Switching-on luminescence in anilate-based molecular materials

Slow magnetic relaxation in a heteroleptic anilate-based DyIII metal-organic framework

Novel heteroleptic anilate-based lanthanide MOFs (LnIII = Tb, Dy, Ho) have been obtained under hydrothermal conditions by the ancillary ligand synthetic strategy. These structurally isomorphous species contain octacoordinated LnIII ions with coordination polyhedra approaching an ideal D2d symmetry, best described by a distorted biaugmented trigonal prismatic C2v geometry. In the whole series, only the Dy-MOF exhibits SMM behaviour.

Anilato-Based Coordination Polymers with Slow Relaxation of the Magnetization: Role of the Synthetic Method and Anilato Ligand

We have prepared and characterized three coordination polymers formulated as [Dy2(C6O4Cl2)3(fma)6] ⋅ 4.5fma (1) and [Dy2(C6O4X2)3(fma)6] ⋅ 4fma ⋅ 2H2O with X=Br (2) and Cl (3), where fma=formamide and C6O4X2 2-=3,6-disubstituted-2,5-dihydroxy-1,4-benzoquinone dianion with X=Cl (chloranilato) and Br (bromanilato). Compounds 1 and 3 are solvates obtained with slow and fast precipitation methods, respectively. Compounds 2 and 3 are isostructural and only differ in the X group of the anilato ligand. The three compounds present (6,3)-gon two-dimensional hexagonal honey-comb structures. Magnetic measurements indicate that the three compounds show slow relaxation of the magnetization at low temperatures when a continuous magnetic field is applied, although with different relaxation times and energy barriers depending on X and the crystallisation molecules. Compounds 1-3 represent the first examples of anilato-based lattices with formamide and field-induced slow relaxation of the magnetization.

Tuning the slow magnetic relaxation with the substituents in anilate bridged bis(dysprosium) complexes

Dinuclear lanthanide complexes [((HB(pz)3)2Dy)2(μ-Th2An)] (1Dy) and [((HB(pz)3)2Dy)2(μ-ClCNAn)] (2Dy), based on the hydrotris(pyrazol-1-yl)borate (HBpz3-) scorpionate capping ligand and anilate (An2-) bridging linkers, namely homosubstituted dithiophene- and heterosubstituted chlorocyanoanilate, bearing electron-donating and withdrawing substituents at the 3,6-positions of the benzoquinone core, are reported. 1Dy shows an octacoordinated {N6O2} DyIII ion within a D4h distorted square antiprismatic coordination, an ideal geometry for Single-Molecule Magnet (SMM) behavior, given its oblate nature, whereas in 2Dy the octacoordinated DyIII ion adopts a D2d triangular dodecahedron geometry, while maintaining the same {N6O2} coordination sphere. Both complexes show field-induced single molecule magnet (SMM) behaviour, with tuning of the slow magnetic relaxation as a function of the nature of the substituents at the 3,6-positions of the anilate moiety. A comparison of the Arrhenius fitting parameters for 1Dy and 2Dy supports the hypothesis that square antiprismatic DyIII complexes, as 1Dy, exhibit higher energy barriers. This interpretation is supported by ab initio calculations that also shed light on the crucial role of intermolecular dipolar interactions.

Terbium and Europium Chlorocyananilate-Based 2D Coordination Polymers

Two-dimensional layered coordination polymers based on the hetero-substituted 3-chloro-6-cyano-2,5-dihydroxybenzoquinone ligands, hereafter ClCNAn2- anilate, and LnIII ions (Tb and Eu) are reported. Compounds 1 and 2, formulated as Ln2(ClCNAn)3(DMSO)6 (LnIII = Tb, 1; Eu, 2), and their related intermediates 1' and 2', formulated as Ln2(ClCNAn)3(H2O)x·yH2O (x + y likely = 12, Ln = Tb, 1'; and Eu, 2'), were prepared by a conventional one-pot reaction (the latter) and recrystallized from DMSO solvent (the former). Polyhydrated intermediates 1' and 2' show very similar XRPD patterns, while, despite their common stoichiometry, 1 and 2 are not isostructural. Compound 1 consists of a 2D coordination framework of 3,6 topology, where [Tb(DMSO)3]III moieties are bridged by three bis-chelating ClCNAn2- ligands, forming distorted hexagons. Ultrathin nanosheets of 1 were obtained by exfoliation via the liquid-assisted sonication method and characterized by atomic force microscopy, confirming the 2D nature of 1. The crystal structure of 2, still showing the presence of 2D sheets with a "hexagonal" mesh and a common (3,6) connectivity, is based onto flat, non-corrugated slabs. Indeed, at a larger scale, the different "rectangular tiles" show clear roofing in 1, which is totally absent in 2. The magnetic behavior of 1 very likely indicates depopulation of the highest crystal-field levels, as expected for TbIII compounds.

