Effect of structural isomerism on magnetic dynamics: from single-molecule magnet to single-chain magnet

Novel Co5 and Ni4 Metal Complexes and Ferromagnets by the Combination of 2-Pyridyl Oximes with Polycarboxylic Ligands

The use of 2-pyridyl oximes in metal complexes chemistry has been extensively investigated in the last few decades as a fruitful source of species with interesting magnetic properties. In this work, the initial combination of pyridine-2-amidoxime (pyaoxH₂) and 2-methyl pyridyl ketoxime (mpkoH) with isonicotinic acid (HINA) and 3,5-pyrazole dicarboxylic acid (H₃pdc) has provided access to three new compounds, [Ni₄(INA)₂(pyaox)₂(pyaoxH)₂(DMF)₂] (1), [Co₅(mpko)₆(mpkoH)₂(OMe)₂(H₂O)](ClO₄)₆ (2), and [Co₅(OH)(Hpdc)₅(H₂pdc)] (3). 1 displays a square-planar metal topology, being the first example that bears simultaneously HINA and pyaoxH₂ in their neutral or ionic form. The neighbouring Ni₄ units in 1 are held together through strong intermolecular hydrogen bonding interactions, forming a three-dimensional supramolecular framework. 2 and 3 are mixed-valent Co₄^IIICo^II and Co₂^IIICo^II₃ compounds with a bowtie and trigonal bipyramidal metal topology, accordingly. Direct current and alternate current magnetic susceptibility studies revealed that the exchange interactions between the Ni^II ions in 1 are ferromagnetic (J = 1.79(4) cm⁻¹), while 2 exhibits weak AC signals in the presence of a magnetic field. The syntheses, crystal structures, and magnetic properties of 1–3 are discussed in detail.

A single chain magnet based on a 1D polymeric selenite-bridged Mn(iii) complex with an N2O2 donor

A novel molecular magnetic material with the formula of {[Mn2(salen)2(C4H3SSeO2)](ClO4)}n (Complex 1) [salen = N,N′-(ethylene)bis(salicylideneiminato)] was designed, synthesized and characterized structurally and magnetically.

Coexistence of Spin Canting and Metamagnetism in a One-Dimensional Mn(II) Compound Bridged by Alternating Double End-to-End and Double End-On Azido Ligands and the Analog Co(II) Compound

Two new compounds of general formula [M(N3)2(dmbpy)] in which dmbpy = 5,5′-dimethyl-2,2′-bipyridine, and M = Mn(II) or Co(II), have been solvothermally synthesized and characterized structurally and magnetically. The structures consist of zig-zag polymeric chains with alternating bis-µ(azide-N1)2M and bis-µ(azide-N1,N3)2M units in which the cis-octahedrally based coordination geometry is completed by the N,N’-chelating ligand dmbpy. The molecular structures are basically the same for each metal. The Mn(II) compound has a slightly different packing mode compared to the Co(II) compound, resulting from their different space groups. Interestingly, relatively weak interchain interactions are present in both compounds and this originates from π–π stacking between the dmbpy rings. The magnetic properties of both compounds have been investigated down to 2 K. The measurements indicate that the manganese compound shows spin-canted antiferromagnetic ordering with a Néel temperature of TN = 3.4 K and further, a field-induced magnetic transition of metamagnetism at temperatures below the TN. This finding affords the first example of an 1D Mn(II) compound with alternating double end-on (EO) and double end-to-end (EE) azido-bridged ligands, showing the coexistence of spin canting and metamagnetism. The cobalt compound shows a weak ferromagnetism resulting from a spin-canted antiferromagnetism and long-range magnetic ordering with a critical temperature, TC = 16.2 K.

