Zhong-Yi Liu

Two 3D Triazolate−Tricarboxylate-Bridged CuII/I Frameworks by One-Pot Hydrothermal Synthesis Exhibiting Spin-Canted Antiferromagnetism and Strong Antiferromagnetic Couplings

Two 3D coordination polymers with the same components but different structures, [Cu(II)(2)Cu(I)(trz)(3)(Hbtc)](n) (1) and [Cu(4)(Htrz)(2)(mu(3)-OH)(2)(btc)(2)](n) (2), were obtained together by a one-pot hydrothermal reaction of Cu(OAc)(2).H(2)O, 1,2,4-triazole (Htrz), and 1,3,5-benzenetricarboxylic acid (H(3)btc). Complex 1 is a mixed-valence Cu(I/II) honeycomb built from wavy Cu(II)-trz-carboxylate layers and Cu(I) nodes with doubly deprotonated Hbtc(2-) ligands covalently filled in the channels. In contrast, 2 is a tetranuclear [Cu(4)(Htrz)(2)(mu(3)-OH)(2)](6+) cluster-based framework extended by a fully deprotonated btc(3-) ligand, displaying a 3,6-connected topological network. More interestingly, spin-canted antiferromagnetism and overall strong antiferromagnetic couplings up to -147.1 cm(-1) are respectively observed for 1 and 2, which are significantly due to the antisymmetric magnetic exchange in the wavy Cu(II)-trz-carboxylate sublayer of 1 and the cooperative 4-fold heterobridges within the tetranuclear cluster of 2.

Slow Magnetic Relaxation in Two New 1D/0D DyIII Complexes with a Sterically Hindered Carboxylate Ligand

Two carboxylate-bridged Dy(III) complexes, [Dy(2)(piv)(5)(μ(3)-OH)(H(2)O)](n) (1) and [Dy(2)(piv)(6)(phen)(2)] (2) (pivH = pivalic acid; phen = 1,10-phenanthroline), have been synthesized and structurally characterized. Complex 1 takes a one-dimensional (1D) chain structure based on [Dy(4)(μ(3)-OH)(2)(piv)(8)(H(2)O)(2)](2+) units, while complex 2 is a dinuclear structure bridged by syn,syn-carboxylates. Magnetic investigation indicates weak ferromagnetic interaction between adjacent Dy(III) ions of the Dy(4) unit in 1 and weak intramolecular antiferromagnetic interaction between Dy(III) ions and/or depopulation of the Dy(III) excited-state Stark sublevels in 2. Alternating-current susceptibility measurements revealed frequency- and temperature-dependent out-of-phase signals under a zero direct-current field in 1, with typical slow magnetic relaxation behavior with an anisotropic barrier U ≈ 4.5 K, while 2 exhibits field-induced single-molecule-magnet behavior with ΔE/k(B) = 28.43 K under a 2 kOe external field.

A Unique Substituted Co(II)-Formate Coordination Framework Exhibits Weak Ferromagnetic Single-Chain-Magnet Like Behavior

A magnetic isolated chain-based substituted cobalt-formate framework was obtained with isonicotine as a spacer. In the chain, canted antiferromagnetic interactions exist in between the Co(II) ions, and slow magnetic relaxation is detected at low temperature. For the block effects of the isonicotine ligands, the complex could be considered as a peculiar example of a weak ferromagnetic single-chain-magnet.

Three Isostructural One-Dimensional LnIII Chains with Distorted Cubane Motifs Showing Dual Fluorescence and Slow Magnetic Relaxation/Magnetocaloric Effect

