand for each metal centre. [Tb(H 2 O) 8 ] 2 [BT] 3 ⋅ x  H 2 O ( 6 ) and [Er(H 2 O) 8 ] 2 [BT] 3 ⋅ x  H 2 O ( 7 ) are salt‐like compounds that do not exhibit any significant metal–nitrogen contacts. In the BTT–samarium compound 9 , discrete molecules were found in which BTT 3− acts as a tridentate ligand with three SmN bonds.