Hydrothermal synthesis,crystal structure and magnetic properties of a copper(II) phosphonate

The treatment of 3-ammonium-1-hydroxypropylidene-1,1′-bisphosphonate (H₇ahdp) and 4,4′-bipy with CuCl₂?·?2H₂O resulted in a metal phosphonate [Cu(H₅ahdp)?·?H₂O] _n . Its crystal structure has been characterized by single X-ray crystallography. Although there is no 4,4′-bipy in the lattice structure, it plays a very important role in forming the one-dimensional chain of the polymer. Hydrogen bonds link the chains into a 3D network. The dinuclear secondary building units are observed in the compound. The determination of variable-temperature magnetic susceptibilities (5?～?300?K) shows weak intrachain antiferromagnetic coupling between copper(II) centers. The magnetic data were fitted to the appropriate equations derived from the Hamiltonian H?=??2JS ₁ S ₂, giving the parameter J?=??25.78?cm^?1. Its thermal properties were also investigated.     

The silica-like extended polymorphism of cobalt(II) imidazolate three-dimensional frameworks: X-ray single-crystal structures and magnetic properties

Five polymorphous frameworks of cobalt(II) imidazolates (1-5) have been prepared by solvatothermal syntheses. Of these, compound 3 has already been synthesized in a gas-phase reaction by Seel et al. in 1969 and structurally characterized by Sturm et al. in 1975. The new synthetic strategy affords four polymorphous frameworks of cobalt(II) imidazolates (1, 2, 4, 5) of crystalline substances, of which the compound 4 (a = b = 23.450(3), c = 12.460(3) A, tetragonal, I4(1)cd, Z = 16) is an isomorphous compound of [Zn(im)(2)]( infinity ), which was also synthesized in a gas-phase reaction in 1980. The frameworks of compounds 1 and 2 are porous and isostructural; they have the same framework topology that represents a novel uninodal (6,4)-net: 1: a = 18.513(4), b = 24.368(5), c = 9.2940(19) A, orthorhombic, Fdd2, Z = 16; 2: a = 17.635(4), b = 27.706(6), c = 9.0810(18) A, orthorhombic, Fdd2, Z = 16. The framework of compound 5 exhibits a topology of zeolitic structure with the unit-cell parameters: a = 24.3406(8), b = 9.4526(3), c = 24.8470(8) A, beta = 91.977(1) degrees, monoclinic, P2(1)/n, Z = 4. All polymorphous frameworks of cobalt(II) imidazolates reflect the structural features of silica (SiO(2)) and also exhibit different magnetic behaviors, although the imidazolates transmit the antiferromagnetic coupling between the cobalt(II) ions in all cases. However, the uncompensated antiferromagnetic couplings arise from spin-canting are sensitive to the structures: compound 1 is an antiferromagnet with T(N) = 13.11 K; compounds 2-4 are weak ferromagnets (canted antiferromagnets): 2 shows a very weak ferromagnetism below 15 K, 3 exhibits a relatively strong ferromagnetism below 11.5 K and a coercive field (H(C)) of 1800 Oe at 1.8 K, and 4 displays the strongest ferromagnetism of the three cobalt imidazolates and demonstrates a T(C) of 15.5 K with a coercive field, H(C), of 7300 Oe at 1.8 K. However, compound 5 seems to be a hidden canted antiferromagnet with a magnetic ordering temperature of 10.6 K.     

Synthesis, crystal structure, and magnetic properties of a cobalt(II) complex with (3,5-dichloropyridin-4-yl)(pyridin-4-yl)methanol

A novel bridging ligand, (3,5-dichloropyridin-4-yl)(pyridin-4-yl)methanol (I), and its cobalt(II) complex, [Co(I)₂(NCS)₂]_n (II), were prepared. The structures of ligand I and complex II were determined by single crystal X-ray analysis. Magnetic susceptibility measurements were performed for cobalt (II) complex II. Compound I crystallised in orthorhombic space group Pbca with a = 7.6585(14) Å, b = 12.209(2) Å, c = 23.207(4) Å, V= 2170.0(7) ų and Z=8. Complex II crystallised in monoclinic space group P2₁/n with a = 13.223(8) Å, b = 16.959(10) Å, c = 13.948(8) Å, β = 115.395(10)°, V= 2826(3) ų and Z = 4. Each cobalt(II) ion is surrounded by two NCS^? anions and four pyridyl moieties from two bridging ligands. Each bridging ligand connects two neighbouring Co(II) ions to form a 2-dimensional structure. Temperature dependence of the molar magnetic susceptibilities in the temperature range of 2–300 K revealed that magnetic interactions between the cobalt ions are weak.     

