Europium(III) Photoluminescence Governed by d⁸–d¹⁰ Heterometallophilic Interactions in Trimetallic Cyanido-Bridged Coordination Frameworks

We report an efficient pathway toward sensitization of red room temperature EuIII emission by the charge-transfer (CT) states related to d8–d10 heterometallophilic interactions achieved by the simultaneous application of tetracyanidometallates of PtII/PdII and dicyanidometallates of AuI/AgI in the construction of a trimetallic d–d–f assembly. The combination of Eu3+, [MII(CN)4]2– (M = Pt, Pd), and [MI(CN)2]− (M = Au, Ag) ions along with 4,4′-bipyridine N,N′-dioxide (4,4′-bpdo) results in four novel isostructural 2D {[EuIII(4,4′-bpdo)­(H2O)2]­[MII(CN)4]}·[MI(CN)2]·H2O (MII/MI = Pt/Au, 1; Pt/Ag, 2; Pd/Au, 3; Pd/Ag, 4) coordination networks. They are built of hybrid coordination layers, based on cyanido-bridged {EuIII[MII(CN)4]}n square grids coexisting with metal–organic {EuIII(4,4′-bpdo)}n chains, with the further attachment of [MI(CN)2]− ions through metallophilic {MII–MI} interactions. This results in dinuclear {MIIMI} units generating an orange emissive metal-to-metal-to-ligand charge-transfer (MMLCT) state, whose energy is tuned by the applied d8–d10 metal centers. Thanks to these CT states, 1–4 exhibit room temperature red EuIII photoluminescence enhanced by energy transfer from {MIIMI} units, with the additional role of 4,4′-bpdo also transferring the energy to lanthanides. These donor CT states lying in the visible range successfully broaden the available efficient excitation range up to 500 nm. The overall emission quantum yield ranges from 8(1)% for 4 to 15(2)% for 1, with the intermediate values for 2 and 3 relatively high among the reported EuIII-based compounds with tetracyanido- and dicyanidometallates. We found that the sensitization efficiency is equally high for all compounds because of the similar energies of the CT states, while the main differences are related to the observed emission lifetimes ranging from ca. 80 μs for 4 to 120–130 μs for 2 and 3 to ca. 180 μs for 1. This phenomenon was correlated with the energies of the vibrational states, e.g., cyanide stretching vibrations, responsible for nonradiative deactivation of EuIII excited states, which are the highest for the Pd/Ag pair of 4 and the lowest for the Pt/Au pair in 1. Thus, the heaviest pair of PtII/AuI cyanide metal complexes is proven to be the best candidate for the sensitization of room temperature EuIII luminescence

Covalent Modification by Click Mechanochemistry: Systematic Installation of Pendant OH Groups in a MOF for Rigidity Control and Luminescence-Based Water Detection

Covalent linker transformations in metal–organic frameworks (MOFs) enable their functionalization but often suffer from low conversions or require harsh conditions, including heating, corrosive reactants and solvents, or catalysts. In this work, using solvent-free mechanochemistry for the first time for such conversions, we demonstrate the systematic MOF pore modification with pendant hydroxyl groups and the resulting effects on the network rigidity, its luminescent properties, as well as adsorption of CO2 and vapors of methanol, ethanol, isopropanol, D2O, and H2O. A new zinc-based heterolinker MOF (JUK-20) containing both protic luminescent units and reactive tetrazine cores was used as a model and subjected to an inverse electron-demand Diels–Alder (iEDDA) click reaction with a series of dienophiles (x) of different lengths having OH groups. From the obtained series of JUK-20(Zn)-x MOFs, a flexible material capable of luminescent humidity sensing was identified, and the influence of water on the luminescence of the material was explained by analogy with the excited-state intramolecular proton transfer (ESIPT) model. In general, our results provide guidance for designing and tuning MOFs for luminescence-based detection using a stepwise synthetic approach

Tuning of Ratiometric Optical Thermometry in the Family of Magnetic {Nd_1–<i>x</i>^IIIYb^III<i>_x</i>[Cu₂^I(CN)₅]} Frameworks Showing the Large SHG Response

