Four 1,2,3-triazolate-based coordination polymers (CPs) with varied dimensionality, different nuclearity numbers and core topologies, [Cu4(μ-OH)(μ3-OH)(ta)2(btec)]n (1), {[Cu6(μ3-OH)2(ta)8(tp)]·2.5H2O}n (2), {[Cu5(μ3-OH)2(ta)4(ip)2]·2H2O}n (3) and {[Cu5(μ-OH)2(μ3-OH)2(ta)2(pa)2]·2H2O}n (4) (ta = 1,2,3-triazolate, btec = 1,2,4,5-benzenetetracarboxylate, tp = terephthalate, ip = isophthalate and pa = phthalate), were hydrothermally synthesized by varying the numbers and positions of the carboxylate group appended on the phenyl tether, and structurally and magnetically characterized. The former three entities are three-dimensional (3D) robust frameworks with a (4(4)·6(2))(4(11)·6(5))2(4(13)·6(10)·8(5)) topological net containing centrosymmetric Cu(II)7 clusters, square-planar Cu(II)1 cores and tetratopic btec(4-) linkers for 1, a pillared-layered structure consisting of Cu(II)5 + Cu(II)1-based coplanar layers and ditopic tp(2-) pillars for 2 as well as a microporous architecture derived from Cu(II)5 clusters and directional ip(2-) connectors for 3. In contrast, complex exhibits an undulated two-dimensional (2D) layer with alternating Cu(II)4 + Cu(II)1 chains interconnected by anionic pa(2-) connectors. Crystallographically, the increment of the local nuclearity from Cu(II)4 up to Cu(II)7 in 1-4 benefits greatly from the synergistic co-coordination of the hydroxyl group and the coplanar ta(-) ligand towards the metal ion, and the interlayer/interchain compactness is significantly tuned by the position isomerism of the dicarboxylate moieties. Due to the antiferromagnetic coupling in the local clusters and the asymmetric superexchange by μ3-ta(-) mediator, these complexes 4 exhibit different spin ground states (paramagnetic S = 1 and 1/2, ferrimagnetic S = 1/2 as well as spin canting) at low temperatures, which are informative for polynuclear-based magnetic materials.
Three new heterometallic single-molecule magnets (SMMs), [Dy Ni (bipy) (RC H COO) ] [bipy=2,2'-bipyridine, R=H (1), CH (2), and NO (3)], are synthesized solvothermally with different 3-substituted benzoate ligands (RC H COO ), and are characterized both structurally and magnetically. Structural analyses reveal that the three entities are structurally analogous, exhibiting an approximately linear {Dy Ni } core bridged by ten carboxylate moieties from the RC H COO ligands. A noncoordinating substituent group attached on the phenyl ring results in minor geometry distortions of 1-3, but causes a significant decrease in the Mulliken atomic charge on the axially shortest O donor through inductive and/or conjugative effects. Weak intramolecular ferromagnetic (for Dy ⋅⋅⋅Dy ) and antiferromagnetic (for Dy ⋅⋅⋅Ni ) interactions with slightly different coupling strengths are observed in 1-3 at low temperatures, and the effective anisotropy barriers to block the magnetization reversal are 39.9, 25.9, and 2.8 cm , respectively, under zero direct-current field. Ab initio calculations reveal that ligand substitution by the noncoordinating electron-withdrawing/electron-donating group can give rise to good modulation of the energy gap between the two lowest Kramers doublets, as well as the orientation of the local easy axis of the Dy ion magnetization. The directions of the local easy axis of the Dy ion can further influence the dipole spin-spin interaction and the molecular anisotropy of the entire molecule, which, together with the energy separation between the ground and first excited ground states, become the significant factors determining the effective anisotropy barrier heights of 1-3. These important results demonstrate that the charge distributions of the ligand-field environments play essential roles in SMM performance, which should be considered seriously and utilized efficiently during the rational design of new, more feasible and practical SMMs.
Abstract. Three lanthanide complexes with the ligand 4-sulfophthalate (2), and Er (3)], were solvo-/ hydrothermally synthesized by changing the rare earth cations, and were characterized structurally and photophysically. Complexes 1-3 are isostructural, exhibiting a two-dimensional layered structure with centrosymmetric dinuclear subunits infinitely extended by 4-connected
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