ZnII and CuII-Based Coordination Polymers and Metal Organic Frameworks by the of Use of 2-Pyridyl Oximes and 1,3,5-Benzenetricarboxylic Acid

The simultaneous use of 2-pyridyl oximes (pyridine-2 amidoxime, H2pyaox; 2-methyl pyridyl ketoxime, Hmpko) and 1,3,5-benzenetricarboxylic acid (H3btc) provided access to five new compounds, namely [Zn(H2btc)2(H2pyaox)2]•2H2O (1•2H2O), [Zn(Hbtc)(H2pyaox)2]n (2), [Cu(Hbtc)(H2pyaox)]n (3), [Cu(Hbtc)(HmpKo)]n (4) and [Cu2(Hbtc)2(Hmpko)2(H2O)2]•4H2O (5•4H2O). Among them, 3 is the first example of a metal-organic framework (MOF) containing H2pyaox. Its framework can be described as a 3-c uninodal net of hcb topology with the layers being parallel to the (1,0,1) plane. Furthermore, 3 is the third reported MOF based on a 2-pyridyl oxime in general. 2 and 4 are new members of a small family of coordination polymers containing an oximic ligand. 1-5 form 3D networks through strong intermolecular interactions. Dc magnetic susceptibility studies were carried out in a crystalline sample of 3 and revealed the presence of weak exchange interactions between the metal centres; the experimental data were fitted to a theoretical model with the fitting parameters being J = -0.16(1) cm-1 and g = 2.085(1). The isotropic g value was also confirmed by electronic paramagnetic resonance (EPR) spectroscopy. Reactivity studies were performed for 3 in the presence of metal ions; the reaction progress was studied and discussed for Fe(NO3)3 by the use of several characterization techniques, including single crystal X-ray crystallography and IR spectroscopy.

Crystal structures and magnetic properties of one-dimensional compounds constructed from Mn2(salen)2 building blocks and organic selenite acid ligands

Two new compounds composed of MnIII salen building blocks and organic selenite acid with ClO4− counter anions, namely [Mn2(salen)2(C6H5SeO2)](ClO4)(1) and [Mn2(salen)2(C6H4FSeO2)](ClO4)(2) [salen = N,N′-bis(salicylidene)-ethylenediamine], were synthesized through a one-pot reaction and characterized structurally and magnetically.

From 1D Coordination Polymers to Metal Organic Frameworks by the Use of 2-Pyridyl Oximes

The synthesis and characterization of coordination polymers and metal-organic frameworks (MOFs) has attracted a significant interest over the last decades due to their fascinating physical properties, as well as their use in a wide range of technological, environmental, and biomedical applications. The initial use of 2-pyridyl oximic ligands such as pyridine-2 amidoxime (H2pyaox) and 2-methyl pyridyl ketoxime (Hmpko) in combination with 1,2,4,5-benzene tetracarboxylic acid (pyromellitic acid), H4pma, provided access to nine new compounds whose structures and properties are discussed in detail. Among them, [Zn2(pma)(H2pyaox)2(H2O)2]n (3) and [Cu4(OH)2(pma)(mpko)2]n (9) are the first MOFs based on a 2-pyridyl oxime with 9 possessing a novel 3,4,5,8-c net topology. [Zn2(pma)(H2pyaox)2]n (2), [Cu2(pma)(H2pyaox)2(DMF)2]n (6), and [Cu2(pma)(Hmpko)2(DMF)2]n (8) join a small family of coordination polymers containing an oximic ligand. 9 exhibits selectivity for FeIII ions adsorption, as was demonstrated by a variety of techniques including UV-vis, EDX, and magnetism. DC magnetic susceptibility studies in 9 revealed the presence of strong antiferromagnetic interactions between the metal centers, which lead to a diamagnetic ground state; it was also found that the magnetic properties of 9 are affected by the amount of the encapsulated Fe3+ ions, which is a very desirable property for the development of magnetism-based sensors.

Slow magnetic relaxation in O–Se–O bridged manganese(iii) Schiff base complexes

Two new chain complexes consisting of a Mn(salen) building block bridged by O–Se–O units, [Mn₂(salen)₂(L)](ClO₄) (1) and {[Mn(salen)]₂(L)₂}·Y (2) (salen = N,N′-bis(salicylidene)-ethylenediamine, L = 3,4,5-trifluorobenzeneseleninic acid, Y = salicylaldehyde) have been synthesized and characterized structurally and magnetically.

