Weak Antiferromagnetic Exchange Research Articles

Copper(II) salts and complexes of 2-amino-5-nitropyridine*

Four new copper compounds of 2-amino-5-nitropyridine/pyridinium (5NAP/5NAPH) have been prepared and characterized: (5NAPH)2[CuBr4], 2; (d2-5NAPD)2[CuBr4], 2a; (5NAP)2CuCl2, 3; (5NAP)2CuBr2, 4. Compounds 2 and 2a are isomorphous and crystallize in the triclinic space group P-1. Packing is stabilized by hydrogen/deuterium bonds. Short Br…Br contacts provide potential magnetic superexchange pathways, but only very weak antiferromagnetic exchange is observed (J/kB∼-2 K). Compounds 3 and 4 are also isomorphous and crystallize in the monoclinic space group P21/c. The molecules are linked into chains by bihalide bridges, and the chains linked into rectangular/square layers by short X…X. contacts. Variable temperature magnetic data were best fit by the S = ½ antiferromagnetic rectangular model for 3 (C = 0.429(1) emu-K/mol-Oe, J/kB = −9.38(6) K, J’/kB = −5.91(4) K). Variable temperature magnetic susceptibility data for 4 were best fit by the two-dimensional antiferromagnetic square lattice model (C = 0.43(1) emu-K/mol-Oe, J/kB = −36.5(2) K).

Antiferromagnetic resorcinol bridged dinuclear square-planar copper (II) complexes: Syntheses, structural, spectroscopic and magnetic properties

A new C2-symmetric Schiff base ligand (H2L) featuring a core resorcinol bridging unit has been created, utilizing the Duff formylation reaction followed by the Schiff base condensation reaction. The ligand was characterized by various spectroscopic techniques. Cu(II) salts with varying coordinating anions (Cl− and SCN−) in methanol were allowed to react with this ligand in a 2:1 M ratio to create dinuclear Cu(II) complexes. The complexes were isolated in pure form and characterized by, elemental analysis,single crystal X-ray crystallography and various spectroscopic techniques. X-ray analysis discloses that both complexes are dinuclear, where the ligand (H2L) being tridentate in nature, coordinates to Cu(II) through its two N donor atoms and one O donor atom in the equatorial positions. The respective anions (−Cl− for 1 and –SCN− for 2) coordinate to Cu(II) to complete its square planar geometry. Temperature dependent magnetic susceptibility measurements indicate weak antiferromagnetic exchange interactions with a coupling constant of J = −5.9(1) cm−1 and g = 2.148(1) for 1 and J = −10.08(1) cm−1 and g = 2.106(1) for 2.

Lanthanide complexes of monosubstituted Calix[4]arene-ligands: Synthesis, structures, and magnetic properties of [Ln2(L)2(MeOH)4] (Ln = La, Gd, Tb, Tm) (H3L = mono-O-propargyl-calix[4]arene)

The ability of the propargylated calix[4]arene ligand H3L (= 25-(2-propynyloxy)-26,27,28-trihydroxy-calix[4]arene) to bind lanthanide ions has been studied. The triply deprotonated ligand was found to support dinuclear neutral complexes of composition [Ln2L2(MeOH)4] (Ln= La (1), Gd (2), Tb (3), Tm (4)). Spectroscopic data for 1–4 as well as X-ray crystallographic analysis of single crystals of 1∙(MeOH)2 and 2∙(MeOH)2 reveal that two [LnL] entities dimerize via two phenolato groups to generate a centrosymmetric (MeOH)2O3Ln(μ-O)2LnO3(OHMe)2 core structure. The Ln3+ ions reside in a distorted mono-capped octahedral coordination environment. Squid magnetic measurements for the Gd3+ and Tb3+ complexes agree with the formulation as dinuclear compounds, and reveal the presence of very weak antiferromagnetic exchange interactions (J < 0.1 cm−1). The ability of the La3+ complex to react with azides in a click reaction is also demonstrated.