Metal-Organic Framework vs. Coordination Polymer—Influence of the Lanthanide on the Nature of the Heteroleptic Anilate/Terephtalate 3D Network

Metal-organic frameworks (MOFs), whose definition has been regularly debated, are a sub-class of coordination polymers (CPs) which may feature both an overall 3D architecture and some degree of porosity. In this context, MOFs based on lanthanides (Ln-MOFs) could find many applications due to the combination of sorption properties and magnetic/luminescent behaviors. Here we report rare examples of 3D Ln-CPs based on anilate linkers, obtained under solvothermal conditions using a heteroleptic strategy. The three compounds of formula [Yb2(μ-ClCNAn)2(μ-F4BDC)(H2O)4]·(H2O)3 (1), [Er2(μ-ClCNAn)2(μ-F4BDC)(H2O)4]·(H2O)4 (2) and [Eu2(μ-ClCNAn)2(μ-F4BDC)(H2O)6] (3) have been characterized by single-crystal X-ray diffraction, thermogravimetric analysis, and optical measurements. Structural characterization revealed that compounds 1 and 2 present an interesting MOF architecture with extended rectangular cavities which are only filled with water molecules. On the other hand, compound 3 shows a much more complex topology with no apparent cavities. We discuss here the origins of such differences and highlight the crucial role of the Ln(III) ion nature for the topology of the CP. Compounds 1 and 2 now offer a playground to investigate the possible synergy between gas/solvent sorption and magnetic/luminescent properties of Ln-MOFs.

Combined Experimental/Theoretical Study on the Luminescent Properties of Homoleptic/Heteroleptic Erbium(III) Anilate-Based 2D Coordination Polymers

The synthesis, structural and photophysical characterization, and theoretical studies on homo/heteroleptic neutral 2D-layered coordination polymers (CPs), obtained by combining the Er^III ion with chlorocyananilate (ClCNAn) and/or tetrafluoroterephthalate (F₄BDC) linkers, are herein reported. The structure of the heteroleptic Er^III-based CP, formulated as [Er₂(ClCNAn)₂(F₄BDC)(DMSO)₆]_n (1) is also reported. 1 crystallizes in the triclinic P1̅ space group, and the structure consists of neutral 2D layers formed by Er^III ions linked through the two linkers oriented in such a way that the neighboring 2D layers are eclipsed along the a axis, leading to parallelogram-like cavities. Photophysical measurements highlight the prominent role of chlorocyananilate linkers as optical antennas toward lanthanide ions, while wave-function-theory analysis supports the experimental findings, providing evidence for the effect of ligand substitution on the luminescence properties of homo/heteroleptic 2D CPs.

Slow Relaxation of the Magnetization in Anilato-Based Dy(III) 2D Lattices

The search for two- and three-dimensional materials with slow relaxation of the magnetization (single-ion magnets, SIM and single-molecule magnets, SMM) has become a very active area in recent years. Here we show how it is possible to prepare two-dimensional SIMs by combining Dy(III) with two different anilato-type ligands (dianions of the 3,6-disubstituted-2,5-dihydroxy-1,4-benzoquinone: C₆O₄X₂²⁻, with X = H and Cl) in dimethyl sulfoxide (dmso). The two compounds prepared, formulated as: [Dy₂(C₆O₄H₂)₃(dmso)₂(H₂O)₂]·2dmso·18H₂O (1) and [Dy₂(C₆O₄Cl₂)₃(dmso)₄]·2dmso·2H₂O (2) show distorted hexagonal honeycomb layers with the solvent molecules (dmso and H₂O) located in the interlayer space and in the hexagonal channels that run perpendicular to the layers. The magnetic measurements of compounds 1, 2 and [Dy₂(C₆O₄(CN)Cl)₃(dmso)₆] (3), a recently reported related compound, show that the three compounds present slow relaxation of the magnetization. In compound 1 the SIM behaviour does not need the application of a DC field whereas 2 and 3 are field-induced SIM (FI-SIM) since they show slow relaxation of the magnetization when a DC field is applied. We discuss the differences observed in the crystal structures and magnetic properties based on the X group of the anilato ligands (H, Cl and Cl/CN) in 1–3 and in the recently reported derivative [Dy₂(C₆O₄Br₂)₃(dmso)₄]·2dmso·2H₂O (4) with X = Br, that is also a FI-SIM.

