Weak Antiferromagnetic Interactions Research Articles

Synthesis, characterization and study of magnetic property of two isomorphic Cu(II) coordination polymers (CP) with chromone based ligand systems

Synthesis, characterization and magnetic properties of two Cu(II)-based coordination polymers (CPs, [{Cu(L1)(N(CN)2)}(ClO4)]n L1 = 3-(((2-(diethylamino)ethyl)imino)methyl)-4H-chromen-4-one (1) and [{Cu(L2)(N(CN)2)}(ClO4)]n L2 = 3-(((2-(dimethylamino)ethyl)imino)methyl)-4H-chromen-4-one (2)) involving chromone based chelating ligands and dicyanamide bridging ligands are reported. Both compounds have been characterized by physicochemical methods and the crystal structures have been determined by X-ray diffraction analysis, disclosing that they are isostructural and isomorphous compounds of polymeric linear chains where the central metal has adopted distorted square pyramidal coordination geometry. The magnetic studies reveal that the synthesized compounds show a prevailing paramagnetic behavior. Only below 15 K does a weak antiferromagnetic interaction become effective in these systems, and they have been further analyzed and interpreted.

Low-temperature magnetism of Ln2Ba (Ln = Nd, Er, Ho) furoate-based polymeric chains: Slow relaxation, magnetic anisotropy and interactions

The synthesis, structure and magnetothermal properties of three new lanthanide 1D polymeric complexes, {[Ln2Ba(α-fur)8(H2O)4]}n for Ln = Nd (1), Er (2) and {[Ho2Ba(α-fur)8(H2O)4]⋅2H2O}n (3), based on carboxylic α-fur = C4H3OCOO ligands is reported. The α-furoate ligands consolidate zigzag chains formed by Ln2 dimers separated by Ba ions. Ab initio calculations, in combination with the fit of experimental static magnetization and heat capacity, predict the magnetic ground state, energy levels and magnetic interactions in these heteronuclear nanomagnets. Nd2Ba (1) presents two different coordination sites for Nd, with an orthorhombic magnetic ground state. Nd ions are coupled along the chain through a weak antiferromagnetic (AF) interaction J″/kB = −0.08 K. Er(III) ions in Er2Ba (2) present a highly axial ground state, forming magnetic dimers with an interaction of J′/kB = −8.6 K, while interdimer coupling along the chain is J″/kB = −0.28 K. The Ho2Ba (3) complex consists of a highly anisotropic quasi-doublet with a ΔHo/kB = 0.7 K gap. Non-Kramers Ho ions form magnetic dimers within the Ho2Ba cluster, coupled by an AF intradimer interaction J′/kB = −2.5 K. The three complexes exhibit in-field slow relaxation of the magnetization: 1 relaxes through an Orbach process at high temperatures [Ueff/kB = 60(1) K] evolving to quantum tunneling below 3 K [τQT = 0.05(1) s]; 2 exhibits a rapid Orbach-like process [τ0 = 8(6)⋅10–8 s and Ueff/kB = 10(2) K] and 3 shows a direct process [τ = 0.4(1) s].

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.

Aliovalent Substitution Tunes Physical Properties in a Conductive Bis(dithiolene) Two-Dimensional Metal-Organic Framework.

Two-dimensional conductive metal-organic frameworks have emerged as promising electronic materials for applications in (opto)electronic, thermoelectric, magnetic, electrocatalytic, and energy storage devices. Many bottom-up or postsynthetic protocols have been developed to isolate these materials or further modulate their electronic properties. However, some methodologies commonly used in classic semiconductors, notably, aliovalent substitution, are conspicuously absent. Here, we demonstrate how aliovalent Fe(III) to Ni(II) substitution enables the isolation of a Ni bis(dithiolene) material from a previously reported Fe analogue. Detailed characterization supports the idea that aliovalent substitution of Fe(III) to Ni(II) results in an in situ oxidation of the organic dithiolene linker. This substitution-induced redox tuning modulates the electronic properties in the system, leading to higher electrical conductivity and Hall mobility but slightly lower carrier densities and weaker antiferromagnetic interactions. Moreover, this aliovalent substitution improves the material's electrochemical stability and thus enables pseudocapacitive behavior in the Ni material. These results demonstrate how classic aliovalent substitution strategies in semiconductors can also be leveraged in conductive MOFs and add further support to this class of compounds as emerging electronic materials.

