Spin Frustration and Long-Range Ordering in an AlB₂-like Metal-Organic Framework with Unprecedented N,N,N-Tris-tetrazol-5-yl-amine Ligand

Solvothermal treatment of a mixture of Co(OAc)2, NaN3, NaN(CN)2, HF, MeCN, and H2O generated an AlB2-like metal-organic framework, namely, [{(Co3F)3(trta)2(H2O)9}{Co(Hbta)3}2]·11H2O (1) (H3trta = N,N,N-tris-tetrazol-5-yl-amine; H3bta = N,N-bis-tetrazol-5-yl-amine), in which supertrianglar supramolecular building blocks (SBBs) {(Co3F)3(trta)2} act as 12-connected nodes of hexagonal prisms. The unprecedented ligand N,N,N-tris-tetrazol-5-yl-amine is in situ generated via metal-assisted reactions of NaN(CN)2, MeCN, and NaN3, and a possible mechanism involves both 1,3-dipolar cycloaddition and nucleophilic addition. The F-centered Co3 triangles are bridged by trta groups to result in supertriangular {(Co3F)3(trta)2} SBBs that are further arranged in a frustrated triangular lattice. The long-range ordering temperature is reduced to 4.8 K due to strong spin frustration.