A Three-Dimensional Coordination Framework with a Ferromagnetic Coupled Ni(II)-CrO4 Layer: Synthesis, Structure, and Magnetic Studies.

We report herein on the crystal structure and magnetic studies of a three-dimensional (3D) Ni(II)-chromate coordination polymer, [Ni(CrO4)(bpym)(H2O)]n (1; bpym = 5,5'-bipyrimidin), prepared by self-assembly of Ni(II) and chromate ions with a multi-N donor auxiliary ligands, bpym, through hydrothermal processes. The structure of 1 is composed of Ni(II)-CrO4 layers with [Ni3(µ3-CrO4)] triangular motifs, in which the Ni(II) centers are bridged by O':O':O':µ3-CrO42- anions, and the resulting layers are further connected by twisted trans-µ2-N,N'-bpym auxiliary ligands to form a 3D pillar-layered network with an hms topology. The magnetic properties of compound 1 were illustrated by variable field and temperature magnetic susceptibility measurements. The findings reveal that compound 1 shows intralayer ferromagnetic interactions within Ni(II)-CrO4 layers, and furthers the 3D antiferromagnetic ordering in the resulting of interlayer antiferromagnetic couplings with a Néel temperature (TN) of 5.6 K. In addition, compound 1 shows the field-induced metamagnetic behavior at temperature below the TN.

Cobalt Iron Oxides Prepared by Acidic Redox-Assisted Precipitation: Characterization, Applications, and New Opportunities.

The microscopic homogeneity of mixed metals in a single-phase oxide is a critical issue in improving material performance. Aqueous alkaline precipitation is the most common approach but it has the limits of microscopic inhomogeneity because of intrinsically different precipitation rates between metal cations. Herein, we demonstrate a new preparation of uniformly structural substituted cobalt iron oxides via acidic redox-assisted precipitation (ARP) upon the interaction of CoII and K2FeO4. This low-pH synthesis features the redox process between Co and Fe, presumably through the formation of inner-sphere complexes such as [(H2O)5CoII-O-FeVIO3]. With the nucleation starting from such complexes, one obtains a product with predominantly mixed-metal Co-O-Fe moieties, which improves the electrical conductivity of the product. This work further analyzes how the properties of the product species evolve during the hydrothermal synthesis step in the ARP process. We see that the Co/Fe ratio slowly increases from about 1:1 to a final value of 2:1, but does not reach the expected redox stoichiometry of 3:1. At the same time, the magnetization also increases, reaching a value of 16.9 emu g-1 for the final superparamagnetic product, which is three times higher than the value of monometallic Co3O4 and Fe2O3. The cobalt iron oxide samples obtained from ARP also possess superior oxygen evolution activity (307 mV overpotential at 10 mA cm-2 µg-1) compared to a mixture of Co3O4 and Fe2O3 (422 mV) or pure cobalt oxide (350 mV), highlighting the structure-induced enhancement of the catalytic activity. The difficult synthesis of evenly blended trinary/quaternary metals in a single-oxide phase may become possible in the future via ARP.

Perovskite-like Framework Encapsulated with Fe-Based Magnetic Units in Ba10Fe3Sb7Se24.

Ba10Fe3Sb7Se24 was synthesized using a KBr flux at 850 °C (Crystal Data: orthorhombic, Cmc21, a = 9.3412(2) Å, b = 44.6666(10) Å, c = 12.5496(3) Å, V = 5236.2(2) Å3, and Z = 4). The compound adopts a new three-dimensional framework constructed by the layer to include Fe2Se6 dimers and FeSe4 tetrahedra in the linkage motifs of [Fe2SbSe10] and [FeSb6Se14], respectively. Alternatively, the all Sb-based polyhedra are assembled as a semiconducting, perovskite-like framework lacking an inversion center where these Fe-based magnetic units are trapped within the interstices. The strong antiferromagnetic interaction is revealed by a high Curie constant of -113 K, but the curvature of field-cooled and zero-field-cooled magnetic susceptibilities bifurcating at ∼19 K is observed. The critical temperature is well verified by a broad peak of χM″ signal showing a rapid increase below 19 K under an alternating current field. The Fe2Se6 dimer featuring distorted edge-sharing tetrahedra to induce the spin-canted antiferromagnetic ordering strongly dominates such magnetic ordering. Finally, a weak hysteresis loop is clearly observed at 2.0 K. This dilute magnetic selenide displays a direct bandgap at ∼1.54 eV, analyzed by the Tauc equation. Interestingly, the use of second-harmonic-generation temperature dependence shows a turning point at ∼20 ± 1 K, which precisely corresponds to the magnetic ordering temperature within the error bar, thereby demonstrating the versatility of the technique for probing magnetic phase transition.