New in situ generated acylhydrazidate-coordinated complexes: Syntheses, structural characterizations and magnetic properties

The present study reports the successful synthesis of three new magnetic coordination polymers, namely [Mn(BPTH)(H2O)]n (1), [Co(BPTH)(phen)]n (2), and [Co(BPTA)(phen)(H2O)2]n (3), through a solvothermal method (H2BPTH = biphenyl-3,3′,4,4′-tetracarboxyhydrazide, H2BPTA = biphenyl-3,3′,4,4′-tetracarboxylic acid, phen = 1,10-phenanthroline). In compounds 1 and 2, the bishydrazide ligand H2BPTH is formed by in situ acylation of H2BPTA with hydrazine hydrate. All the three title compounds contain M2O2 clusters (M=Mn(1), Co(2) and Co(3)). In compound 1, the amido-oxygen atoms O1 coordinate with Mn2+ to form a Mn2O2 cluster, while the adjacent Mn2O2 cluster is interconnected by the ligand's oxygen atoms O3 and O4, resulting in an infinite expansion into a 3D network structure. Compound 2 exhibits a 1D chain structure containing Co2O2 clusters, which further extends into a 2D supramolecular layer through π···π stacking interactions. Compound 3 comprises adjacent Co2O2 clusters interconnected by oxygen atoms O1, O2, and O5 on the ligand to form a 2D layered architecture. The 2D layers are linked through intermolecular O–H···O hydrogen bonds of H2BPTA ligands to form a 3D supramolecular network. Magnetic measurements reveal weak ferromagnetic behavior for compound 1 while compounds 2 and 3 exhibit weak antiferromagnetic interactions at different temperatures. Overall, this research presents new insights into the design and synthesis of coordination polymers with diverse structures and magnetic properties.

Hydrothermal synthesis of (C5H14N2)[CoCl4]⸳0.5H2O: Crystal structure, spectroscopic characterization, thermal behavior, magnetic properties and biological evaluation

The organic-inorganic compound (C5H14N2)[CoCl4]⸳0.5H2O, I, was characterized by various physicochemical techniques. The X-ray diffraction analysis revealed that the compound crystallizes in the centrosymmetric space group C2/c of the monoclinic system. The atomic arrangement the Co(II) complex is built from isolated [CoCl4]2– anions, 1-methylpiperazine-1,4-diium [C5H14N2]2+ cations and free water molecules. The crystal structure study showed that the cohesion of I is assured through N–H···Cl and N–H···O hydrogen bonds giving birth to a 3-D architecture. Hirshfeld surface analysis revealed that Cl···H/H···Cl and H···H (58.5 and 36.4%, respectively) are the most significant interactions between species. Minor O···H/H···O interactions are also present. The compound was characterized by thermal analysis, TGA-DTA showed the removal of the co-crystallized water before 100 °C and a first mass loss at around 120 °C. Magnetic measurements are in good agreement with isolated, S = 3/2, tetrahedral [CoCl4]2− anions. The negative Weiss constant of -1.35 indicates single-ion anisotropy and very weak antiferromagnetic interactions. UV–visible spectroscopy reveals three weak absorption bands in the visible range due to the d-d electronic transitions typical of the Co(II) tetra-coordinated. A bioassay showed antibacterial activity against the gram negative Klebsiella pneumonia and gram positive Bacillus ceureus, Listeria monocytogenes, and Micrococcus lutues.