Nitrochloranilic acid: a novel asymmetrically substituted quinoid bridging ligand for design of coordination polymers

A series of alkali salts and transition metal complexes of a novel asymmetrically substituted quinoid ligand, 3-nitro-6-chloro-2,5-dihydroxyquinone (nitrochloranilic acid, H₂NCA) was prepared and characterised.

Lanthanoid-Anilato Complexes and Lattices

In this review, we describe all the structurally characterized complexes containing lanthanoids (Ln, including La and group 3 metals: Y and Lu) and any anilato-type ligand (3,6-disubstituted-2,5-dihydroxy-1,4-benzoquinone dianion = C6O4X22−). We present all the anilato-Ln compounds including those where, besides the anilato-type ligand, there is one or more coligands or solvent molecules coordinated to the lanthanoid ions. We show the different structural types observed in these compounds: from discrete monomers, dimers and tetramers to extended 1D, 2D and 3D lattices with different topologies. We also revise the magnetic properties of these Ln-anilato compounds, including single-molecule magnet (SMM) and single-ion magnet (SIM) behaviours. Finally, we show the luminescent and electrochemical properties of some of them, their gas/solvent adsorption/absorption and exchange capacity and the attempts to prepare them as thin films.

Insensitivity of Magnetic Coupling to Ligand Substitution in a Series of Tetraoxolene Radical-Bridged Fe2 Complexes

The elucidation of magnetostructural correlations between bridging ligand substitution and strength of magnetic coupling is essential to the development of high-temperature molecule-based magnetic materials. Toward this end, we report the series of tetraoxolene-bridged Fe^II₂ complexes [(Me₃TPyA)₂Fe₂(^RL)]ⁿ⁺ (Me₃TPyA = tris(6-methyl-2-pyridylmethyl)amine; n = 2: ^OMeLH₂ = 3,6-dimethoxy-2,5-dihydroxo-1,4-benzoquinone, ^ClLH₂ = 3,6-dichloro-2,5-dihydroxo-1,4-benzoquinone, Na₂[^NO₂L] = sodium 3,6-dinitro-2,5-dihydroxo-1,4-benzoquinone; n = 4: ^SMe₂L = 3,6-bis(dimethylsulfonium)-2,5-dihydroxo-1,4-benzoquinone diylide) and their one-electron-reduced analogues. Variable-temperature dc magnetic susceptibility data reveal the presence of weak ferromagnetic superexchange between Fe^II centers in the oxidized species, with exchange constants of J = +1.2(2) (R = OMe, Cl) and +0.3(1) (R = NO₂, SMe₂) cm^-1. In contrast, X-ray diffraction, cyclic voltammetry, and Mössbauer spectroscopy establish a ligand-centered radical in the reduced complexes. Magnetic measurements for the radical-bridged species reveal the presence of strong antiferromagnetic metal-radical coupling, with J = -57(10), -60(7), -58(6), and -65(8) cm^-1 for R = OMe, Cl, NO₂, and SMe₂, respectively. The minimal effects of substituents in the 3- and 6-positions of ^RL^x-• on the magnetic coupling strength is understood through electronic structure calculations, which show negligible spin density on the substituents and associated C atoms of the ring. Finally, the radical-bridged complexes are single-molecule magnets, with relaxation barriers of U_eff = 50(1), 41(1), 38(1), and 33(1) cm^-1 for R = OMe, Cl, NO₂, and SMe₂, respectively. Taken together, these results provide the first examination of how bridging ligand substitution influences magnetic coupling in semiquinoid-bridged compounds, and they establish design criteria for the synthesis of semiquinoid-based molecules and materials.

