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 (T_N) of 5.6 K. In addition, compound 1 shows the field-induced metamagnetic behavior at temperature below the T_N.

Modulating Magnetic and Photoluminescence Properties in 2-Aminonicotinate-Based Bifunctional Coordination Polymers by Merging 3d Metal Ions

Herein, the synthesis and study of bifunctional coordination polymers (CPs) with both magnetic and photoluminescence properties, derived from a heterometallic environment, are reported. As a starting point, three isostructural monometallic CPs with the formula [M(μ-2ani)₂ ]_n (M^II =Mn (1_Mn ), Co (3_Co ) and Ni (4_Ni ); 2ani=2-aminonicotinate), crystallise as chiral 2D-layered structures stacked by means of supramolecular interactions. These compounds show high thermal stability in the solid state (above 350 °C), despite which, in aqueous solution, compound 1_Mn is shown to partially transform into a novel 1D chain CP with the formula [Mn(2ani)₂ (μ-H₂ O)₂ ]_n (2_Mn ). A study of the direct current (dc) magnetic properties of 1_Mn , 3_Co and 4_Ni reveals a spin-canted structure derived from antisymmetric antiferromagnetic weak exchanges along the chiral network (as confirmed by DFT calculations) and magnetic anisotropy of the ions, in such a way that long-range ordering is observed with variable magnitude for the spin carriers. Moreover, compounds 3_Co and 4_Ni show no frequency-dependent alternating current (ac) susceptibility curves under zero dc field; this is characteristic behaviour of a glassy state that may be partially supressed for 3_Co by applying an external dc field. To overcome long-range magnetic ordering, Co^II ions are diluted in a diamagnetic Zn^II -based matrix, which enables single-molecule magnet behaviour. Interestingly, this strategy allows a bifunctional Co_x Zn_1-x 2ani material, which is imbued with a strong photoluminescent emitting capacity, as characterised by an intense blue light followed by a green afterglow, to be obtained.

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.

An unusual homospin CoII ferrimagnetic single-chain magnet with large hysteresis

A homospin Co(ii) ferrimagnetic SCM was obtained with coexistence of 1D ferrimagnetic chains, SCM-based slow magnetic dynamics and large hysteresis.

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.

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, T_C = 33.0 K, and furthers the field-induced magnetic transitions of metamagnetism at temperatures below T_C. Compound 2 shows an antiferromagnetic ordering with T_N = 3.05 K and a field-induced magnetic transition of spin-flop at temperatures below the T_N.

New discrete iodometallates with in situ generated triimidazole derivatives as countercations (Mn+ = Ag+, Pb2+, Bi3+)

By employing solvothermal in situ N-alkylation of organic bases with alcohols, four new iodometallates were obtained, and their structures are reported.

New in situ generated acylhydrazidate-coordinated complexes and acylhydrazide molecules: Synthesis, structural characterization and photoluminescence property

By utilizing the hydrothermal in situ acylation of organic acids with N2H4, three acylhydrazidate-coordinated compounds [Mn(L1)2(H2O)2] (L1=2,3-quinolinedicarboxylhydrazidate; HL1=2,3-dihydropyridazino[4,5-b] quinoline-1,4-dione) 1, [Mn2(ox)(L2)2(H2O)6]·2H2O (L2=benzimidazolate-5,6-dicarboxylhydrazide; HL2=6,7-dihydro-1H-imidazo[4,5-g]phthalazine-5,8-dione; ox=oxalate) 2, and [Cd(HL3)(bpy)] (L3=4,5-di(3'-carboxylphenyl)phthalhydrazidate; H3L3=6,7-dihydro-1H-imidazo[4,5-g]phthalazine-5,8-dione; bpy=2,2'-bipyridine) 3, as well as two acylhydrazide molecules L4 (L4=oxepino[2,3,4-de:7,6,5-d'e']diphthalazine-4,10(5H,9H)-dione) 4 and L5 (L5=4,5-dibromophthalhydrazide; L5=6,7-dibromo-2,3-dihydrophthalazine-1,4-dione) 5 were obtained. X-ray single-crystal diffraction analysis reveals that (i) 1 only possesses a mononuclear structure, but it self-assembles into a 2-D supramolecular network via the NhydrazineH⋯Nhydrazine and OwH⋯Ohydroxylimino interactions; (ii) 2 exhibits a dinuclear structure. Ox acts as the linker, while L2 just serves as a terminal ligand; (iii) In 3, L3 acts as a 3-connected node to propagate the 7-coordinated Cd(2+) centers into a 1-D double-chain structure; (iv) 4 is a special acylhydrazide molecule. Two OH groups for the intermediates 3,3'-biphthalhydrazide further lose one water molecule to form 4; (v) 5 is a common monoacylhydrazide molecule. Via the NhydrazineH⋯Ohydrazine, OhydroxyliminoH⋯Oacylamino and the π⋯π interactions, it self-assembles into a 2-D supramolecular network. The photoluminescence analysis reveals that 4 emits light with the maxima at 510nm.

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).

Spontaneous Magnetization in Homometallic μ6-Oxalate Coordination Polymers

The reaction of 1,2,4-triazole and NaF with M(ox) (M = transition-metal dication; ox = oxalate dianion) under hydrothermal conditions has led to the isolation of a variety of hybrid organic-inorganic coordination polymers. Four structurally different 3D networks were obtained, depending on the transition metal, with stoichiometry [M2(H2O)(μ2-ox)][M2(μ3-trz)6] [M = Fe (1), Co (2), Ni (3)], [Zn2(H2O)(μ3-trz)2(μ2-ox)] (4), [Mn3(μ3-trz)2(μ6-ox)(μ3-F)2] (5), and [Fe3(μ3-trz)2(μ6-ox)(μ2-F)2] (6). In all cases, the magnetic behavior is dominated by antiferromagnetic exchange interactions between paramagnetic centers. Remarkably, 5 and 6 present a novel magnetic connectivity around the oxalate anion: a μ6-bridging mode. This magnetic geometry promotes multiple triangular arrangements among antiferromagnetically coupled spin carriers, resulting in a complex magnetic network because of the presence of competing interactions. These materials exhibit spontaneous magnetization below 9 and 66 K, respectively.

Synthesis, characterization and magnetism of metal–organic compounds: role of the positions of the coordinating groups of a meso-flexible ligand in placing anisotropy to exhibit spin-canting behaviour

Magnetic anisotropy can be included in metal–organic coordination polymers by altering the position of the coordinating groups on the skeleton of the ligand.