Novel Trinuclear Copper(II) Complex: Crystal Structure at 100 K and Magnetic Properties of (R, S)-di[(6,7-dimethoxy-isoquinolin-1-yl)-(3,4-dimethoxy-phenyl)-methanolato]-tetra(2-hydroxybenzoato)-diaqua-tricopper dihydrate, [Cu3(C7H5O3)4(C20H20NO5)2(H2O)2]·2(H2O)

The crystal structure of [Cu3(C7H5O3)4(C20H20NO5)2(H2O)2]·2(H2O) (1) and analysis of temperature and field dependence of magnetic susceptibility is reported in this work. The structure of 1 is composed of trinuclear complex units and water molecules. The middle copper atom occupies the center of symmetry. N, O-bonded (6,7-dimethoxy-isoquinolin-1-yl)-(3,4-di­methoxy-phenyl)-methanolato ligands, 2-hydroxybenzoates with bridging carboxylic groups, and oxo-bridged water molecules connect the middle Cu(II) atom with the terminal copper atoms. Two 2-hydroxybenzoates coordinate the terminal copper atoms via one carboxylic oxygen and an O atom of the hydroxyl group. The analysis of copper coordination by bond-valence sum approach and relevant structural correlation is consistent with hexacoordinated Cu(II) centers. Cu···Cu separation is 3.0269(3) Å. The magnetism of 1 shows a strong ferromagnetic interaction between the neighboring metallic centers accompanied by very weak antiferromagnetic intermolecular interactions. The complex units are mutually held by π···π stack interactions of 2-hydroxybenzoates and hydrogen bonds.Graphical A new N,O bonded ligands, (R, S)-[(6,7-dimethoxy-isoquinolin-1-yl)-(3,4-dimethoxy-phenyl)-methanolate] coordinate the terminal atoms of the trinuclear copper(II) complex.

Intensity and lifetime ratiometric luminescent thermometer based on a Tb(III) coordination polymer.

A three-dimensional terbium(III) coordination polymer of formula [Tb(bttb)0.5(2,5-pzdc)0.5]n (1) [H4bttb = 1,2,4,5-tetrakis(4'-carboxyphenyl)benzene and H2-2,5-pzdc = 2,5-pyrazinedicarboxylic acid] was obtained under hydrothermal conditions. The bttb4- tetraanion in 1 adopts the bridging and chelating-bridging pseudo-oxo coordination modes while the 2,5-pzdc2- dianion exhibits a rather unusual bis-bidentate bridging pseudo-oxo coordination mode, both ligands being responsible for the stiffness of the resulting 3D structure. Solid-state photoluminescent measurements illustrate that 1 exhibits remarkable green luminescence emission, the most intense band occurring in the region of 550 nm (5D4 → 7F5) with lifetimes at the millisecond scale. Thermometric performances of 1 reveal a maximum relative sensitivity (Sm) of 0.76% K-1 at 295 K (δT = 0.05 K), constituting a TbIII ratiometric solid luminescent thermometer over the physiological temperature range. Variable-temperature static (dc) magnetic susceptibility measurements for 1 in the temperature range 2.0-300 K show the expected behavior for the depopulation of the splitted mJ levels of the 7F7 ground state of the magnetically anisotropic terbium(III) ion plus a weak antiferromagnetic interaction through the carboxylate bridges. No significant out-of-phase magnetic susceptibility signals were observed for 1 in the temperature range 2.0-10.0 K, either in the absence or presence of a static dc magnetic field.

Crystal structure, optical, magnetic and antibacterial properties of a new tetrachlorocobaltate(II) salt with 4-nitrobenzyl substituted 2-methyl pyridinium

In this paper, a new organic-inorganic hybrid crystal material, 4-nitrobenzyl-2-methylpyridinium tetrachlorocobaltate(II) [4-NO2Bz-2-MePy]2[CoCl4](1), had been obtained by the slow-evaporation solution growth method. The single-crystal X-ray diffraction analysis showed that 1 crystallized in the monoclinic space group P21/n, composed of two [4-NO2Bz-2-MePy]+ cations and a [CoCl4]2− anion, where the cations represented Λ-shaped structure and the [CoCl4]2− anions exhibited a tetrahedral geometry. The PXRD spectrum confirmed the bulk phase purity, homogeneity, and crystalline nature of the material. The HOMO-LUMO energy gap and UV-visible diffuse reflectance spectrum explained the charge transfer interactions between the [CoCl4]2− anions and the [4-NO2Bz-2-MePy]+ cations. Furthermore, the low band gap values (1.27 eV for the experimental value and 1.65 eV for the calculated value) indicated the appropriateness of the crystal for optical applications. The first hyperpolarizability (βtot) of the salt was more than 6600 times higher than the standard KDP crystal (βKDP = 6.85 × 10−31 esu), suggesting that the title crystal was a superior material for NLO applications. The results of the antimicrobial experiment revealed that the compound exhibited excellent antimicrobial activity against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). The title salt displayed weak antiferromagnetic interaction with the lowering of temperature.

