Coordination compounds of bis(5-tetrazolyl)amine with manganese(ii), zinc(ii) and cadmium(ii): synthesis, structure and magnetic properties

Abstract

Six coordination compounds of bis(5-tetrazolyl)amine (H₂bta) with different metal ions, M{M₃(μ₃-X)(bta)₃(H₂O)₆}₂] (X = OH for M = Mn^II1, and Cd^II2; X = F for M = Mn^II3), [Mn(bta)(H₂O)₃]·0.5H₂O (4), [Zn(bta)(NH₃)₂]·0.5H₂O (5) and [Zn(Hbta)₂(H₂O)₂]·H₂O (6) have been described. The compounds were synthesized using one-pot hydrothermal methods involving the in situ generation of the ligand from dicyanamide and azide (1–4, 6), or by the methods using the pre-synthesized H₂bta ligand (4, 5). The bta ligand in 1–3 assumes the μ₃ tetradentate mode with both 1,2- and 1,4-tetrazole bridges, generating an unusual 2D layer, in which [M₃(μ₃-X)] triangular motifs act as three-connecting nodes and the mononuclear motifs acting as six-connecting nodes that are inter-linked by the ligands. The 2D layer in 1 and 3 represents a novel type of a geometrically spin-frustrated lattice. Both 4 and 5 consist of co-crystallized binuclear motifs and 1D polymeric chain motifs, which arise from two different μ₂ tridentate bridging modes of bta with 1,2- and 1,4-tetrazole bridges, respectively. In 6, the mono-anionic Hbta ligands chelate Zn in the non-bridging bidentate mode to generate mononuclear molecules, which are assembled through extended hydrogen bonds to generate a 3D architecture with a ten-connected net topology. Magnetic investigations revealed that interactions through the different bridges in 3 and 4 are all antiferromagnetic, and also confirmed that 3 is a geometrically-frustrated antiferromagnet (T_N = 2.5 K).