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Electronic effect and geometry distortion of a low-symmetry ligand-field on the anisotropy barrier of spin reversal have been compared in three Dy(iii) single-ion magnets through simultaneous binding of heterodonor chelating ligands.

Multinuclear hetero-tri-spin complexes based on a methyl-pyrazole nitronyl nitroxide radical, namely, [Ln2Cu3(hfac)12(4-NIT-MePyz)4] (Ln = Gd(1), Tb(2), Dy(3); hfac = hexafluoroacetylacetone; 4-NIT-MePyz = 2-{4-(1-methyl)-pyrazolyl}-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) have been successfully obtained through a one-pot reaction of the radical ligand (4-NIT-MePyz) with Cu(hfac)2 and Ln(hfac)3. These 2p–3d–4f complexes exhibit five-nuclear structures with the sequence [Cu–Rad–Ln–Rad–Cu–Rad–Ln–Rad–Cu], in which each 4-NIT-MePyz radical acting as a bidentate bridging ligand is coordinated to one Ln(hfac)3 unit through one oxygen atom of the NO groups and to one Cu(hfac)2 unit with one nitrogen atom from the pyrazole ring. For complex 1, based on the spin Hamiltonian calculations and MAGPACK program, it is concluded that there exist ferromagnetic couplings between GdIII and NIT radicals, as well as between CuII and free radicals with J1 = 6.8(1) and J3 = 1.3(2) cm−1, respectively, and antiferromagnetic interactions between radical and radical with J2 = −2.8(5) cm−1. Complex 2 shows frequency-dependent out-of-phase signals under a zero or 2000 Oe dc field indicating single-molecule magnetic behavior.

The combination of LnIII ions (GdIII, TbIII or DyIII) and a pyrazole nitronyl nitroxide radical results in three isomorphous complexes, namely, [Ln(hfac)3(NIT-Pyz)]2 (Ln = Gd(1), Tb(2), Dy(3); hfac = hexafluoroacetylacetone; NIT-Pyz = 2-{3-pyrazolyl}-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide). Single crystal X-ray diffraction studies revealed that all of them are composed of two crystallographically independent mononuclear systems, in which the central LnIII ions are coordinated by three hfac and one bidentate chelating NIT-Pyz radical. The central LnIII ions are all in square antiprism geometry (D4d) polyhedron configurations. Based on the spin Hamiltonian calculations, there exist antiferromagnetic couplings in the GdIII-NIT radical system in complex 1. Complexes 2 and 3 show frequency-dependent out-of-phase signals in a zero field indicating single-molecule magnetic behavior. Moreover, Tb's complex (2) shows a single thermal relaxation process with an energy barrier of 26 K. For Dy's complex (3), the Orbach and Raman processes both contribute to the magnetic relaxation behaviors.

Disc-like CoII7 core-derived (4,4)- and (3,6)-connected layers, {[Co7(C2H5OH)1.5(H2O)0.5(Hdatrz)2(μ3-OH)4(ip)5]·2.5H2O·C2H5OH}n (1) and [Co7(H2O)4(ade)2(μ3-OH)6(sip)2]n (2) (Hdatrz = 3,5-diamino-1,2,4-triazole, ade− = adeninate, ip2− = isophthalate and sip3− = 5-sulfoisophthalate) were solvothermally generated and structurally and magnetically characterized. The effect of magnetic anisotropy and exchange coupling from the local CoII7 cores on the resulting magnetism properties are discussed. A crystallographically asymmetric CoII7 core in 1 exhibited an unusual single-molecule magnet (SMM)-like response under zero dc field resulting from strong anisotropy generated by two different types of CoII polyhedra and highly anisotropic exchange interactions. By contrast, a highly symmetric CoII7 disc in 2 belonging to the C2h point group showed only strong ferromagnetic exchange, to lead to an overall ST = 7/2 spin ground-state at low temperature. Thus, the interplay of magnetic anisotropy and exchange coupling has a great and complicated influence on the overall magnetic phenomena, which should be fully considered for the design and preparation of new CoII-SMMs.

Four magnetic MOFs with anisotropic CoII ions, {[Co5(H2O)2(μ3-OH)2(atz)2(stp)2]·1.5H2O}n (1), {[Co5(H2O)2(μ3-OH)2(trz)2(stp)2]·1.3H2O}n (2), {[Co5(H2O)6(μ3-OH)2(trz)2(stp)2]·2.5CH3OH}n (3) and {[Co3(H2O)4(Hdatrz)2(stp)2]·3H2O}n (4) (stp3− = 2-sulfoterephthalate, trz− = 1,2,4-triazolate, atz− = 3-amino-1,2,4-triazolate and Hdatrz = 3,5-diamino-1,2,4-triazole) were solvothermally isolated by varying the substituent groups appended on the N-heterocyclic triazole and structurally and magnetically characterized. Structural analyses indicate that the former two complexes are crystallographically isostructural, exhibiting pillared-layer frameworks with mixed triazolyl and carboxylate extended CoII4 + CoII1 layers supported by rigid stp3− connectors. Complex 3 is built from butterfly-shaped CoII4 cluster-based layers, which are interconnected with single cobalt(II) octahedra by ditopic stp3− bridges. By contrast, complex 4 consists of linear {Co3(μ-N1,N4-Hdatrz)2} subunits, which are extended by 3-connected stp3− linkers into a stable 3D framework. Magnetically, 1 exhibits ferromagnetic ordering below 2.7 K due to the well-organized alignment of the non-compensated resultant moment from octahedra and tetrahedral cobalt(II) carriers, while 3 is in a non-zero paramagnetic state above 2.0 K resulting from the coexistence of intermetallic ferromagnetic and antiferromagnetic interactions. The magnetic competition between weak inter-subunit antiferromagnetic interactions and the external magnetic field makes 4 behave as a field-induced metamagnet with a critical field of 27.5 kOe. These interesting magnetostructural results suggest that the anisotropy of the moment carrier and the interlayer/intersubunit separations significantly dominate the magnetic responses in extended MOFs, providing an informative platform for the further development of interesting magnetic materials, both of academic and industrial interest.