Three-dimensional (3-D) coordination networks provide a stable framework preferable to designing materials with tunable properties by various chemical modifications, such as solvent exchange, element doping, etc. In this work, we explored extensively the 3-D cyanido-bridged heterometallic assemblies having Nd(III) and Yb(III) centers in combination with polycyanidocuprate(I) ions, that is, the family of [Nd1–xIIIYbIIIx(2,2′-bpdo)2(H2O)][Cu2I(CN)5]·5H2O (x = 0, 0.25, 0.5, 0.75, 1 (1–5); 2,2′-bpdo = 2,2′-bipyridine N,N′-dioxide) coordination networks. To form a lanthanide-incorporating molecule-based matrix, two different types of cuprate(I) moieties are spontaneously formed during crystallization, resulting in trigonal planar tricyanido and tetrahedral tetracyanidocopper(I)-based molecular anions. 1–5 exhibit optical thermometry based on near-infrared (NIR) luminescence. The relative thermal sensitivity of Nd(III)-containing 1 is considerably improved through the preparation of the analogous mixed heterometallic compounds by introducing Yb3+ ions, which also enables tunability over the operating temperature range. Since all 3-D networks crystallize within a non-centrosymmetric Cc space group, they exhibit a second-harmonic generation (SHG) phenomenon, with the signal highest among the materials based on cyanido-bridged metal assemblies (the SHG efficiency of ∼120% of the reference potassium dihydrogen phosphate). Furthermore, 1–5 show field-induced single-molecule magnet (SMM) behavior related to lanthanide(3+) ions, with a slow magnetic relaxation occurring via Raman and direct relaxation processes

Tuning of Ratiometric Optical Thermometry in the Family of Magnetic {Nd_1–<i>x</i>^IIIYb^III<i>_x</i>[Cu₂^I(CN)₅]} Frameworks Showing the Large SHG Response

Three-dimensional (3-D) coordination networks provide a stable framework preferable to designing materials with tunable properties by various chemical modifications, such as solvent exchange, element doping, etc. In this work, we explored extensively the 3-D cyanido-bridged heterometallic assemblies having Nd(III) and Yb(III) centers in combination with polycyanidocuprate(I) ions, that is, the family of [Nd1–xIIIYbIIIx(2,2′-bpdo)2(H2O)][Cu2I(CN)5]·5H2O (x = 0, 0.25, 0.5, 0.75, 1 (1–5); 2,2′-bpdo = 2,2′-bipyridine N,N′-dioxide) coordination networks. To form a lanthanide-incorporating molecule-based matrix, two different types of cuprate(I) moieties are spontaneously formed during crystallization, resulting in trigonal planar tricyanido and tetrahedral tetracyanidocopper(I)-based molecular anions. 1–5 exhibit optical thermometry based on near-infrared (NIR) luminescence. The relative thermal sensitivity of Nd(III)-containing 1 is considerably improved through the preparation of the analogous mixed heterometallic compounds by introducing Yb3+ ions, which also enables tunability over the operating temperature range. Since all 3-D networks crystallize within a non-centrosymmetric Cc space group, they exhibit a second-harmonic generation (SHG) phenomenon, with the signal highest among the materials based on cyanido-bridged metal assemblies (the SHG efficiency of ∼120% of the reference potassium dihydrogen phosphate). Furthermore, 1–5 show field-induced single-molecule magnet (SMM) behavior related to lanthanide(3+) ions, with a slow magnetic relaxation occurring via Raman and direct relaxation processes

Tuning of Ratiometric Optical Thermometry in the Family of Magnetic {Nd_1–<i>x</i>^IIIYb^III<i>_x</i>[Cu₂^I(CN)₅]} Frameworks Showing the Large SHG Response

