Crystal Structure and Magnetic Properties of Trinuclear Transition Metal Complexes (MnII, CoII, NiII and CuII) with Bridging Sulfonate-Functionalized 1,2,4-Triazole Derivatives

Here we present the synthesis, structure and magnetic properties of complexes of general formula (Mn)(Me₂NH₂)₄][Mn₃(μ-L)₆(H₂O)₆] and (Me₂NH₂)₆[M₃(μ-L)₆(H₂O)₆] (M = Co^II, Ni^II and Cu^II); L⁻² = 4-(1,2,4-triazol-4-yl) ethanedisulfonate). The trinuclear polyanions were isolated as dimethylammonium salts, and their crystal structures determined by single crystal and powder X-ray diffraction data. The polyanionic part of these salts have the same molecular structure, which consists of a linear array of metal(II) ions linked by triple N1-N2-triazole bridges. In turn, the composition and crystal packing of the Mn^II salt differs from the rest of the complexes (with six dimethyl ammonia as countercations) in containing one Mn⁺² and four dimethyl ammonia as countercations. Magnetic data indicate dominant intramolecular antiferromagnetic interactions stabilizing a paramagnetic ground state. Susceptibility data have been successfully modeled with a simple isotropic Hamiltonian for a centrosymmetric linear trimer, H = −2J (S₁S₂ + S₂S₃) with super-exchange parameters J = −0.4 K for Mn^II, −7.5 K for Ni^II and −45 K for Cu^II complex. The magnetic properties of these complexes and their easy processing opens unique possibilities for their incorporation as magnetic molecular probes into such hybrid materials as magnetic/conducting multifunctional materials or as dopant for organic conducting polymers.

Slow magnetic relaxation in hexacoordinated cobalt(ii) field-induced single-ion magnets

To gain an insight into the factors affecting the enhancement of the energy barrier in SMM/SIM, hexacoordinate pseudohalide Co(ii) complexes based on the tridentate ligand were investigated.

Embedding 1D or 2D cobalt–carboxylate substrates in 3D coordination polymers exhibiting slow magnetic relaxation behaviors: crystal structures, high-field EPR, and magnetic studies

A novel 3D coordination polymer containing 2D cobalt–carboxylate layer had been constructed, exhibiting slow magnetic relaxation.

Di- and octa-nuclear dysprosium clusters derived from pyridyl-triazole based ligand: {Dy2} showing single molecule magnetic behaviour

Dy^III-based two complexes, {Dy₂} (1) and {Dy₈} (2), were successfully isolated with H₂bpte ligand. In 1, H₂bpte bears trans,trans- while in 2 has cis,cis- coordination modes. {Dy₂} displays the single-molecule magnet behaviour with an energy barrier U_eff = 59(4) K.

Different topologies in three manganese-μ-azido 1D compounds: magnetic behavior and DFT-quantum Monte Carlo calculations

The syntheses and structural characterization of three new monodimensional azido-bridged manganese(ii) complexes with empirical formulae [Mn(N3)2(aminopyz)2]n (1), [Mn(N3)2(4-azpy)2]n (2) and [Mn(N3)2(4-Bzpy)2]n (3) (pyz = pyrazine (1,4-diazine)), 4-azpy = 4-azidopyridine and 4-Bzpy = 4-benzoylpyridine) are reported. 1 is a monodimensional compound with double EO azido bridges, 2 is an alternating monodimensional compound with double end-on and double end-to-end azido bridges in the sequence di-EO-di-EE and 3 is a monodimensional compound with double end-on and double end-to-end azido bridges in the sequence di-EO-di-EO-diEO-di-EO-di-EE. The magnetic properties of 1-3 are reported. Periodic DFT calculations were performed to estimate the J values and quantum Monte Carlo simulations were carried out using the calculated J values to check their accuracy in comparison with the experimental magnetic measurements. From this theoretical analysis, two appealing features of the di-EO Mn(ii) compounds can be extracted: first, the exchange coupling becomes more ferromagnetic when the Mn-N-Mn bridging angle becomes larger and the spin density of the bridging nitrogen atoms has an opposite sign to that of the Mn(II) centers.