Topological magnon–polaron transport in a bilayer van der Waals magnet

The stacking of intrinsically magnetic van der Waals materials provides a fertile platform to explore tunable transport effects of magnons, presenting significant prospects for spintronic applications. The possibility of having topologically nontrivial magnons in these systems can further expand the scope of exploration. In this work, we consider a bilayer system with intralayer ferromagnetic exchange and a weak interlayer antiferromagnetic exchange and study the topological magnon-polaron excitations induced by magnetoelastic couplings. Under an applied magnetic field, the system features a metamagnetic transition, where the magnetic ground state changes from antiparallel layers to parallel. We show that the metamagnetic transition is accompanied by a transition of the topological structure of the magnon polarons, which results in discernible changes in the topology induced transport effects. The magnetic-field dependence of the thermal Hall conductivity and spin Nernst coefficient is analyzed with linear response theories.

Lanthanide Metal-Organic Frameworks Exhibiting Fluoro-Bridged Extended Chains: Synthesis, Crystal Structures, and Magnetic Properties.

Two fluoro-bridged lanthanide-containing metal-organic frameworks (MOFs) were synthesized using 2,2'-bipyridine-4,4'-dicarboxylic acid (BPDC), a fluorinated modulator, and a lanthanide nitrate. The syntheses of MOFs containing Gd3+ or Tb3+ and a closely related MOF structure containing Ho3+, Gd3+, or Tb3+ are presented. The presence of the fluorinated metal chains in these MOFs is shown through single crystal X-ray diffraction, energy dispersion X-ray spectroscopy, 19F nuclear magnetic resonance, and X-ray photoelectron spectroscopy. Magnetic measurements reveal weak antiferromagnetic exchange between the Ln3+ ions mediated by fluoride anions along the zigzag ladder chains present in the crystal structures of these MOFs.

Synthesis, coordination modes, structures, and magnetic properties of halogen-substituted 2-hydroxypyridine copper(II) chloride coordination compounds

A family of 6-X-2-hydroxyprydine/pyridone (6-X-2-HOpy/pyridone) Cu(II) compounds, [Cu(6-X-2-HOpy)2Cl2] (1 X = F; 2 X = Cl) and [(6-X-2-pyridone)CuCl(μ-Cl)]2 (3 X = Cl; 4 X = Br), has been prepared. Solution-based infrared spectra displayed a correlation between tautomeric state, primarily driven by halogen identity, and coordination mode with neutral nitrogen coordination mode favored as Br ≪ Cl < F. The tautomeric state of 6-Cl-2-HOpy is influenced by metal ion concentration (M) with lactam concentration increasing as M increases. Compound 1 has F–F contacts less than the sum of the van der Waals radii but falls outside of the typical halogen bonding angle parameters, R–X•••Y = R–Y•••X = 138.2°. Compounds 1 and 2 exhibit weak antiferromagnetic exchanges, fit with a one-dimensional quantum Heisenberg antiferromagnetic linear chain (1D-QHAF) model and J/kB = −1.99(1) K and −0.92(7) K, respectively. Compounds 3 and 4 exhibit a dominating ferromagnetic exchange and an antiferromagnetic exchange and were qualitatively fit to a ferromagnetic linear chain with an interchain interaction model. This model does not accurately represent the physical parameters of the system and was used to show that both exchanges exist and are nontrivial.

Structural and Electronic Diversity as a Function of Metal Ions and Co‐ligands in Deprotonated Epindolidione Bridged Diruthenium and Diosmium Set‐up