A mixed‐valence complex of cobalt based on 3‐methoxysalicylaldoxime

A new tetranuclear mixed‐valence cobalt complex, namely di‐μ₂‐azido‐diazidodiethanolbis{μ₂‐2‐[(hydroxyimino)methyl]‐6‐methoxyphenolato}bis{μ₃‐6‐methoxy‐2‐[(oxidoimino)methyl]phenolato}dicobalt(II)dicobalt(III) ethanol disolvate, [Co^II₂Co^III₂(C₈H₇NO₃)₂(C₈H₈NO₃)₂(N₃)₄(C₂H₅OH)₂]·2C₂H₅OH, has been synthesized by the reaction of Co(OAc)₂·4H₂O (OAc is acetate) with 3‐methoxysalicylaldoxime (H₂mosao) in an ethanol solution. In the complex, the four Co cations all display distorted octahedral coordination environments and they are bridged by two κ²,κ¹,κ¹;μ₃‐mosao²⁻ ligands, two κ²,κ²;μ₂‐Hmosao⁻ ligands and two μ₂‐N₃⁻ anions to form a tetranuclear [Co₄N₄O₄] cluster. Adjacent clusters are connected through weak C—H...N and C—H...O interactions, resulting in a two‐dimensional supramolecular network parallel to the ac plane. The magnetic properties of the complex have also been studied.     

Magnetization Slow Dynamics in Ferrocenium Complexes

The single-molecule magnet (SMM) properties of a series of ferrocenium complexes, [Fe(η⁵-C₅R₅)₂]⁺ (R=Me, Bn), are reported. In the presence of an applied dc field, the slow dynamics of the magnetization in [Fe(η⁵-C₅Me₅)₂]BAr_F are revealed. Multireference quantum mechanical calculations show a large energy difference between the ground and first excited states, excluding the commonly invoked, thermally activated (Orbach-like) mechanism of relaxation. In contrast, a detailed analysis of the relaxation time highlights that both direct and Raman processes are responsible for the SMM properties. Similarly, the bulky ferrocenium complexes, [Fe(η⁵-C₅Bn₅)₂]BF₄ and [Fe(η⁵-C₅Bn₅)₂]PF₆, also exhibit magnetization slow dynamics, however an additional relaxation process is clearly detected for these analogous systems.     

Enhanced Magnetic Hardness in a Nanoscale Metal–Organic Hybrid Ferrimagnet

A new layered metal–organic hybrid compound, namely, [Co₃(μ₃‐OH)₂(BTP)₂] ( 1 ; BTP=4‐(3‐bromothienyl)phosphonate), is reported. The inorganic layer can be viewed as a pseudo‐Kagomé lattice composed of corner‐sharing irregular triangles of Co₃(μ₃‐OH), with the cavities filled with the PO₃ groups. The interlayer space is occupied by the 3‐bromothienyl groups of BTP^2?. The bulk sample of compound 1 experiences a long‐range ferromagnetic ordering below 30.5 K, with a coercivity (H_c) of 5.04 kOe at 5 K. A systematic study on the size‐dependent magnetic coercivity of 1 reveals that the coercivity of 1 increases with reduced particle size from the micrometer to the nanometer scale. When the particle size is about 50–200 nm, the coercivity reaches 24.2 kOe at 5 K. The results demonstrate that compound 1 can vary from a soft magnet to one of the hardest molecule‐based magnets, simply by reducing the particle size to nanoscale region.     

Cobalt-lanthanide coordination polymers constructed with metalloligands: a ferromagnetic coupled quasi-1D Dy3+ chain showing slow relaxation