An aromatic selenite bridged Mn(iii) chain compound showing the coexistence of single chain magnet and metamagnet behaviour

A new chain compound consisting of Mn₂(salen)₂ building blocks bridged by aromatic selenite was synthesized and characterized.

Heterobimetallic complexes from 0D clusters to 3D networks based on various polycyanometallates and [Cu(dmpn)2]2+ (dmpn = 2,2-dimethyl-1,3-diaminopropane): synthesis, crystal structures and magnetic properties

Six new cyanide-bridged complexes (0–3D) have been assembled by employing one copper compound and six cyano precursors. Investigation of the magnetic properties revealed the ferro- or antiferromagnetic coupling between Fe^III/Cr^I ion and Cu^II ion.

A cobalt(ii) chain based on pymca generated in situ from the hydrolysis of 2-cyanopyrimidine: spin canting and magnetic relaxation

A one-dimensional (1D) coordination polymer, [{Co2(pymca)2·(H2O)4}SO4·2H2O] n (1) (pymca = 2-carboxypyrimidine), was solvothermally synthesized via the reaction of 2-cyanopyrimidine and Co(SCN)2. A bidentate pymca ligand was formed in situ by the hydrolysis of 2-cyanopyrimidine. Furthermore, in this study, the magnetic properties of complex 1 were investigated in detail. The results indicated that complex 1 showed a single-chain magnet (SCM) behavior below ca. 3 K. The energy barrier (Δτ 1/k B) and preexponential factor (τ 0) of SCM were 31.2 K and 5.4 × 10-9 s, respectively.

Low pH constructed Co(ii) and Ni(ii) 1D coordination polymers based on Cα-substituted analogues of zoledronic acid: structural characterization, and spectroscopic and magnetic properties

Three novel coordination compounds based on α,α-disubstituted analogues of zoledronic acid with a cyclopropane (cpp) or cyclobutane (cbt) ring on the C_α carbon, isomorphous [Co(H₂cppZol)(H₂O)]·H₂O (1a), [Ni(H₂cppZol)(H₂O)]·H₂O (1b) and [Co(H₂cbtZol)(H₂O)]·H₂O (2a), were synthesized under hydrothermal conditions at low pH. Single-crystal X-ray diffraction analysis revealed that all the compounds had a 1D double zig–zag chain architecture with an 8 + 8 ring motif formed by alternately arranged symmetrical (–O–P–O–)₂ bridges linking equivalent octahedral metal centres. Both the ligand coordination mode and chain architecture displayed by 1a, 1b and 2a are unique among 1D [M(H₂L)(H₂O)_x]·yH₂O coordination polymers based on nitrogen-containing bisphosphonates reported so far. All the compounds exhibit similar decomposition pathways upon heating with thermal stabilities decreasing in the order 1b > 1a > 2a. The IR spectra revealed that lattice water release above 227, 178 and 97 °C, respectively, does not change the chain architecture leaving them intact up to ca. 320, 280 and 240 °C. Magnetic behaviour investigations indicated that 1a, 2a and 1b exhibit weak alternating antiferromagnetic–ferromagnetic exchange interactions propagated between the magnetic centres through double (–O–P–O–)₂ bridges. The boundary between antiferro- and ferromagnetic couplings for the Co–O⋯O–Co angle in 1a and 2a was estimated to be ca. 80°. This value is also applicable for recently reported [M₃(HL)₂(H₂O)₆]·6H₂O (M = Co, Ni) complexes based on α,α-disubstituted analogues of zoledronic acid and can be used to the explain magnetic behaviour of 1b.

1D Co(ii)/Ni(ii) coordination polymers with alternating antiferromagnetic–ferromagnetic exchange interactions between metal centers propagated through double (–O–P–O–)₂ bridges.