AbstractThe article dealt with the structurally validated L2− (H2L=epindolidione=5,11‐dihydroquinolino[3,2‐b]quinoline‐6,12‐dione, a heteroatom‐modified tetracene and a structural isomer of indigo dye) bridged {(acac)2RuIII}2(μ‐L2−) 1/2 (S=1, acac=acetylacetonate) and [{(bpy)2OsII}2(μ‐L2−)](ClO4)2 [3](ClO4)2/[(pap)2OsII}2(μ‐L2−)](ClO4)2 [4](ClO4)2 (S=0, bpy=2,2′‐bipyridine, pap=2‐phenylazopyridine). 1/2 and [3](ClO4)2/[4](ClO4)2 with a metal‐metal separation of ≈7 Å stabilized selectively in meso(ΔΛ)/rac(ΔΔ/ΛΛ) and meso diastereomeric forms, respectively, in spite of calculated minor difference in energy between the diastereomers in each case. Though 2, [3](ClO4)2/[4](ClO4)2) exhibited intermolecular π–π interactions, no such non‐covalent interaction was perceived in 1. RuIIIRuIII derived 1/2 (S=1, 2.63/2.57 μB at 300 K) attributed to non‐interacting two Ru(III) (S=1/2) spins with an intermolecular through space weak antiferromagnetic exchange interaction below 12 K and its variable temperature 1H NMR revealed Fermi and pseudo‐contact shifts. Multiple redox steps of the complexes varied as a function of metal ion (Ru versus Os), its oxidation state (III versus II) and ancillary ligand (acac versus bpy versus pap). A collective consideration of DFT calculated MOs and Mulliken spin densities suggested delicate electronic forms along the redox chain due to the participation of bridge largely in the oxidation processes as a consequence of its redox non‐innocent feature. Reductions were however mostly centered around the metal (RuIII to RuII) and ancillary ligands (bpy/pap) in 1/2 and 32+/42+, respectively. 1n/2n, [3]2+/[4]2+ displayed mixed metal/ligand based weak low‐energy (800‐1400 nm) transitions in addition to intense visible bands as corroborated by TD‐DFT calculations.

Mn(III)–Salen Complexes with Metallophilic Interactions

We synthesized a series of five novel Mn–salen-based compounds (1a–1c, 2a, 2b) through the reaction between precursor chloride complexes and potassium silver/gold dicyanide. The prepared compounds were structurally and magnetically characterized. Our findings revealed that all the Mn(III) central atoms exhibited an axially elongated coordination polyhedron, leading to the observation of axial magnetic anisotropy as indicated by the negative axial magnetic parameter D, which was determined through fitting the experimental magnetic data and supported by theoretical CASSCF/NEVPT2 calculations. Furthermore, we observed magnetic-exchange interactions only in compounds with a special supramolecular topology involving O–H···O hydrogen-bonded dimers. In these cases, the weak magnetic exchange (J/cm−1 = −0.58(2) in 1b and −0.73(7) in 2b) was mediated by the O–H···O hydrogen bonds. These findings were further supported by BS–DFT calculations, which predicted weak antiferromagnetic exchanges in these complexes and ruled out exchange interactions mediated by diamagnetic cyanido metallo–complex bridges. Additionally, we investigated the observed Ag···π (1b) and Au···Au (2b) interactions using QT–AIM calculations, confirming their non-covalent nature. We compared these results with previously reported Mn–salen-based compounds with metallophilic interactions arising from the presence of the [Ag/Au(CN)2]− bridging units.

Investigation of dipodal acetoguanamine-Schiff bases and their homonuclear FeIII complexes

The ligands 2,4-bis(2-hydroxyphenyliminomethyl)-6-methyl-1,3,5-triazine (AGSAL), 2,4-bis(2-carboxyphneyliminomethyl)-6-methyl-1,3,5-triazine (AG2FBA), and 2,4-bis(4-carboxyphneyliminomethyl)-6-methyl-1,3,5-triazine (AG4FBA) were prepared with a Schiff base condensation between acetoguanamine and the corresponding salicylaldehyde, 2-formylbenzoic acid, and 4-formylbenzoic acid. High-spin (S = 5/2) complex [FeIII(AGSAL)Cl] was obtained by complexation of AGSAL with FeCl3. Then, binuclear complexes [{FeIII(AGSAL)}2(AG2FBA)] and [{FeIII(AGSAL)}2(AG4FBA)] were prepared by combination of [FeIII(AGSAL)Cl] and “(AG2FBA), (AG4FBA),” respectively. Then, trinuclear complexes [{FeIII(AGSAL)}2(FeIIIAG2FBA)] and [{FeIII(AGSAL)}2(FeIIIAG4FBA)] of the ligands were prepared by reaction of the binuclear complexes and FeCl3 salt. A weak antiferromagnetic exchange was found for all complexes. Finally, the structures of ligands and complexes were identified by using elemental analysis, magnetic susceptibility, 1H NMR, 13C NMR and FT-IR spectral data.