Magnetic Molecular Conductors Based on Bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) and the Tris(chlorocyananilato)ferrate(III) Complex

Electrocrystallization of the bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) organic donor in the presence of the [Fe(ClCNAn)₃]^3- tris(chlorocyananilato)ferrate(III) paramagnetic anion in different stoichiometric ratios and solvent mixtures afforded two different hybrid systems formulated as [BEDT-TTF]₄[Fe(ClCNAn)₃]·3H₂O (1) and [BEDT-TTF]₅[Fe(ClCNAn)₃]₂·2CH₃CN (2) (An = anilato). Compounds 1 and 2 present unusual structures without the typical segregated organic and inorganic layers, where layers of 1 are formed by Λ and Δ enantiomers of the anionic paramagnetic complex together with mixed-valence BEDT-TTF tetramers, while layers of 2 are formed by Λ and Δ enantiomers of the paramagnetic complex together with dicationic BEDT-TTF dimers and monomers. Compounds 1 and 2 show semiconducting behaviors with room-temperature conductivities of ca. 6 × 10^-3 S cm^-1 (ambient pressure) and 1 × 10^-3 S cm^-1 (under applied pressure of 12.1 GPa), respectively, due to strong dimerization between the donors. Magnetic measurements performed on compound 1 indicate weak antiferromagnetic coupling between high-spin Fe^III (S_Fe = 5/2) and mixed-valence radical cation diyads (BEDT-TTF)₂⁺ (S_rad = 1/2) mediated by the anilate ligands, together with an important Pauli paramagnetism typical for conducting systems.

Dysprosium Chlorocyanoanilate-Based 2D-Layered Coordination Polymers

A series of two-dimensional (2D)-layered coordination polymers (CPs) based on the heterosubstituted anilate ligand ClCNAn^2- derived from 3-chloro-6-cyano-2,5-dihydroxybenzoquinone and Dy^III are reported. By changes in the synthetic methods (layering technique, solvothermal or conventional one-pot reactions) and conditions (solvent, concentration, etc.), different types of 2D extended networks could be prepared and structurally characterized. Compounds 1 and 1', two polymorphs with the formula [Dy₂(ClCNAn)₃(DMSO)₆]_n·(H₂O)_x [x = 7 (1), 0 (1')], were prepared by a conventional one-pot reaction and recrystallized at different concentrations. Compound 2, formulated as [Dy₂(ClCNAn)₃(DMF)₆]_n, was prepared by a layering technique, while compound 3, formulated as {(Me₂NH₂)₂[Dy₂(ClCNAn)₄(H₂O)₂]·(DMF)₂·(H₂O)₅}_n, was obtained by a solvothermal method. Compounds 1 and 2 are neutral 2D CPs of the ClCNAn^2- ligand and Dy^III ions, while 3 presents 2D anionic layers of [Dy₂(ClCNAn)₄(H₂O)₂]^2- alternating with cationic layers of Me₂NH₂⁺ ions. These compounds show very diverse networks, with compound 1 forming 2D (8,3) and (4,3) topology with eight- and four-membered rings with square cavities, 1' and 2, respectively, a 2D (6,3) topology with six-membered rings (a rectangular cavity for 1' and a regular hexagonal cavity for 2), and 3 a 2D (4,4) topology with distorted square cavities. In this respect, 1 and 1' represent the first examples of polymorphism in the family of anilate-based CPs. Thermal analysis measurements (differential scanning calorimetry and thermogravimetry) show an exothermic polymorphic transformation from the kinetically stable 1' phase to the thermodynamically stable phase 1. The magnetic behavior of 1-3 very likely indicates depopulation of the m_J levels, while the presence of weak antiferromagnetic coupling between the Dy^III centers mediated by the anilate bridge cannot be excluded.

Two Dimensional Magnetic Coordination Polymers Formed by Lanthanoids and Chlorocyananilato

Here we show the important role played by the size of the lanthanoid and the solvent used in the final structures of several two-dimensional magnetic coordination polymers with the ligand chlorocyananilato, (C6O4(CN)Cl)2−. With this aim we have prepared five compounds: [Nd2(C6O4(CN)Cl)3(DMF)6] (1) (DMF = dimethylformamide), [Dy2(C6O4(CN)Cl)3(DMF)6]·4H2O (2), [Ho2(C6O4(CN)Cl)3(DMF)6]·2H2O (3), and [Ln2(C6O4(CN)Cl)3(DMSO)6] with Ln = Ce (4) and Nd (5) (DMSO = dimethylsulfoxide). These compounds are formed by two dimensional networks with a (6,3)-topology but, depending on the size of the lanthanoid and on the solvent used, show important structural differences, including the size, shape, distortion and content of the cavities as well as the flatness of the layers. The comparison of compounds 1–3 and 4–5 shows the role played by the size of the lanthanoid while keeping constant the solvent, whereas, the comparison of compounds 1 and 5 shows the role of the solvent (DMF vs. DMSO) while keeping constant the lanthanoid. The magnetic properties of all of them show the absence of noticeable magnetic interactions, in agreement with previous results that can be explained by the internal character of the 4f electron and the weak magnetic coupling mediated by these anilato-based ligands.