Weak ferromagnetism derived from spin canting in an amido-bridged homochiral Mn(iii) 1-D coordination polymer

An amido-bridged homochiral one-dimensional (1D) Mn(iii) coordination polymer behaves as a weak ferromagnet arising from spin canting with a coercive field of 3.0 kOe.

The effect of the orientation of the Jahn–Teller distortion on the magnetic interactions of trinuclear mixed-valence Mn(ii)/Mn(iii) complexes

The effect of the orientation of the Jahn–Teller distortion on the magnetic interactions in two new mixed-valence trinuclear Mn(iii)–Mn(ii)–Mn(iii) complexes has been investigated.

The use of a semi-flexible bipyrimidyl ligand for the construction of azide-based coordination polymers: structural diversities and magnetic properties

Using a semi-flexible quadritopic N-donor ligand, 5,5'-bipyrimidine (bpym), four new azide-based coordination polymers, {[Co2(bpym)(N3)4]·MeCN}n (1), [Co(bpym)(N3)2]n (2), [Mn(bpym)(N3)2]n (3) and {[Ni3(bpym)3(N3)6]·2H2O}n (4) were synthesized and structurally characterized. With bpym aciting as a planar μ4-bridging ligand, the resulting compound, 1, comprised a net-to-net 3D framework composed of two grid-like 44-subnets, Co(EE-N3)2-based and Co2(bpym)-based sheets, with a (4,6)-connected (42·64)(48·66·8)2 topology. Compound 2 adopted a 3D pillared-layer framework with a pts topology based on six-connected Co(ii) centers and four-connected twisted μ4-bpym ligands, while compound 3 adopted a 3D pillared-layer structure with a bcu topology based on Co(EE-N3)2-based 44-layers and two-connected twisted μ2-bpym pillars. In contrast, compound 4 had a 2D layered structure composed of 1D Ni(ii) chains with alternating double EE-N3 and double EO-N3 bridges in an EE-EE-EO sequence and two-connected bpym linkers. The magnetic properties of 1-4 were investigated. The findings indicate that 1 showed weak ferromagnetism due to spin-canted antiferromagnetism and long-range magnetic ordering with a critical temperature, TC = 12.6 K. In contrast, compound 2 exhibited weak ferromagnetism due to spin-canted antiferromagnetism and antiferromagnetic ordering. In compound 3, antiferromagnetic interactions dominated between the Mn(ii) centers through the EE-N3 bridges. In compound 4, the antiferromagnetic and ferromagnetic interactions were transmitted through double EE-N3 and double EO-N3 bridges, respectively, resulting in an AF-AF-F topological ferrimagnetic Ni(ii) chain. Furthermore, field-induced magnetic phase transitions of metamagnetism for 2 and 4 were also observed below TN = 3.6 K and 8.2 K, respectively.

Mixed metal CoII1−xZnIIx–organic frameworks based on chains with mixed carboxylate and azide bridges: magnetic coupling and slow relaxation

A series of isomorphous three-dimensional metal–organic frameworks [Co^II_1−xZn^II_x(L)(N₃)]·H₂O (x = 0.26, 0.56 and 0.85) based on bimetallic Co^II_1−xZn^II_x (x = 0.26, 0.56 and 0.85) chains with random metal sites have been synthesized and magnetically characterized. The Co^II_1−xZn^II_x series, which intrinsically feature random anisotropic/diamagnetic sites, shows complex magnetic interactions. By gradually introducing the diamagnetic Zn^II ions into the pure anisotropic Co^II single-chain magnets system, the ferromagnetic interactions between Co^II ions are gradually diluted. Moreover, the slow magnetic relaxation behaviour of the mixed metal Co^II_1−xZn^II_x systems also changes. In this bimetallic series Co^II_1−xZn^II_x, the Co-rich materials exhibit slow relaxation processes that may arise from SCM mechanism, while the Zn^II-rich materials show significantly low slow magnetic relaxation. A general trend is that the activation energy and the blocking temperature decrease with the increase in diamagnetic Zn^II content, emphasizing the importance of anisotropy for slow relaxation of magnetization.