Three-dimensional (3-D) coordination networks provide a stable framework preferable to designing materials with tunable properties by various chemical modifications, such as solvent exchange, element doping, etc. In this work, we explored extensively the 3-D cyanido-bridged heterometallic assemblies having Nd(III) and Yb(III) centers in combination with polycyanidocuprate(I) ions, that is, the family of [Nd1–xIIIYbIIIx(2,2′-bpdo)2(H2O)][Cu2I(CN)5]·5H2O (x = 0, 0.25, 0.5, 0.75, 1 (1–5); 2,2′-bpdo = 2,2′-bipyridine N,N′-dioxide) coordination networks. To form a lanthanide-incorporating molecule-based matrix, two different types of cuprate(I) moieties are spontaneously formed during crystallization, resulting in trigonal planar tricyanido and tetrahedral tetracyanidocopper(I)-based molecular anions. 1–5 exhibit optical thermometry based on near-infrared (NIR) luminescence. The relative thermal sensitivity of Nd(III)-containing 1 is considerably improved through the preparation of the analogous mixed heterometallic compounds by introducing Yb3+ ions, which also enables tunability over the operating temperature range. Since all 3-D networks crystallize within a non-centrosymmetric Cc space group, they exhibit a second-harmonic generation (SHG) phenomenon, with the signal highest among the materials based on cyanido-bridged metal assemblies (the SHG efficiency of ∼120% of the reference potassium dihydrogen phosphate). Furthermore, 1–5 show field-induced single-molecule magnet (SMM) behavior related to lanthanide(3+) ions, with a slow magnetic relaxation occurring via Raman and direct relaxation processes

Dehydration–Hydration Switching of Single-Molecule Magnet Behavior and Visible Photoluminescence in a Cyanido-Bridged Dy^IIICo^III Framework

Microporous magnets compose a class of multifunctional molecule-based materials where desolvation-driven structural transformation leads to the switching of magnetic properties. Herein, we present a special type of microporous magnet where a dehydration–hydration process within a bimetal coordination framework results in the switching of emissive DyIII single-molecule magnets (SMMs). We report a three-dimensional (3-D) cyanido-bridged coordination polymer, {[DyIII(H2O)2]­[CoIII(CN)6]}·2.2H2O (1), and its dehydrated form of {DyIII[CoIII(CN)6]} (2), which was obtained through a reversible single-crystal-to-single-crystal transformation. Both phases are composed of paramagnetic DyIII centers alternately arranged with diamagnetic hexacyanidocobaltates­(III). The hydrated phase contains eight-coordinated [DyIII(μ-NC)6(H2O)2]3– complexes of a square antiprism geometry, while the dehydrated form contains six-coordinated [DyIII(μ-NC)6]3– moieties of a trigonal prism geometry. This change in coordination geometry results in the generation of DyIII single-molecule magnets in 2, whereas slow magnetic relaxation effect is not observed for DyIII sites in 1. The D4d-to-D3h symmetry change of DyIII complexes produces also the shift of photoluminescent color from nearly white to deep yellow thanks to the modulation of emission bands of f–f electronic transitions. A combined approach utilizing dc magnetic data and low-temperature emission spectra confirmed an axial crystal field of trigonal prismatic DyIII complexes in 2, which produces an Orbach type of slow magnetic relaxation. Therefore, we present a unique route to the efficient switching of SMM behavior and photoluminescence of DyIII complexes embedded in a 3-D cyanido-bridged framework

Dehydration–Hydration Switching of Single-Molecule Magnet Behavior and Visible Photoluminescence in a Cyanido-Bridged Dy^IIICo^III Framework

Microporous magnets compose a class of multifunctional molecule-based materials where desolvation-driven structural transformation leads to the switching of magnetic properties. Herein, we present a special type of microporous magnet where a dehydration–hydration process within a bimetal coordination framework results in the switching of emissive DyIII single-molecule magnets (SMMs). We report a three-dimensional (3-D) cyanido-bridged coordination polymer, {[DyIII(H2O)2]­[CoIII(CN)6]}·2.2H2O (1), and its dehydrated form of {DyIII[CoIII(CN)6]} (2), which was obtained through a reversible single-crystal-to-single-crystal transformation. Both phases are composed of paramagnetic DyIII centers alternately arranged with diamagnetic hexacyanidocobaltates­(III). The hydrated phase contains eight-coordinated [DyIII(μ-NC)6(H2O)2]3– complexes of a square antiprism geometry, while the dehydrated form contains six-coordinated [DyIII(μ-NC)6]3– moieties of a trigonal prism geometry. This change in coordination geometry results in the generation of DyIII single-molecule magnets in 2, whereas slow magnetic relaxation effect is not observed for DyIII sites in 1. The D4d-to-D3h symmetry change of DyIII complexes produces also the shift of photoluminescent color from nearly white to deep yellow thanks to the modulation of emission bands of f–f electronic transitions. A combined approach utilizing dc magnetic data and low-temperature emission spectra confirmed an axial crystal field of trigonal prismatic DyIII complexes in 2, which produces an Orbach type of slow magnetic relaxation. Therefore, we present a unique route to the efficient switching of SMM behavior and photoluminescence of DyIII complexes embedded in a 3-D cyanido-bridged framework