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.

One-pot cocrystallization of 1D linear and zigzag cobalt(II) polymers assembled by triclopyr and 4,4′-bipyridine: Structural comparison, conformational analysis, non-covalent interactions as well as the magnetic property of the latter

A pair of cobalt(II) compounds with formulas of [Co(3,5,6-tcpa)2(4,4′-bipy)(EtOH)]n (1A) and [Co(3,5,6-tcpa)2(4,4′-bipy)(EtOH)2]n (1B), have been cosynthesized through the solvothermal reaction of cobalt chloride hexahydrate with triclopyr (systematic name 2-((3,5,6-trichloropyridin-2-yl) oxy)acetic acid, abbreviation 3,5,6-Htcpa) and 4,4′-bipyridine (4,4′-bipy) coligands. Single-crystal X-ray diffraction analysis indicated that complex 1A has orthorhombic system, space group Aea 2 (no. 41), while 1B showed monoclinic system, space group I2/a (no. 15). Compound 1A displays a 1D linear chain but 1B presents a zigzag chain, and 3,5,6-tcpa anion are both unidentate between them. The non-covalent interactions of CH···O/CH···Cl hydrogen bonds and Cl···O/ Cl···Cl halogen bonds undertake a significant role in their 3D molecule packing, which have been further verified by the careful Hirshfeld surface analyses. Based on the deeply structural comparisons, it was supposed that conformational flexibility of 3,5,6-tcpa might be responsible for the cocrystallization of 1A and 1B. Besides, the magnetic determinations revealed weak antiferromagnetic interactions for intrachain cobalt(II) ions in 1B.

An Influence of Fluorinated Alkyl Substituents on Structure and Magnetic Properties of Mn(II) Complexes with Pyrazolyl-Substituted Nitronyl Nitroxides

New complexes of manganese(II) hexafluoroacetylacetonate [Mn(hfac)2] with 2-(1-R-3-pyrazol-4-yl)-4,4,5,5-tetramethyl-2-imidazoline-3-oxide-1-oxyl (R = CHF2, CH2CH2F, CH2CHF2 or CH2CF3) were synthesised and characterised structurally and magnetically. All complexes were prepared under similar conditions. Nonetheless, their crystal structures were considerably different. Depending on the structure of fluorinated alkyl substituent R, the complexation reaction led to complexes of three types: chain-polymeric complexes with the head-to-head or head-to-tail motif and complexes of molecular structure. All complexes show strong antiferromagnetic behaviour in a high-temperature region (150–300 K) and weak ferro- or antiferromagnetic exchange interactions at low temperatures. The stronger antiferromagnetic exchange, −101.7 ± 1.5 or −136 ± 10 cm−1, −82.3 ± 1.3 cm−1 and −87.4 ± 1.3 cm−1, was attributed to the magnetic interaction in three- or two-spin clusters: {&gt;N∸O–Mn2+–O∸N&lt;} or {&gt;N∸O–Mn2+}, respectively. The weaker antiferromagnetic interaction, −0.005, between three-spin clusters or ferromagnetic interactions, 0.18–0.81 cm−1, between two-spin clusters are realised through the pyrazole ring or intermolecular contacts.

