1,2,4-Triazolyl-Carboxylate-Based MOFs Incorporating Triangular Cu(II)-Hydroxo Clusters: Topological Metamorphosis and Magnetism

Abstract

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 α-amino acid precursors revealed unique binding abilities in the construction of Cu(II)-coordination polymers composing discrete triangular [Cu3(μ3-OH)] clusters. A related series of MOFs, [Cu3(μ3-OH)(trgly)3(SO4)]·2H2O (1a), [Cu3(μ3-OH)(trgly)3(H2O)3]SO4·16H2O (1b), Cu3(μ3-OH)(d-trala)3(ClO4)0.5](ClO4)1.5·1.5H2O (2), was prepared, and their crystal structures were determined by means of X-ray diffraction. Being singly deprotonated, the organic ligands act as multidentate μ3- or μ4-donors using tr and -COO(-) moieties. The generated [Cu3(μ3-OH)(tr)3] cluster core is primarily supported by three [-N-N-] triazole heterocycles in a basal plane and tripodal-assisted μ3-anions (SO4(2-): 1a; ClO4(-): 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 α-Po (pcu: 4(12).6(3)) and crystallizes in the noncentrosymmetric space group I4̅3m, in which the six-connected [Cu3(μ3-OH)] clusters and trgly self-assemble in an open-channel cubic array possessing ∼56% solvent-accessible volume. Upon slight thermal treatment (∼60 °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 {4(18).6(18)}{4(2).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.

Syntheses, Crystal Structures, and Properties of Four Metal–Organic Complexes Based on 1,4,5,6,7,7-Hexachlorobicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic Acid

“…For 3, the χMT value is 0.36 cm 3 K mol −1 at 300 K, which is lower than the value expected for single high-spin Cu II ion (0.375 cm 3 mol -1 K, assuming g = 2.0). [61][62] The χMT value slowly decreases to 0.34 cm 3 K mol −1 at 15 K and then descends more sharply, reaching a value of 0.27 cm 3 K mol −1 at 1.8 K. It indicates a very weak antiferromagnetic behavior presented in the complex. The inverse magnetic susceptibility curve shows a linear behavior in 100−300 K range and can be fitted to the Curie−Weiss law, χ = C/(T − θ), yielding C = 0.37 cm 3 mol −1 K and θ = −2.24 K. The negative θ value for 3 also suggests an antiferromagnetic property, the same as 1 and 2.…”

Recent Advances of Precise Cu Nanoclusters in Microporous Materials

“…[69] Recently, Wang et al firstly reported a rigid copper thiolate cluster-assembled material (Cu 12 bpy, bpy = 4,4'-bipyridine). [74] They demonstrated an increase in the content of dense copper of copper azide composites, which contributed to the high output energy of copper azide-based explosives.…”

“…Besides the presence of nodal Cu-core in MOFs, specific framework functionalities can also be utilised to incorporate or encapsulate extra-framework Cu species. [74] Chapman et al have functionalised NU-1000 (a Zr-based MOF) with Cu through atomic layer deposition. [75] The local structure of the supported Cu species was probed by combining pair distribution function analysis and difference envelope density analysis of the in situ synchrotron-based X-ray scattering data (see Figure 9).…”

Crystal structure, infrared spectra and luminescence of a 1D Cd coordination polymer with 4-nitrophthalic acid and 1,10-phenanthroline monohydrate ligands

“…Among these factors, the organic ligand plays an important role because changing it can control and adjust the coordination frameworks and topologies [16][17][18][19]. Since a carboxylate group can bridge metal ions and lock their position into M-O-C clusters, which can act as rigid entities and improve the stabilization of the compounds, di and polycarboxylic acids are widely used as bridging ligands to construct coordination frameworks with versatile structures [20][21][22][23][24][25]. As a member of dicarboxylate ligands, 4 nitrophthalic acid (H 2 NPTA) contains four potential metal binding sites, which can yield the formation of a coordination poly mer through multiple bonding interactions, adopt dif ferent conformations and coordination modes, and provide abundant structural motifs.…”