A series of mixed-metal systems consisting of Co^II_1−xZn^II_x chains with (μ-COO)₂(μ-EO-N₃) bridges were prepared, exhibiting interesting magnetic coupling and slow magnetic relaxation.

1D Co(ii) coordination polymers based on cyclobutyl- and cyclopentyl-substituted zoledronate analogues: synthesis, structural comparison, thermal stability and magnetic properties

Competing magnetic exchange in 1a and 2a with predominant participation of antiferromagnetic interactions in 1a and ferromagnetic exchange in 2a.

Slow relaxation of the magnetization observed in an antiferromagnetically ordered phase for SCM-based two-dimensional layered compounds

We showed 2D-layered compounds exhibiting SCM-like behavior in an AF ordered phase. By introducing counteranions with a different size, Néel temperature and spin-flip inversion field could be tuned.

Two isomorphous Co(ii) coordination polymers based on new α,α-disubstituted derivatives of zoledronic acid: synthesis, structures and properties

1D Co(ii) coordination polymers based on new derivatives of zoledronic acid. Spectroscopic and magnetic characterization.

Two Isostructural Metal-Organic Frameworks Directed by the Different Center Metal Ions, Exhibiting the Ferrimagnetic Behavior and Slow Magnetic Relaxation

Two 3D isostructural metal-organic frameworks with 1D ferrimagnetic chains, formulated as [M3(L)(μ3-OH)2(H2O)4] [H4L = (1,1':4',1″-terphenyl)-2',3,3″,5'-tetracarboxylic acid, where M = Mn for 1 and Co for 2], have been successfully synthesized by employing different center metal ions and a multicarboxylate ligand under identical reaction conditions in this work. The single-crystal X-ray diffraction data of 1 and 2 reveal that the complexes are two 3D isostructural frameworks based on 1D [M3(OH)2]n chains composed of triangular subunits as rod-shaped secondary building units, which are classified as binodal 4,6-connected fry nets with the point symbol (5(10)·6(3)·7(8))(5(4)·6(2)). The magnetic properties revealed that complexes 1 and 2 exhibit ferrimagnetic behavior. Also, the alternating-current susceptibility of 2 displays slow magnetic relaxation, showing interesting magnetic behavior of a single-chain magnet with an effective energy barrier of 32 K.

Transition metal phosphonates with supramolecular structures: syntheses, structures, surface photovoltage and luminescence properties

Four new transition metal phosphonates with 2D and 3D supramolecular structures have been hydrothermally synthesized. The surface photovoltage and luminescence properties of the title compounds have also been studied.

Azide-bridged Cu(ii), Mn(ii) and Co(ii) coordination polymers constructed with a bifunctional ligand of 6-(1H-tetrazol-5-yl)-2,2′-bipyridine

Three new azide-bridged coordination polymers, [M(N₃)(tzbp)]_n (M = Cu, 1·Cu; Mn, 2·Mn; Co, 3·Co), were successfully prepared by introducing a bifunctional tetrazolate/2,2′-bipyridine ligand, 6-(1H-tetrazol-5-yl)-2,2′-bipyridine (Htzbp).

Lanthanide salen-type complexes exhibiting single ion magnet and photoluminescent properties

Mononuclear lanthanide complexes with formula (Et₃NH)[Ln(3-NO₂-salen)₂]·solvent (Ln = Eu (1Eu), Tb (2Tb), Dy (3Dy), Ho (4Ho), Er (5Er), Yb (6Yb); 3-NO₂-salen²⁻ = N,N′-bis(3-nitro-salicylaldehyde)ethylenediamine dianion) are reported.