Structural and magnetocaloric properties of Gd2-xMnxO3 nanoparticles

Magnetic cooling is considered to be an important component of future green refrigeration. On this subject, rare earth oxides (RE2O3) are seen as a promising class of magnetic materials for low-temperature magnetic cooling technology. In this work, we report the influence of Mn substitution on the structural, magnetic and magnetocaloric characteristics of Gd2O3 powders synthesized by sol–gel route. Structural analysis using Rietveld refinement technique confirmed the cubic-bixbyite structure with the Ia3¯ space group. The lattice parameter slightly decreases with the Mn doping degree. Temperature dependent magnetization measurements demonstrated a paramagnetic behavior sustained in Gd2-xMnxO3 in the whole temperature range of 2–400 K and the presence of weak antiferromagnetic interactions at low temperature (≤2K). The measured hysteresis loops are linear and completely reversible (2 K), which is typical for paramagnetic system and suitable for cryogenics magnetic refrigeration. The variation of the magnetic entropy was measured indirectly using the Maxwell approach with increasing magnetic field.

Phenylalanine-Based Co2+ and Cd2+ 1D Coordination Polymers: Structural Properties and Catalytic Application for Solvent-Free Aerobic Oxidation of Cycloalkene.

Two 1D coordination polymers (CPs) with general formula [M(L)(H2O)(AcO)]n, (M = Co (1) or Cd (2), AcO = acetate anion and L denotes l-phenylalanine based ligand), were synthesized and fully characterized by various spectroscopies (UV-vis, FTIR, and NMR), thermal techniques, magnetic measurements (for 1), and single-crystal and powder X-ray diffraction studies. They can be described as "ribbon-like" 1D polymers constructed through a zigzag arrangement. The polymeric structure is developed due to the coordination mode adopted by the amino acid ligand, classified as μ3-N1O1:O1:O2, which simultaneously links three metal centers. This moiety also plays an important role as a magnetic coupler between metal centers in the cobalt system, which shows a weak antiferromagnetic interaction. Both CPs have also been used in the catalytic oxidation of cyclohexene with molecular oxygen (O2) as an oxidant. Under mild conditions, both compounds demonstrated remarkable catalytic activity, with the cobalt system being more efficient than the cadmium analogue (conversion: 73 and 58% and selectivity for the major product, 2-cyclohexanone: 63 and 55%, for 1 and 2, respectively). Leaching experiments and the results obtained using a radical quencher are consistent with a radical-mediated mechanism for the Co compound. The presence of the superoxide radical was also confirmed using EPR spectroscopy and DMPO as a spin trap, which was further validated by DFT calculations. The activity observed for the Cd analogue is attributed to the organic scaffold assisted by the templating effect of the metal ion.

Biphenol-based tetradentate N2O2 donor scaffold binuclear Zn(II) and trinuclear Cu(II) Complexes: Synthesis, Structure, Characterizations, and catalytic cyanosilylation of aldehydes at room temperature

In this work, two dinuclear Zn(II) complexes [Zn(H2L1)]2(complex 1), [Zn(H2L2)]2(complex 2), and a trinuclear Cu(II) complex [Cu(H2L2)]3 (complex 3) (H2L1 = 3,3′-bis-[(2,6-dimethyl-phenylimino)-methyl]-[1,1′]-biphenyl-2,2′-diol, H2L2 = 2,6-diethyl phenylimino)-ethyl]-[1,1′]-biphenyl-2,2′- diol) are reported. The complexes 1, 2 &3 have been produced and isolated for the first time in a well-defined and air-stable form by reacting biphenol-based tetradentate N2O2-type (H2L1 and H2L2) ligands with the respective metal acetate salts. The synthesised compounds were characterized by UV–Vis spectroscopy, elemental analysis, mass spectrometry and Fourier-transform infrared spectroscopy (FT-IR). Single crystal X-ray diffraction (SCXRD) study revealed distorted tetrahedral geometry surrounding the core Zn2+ cations (1–2) that were bridging the teradentate N2O2 ligands. In complex-3, the Cu(II) center is four-coordinated via tetradentate N2O2 donor ligand, forming slightly distorted square planar geometry with an angular C2-symmetric core and exhibits weak antiferromagnetic (AF) interactions. Hirshfeld surface analysis and fingerprint plots were used to investigate the intermolecular interactions in the crystalline state. Strong H…H and H… C/C…H intermolecular interactions were seen on the Hirshfeld surface when it was mapped over dnorm, shape index, and curvature. These interactions were found to be the main contributors to crystal packing. Excellent catalytic activity was demonstrated for the dinuclear zinc(II) complexes [Zn(H2L1)]2 (1)and [Zn(H2L2)]2 (2) in the cyanosilylation reaction of various aryl aldehydes into value-added cyanohydrins at room temperature and under solvent free conditions.