Three new homometallic lanthanide complexes with mixed carboxylate-modified rigid ligands, [Ln(μ3-OH)(na)(pyzc)]n (na(-) = 1-naphtholate, pyzc(-) = 2-pyrazinecarboxylate, Ln = Dy (1), Yb (2), and Gd (3)), were solvothermally synthesized, and their structures and magnetic as well as photophysical properties were completely investigated. Complexes 1-3 are crystallographically isostructural, exhibiting linear chains with four bidentate bridging μ-COO(-) moieties encapsulated cubic {Ln4(μ3-OH)4}(8+) clusters repeatedly extended by 4-fold chelating-bridging-pyzc(-) connectors. Magnetically, the former two complexes with highly anisotropic Dy(III) and weak anisotropic Yb(III) ions in the distorted NO7 triangular dodecahedron coordination environment display field-induced slow relaxation of magnetization. Fitting the dynamic magnetic data to the Arrhenius law gives energy barrier ΔE/kB = 39.6 K and pre-exponential factor τo = 1.52 × 10(-8) s for 1 and ΔE/kB = 14.1 K and τo = 2.13 × 10(-7) s for 2. By contrast, complex 3 with isotropic Gd(III) ion and weak intracluster antiferromagnetic coupling shows a significant cryogenic magnetocaloric effect, with a maximum -ΔSm value of 30.0 J kg(-1) K(-1) at 2.5 K and 70 kOe. Additionally, the chromophoric na(-) and pyzc(-) ligands can serve as antenna groups, selectively sensitizing the Dy(III)- and Yb(III)-based luminescence of 1 and 2 in the UV-visible region by an intramolecular energy transfer process. Thus, complexes 1-3, incorporating field-induced slow magnetic magnetization and interesting luminescence together, can be used as composite magneto-optical materials. More importantly, these interesting results further demonstrate that the mixed-ligand system with rigid carboxylate-functionalized chromophores can be excellent candidates for the preparations of new bifunctional magneto-optical materials.

Two unique antiferromagnetic 3D frameworks with unusual CuII4 cluster and alternate CuII4 + CuII1 structural motif tuned by aromatic polycarboxylate coligand

Two new 3-amino-1,2,4-triazole (amtrz)-based 3D MOFs, [Cu4(amtrz)2(μ3-OH)2(btc)2]n (1), and [Cu5(amtrz)2(H2O)2(μ3-OH)2(btec)2]n (2) (btc3− = 1,3,5-benzenetricarboxylate and btec4− = 1,2,4,5-benzenetetracarboxylate), were hydrothermally synthesized and structurally and magnetically characterized. Each cationic [Cu4(amtrz)2(μ3-OH)2]6+ cluster in 1 is periodically extended into an infinite 3,6-connected rtl-type topological network via six btc3− ligands. In contrast, analogous CuII4 clusters to 1 and square-planar CuII1 cores in 2 are alternately interlinked through btec4− linkers to generate a 3D (44·62)2(46·64)4(48·66·8)3 framework, which is a scarcely observed higher-dimensional coordination polymer with a CuII4 + CuII1 motif. More interestingly, both the coordination polymers display strong antiferromagnetic couplings up to −154.6 cm−1 due to the favorable multiple heterobridges in the analogous CuII4 component.

Diverse mixed-ligand metal complexes with in situ generated 5-(pyrazinyl)tetrazolate chelating-bridging ligand: in situ synthesis, crystal structures, magnetic and luminescent properties

The purpose of this work is to systematically investigate the influence of the functional co-ligands and metal ions on the self-assembly and properties of the in situ generated 5-(pyrazinyl)tetrazolate (ptz−)-based metal complexes. A series of nine metal complexes, {[Co3(H2O)4(ptz)2(btec)]·5H2O}n (1), [Cu2(H2O)4(ptz)2(H2btec)]n (2), [Hg2(ptz)2Cl2]n (3), [Hg3(H2O)2(ptz)4(μ1,1-N3)2]·2H2O (4), Hg(H2O)2(ptz)2 (5), [Cd2(H2O)2(ptz)2(ox)]n (6), [Cd(H2O)(ptz)I]n (7), {[Cd(H2O)(ptz)X]·H2O}n (X = Br for 8 and Cl for 9) (btec = 1,2,4,5–benzenetetracarboxylate and ox = oxalate), was obtained by a subtle variation of co-ligands and metal ions, in which the HgII ion is firstly observed as an efficient Lewis acid to catalyze the in situ reaction. Significantly, resulted from the cooperative and/or competitive binding between the mixed ligands and the metal ions with different coordination geometry, complexes 1–9 feature interesting structural subunits (mono-, bi- and tri-metallic core) and various dimensionalities ranged from polymeric three-dimensional (3D) frameworks to discrete zero-dimensional (0D) entities. Three high-dimensional complexes with a binodal (3,8)-connected tfz-d microporous framework for 1, a trinodal (3,4)-connected unusual (6·82)2(6·83·102) topology for 3, and a six-connected α-polonium-type network for 6 are observed, respectively. Complexes 2 and 7–9 are bi-metallic node-based 2D layers (7) and 1D chains (2, 8, and 9). In contrast, the rarely linear tri-metallic core and commonly observed mononuclear entities are generated for 4 and 5, respectively. Additionally, CuII-based polymer 2 displays weak intra-dimeric antiferromagnetic coupling interaction. Complexes 1 and 3–9 with considerable metal ion-dependent thermal stability exhibit ptz−-based photoluminescence with variable intensity.