Temperature-Controlled Assembly/Reassembly of Two Dicarboxylate-Based Three-Dimensional Co(II) Coordination Polymers with an Antiferromagnetic Metallic Layer and a Ferromagnetic Metallic Chain.

Two new dicarboxylate-based three-dimensional cobalt coordination polymers, [Co(Me2mal)(bpe)0.5(H2O)]n (1) and [Co(Me2mal)(bpe)0.5]n (2), were synthesized from dimethylmalonic acid (H2-Me2mal) in temperature-controlled solvothermal reactions. Lower temperatures (6080 °C) favored the formation of 1, while higher temperatures (120 °C) favored the production of 2. Compound 1 is comprised of Co(II) corrugated layers linked by syn-anti carboxylate bridges from the Me2mal2- ligands and pillared through bis-monodentate bpe groups. Compound 2 is comprised of a three-dimensional network involving one-dimensional Co-carboxylate chains bonded by antisymmetric µ4-Me2mal2- ligands and aligned parallel to the [001] direction. The solvothermal retreatment of crystalline samples of 1 in a DMF/H2O solvent at 120 °C allowed the structural reassembly, with complete conversion within 2 over 48 h. Magnetic analyses revealed that compound 1 exhibits both spin-orbital coupling and antiferromagnetic interactions through a syn-anti carboxylate (Me2mal2-) bridge exchange pathway [Co-Co separation of 5.478 Å] and compound 2 showed a ferromagnetic interaction resulting from the short Co-Co separation (3.150 Å) and the small Co-O-Co bridging angles (98.5° and 95.3°) exchange pathway which was provided by µ4-Me2mal2- bridging ligand.

A Three-Dimensional Nickel(II) Framework from a Semi-Flexible Bipyrimidyl Ligand Showing Weak Ferromagnetic Behavior.

A semi-flexible bipyrimidyl ligand, 5,5'-bipyrimidin (bpym), was used for the self-assembly of a transition metal coordination polymer, resulting in the formation of a nickel(II) compound, [Ni(Br)2(bpym)2]n (1) with a three-dimemsional (3D) structure. Single-crystal X-ray analysis showed that compound 1 crystallizes in the monoclinic space group C2/c and the structure represents a 3D (4,4)-connected bbe topological framework constructed of nickel(II) ions, twisted cis-µ-bpym and planar trans-µ-bpym groups. Magnetic characterization revealed that 1 shows antiferromagnetic coupling between the pyrimidyl-bridged Ni(II) ions along with weak ferromagnetism due to spin canting with a magnetic ordering below Tc = 3.4 K.

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.

A Co(ii) framework derived from a tris(4-(triazol-1-yl)phenyl)amine redox-active linker: an electrochemical and magnetic study.

A new 3D coordination polymer {[Co2(µ-OH2)(TTPA)(DTDN)2·DMF]·H2O}n (1, TTPA = tris(4-(1H-1,2,4-triazol-1-yl)phenyl)amine, DTDN = 6,6'-dithiodinicotinate) was synthesised and characterised. The redox properties of this framework were elucidated by solid state electrochemical and spectroelectrochemical data. This is the first investigation of the redox behaviour of TTPA in coordination polymers. Furthermore, the incorporation of a paramagnetic Co(ii) metal ion into the framework caused 1 to show spin-flop behaviour as the result of a field-induced magnetic transition. The incorporation of two flexible ligands and Co(ii) metal ions represents a feasible approach for the advancement of multifunctional materials.

Two New Three-Dimensional Pillared-Layer Co(II) and Cu(II) Frameworks Involving a [M2(EO-N3)2] Motif from a Semi-Flexible N-Donor Ligand, 5,5'-Bipyrimidin: Syntheses, Structures and Magnetic Properties.