Two different 4,5-dichlorophthalate-extended Cu(II) 1D coordination polymers. Crystal structures, solvatochromism, and magnetic studies

A new 1D Cu-coordination polymer with formula {[Cu2(tmeda)2(dcpa)2(H2O)]·H2O}∞, 1 (tmeda=N,N,N´,N´-tetramethylethylenediamine, dcpa=4,5-dichlorophthalate) has been synthesized by a self-assembly solution reaction between the aqua complex [Cu(tmeda)(H2O)x](ClO4)2 and the salt K2dcpa. The use of piperidinium (Pip) salt of dcpa under the same conditions induced the crystallization of a different 1D polymer {[Cu(tmeda)(dcpa)]·Pip(ClO4)}∞, 2. The 1D Cu-polymers-based 1–2 were structurally analyzed by single-crystal X-ray diffraction, Hirshfeld surfaces, scanning electron microscopy with energy-dispersive X-ray spectroscopy, and multiple spectroscopic tools. X-ray analysis showed that the unusual inclusion of the ionic pair (PipClO4) into the single-crystal of 2 modified the Cu(II)…Cu(II) distances, Cu(II) geometries, supramolecular interactions, UV–Vis absorptions, and magnetic properties compared to 1.Polymer 1 consists of dinuclear Cu2 units bridged by deprotonated dcpa ligands with weak antiferromagnetic interactions (C = 0.74 emu K/mol, θ= −3.89 K). In contrast, polymer 2 is formed by mononuclear Cu units with antiferromagnetic interactions (C = 0.35 emu K/mol, θ= −4.49 K).Polymer 1 shows solvatochromism in the presence of non-protic solvents, and the solvent-dependent absorption maxima in the visible region (λmax = 637–685 nm) has a linear behavior as a function of the dielectric constant. The visible absorption bands of 1 originated from a combination of d-d transitions and ligand-to-metal charge transfers, as is evidenced by time-dependent density-functional theory calculations.

A novel mixed azido/phenoxido bridged 1D CuII coordination polymer containing o-vanillin-based compartmental ligand: Synthesis, magnetism, phenoxazinone synthase and catalytic activity in epoxidation of alkenes

A novel 1-D coordination polymer, formulated as [Cu2(L)(N3)3]·H2O (1), has been synthesized by reacting the Schiff base ligand, 2-methoxy-6-((2-(2-hydroxyethylamino)ethylimino) methyl)-phenol (HL), with copper(II) chloride dihydrate in the presence of sodium azide. The X-ray structural analysis shows that compound 1 consists of tetranuclear [Cu2(L)(N3)3]2 units bearing a central double asymmetric μ1,1-N3 bridge and terminal mixed µ1,1-N3/phenoxido bridges that are linked via a double µ1,1,3-N3 bridge forming a 1-D network. The magnetic properties of 1 show the presence of ferromagnetic Cu···Cu interactions through the central double μ1,1-N3 bridge (J1 = 81.7(3) cm−1) coexisting with antiferromagnetic Cu···Cu interactions through the double µ1,1-N3/phenoxido bridge (J2 = –62.3(4)cm−1). Additionally, there is a very weak antiferromagnetic interaction (zJ = –0.12(2) cm−1) through the asymmetric µ1,1,3-N3 bridge connecting the tetranuclear units. Using o-aminophenol (OAP) as a substrate, the phenoxazinone synthase-like catalytic activity of the CuII coordination polymer 1 has been studied. The compound efficiently catalyzes the aerobic oxidation of o-aminophenol in DMF medium with a turnover number Kcat = 31.69 h−1. Moreover, 1 has been used as an active catalyst for the epoxidation of cis-cyclooctene, as a model alkene, with tert-butyl hydroperoxide (TBHP), showing an excellent epoxide yield and selectivity in CHCl3 under reflux conditions. To enlarge the scope of the reaction, the efficacy of the catalytic method has also been investigated in the epoxidation of some other substituted alkenes.