Three Zn(II)-triazole-H3btc complexes regulated by mixed ligands protonation upon stepwise crystallization

By reaction of a zinc salt, 1,3,5-benzenetricarboxylic acid (H3btc) and 1,2,4-triazole (Htrz) under hydrothermal conditions, three mixed ligands protonation-dominated crystals, showing a 3-D microporous framework for 1, a 3-D pillared-layer structure for 2, and a 1-D chain motif for 3, have been stepwise isolated by crystallization of the reaction mixture and evaporation of the filtrates.

Diverse Self-Assembly from Predesigned Conformationally Flexible Pentanuclear Clusters Observed in a Ternary Copper(II)-Triazolate-Sulfoisophthalate System: Synthesis, Structure, and Magnetism

Self-assembly from the predesigned Cu(II)5 secondary building unit (SBU) in the ternary Cu(II)-triazolate-sulfoisophthalate system generates three interesting magnetic samples: an open pillared-layer framework with nanosized Cu(II)30 metallamacrocycle-based sublayer (1), a (3,6)-connected 2-fold interpenetrating network consisting of alternating Cu(II)5 and Cu(II)1 cores (2), and a (4,8)-connected architecture constructed from centrosymmetric Cu(II)7 clusters and four-branched 5-sulfoisophthalate (sip(3-)) connectors (3). These various structures significantly result from the variable connectivity and the slight expansion of the predetermined conformationally flexible Cu(II)5 SBUs. Furthermore, these intriguing structural motifs in 1-3 essentially induce different magnetic phenomena. A field-dependent metamagnetic transition from antiferromagnetic ordering to weak ferromagnetism is observed in the frustrated Cu(II)30-based sublayer of 1. The paramagnetic Cu(II)1 core in 2 virtually contributes to an S = (1)/2 spin ground state due to the completely compensated magnetic moment in the 1,2,3-triazolate (ta(-))-bridged Cu(II)5 cluster containing ribbon. In contrast, strong antiferromagnetic interactions in the locally centrosymmetric Cu(II)7 cluster lead to an overall S = (1)/2 spin ground state of 3. Thus, the SBU-derived self-assembly strategy provides important hints for polymetallic cluster based high-dimensional magnetic materials, which also brings a new vision for the design and construction of novel functional materials.

Long-range ferromagnetic ordering in a 3D CuII-tetracarboxylate framework assisted by an unprecedented bidentate μ2-O1,N4 hypoxanthine nucleobase

The first hypoxanthine (hypH)-assisted 3D Cu(II)-tetracarboxylate framework, {[Cu(2)(hypH)(0.5)(H(2)O)(0.5)(btec)]·1.5H(2)O}(n) (btec = 1,2,4,5-benzenetetracarboxylate), was synthesized and exhibits long-range ferromagnetic ordering below 4.5 K, which opens a new window for the applications of nucleobase-based MOFs as magnetic materials.

A Kagomé layer-based 3D MnII framework showing coexistence of spin-canting, spin-frustration, field-induced metamagnetic and spin-flop transitions

A novel 3D Mn(II) coordination framework with Kagomé sublattice, [Mn(3)(py)(2)(nip)(2)](n) (py(-) = 2-((1H-tetrazol-5-yl)methyl)pyridine and nip(2-) = 5-nitroisophathalate), was in situ solvothermally synthesized and shows the coexistence of spin-canting, spin-frustration as well as field-induced metamagnetic and spin-flop transitions at 2.9 K.