Synthesis, Structures, and Magnetism of Four One-Dimensional Complexes Using [Ni(CN)4]2- and Macrocyclic Metal Complexes.

Four one-dimensional complexes, denoted as [NiL1][Ni(CN)4] (1), [CuL1][Ni(CN)4] (2), [NiL2][Ni(CN)4]·2H2O (3), and [CuL2][Ni(CN)4]·2H2O (4) (L1 = 1,8-dimethyl-1,3,6,8,10,13-hexaaza-cyclotetradecane; L2 = 1,8-dipropyl-1,3,6,8,10,13-hexaazacyclotetradecane) were synthesized by reacting nickel/copper macrocyclic complexes with K2[Ni(CN)4]. Subsequently, the synthesized complexes were characterized using elemental analysis, infrared spectroscopy analysis, thermogravimetric analysis, and X-ray powder diffraction. Single-crystal structure analysis revealed that the Ni(II)/Cu(II) atoms were coordinated by two nitrogen atoms from [Ni(CN)4]2- with four nitrogen atoms from a macrocyclic ligand, forming a six-coordinated octahedral coordination geometry. Nickel/copper macrocyclic complexes were bridged by [Ni(CN)4]2- to construct one-dimensional chain structures in 1-4. The characterization results showed that the four complexes obeyed the Curie-Weiss law with a weak antiferromagnetic exchange coupling.

Spin Crossover Behavior of FeII Complexes Bridged by Thiophene‐Functionalized Triazole Ligands with Different Sizes and Rigidities

AbstractFour thiophene functionalized triazole ligands (L1=4‐(thenyl)‐1,2,4‐triazole, L2=4‐(thiophene ethyl)‐1,2,4‐triazole, L3=N‐Thiophenylidene‐4H‐1,2,4‐triazole‐4‐amine, and L4=(4‐[(E)‐2‐(5‐sulfothiophene)vinyl]‐1,2,4‐triazole) were synthesized. These ligands have different lengths and rigidities, while ligand L4 has a sulfonic acid group that can form a hydrogen bond. Five 1D FeII chain complexes were synthesized: [Fe(L1)3](X)2 ⋅ nH2O [X=BF4−, n=1.5 (C1); X=ClO4−, n=1 (C2)], [Fe(L2)3](BF4)2 ⋅ 1.5H2O (C3); [Fe(L3)3](X)2 ⋅ nH2O [X=BF4−, n=2 (C4); X=ClO4−, n=2.5 (C5)]. The results of temperature‐dependent magnetic susceptibility reveal that complexes C1, C2, and C3 experienced the transition between two spin states. And C4 and C5 maintain high spin states at all temperature ranges. Binuclear complex [Fe2(L3)5(SCN)4] (C6) and mononuclear material [Fe(L4)2(H2O)4] ⋅ 2H2O (C7), these two zero‐dimensional molecules were also synthesized. They all display weak antiferromagnetic exchange coupling and a high spin state in the whole process.