Lanthanide dimers in coordination chains constructed by sole dicarboxylate ligand for single-molecule magnet behavior and magnetocaloric effect

The solvothermal reaction of Dy(III) and Gd(III) ions with 2,5-di‑hydroxy-benzene-1,4-di-carboxylic acid (H4dhbdc) produced two new isostructural lanthanide(III) coordination chains with the general formula {[Ln2(H2dhbdc)3(H2O)8]·6H2O}n [Ln = Dy (1) and Gd (2)]. The chains consist of carboxylate-bridged dilanthanide(III) units linked by H2dhbdc2− ligands in an end-to-end bridging mode. The Dy3+ and Gd3+ ions are located in slightly distorted biaugmented trigonal prism (C2v) and triangular dodecahedron (D2d) coordination environments, respectively. Magnetic studies reveal the extremely weak antiferromagnetic interaction (J = -0.041 cm−1) between the magnetically isotropic GdIII ions in 2. The dysprosium analogue was found to exhibit single-molecule magnet (SMM) behavior with a prominent QTM effect under zero dc field, which is largely due to large single-ion magnetic anisotropy of individual Dy3+ ions and weak antiferromagnetic interaction. For the gadolinium chain, the magnetocaloric effect (MCE) was observed with a magnetic entropy change of 20.2 J kg−1 K − 1. These results demonstrate a dicarboxylate synthetic route for the preparation of coordination polymers containing dilanthanide units for SMM and MCE applications.

Rare Nuclearities and Unprecedented Structural Motifs in Manganese Cluster Chemistry from the Combined Use of Di-2-Pyridyl Ketone with Selected Diols

The combined use of di-2-pyridyl ketone ((py)2CO) with various diols in Mn cluster chemistry has afforded five new compounds, namely, [Mn11O2(OH)2{(py)2CO2}5(pd)(MeCO2)3(N3)3(NO3)2(DMF)4](NO3)∙2DMF∙H2O (1∙2DMF∙H2O), [Mn11O2(OH)2{(py)2CO2}5(mpd)(MeCO2)3(N3)3(NO3)2(DMF)4](NO3) (2), [Mn12O4(OH)2{(py)2CO2}4(mpd)2(Me3CCO2)4(NO3)4(H2O)6](NO3)2∙2MeCN (3∙2MeCN), [Mn4(OMe)2{(py)2C(OMe)O}2(2-hp)2(NO3)2(DMF)2] (4), and [Mn7{(py)2CO2}4(2-hp)4(NO3)2(DMF)2](ClO4)∙DMF (5∙DMF) ((py)2CO22− and (py)2C(OMe)O− = gem-diol and hemiketal derivatives of di-2-pyridyl ketone, pdH2 = 1,3-propanediol, mpdH2 = 2-metly-1,3-propanediol, 2-hpH2 = 2-(hydroxymethyl)phenol). Complexes 1 and 2 are isostructural, possessing an asymmetric [MnIII5MnII6(μ4-O)(μ3-O)(μ3-OH)(μ-OH)(μ3-OR)2(μ-OR)10(μ-N3)]8+ core. Compound 3 is based on a multilayer [MnIII8MnII4(μ4-O)2(μ3-O)2(μ3-OH)2(μ-OR)12]10+ core, while complex 4 comprises a defective dicubane core. The crystal structure of 5 reveals that it is based on an unusual non-planar [MnIII5MnII2(μ-OR)12]7+ core with a serpentine-like topology. Direct current (dc) magnetic susceptibility studies revealed the presence of dominant antiferromagnetic exchange interactions in complex 3, while ferromagnetic coupling between the Mn ions was detected in the case of compound 5. Fitting of the magnetic data for complex 4 revealed weak antiferromagnetic interactions along the peripheral MnII∙∙∙MnIII ions (Jwb = −0.33 (1) cm−1) and ferromagnetic interactions between the central MnIII∙∙∙MnIII ions (Jbb = 6.28 (1) cm−1).