Two new three-dimensional (3D) Co(II)- and Cu(II)-azido frameworks, [Co2(N3)4(bpym)2]n (1) and [Cu2(N3)4(bpym)]n (2), were successfully synthesized by introducing a semi-flexible N-donor ligand, 5,5'-bipyrimidin (bpym), with different bridging modes and orientations. Compounds 1 and 2 were structurally characterized by X-ray crystallography, IR spectroscopy, thermogravimetry and elemental analysis. Compounds 1 and 2 are 3D pillared-layer frameworks with double end-on (EO) azido bridged dinuclear motifs, [M2(EO-N3)2]. In Compound 1, the bpym ligands show trans µ2-bridging mode and the role as pillars to connect the Co(II)-azido layers, composed of [Co2(EO-N3)2] motifs and single end-to-end (EE) azido bridges, to a 3D network with BN topology. In contrast, in 2, the bpym ligand adopts a twisted µ4-bridging mode, which not only connects the adjacent [Cu2(EO-N3)2] units to a layer, but also functions as a pillar for the layers of the 3D structure. The structural diversities between the two types of architectures can be attributed to the coordination geometry preference of the metal ions (octahedral for Co2+ and square pyramidal for Cu2+). Magnetic investigations revealed that Compound 1 exhibits ferromagnetic-like magnetic ordering due to spin canting with a critical temperature, TC = 33.0 K, and furthers the field-induced magnetic transitions of metamagnetism at temperatures below TC. Compound 2 shows an antiferromagnetic ordering with TN = 3.05 K and a field-induced magnetic transition of spin-flop at temperatures below the TN.

The synthesis of three new Cu5, Cu8 and Cu12 clusters via the use of a semi-flexible aminotriazine-based bis-methylpyridine ligand.

The synthesis of three new polynuclear Cu5, Cu8 and Cu12 clusters has been achieved using a semi-flexible aminotriazine-based bis-methylpyridine ligand, N2,N2-dibenzyl-N4,N6-di(pyridylmethyl)-1,3,5-triazine-2,4,6-triamine (H2dpmta). The reaction of Cu(ClO4)2·6H2O with H2dpmta in i-PrOH afforded the complex [Cu5(OH)4(H2dpmta)2(ClO4)4(H2O)4](ClO4)2·Et2O·5i-PrOH (1). A similar reaction of Cu(ClO4)2·6H2O and H2dpmta in the presence of PhCO2Na in i-PrOH/CH2Cl2 gave the complex [Cu8(OH)6(O2CPh)4(H2dpmta)2(ClO4)4(i-PrOH)2](ClO4)2·2CH2Cl2·2i-PrOH (2). The complex [Cu12O3(OH)2(Hdpmta)2(dpmta)2(O2CMe)8](ClO4)2·2MeCN (3) was produced from the reaction of [Cu2(O2CMe)4]·2H2O with H2dpmta and NaClO4 in MeCN/CH2Cl2. Single-crystal X-ray diffraction measurements were carried out on these complexes. The Cu5 cluster of 1 consisted of a planar [Cu5(µ-OH)4]6+ core in a rectangle-like arrangement. The Cu12 cluster of 2 represented a [Cu8(µ3-OH)4(µ-OH)2]10+ core infusion of two [Cu4(OH)2]6+ butterfly subunits. Complex 3 possesses a bent [Cu12(µ4-O)3(µ-OH)2]16+ core structure, in which a central [Cu4(µ4-O2-)] square planar moiety was fused with two butterfly-like [Cu4(µ4-O)(µ3-OH)] subunits. The magnetic properties of these three complexes were characterized by the measurements of variable-temperature and field magnetic susceptibility. The magnetic analysis showed that a strong antiferromagnetic interaction was mediated between Cu(ii) ions by the single OH- bridge in 1 and resulted a S = 3/2 spin ground state. In complex 2, both intramolecular antiferro- and ferromagnetic interactions were dominated between Cu(ii) ions resulting a spin ground state of S = 2. Indeed, complex 3 displayed an overall antiferromagnetic coupling.