A new oxime-derived {DyIII4NiII6} cluster with a paramagnetic butterfly-shaped DyIII4 core and peripheral diamagnetic planar-square NiII ions was solvothermally synthesized. The weak ferromagnetically coupled cluster exhibits field-induced single-molecule magnetic behavior with two thermally activated single-ion relaxations.

The crystal structures and magnetic behaviours of two water-bridged one-dimensional (1D) cobalt(II) chains with different isomeric naphthoate (na(-)) terminals, [Co(H2O)3(2-na)2]n (1) and {[Co(H2O)3(1-na)2]·2H2O}n (2), were reported to investigate the effect of interchain distance on their magnetic properties. Complex 1 with trans-2-na(-) blocks and dense interchain separation exhibits a metamagnetic transition from antiferromagnetic ordering to a saturated paramagnetic phase. By contrast, complex 2 possessing cis-arranged 1-na(-) spacers and good interchain isolation shows unusual single-chain magnetic behavior under a zero dc field. Thus, completely different interchain packing by isomeric naphthoate ligands governs the ratio of intra- to inter-chain magnetic interactions and further results in different magnetic phenomena, which provide significant magnetostructural information on 1D magnetic systems.

Four new 4-amino-1,2,4-triazole (atr)-based coordination polymers, {[Cu2(atr)(H2O)(μ-OH)2(pa)]·H2O}n (), {[Cu3(atr)2(H2O)2(μ-OH)2(npa)2]·2H2O}n (), {[Cu3(atr)5(dca)(μ-OH)(ClO4)2](ClO4)2}n () and {[Cu3(atr)2(H2O)(μ3-OH)(μ-OH)2(spa)]·1.5H2O}n () (pa(2-) = phthalate, npa(2-) = 3-nitrophthalate, dca(-) = dicyanamide and spa(3-) = 4-sulfophthalate), were successfully obtained by varying the carboxylate- and cyanide-modified magnetic bridges. Structural determinations reveal that the former three samples are bent one-dimensional chains constructed from linear Cu(II)3 subunits and different inter-subunit connections. In , linear {Cu3(μ-N1,N2-atr)2(μ-OH)2}(4+) and {Cu3(μ-COO)2(μ-OH)2}(4+) subunits are alternately connected in a sharing-vertex manner to give a ferrimagnetic S = 1/2 spin ground-state. The linear {Cu3(μ-N1,N2-atr)2(μ-OH)2}(4+) building block of is repeatedly bridged by pairs of single-atom bridging carboxylate groups of the npa(2-) ligand leading to a paramagnetic S = 1/2 spin ground-state. By contrast, each linear {Cu3(μ-N1,N2-atr)4}(6+) core in is periodically propagated by four-fold heterobridges (μ-OH(-), μ-ClO4(-), μ-N1,N2-atr and μ-dca(-)) to generate an overall diamagnetic S = 0 spin ground-state. Complex is a three-dimensional pillared-layer framework composed of linear {Cu3(μ-N1,N2-atr)2(μ-OH)2}(4+)-based layers and ditopic spa(3-) connectors, which exhibits a ferrimagnetic S = 1/2 spin ground-state and a metamagnetic transition resulting from the competition between the weak interchain/interlayer antiferromagnetic interaction and the enhanced external magnetic field. In addition, different intra- and inter-subunit magnetic strengths are observed in with the coupling constants 182-Jintra43 and -127Jinter51.2 cm(-1). These interesting magnetostructural results are significant and helpful for the cyclic polyazolate-based magnetic materials.

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 (44·62)(411·65)2(413·610·85) topological net containing centrosymmetric CuII7 clusters, square-planar CuII1 cores and tetratopic btec4− linkers for 1, a pillared-layered structure consisting of CuII5 + CuII1-based coplanar layers and ditopic tp2− pillars for 2 as well as a microporous architecture derived from CuII5 clusters and directional ip2− connectors for 3. In contrast, complex 4 exhibits an undulated two-dimensional (2D) layer with alternating CuII4 + CuII1 chains interconnected by anionic pa2− connectors. Crystallographically, the increment of the local nuclearity from CuII4 up to CuII7 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 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.

A [Co(6)(μ(3)-OH)(4)(datrz)(2)](6+) ribbon-based blue framework with a metamagnetic transition from an antiferromagnetic ordering to a weak spontaneous magnetization state, {[Co(3)(CH(3)OH)(μ(3)-OH)(2)(datrz)(sip)]·2.25H(2)O}(n) (1, Hdatrz = 3,5-diamino-1,2,4-triazole, sip(3-) = 3,5-dicarboxybenzenesulfonate), was solvothermally synthesized. 1 exhibits a reversible single-crystal-to-single-crystal transformation by solvent exchange to generate a pink antiferromagnetic ordering coordination layer with a similar [Co(6)(μ(3)-OH)(4)(datrz)(2)](6+) ribbon to 1, {[Co(3)(H(2)O)(3)(μ(3)-OH)(2)(datrz)(sip)]·2.125H(2)O}(n) (2). Such concomitant solvatochromic and solvatomagnetic effects are scarcely observed and are significantly due to the coexistence of differently distorted metal coordination spheres and the cleavage/generation of the weak coordination bond.

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.