Cobalt and copper pyridylmethylphosphonates with two- and three-dimensional structures and field-induced magnetic transitions

Two novel metal pyridylmethylphosphonates, namely, [Co(4-pmp)] (1) and [Cu(4-pmp)(H2O)] (2), (4-pmpH2 = 4-pyridylmethylphosphonic acid), have been hydrothermally synthesized and characterized by X-ray diffraction, infrared spectroscopy, elemental analysis, and thermogravimetric analysis. In compound 1, each {PO3C} tetrahedron is corner-shared with three {CoNO3} tetrahedra and vice versa, thus forming a one-dimensional (1-D) inorganic chain along the a axis containing 8-membered rings of [(Co-O-P-O)2]. The inorganic chains are further connected by a 4-pmp(2-) ligand, generating a 2-D layered structure. Compound 2 displays a three-dimensional (3-D) framework structure, in which the inorganic layers are pillared by the pyridyl groups of the ligand, generating a 3-D pillared-layered structure. The magnetic properties of 1 and 2 have been studied. Compounds 1 and 2 behave as metamagnets at low temperature. The critical fields are about 70 kOe for 1 and 47 kOe for 2 at 1.8 K.

Racemic cobalt phosphonates incorporating flexible bis(imidazole) co-ligands

By incorporating flexible bis(imidazol-1-ylmethyl)benzene (bix) co-ligands, four new racemic cobalt phosphonates with formulae Co3(3-ppap)2(1,4-bix)2(H2O)4·4H2O (1), Co3(3-ppap)2(1,3-bix)2(H2O)4·5H2O (2), Co3(3-ppap)2(1,2-bix)2(H2O)4·4H2O (3) and Co3(ppa)2(1,2-bix)2·4H2O (4) are isolated, where 3-ppapH3 represents 3-phenyl-3-((phosphonomethyl)amino)propanoic acid and ppaH3 is 2-phenyl-2-(phosphonomethylamino)acetic acid. Compounds 1-3 crystallize in the monoclinic space group P21/c and show two-dimensional structures in which the Co3(3-ppap)2 chains are bridged by 1,4-bix, 1,3-bix and 1,2-bix ligands in trans-modes, respectively. Within the chain, a racemic dimer of Co2(3-ppap)2(2-) is found, where the Co atoms are doubly bridged by O-P-O units from the (S)- and (R)-3-ppap(3-) ligands. The dimers are connected by another crystallographically independent Co atom through O-P-O linkages to form an infinite racemic chain. The packing modes of the layers in 1-3 are quite different, however, which are ABAB in the cases of 1 and 3 while ABCDABCD in the case of 2, attributed to the positional isomerism of the bix co-ligands. Compound 4 displays a chain structure in which the 1,2-bix bridges the Co atoms in cis-mode within the chain. Magnetic properties are investigated for all compounds.

A single-chain magnet based on linear [Mn(III)2Mn(II)] units

The synthesis, structural characterization and magnetic properties of a 1D coordination polymer based on a linear mixed valent [Mn(III)2Mn(II)] repeating unit are described. It displays single-chain magnet (SCM) behaviour with an energy barrier of ∼38 K and represents the first example of a mixed valent Mn-carboxylate SCM with a linear architecture.

The O–P–O bridged Mn2(salen)2chains showing coexistence of single chain magnet and metamagnet behaviour

Three chain compounds in which the Mn₂(salen)₂dimers are bridged by O–P–O units are reported, two of which display coexistence of SCM behavior and metamagnetism at low temperature.

Two water-bridged cobalt(ii) chains with isomeric naphthoate spacers: from metamagnetic to single-chain magnetic behaviour

Two water-bridged cobalt(ii) chains with isomeric naphthoate spacers exhibit metamagnetic and SCM behaviours, arising from the dramatically different interchain stacking induced by naphthoate isomers.

Synthesis, structures and magnetism of a series of dinuclear and one-dimensional Ni–Ln complexes: single-molecule magnetic behavior in one-dimensional nitrate-bridged Dy analogue

By using a salen-type ligand and changing the reaction solvent, a series of Ni^II–Ln^III complexes have been obtained and structurally and magnetically characterized.