The First Tetranuclear Iron(II)‐Gadolinium(III) Carboxylate Complex [Fe2Gd2(piv)10(bpy)2]: Synthesis, Structure Elucidation and Magnetic Properties

AbstractThe interaction of in situ generated iron(II) complex {Fe(piv)2(bpy)} and gadolinium(III) pivalate [Gd(piv)3]n in the ratio Fe : Gd=1 : 1 leads to new tetranuclear heterometallic complex [Fe2Gd2(piv)10(bpy)2] (1) of the rare {FeII2GdIII2} type (piv is pivalate anion, bpy is 2,2′‐bipyridine). According to X‐ray analysis, a tetranuclear zig‐zag {FeGdGdFe} heterometallic core is formed from two {FeGd} fragments connected by two bridging piv‐anions. The coordination environments of two iron(II) (FeO4N2) can be described as strongly distorted octahedrons, while the environment of the gadolinium(III) (GdO7) – as capped trigonal prisms. The coordination environment of each iron(II) is supported by terminal bpy ligands. The measurements of the temperature dependence of magnetic susceptibility of 1 show avery weak antiferromagnetic exchange between high‐spin Gd3+ (SGd=7/2) and Fe2+ (SFe=2) paramagnetic centers. The alternating current magnetic susceptibility measurements did not reveal any sign of magnetization slow relaxation in complex 1.

Structural, Spectroscopic Characterization and Application of a Co(II) Coordination Polymer [Co(suc)(bpm)] ⋅ 2H2O

AbstractA Co(II) coordination polymer [Co(suc)(bpm)] ⋅ 2H2O (1) built from succinate (suc) and bipyrimidine (bpm) is synthesized hydrothermally and characterized by different methods. It crystallizes in a monoclinic space group P21/n with an intriguing 3D polymeric architecture. The weak antiferromagnetic (AF) exchange interactions were evinced by Curie Constant (C)=1.803 cm3mol−1K and a negative Weiss constant (φ)=−30.163 K. Type VI adsorption isotherm behavior of 1 at 77 K revealed its non‐porous property. Compound 1 was investigated and successfully utilized as an additive in lowering the decomposition temperature of ammonium nitrate (AN) based fuels as demonstrated from TG and DSC experiments performed in nitrogen atmosphere.

Structural and electrical properties of Mg–Cu- and Mg–Cu–Li-doped bismuth niobate semiconductors with the pyrochlore structure

This work studies a series of synthesized Bi1.6Mg0.8-xCuxNb1.6O7-δ (x = 0.2, 0.4) semiconductors and their Li-doped compositions. A detailed structure investigation combining high-resolution neutron-, synchrotron-, and X-ray diffraction methods, as well as DFT calculations, revealed the preferential location of Cu and Li atoms at the Bi sites and Mg atoms at the Nb ones. According to high-temperature X-ray diffraction data, a structural modification caused by the activation of oxygen transport occurs at 200 °C. The linear thermal expansion coefficient was found to be 3.6–4.6·10−6 K−1 (50–400 °C). Magnetic susceptibility measurements allowed us to determine weak antiferromagnetic exchange interactions. The direct band gap was predicted using the DFT-HSE03 hybrid functional calculation, and the optical direct band gap was estimated at 2.3–2.4 eV. Impedance spectroscopy and a dc four-probe technique were also employed to examine the samples' electrical properties. The high mixed electronic-ionic conductivity of the pyrochlores was detected, while the vacancies created by Li-doping in Bi1.5-yLiyMg0.375Cu0.375Nb1.5O7-δ have been found not to affect the conductivity. Besides, the pyrochlores are chemically compatible with the La0.7Sr0.3MnO3 perovskite (up to 800 °C). These make us believe that the studied Mg–Cu- and Mg–Cu–Li-doped bismuth niobate semiconductors can become the basis for composite electrodes to boost their oxygen conductivity.

Solvent-Induced Cobalt(II) Cyanoguanidine Bromides: Syntheses, Crystal Structure, Optical and Magnetic Properties

Two different phase-pure cobalt(II) cyanoguanidine bromide coordination compounds, Co(C2N4H4)2(H2O)4·2Br·2H2O (1) and Co3(C2N4H4)8(H2O)8·6Br (2), were precipitated from aqueous and methanol solutions, respectively, and their structures were solved and refined from X-ray single-crystal data at 100 K. Both 1 and 2 crystallize in the triclinic system with space group P1¯. The structure of 1 consists of two crystallographically distinct isolated CoO4N2 octahedral units plus bromide anions and crystal water molecules, whereas 2 is built from both isolated octahedra and discrete binuclear cluster units made from edge-sharing octahedra. Diffuse reflectance spectra and IR analysis then go on to highlight optical and vibrational differences between these two compounds. The magnetic susceptibility of 1 is consistent with either isolated or very weakly interacting Co2+ centers whereas the magnetic susceptibility of 2 evidences the potential weak antiferromagnetic exchange interactions that may arise from superexchange within the binuclear clusters.