Thermally Induced Valence Tautomeric Transition in a Two-Dimensional Fe-Tetraoxolene Honeycomb Network

A novel tetraoxolene-bridged Fe two-dimensional honeycomb layered compound, (NPr₄ )₂ [Fe₂ (Cl₂ An)₃ ] ⋅2 (acetone)⋅H₂ O (1), where Cl₂ An^n- =2,5-dichloro-3,6-dihydroxy-1,4-benzoquinonate and NPr₄⁺ =tetrapropylammonium cation, has been synthesized. 1 revealed a thermally induced valence tautomeric transition at T_1/2 =236 K (cooling)/237 K (heating) between Fe^m+ (m=2 or 3) and Cl₂ An^n- (n=2 or 3) that induced valence modulations between [Fe^II_HS Fe^III_HS (Cl₂ An^2- )₂ (Cl₂ An^.3- )]^2- at T>T_1/2 and [Fe^III_HS Fe^III_HS (Cl₂ An^2- )(Cl₂ An^.3- )₂ ]^2- at T<T_1/2 . Even in a two-dimensional network structure, the low-temperature phase [Fe^III_HS Fe^III_HS (Cl₂ An^2- )(Cl₂ An^.3- )₂ ]^2- valence set can be regarded as a magnetic chain-knit network, where ferrimagnetic Δ and Λ chains of [Fe^III_HS (Cl₂ An^.3- )]_∞ are alternately linked by the diamagnetic Cl₂ An^2- . This results in a slow magnetization behavior attributed to the structure acting as a single-chain magnet at lower temperatures.

Testing the limits of halogen bonding in coordination chemistry

To test the limit of halogen bonds fine-tuning of electron density was performedviaintroduction of heteroatoms and metal cations.

Molden 2.0: quantum chemistry meets proteins

Since the first distribution of Molden in 1995 and the publication of the first article about this software in 2000 work on Molden has continued relentlessly. A few of the many improved or fully novel features such as improved and broadened support for quantum chemistry calculations, preparation of ligands for use in drug design related softwares, and working with proteins for the purpose of ligand docking.

Dihydroxybenzoquinone as Linker for the Synthesis of Permanently Porous Aluminum Metal-Organic Frameworks

Two new dihydroxybenzoquinone-based metal-organic frameworks, ((CH3)2NH2)3[Al4(L1)3(L1(•))3]·3DMF (1, denoted CAU-20) and ((CH3)2NH2)3[Al4(L2)3(L2(•))3]·9DMF (2, denoted CAU-20-Cl2), were synthesized at 120 °C in DMF using 2,5-dihydroxy-p-benzoquinone ((C6H2(OH)2(O)2), H2L1) and 2,5-dichloro-3,6-dihydroxy-p-benzoquinone ((C6Cl2(OH)2(O)2), H2L2), respectively. Compared to other Al-MOFs, which contain carboxylate or phosphonate groups that connect the metal sites, in 1 and 2 the Al(3+) are coordinated by oxido groups. The metal ions are octahedrally surrounded by oxygen atoms of the deprotonated linker molecules to generate honeycomb layers with a metal to linker ratio of Al: L1/L2 = 2:3. The layers contain L1(2-) and L2(2-) ions as well as linker radical ions L1(•3-) and L2(•3-) in a molar ratio of 1 to 1. The presence of radical ions was confirmed by EPR and UV-vis-spectroscopic measurements, and the composition was determined from a combination of PXRD, (1)H NMR, TG, and elemental analyses. Charge balance is accomplished through intercalation of (CH3)2NH2(+) ions which are formed by partial hydrolysis of DMF. In the structures of 1 and 2 the eclipsed layers are AA and ABAB stacked, respectively, and one-dimensional hexagonal channels with diameters of ca. 9 and 6 Å are formed. Both compounds exhibit permanent porosity and have specific surface areas of 1440 and 1430 m(2) g(-1), respectively.