Ultrasonic irradiation assisted syntheses of one-dimensional di(azido)-dipyridylamine Cu(II) coordination polymer nanoparticles

The Cu(II) coordination polymer, [Cu(dpa)(N₃)₂]n (1), has been synthesized by the reaction of 2,2'-dipyridylamine (dpa) and a mixture of Cu(ClO₄)₂·6H₂O and sodium azide under ultrasonic irradiation. The products were characterized by infrared (FT-IR) spectroscopy, X-ray powder diffraction, and scanning electron microscopy (SEM). The CuO nano particles were prepared from calcination of compound 1 at 873 K. The CuO nanoparticles were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM). This study demonstrates that sonochemistry is a suitable method for the preparation of coordination polymer nano-structures and that the calcination temperature can be an effective parameter to control the size of CuO nano-structures prepared by direct calcination of a coordination polymer.

Structural diversities and magnetic properties of azide-containing coordination polymers based on flexible tetra-pyridinate ligands

By utilizing two quadritopic ligands, four new azido-containing coordination polymers have been synthesized and structurally characterized.

Spin-crossover behavior in two new supramolecular isomers

Two spin-crossover (SCO) supramolecular isomers formulated as [Fe(Mebpt){Au(CN)2}]n·xH2O (1, x = 0, and 2·H2O, x = n, MebptH = 3-(5-methyl-2-pyridyl)-5-(2-pyridyl)-1,2,4-triazole) have been successfully isolated and characterized by single-crystal X-ray crystallography, thermogravimetric analysis, differential scanning calorimetry, variable-temperature powder X-ray diffraction, and magnetic measurements. Structural analysis reveals that 1 is a two-dimensional coordination layer and 2·H2O is a one-dimensional coordination ladder structure, in which the Mebpt(-) ligands are coordinated in trans and cis bridging mode in 1 and 2·H2O, respectively. Dramatically, their SCO properties are further influenced by the octahedral coordination configuration of Fe(II). In 1, only the Fe(II) centers in trans configuration exhibit spin transition (Tc = 303 K), while in 2·H2O and the dehydrated 2, gradual two-step SCO (Tc1 = 235 K, Tc2 = 313 K) and one-step SCO behaviors (Tc = 315 K) occur, respectively.

Bis[4-amino-3,5-bis(pyridin-2-yl)-4H-1,2,4-triazole-κ2N1,N5]diaquacobalt(II) bis(perchlorate)

In the title structure, [Co(C₁₂H₁₀N₆)₂(H₂O)₂](ClO₄)₂, the Co^II atom lies on an inversion centre and is coordinated in a slightly distorted octa­hedral geometry by four N atoms from two 4-amino-3,5-bis­(pyridin-2-yl)-4H-1,2,4-triazole (adpt) ligands in equatorial positions and two O atoms from two water mol­ecules in axial positions. An intra­molecular N—H⋯N inter­action stabilizes the mol­ecular conformation. Inter­molecular N—H⋯O and O—H⋯O inter­actions involving the perchlorate counter-anions extend the monomeric compound into a two-dimensional network parallel to the bc plane.

Bis[3-(pyrazin-2-yl)-5-(pyridin-2-yl-κN)-1,2,4-triazol-1-ido-κN(1)]copper(II)

In the mononuclear title complex, [Cu(C₁₁H₇N₆)₂], the Cu^II atom lies on a crystallographic inversion centre and is coordinated by four N atoms from two bidentate chelate monoanionic 3-(pyrazin-2-yl)-5-(pyridin-2-yl-1,2,4-triazol-1-ido ligands, two from the triazolide rings [Cu—N = 1.969 (2) Å] and two from the pyridine rings [Cu—N = 2.027 (2) Å], giving a slightly distorted square-planar geometry.