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 synthesized by the introduction of a bifunctional tetrazolate/2,2'-bipyridine ligand, 6-(1H-tetrazol-5-yl)-2,2'-bipyridine (Htzbp), from the in situ [2 + 3] cycloaddition of 6-cyano-2,2'-bipyridine in the presence of an excess of sodium azide under hydrothermal conditions. Compounds 1·Cu−3·Co were characterized by X-ray crystallography, IR spectroscopy, thermogravimetry, and elemental analysis. With tzbp− ligands acting in the chelating coordination mode, compound 1·Cu was comprised of a single end-on N3− (EO-N3) bridged one-dimensional (1D) zigzag structure. Both compounds 2·Mn and 3·Co adopt two-dimensional (2D) layered structures composed of a double EO-N3 bridged dinuclear motif, [M2(EO-N3)2], which are interlinked by tzbp− ligands in the chelating/bridging mode. The layers of 2·Mn and 3·Co are stacked on each other in ⋯ABAB⋯ and ⋯AAAA⋯ fashions, respectively. Magnetic investigations revealed that intrachain antiferromagnetic interactions were dominant in compound 1·Cu, and both 2·Mn and 3·Co exhibited spin-canted antiferromagnetism with critical temperatures (TN) of 3.0 and 18.4 K, respectively. Furthermore, below TN, the field-induced magnetic transitions of spin-flop and metamagnetism were observed in 2·Mn and 3·Co, respectively.

Zethrene and dibenzozethrene: masked biradical molecules?

The syntheses, structures, and physical properties of dibenzozethrenes were explored. The results thus obtained were compared with those for zethrenes. Dibenzozethrenes were synthesized by the nickel-catalyzed cyclodimerization of 9-ethynyl-1-iodoanthracenes. The substituents in zethrene and dibenzozethrene twisted their backbones, and remarkably influenced their properties. Unlike closed-shell disubstituted derivatives, the parent zethrene and dibenzozethrene are singlet open-shell biradicals, which were studied by variable-temperature (1)H NMR, ESR, SQUID and computational methods. Since substituents were observed to affect significantly the biradical properties, the relevant mechanisms were analyzed. The nonlinear optical performance of each of these compounds depends on its π-conjugation and biradical properties. Dibenzozethrenes have larger two-photon absorption cross-sections than zethrenes, as most strongly evidenced by the parent dibenzothrene [σ(max)=4323 GM at 530 nm].

Utilization of a ligand containing 2,2'-bipyridyl and tetrazolate groups to construct a 2D Co(II) coordination polymer: spin canting and metamagnetism.

The use of anions of 6,6'-bis(1H-tetrazol-5-yl)-2,2'-bipyridine (H2btzbp) as chelating ligands in preparing a coordination polymer is described. The synthesis, X-ray crystal structure and magnetic properties of a new Co(II) coordination polymer, [Co(btzbp)]n (1), are reported. The in situ [2 + 3] cycloaddition reaction of 6,6'-dicyano-2,2'-bipyridine with sodium azide in the presence of Co(ClO4)2 under hydrothermal conditions afforded compound 1. Structural characterization revealed that 1 features a distorted two-dimensional (2D) grid layer generated by both tetrazolate and 2,2'-bipyridyl bridges of the btzbp(2-) ligand. Variable temperature and field magnetic susceptibility measurements indicate that compound 1 exhibits spin canting with T(N) = 4.0 K and metamagnetism with H(c) = 300 G.

A semi-flexible aminotriazine-based bis-methylpyridine ligand for the design of nickel(II) spin clusters.

The self-assembly of a semi-flexible aminotriazine-based bis-methylpyridine ligand, N(2),N(2)-dibenzyl-N(4),N(6)-di(pyridylmethyl)-1,3,5-triazine-2,4,6-triamine (H2L), with NiCl2 and NiBr2 afforded two new nickel(II) clusters, (H2NMe2)2[Ni5(OH)2(H2L)2Cl10] (1) and [Ni6(OH)2(H2L)2Br10(THF)2] (2) showing a high spin ground state of S = 3.

Ferromagnetic interaction and slow magnetic relaxation in a Co3 cluster-based three-dimensional framework.

A Co3 cluster-based three-dimensional (3D) framework, [Co3(4-ptz)4(N3)2(H2O)2]·4DMF (1; 4-Hptz = 4-(1H-tetrazol-5-yl)pyridine), exhibits ferromagnetic interactions and slow-magnetic relaxation behavior.