Four types of cobalt-lanthanide heterometallic compounds based on metalloligand Co(2,5-pydc)(3) (3-) (2,5-H(2)pydc=pyridine-2,5-dicarboxylate acid), [Ln(2)Co(2)(2,5-pydc)(6)(H(2)O)(4)](n) 2n H(2)O (1) (Ln=Tb, Dy for 1 a, 1 b respectively), [Tb(2)Co(2)(2,5-pydc)(6)(H(2)O)(4)](n)3n H(2)O (2), [Tb(2)Co(2)(2,5-pydc)(6)(H(2)O)(9)](n)4n H(2)O (3), and [LaCo(2,5-pydc)(3)(H(2)O)(2)](n)2n H(2)O (4) have been synthesized. Compound 1 has a layer structure with well-isolated carboxylate-bridged Ln(3+) chains, compound 2 is a three-dimensional (3D) porous network with Tb(3+) chains that are also well isolated and carboxylate bridged, 3 is a layer structure based on dinuclear units, and 4 is a 3D network with boron nitride (BN) topology. DC magnetic studies reveal ferromagnetic coupling in all the carboxylate-bridged Ln(3+) chains in 1 a, 1 b, and 2. Compared to the silence of the out-of-phase ac susceptibility of 2, above 1.9 K the magnetic relaxation behavior of both 1 a and 1 b is slow like that of a single-chain magnet.     

A three‐dimensional twofold interpenetrated cobalt(II) MOF containing a flexible carboxylate‐based ligand: synthesis,structure and magnetic properties

The design and synthesis of coordination polymers (CPs) have attracted much interest due to the intriguing diversity of their architectures and topologies. The functional solid catena‐poly[μ₂‐aqua‐triaqua{μ₄‐5‐[4‐carboxyphenoxy)methyl]benzene‐1,3‐dicarboxylato}{μ₃‐5‐[4‐carboxyphenoxy)methyl]benzene‐1,3‐dicarboxylato}dicobalt(II)], [Co₂(C₁₆H₁₀O₇)₂(H₂O)₄]_n or [Co₂(HL)₂(μ₂‐H₂O)(H₂O)₃]_n, was synthesized successfully by self‐assembly of Co^II ions with 5‐[(4‐carboxyphenoxy)methyl]isophthalic acid (H₃L). The title compound was obtained under hydrothermal conditions and exhibits a twofold interpenetrated three‐dimensional skeleton with hms 3,5‐conn topology according to the cluster representation for valence‐bonded metal–organic frameworks (MOFs). It has been characterized by single‐crystal X‐ray diffraction, IR spectroscopy, powder X‐ray diffraction (PXRD), thermogravimetric analysis and susceptibility measurements. The antiferromagnetic coupling between adjacent Co^II centres occurs via superexchange through the ligands.     

Triimidosulfonates as Acute Bite‐Angle Chelates: Slow Relaxation of the Magnetization in Zero Field and Hysteresis Loop of a CoII Complex

Starting from a polyimido sulfonate the four‐coordinate, N,N′‐chelated Co^II complex [Co{(NtBu)₃SMe}₂] ( 1 ) was synthesized, and its molecular structure was elucidated by single‐crystal X‐ray structural analysis. The acute N‐Co‐N bite angle imposed by the N,N′‐chelating ligand (NtBu)₃SMe^? leads to pronounced C_2v distortion of the tetrahedral coordination environment and thus to high anisotropy of the Co^II ion (D≈?58 cm^?1), favorable for single‐molecule‐magnet (SMM) properties. Magnetic measurements revealed a high barrier to spin reversal (U_eff=75 cm^?1) that gives rise to the observation of slow relaxation of the magnetization in zero field and a hysteresis loop at 2 K for this unique complex.     

Conformational polymorphism in a cobalt(II) dithiocarbamate complex

Two conformational polymorphs of (N,N‐dibutyldithiocarbamato‐κ²S,S′)[tris(3,5‐diphenylpyrazol‐1‐yl‐κN²)hydroborato]cobalt(II), [Co(C₄₅H₃₄BN₆)(C₉H₁₈NS₂)] or [Tp^Ph2Co(S₂CNBu₂)], 1 , are accessible by recrystallization from dichloromethane–methanol to give orthorhombic polymorph 1a , while slow evaporation from acetonitrile produces triclinic polymorph 1b . The two polymorphs have been characterized by IR spectroscopy and single‐crystal X‐ray crystallography at 150 K. Polymorphs 1a and 1b crystallize in the orthorhombic space group Pbca and the triclinic space group P, respectively. The polymorphs have a trans ( 1a ) and cis ( 1b ) orientation of the butyl groups with respect to the S₂CN plane of the dithiocarbamate ligand, which results in an intermediate five‐coordinate geometry for 1a and a square‐pyramidal geometry for 1b . Hirshfeld surface analysis reveals minor differences between the two polymorphs, with 1a exhibiting stronger C—H…S interactions and 1b favouring C—H…π interactions.