Field-orientation dependence of quantum phase transitions in the S=12 triangular-lattice antiferromagnet Ba3CoSb2O9

Ba$_3$CoSb$_2$O$_9$ approximates the two-dimensional spin-1/2 triangular-lattice Heisenberg antiferromagnet. This compound displays magnetic-field-induced quantum phase transitions, including the 1/3-magnetization-plateau, but its magnetization processes for the magnetic field $H$ parallel and perpendicular to the $c$ axis are different due to the weak easy-plane anisotropy and the weak interlayer antiferromagnetic exchange interaction. To elucidate how the quantum phase transitions change between these two field directions, we measured the field-angle dependence of the magnetization process in Ba$_3$CoSb$_2$O$_9$ using pulsed high magnetic fields. We compared obtained magnetic field-field angle phase diagram with those obtained by the large-size cluster mean-field method combined with a scaling scheme and the semiclassical theory. We also found a narrow 1/3-magnetization plateau and a high-field transition with a small magnetization jump for $H\,{\parallel}\,c$, not observed in the previous studies.

Heterometallic {Fe18M6} (M = Y, Gd, Dy) Pivalate Wheels Display Solvent-Induced Polymorphism

A new series of heterometallic wheels, isolated as [Fe18M6(piv)12(Htea)18(tea)6(N3)6]·n(solvent) (MIII = Y (1a, 1b), Gd (2a, 2b), and Dy (3a, 3b); Hpiv = pivalic acid, H3tea = triethanolamine), forms by the reaction of trinuclear μ3-oxo-linked or hexanuclear μ-OH-linked Fe(III) pivalate clusters with rare earth nitrates, H3tea, and azide ligands in MeOH/MeCN or EtOH/MeCN media under ultrasonic irradiation. Single-crystal X-ray diffraction showed that wheels 1a–3a prepared from MeOH/MeCN solutions crystallize in the triclinic space group P1̅ and have Ci symmetry, whereas wheels 1b–3b received from EtOH/MeCN solution crystallize in the trigonal space group R3̅ and have C3i symmetry. Magnetic studies reveal medium antiferromagnetic exchange interactions within the Fe3 trimeric unit (with the exchange coupling parameters of JFe3 = −13.1 cm–1 for 1a, JFe3 = −11.6 cm–1 for 1b) and weak intermolecular antiferromagnetic exchange interactions (λmf = −0.366 mol cm–3 and −0.368 mol cm–3 (zJmf = −0.19 cm–1), respectively). This leads to spin ground states of S = 5/2 for each {Fe3} unit. Substitution of diamagnetic Y(III) centers by paramagnetic Ln(III) centers (in 2a/2b by Gd(III) and in 3a/3b by Dy(III) centers) results in ferromagnetic exchange interactions between the Fe(III) and Ln(III) centers in addition to the predominant antiferromagnetic Fe···Fe interactions in 1a/1b.