Dehydration induced 2D-to-3D crystal-to-crystal network re-assembly and ferromagnetism tuning within two chiral copper(II)-tartrate coordination polymers.

The synthesis of two homochiral l-tartrate-copper(II) coordination polymers, [Cu2(C4H4O6)2(H2O)2·xH2O]n (1), and [Cu(C4H4O6)]n (2), under hydrothermal conditions, is reported. Compound 1 adopts a 2D layered network structure with a space group of P21, while compound 2 features a 3D network structure with a space group P21212. Interestingly, the 2D layered structure of compound 1 can undergo a crystal-to-crystal network reassembly, with the formation of the 3D network structure of compound 2 under dehydration conditions. Variable temperature and field magnetic studies reveal the existence of a distinct ferromagnetic interaction between Cu(2+) ions as the result of distinct syn-anti carboxylate bridging coordination modes.

Mn4 single-molecule-magnet-based polymers of a one-dimensional helical chain and a three-dimensional network: syntheses, crystal structures, and magnetic properties.

Two Mn(4) single-molecule-magnet (SMM)-based coordination polymers, {[Mn(4)O(salox)(3)(N(3))(3)(DMF)(2)(H(2)O)(dpp)]·0.5MeOH}(n) (1·0.5MeOH; H(2)salox = salicylaldoxime; dpp = 1,3-di-4-pyridylpropane; DMF = N,N-dimethylformamide) and {[Mn(4)O(Me-salox)(3)(N(3))(3)(dpp)(1.5)]·1.5Et(2)O}(n) (2·1.5Et(2)O; Me-H(2)salox = hydroxyphenylethanone oxime), are self-assembled from Mn(ClO(4))(2)·6H(2)O/H(2)salox and Mn(ClO(4))(2)·6H(2)O/Me-H(2)salox systems with dpp and NaN(3) in DMF/MeOH, respectively. Both compounds comprise a mixed-valence tetranuclear manganese core, [Mn(II)Mn(III)(3)O](9+), which serves as a building unit for subsequent assembly via oximate and azido ligands. The flexible dpp ligand links with a Mn(4) unit, leading to the formation of a one-dimensional helical structure in 1·0.5MeOH and a three-dimensional pcu network in 2·1.5Et(2)O. The magnetic data analysis shows that antiferromagnetic interactions within the Mn(4) units resulted in S = (3)/(2) and (7)/(2) ground states for 1·0.5MeOH and 2·1.5Et(2)O, respectively. Both compounds show SMM behavior, as evidenced by frequency-dependent out-of-phase signals in alternating-current magnetic susceptibility and magnetic hysteresis loop studies with an energy barrier of U(eff) = 37 K for 2·1.5Et(2)O.

Spin-canting magnetization in an unusual Co4 cluster-based layer compound from a 2,3-dihydroxyquinoxaline ligand.

The self-assembly of Co(O(2)CPh)(2) with a 2,3-dihydroxyquinoxaline (H(2)dhq) linker has revealed a new two-dimensional cluster-based compound, [Co(4)(OMe)(2)(O(2)CPh)(2)(dhq)(2)(MeOH)(2)](n), which shows spin-canted magnetization and a definite magnetic hysteresis loop.

Self-adaptation of manganese-chloride arrangement toward high spin Mn5(µ-Cl)4 cluster-based metal-organic framework with S = 15/2.

The self-adaptation of manganese-chloride arrangement with the tripodal ligand 1,3,5-tris(benzimidazoyl-1-ylmethyl)-2,4,6-trimethylbenzene (Me(3)-TBzIm) afforded a rare 3D metal-organic framework, [Mn(5)Cl(10)(Me(3)-TBzIm)(4)](n) (1) showing a high spin ground state with S = 15/2.

Slow magnetic relaxation in a cobalt magnetic chain.

A homospin ladder-like chain, [Co(Hdhq)(OAc)](n) (1; H(2)dhq = 2,3-dihydroxyquinoxaline), shows a single-chain-magnet-like (SCM-like) behavior with the characteristics of frequency dependence of the out-of-phase component in alternating current (ac) magnetic susceptibilities and hysteresis loops.