1,2,4-Triazolyl-Carboxylate-Based MOFs Incorporating Triangular Cu(II)-Hydroxo Clusters: Topological Metamorphosis and Magnetism
文摘
Bifunctional 1,2,4-triazole-carboxylate ligands, an achiral 1,2,4-triazol-4-yl-acetic acid (trgly-H) and a chiral (d)-2-(1,2,4-triazol-4-yl)-propionic acid (d-trala-H), derived from the corresponding 伪-amino acid precursors revealed unique binding abilities in the construction of Cu(II)-coordination polymers composing discrete triangular [Cu3(渭3-OH)] clusters. A related series of MOFs, [Cu3(渭3-OH)(trgly)3(SO4)]路2H2O (1a), [Cu3(渭3-OH)(trgly)3(H2O)3]SO4路16H2O (1b), Cu3(渭3-OH)(d-trala)3(ClO4)0.5](ClO4)1.5路1.5H2O (2), was prepared, and their crystal structures were determined by means of X-ray diffraction. Being singly deprotonated, the organic ligands act as multidentate 渭3- or 渭4-donors using tr and 鈭扖OO鈥?/sup> moieties. The generated [Cu3(渭3-OH)(tr)3] cluster core is primarily supported by three [-N-N-] triazole heterocycles in a basal plane and tripodal-assisted 渭3-anions (SO42鈥?/sup>: 1a; ClO4鈥?/sup>: 2) capping the axial faces. The carboxylate groups join the units into either two-dimensional (2D) layer (1a, 2) or 3D zeolite-like networks (1b). Compound 1b represents the topology of 伪-Po (pcu: 412.63) and crystallizes in the noncentrosymmetric space group I4M3;3m, in which the six-connected [Cu3(渭3-OH)] clusters and trgly self-assemble in an open-channel cubic array possessing 56% solvent-accessible volume. Upon slight thermal treatment (60 掳C), the structure irreversibly shrinks to the nonporous 2D motif 1a that belongs to a uninodal (3,6) network type. In structure 2 (space group R32), due to the [-N-N-] triazole and 1,3-bidentate carboxylate binding mode, each organic ligand bridges three metal clusters affording cross-linking of two adjacent layers with the same (3,6) topology. The resultant 3,9-c net is novel and can be categorized as two-nodal with point symbol {418.618}{42.6}3. Spin frustration and antisymmetric exchange effects, resulting in abnormally low g values in the S = 1/2 states, were observed in the magnetic properties and the EPR spectra.