N-Fluoroalkylpyrazolyl-substituted Nitronyl Nitroxides

The aim of the study was to prepare and investigate structure and properties of a new series of stable nitronyl nitroxides bearing N-fluoroalkylpyrazolyl substituents. According to cyclic voltammetry data, a paramagnet with a difluoromethyl substituent can reversibly undergo electrochemical oxidation and reduction. In contrast, radicals with fluorinated ethyl substituents are electrochemically oxidized reversibly, but their electrochemical reduction is quasi-reversible. Molecular and crystal structures of the nitroxides were confirmed by single-crystal X-ray diffraction analysis. The crystal structures of the radicals were studied quantitatively in terms of pairwise interaction energies and energy framework analysis. Analysis of the energies of molecular pairs revealed that in crystalline phases of all nitroxides, the binding is the strongest in dimers assembled via C–H…O interactions of nitroxide O atoms with pyrazole and/or alkyl H atoms. Other dimers are formed predominantly by C–H…π interactions, and in some cases, their binding energy is almost equal to that for the aforementioned ones. The above contacts are complemented short contacts C–H…A and others, which predetermine the final crystal packing of radicals. A consequence of their packing is the geometry of relative arrangement of nitroxide groups and, above all, distances O…O between the oxygen atoms of the paramagnetic centers. These distances were found to exceed the sum of van der Waals radii; consequently, in solid phases of the paramagnets, weak antiferromagnetic exchange interactions are predominant (|J/kB| ≤ 2.74 K, H = –2J·S1S2.

Radical Cation Salts of N‐Methylpyridone Azines with Halogenido Cuprate Anions

AbstractBis(N‐methylpyridone)azine (MPA) and its derivative bis(N‐methyl‐5‐trifluoromethyl‐pyridone)azine (p‐CF3MPA) are investigated concerning their redox behavior. Reactions with copper(II) halides afford via one electron transfer reactions the radical cation salts MPA[CuCl2], MPA[CuBr2] and p‐CF3MPA[CuBr2], all crystallizing as air‐stable dark needles. Cu(II) is reduced to the corresponding cuprate(I) anions [CuX2]− (X=Cl, Br). In the crystal structures, the planar radical cations form stacks with equidistantly arranged molecules. Low temperature data show a significant lattice parameter contraction resulting in denser packing of the radical cations in the stacking direction. MPA[CuBr2] can be further oxidized by CuBr2 to MPA[Cu2Br4] with MPA2+ in the dicationic state. The oxidation states 0, +1, and +2 of the cations are clearly distinguishable by the bond lengths in the central CNNC azine moiety. All compounds are semiconductors with small band gaps between 0.95 and 1.34 eV. The magnetic properties of MPA[CuX2] are dominated by reduced momenta. At temperatures below 50 K, a small magnetic momentum of about 1/3 of one unpaired electron is observed, which probably arise from paramagnetic impurity in form of Cu2+. For T &gt;50 K magnetic momenta turn into a nearly temperature independent paramagnetism. p‐CF3MPA[CuBr2] is mainly paramagnetic with weak antiferromagnetic exchange (TNéel=6 K, J=−2.1 cm−1).

Solvothermal synthesis, crystal structure, thermal, magnetic properties and DFT computations of a Ytterbium(III) complex derived from pyridine-2,6-dicarboxylic acid

A new ytterbium(III) complex, (DMAH2)3[Yb(Pydc)3].4H2O (1) {Pydc = Pyridine-2,6-dicarboxylate anion, DMAH2 = Dimethylammonium} has been prepared under mild solvothermal conditions and characterized by elemental analysis, IR spectroscopy, thermal analysis and single crystal X-ray diffraction. The DMAH2 molecules in 1, generated in situ from hydrolysis of N,N-dimethylformamide are responsible to assemble 2D coordination polymer through N-H···O and O-H···O hydrogen bonding. Magnetic susceptibility measurements indicate that the complex (1) obeys the Curie Weiss law and the overall magnetic behavior is typical for the presence of weak antiferromagnetic exchange coupling interactions. Theoretical data for geometrical parameters of complex 1 agree well with the experimental data. Large HOMO-LUMO energy gap of 4.33 eV has provided kinetic stability to the complex 1. NBO analysis reflects that intramolecular charge transfer occurred between ligand and metal orbitals with the highest stabilization energy of 1024.04 kcal/mol. The negative electrostatic potential at the nitrogen and dianionic pyridine-2,6-dicarboxylate regions confirms that these are dynamic locations for Yb(III) binding.