Dehydration–Hydration Switching of Single-Molecule Magnet Behavior and Visible Photoluminescence in a Cyanido-Bridged Dy^IIICo^III Framework

Microporous magnets compose a class of multifunctional molecule-based materials where desolvation-driven structural transformation leads to the switching of magnetic properties. Herein, we present a special type of microporous magnet where a dehydration–hydration process within a bimetal coordination framework results in the switching of emissive DyIII single-molecule magnets (SMMs). We report a three-dimensional (3-D) cyanido-bridged coordination polymer, {[DyIII(H2O)2]­[CoIII(CN)6]}·2.2H2O (1), and its dehydrated form of {DyIII[CoIII(CN)6]} (2), which was obtained through a reversible single-crystal-to-single-crystal transformation. Both phases are composed of paramagnetic DyIII centers alternately arranged with diamagnetic hexacyanidocobaltates­(III). The hydrated phase contains eight-coordinated [DyIII(μ-NC)6(H2O)2]3– complexes of a square antiprism geometry, while the dehydrated form contains six-coordinated [DyIII(μ-NC)6]3– moieties of a trigonal prism geometry. This change in coordination geometry results in the generation of DyIII single-molecule magnets in 2, whereas slow magnetic relaxation effect is not observed for DyIII sites in 1. The D4d-to-D3h symmetry change of DyIII complexes produces also the shift of photoluminescent color from nearly white to deep yellow thanks to the modulation of emission bands of f–f electronic transitions. A combined approach utilizing dc magnetic data and low-temperature emission spectra confirmed an axial crystal field of trigonal prismatic DyIII complexes in 2, which produces an Orbach type of slow magnetic relaxation. Therefore, we present a unique route to the efficient switching of SMM behavior and photoluminescence of DyIII complexes embedded in a 3-D cyanido-bridged framework

Dehydration–Hydration Switching of Single-Molecule Magnet Behavior and Visible Photoluminescence in a Cyanido-Bridged Dy^IIICo^III Framework

Microporous magnets compose a class of multifunctional molecule-based materials where desolvation-driven structural transformation leads to the switching of magnetic properties. Herein, we present a special type of microporous magnet where a dehydration–hydration process within a bimetal coordination framework results in the switching of emissive DyIII single-molecule magnets (SMMs). We report a three-dimensional (3-D) cyanido-bridged coordination polymer, {[DyIII(H2O)2]­[CoIII(CN)6]}·2.2H2O (1), and its dehydrated form of {DyIII[CoIII(CN)6]} (2), which was obtained through a reversible single-crystal-to-single-crystal transformation. Both phases are composed of paramagnetic DyIII centers alternately arranged with diamagnetic hexacyanidocobaltates­(III). The hydrated phase contains eight-coordinated [DyIII(μ-NC)6(H2O)2]3– complexes of a square antiprism geometry, while the dehydrated form contains six-coordinated [DyIII(μ-NC)6]3– moieties of a trigonal prism geometry. This change in coordination geometry results in the generation of DyIII single-molecule magnets in 2, whereas slow magnetic relaxation effect is not observed for DyIII sites in 1. The D4d-to-D3h symmetry change of DyIII complexes produces also the shift of photoluminescent color from nearly white to deep yellow thanks to the modulation of emission bands of f–f electronic transitions. A combined approach utilizing dc magnetic data and low-temperature emission spectra confirmed an axial crystal field of trigonal prismatic DyIII complexes in 2, which produces an Orbach type of slow magnetic relaxation. Therefore, we present a unique route to the efficient switching of SMM behavior and photoluminescence of DyIII complexes embedded in a 3-D cyanido-bridged framework

Tuning Crystal Packing and Magnetic Properties in a Series of [Dy₁₂] Metallocubanes Based on Azobenzene Derivatives of Salicylic Acid

A series of four new Dy12 dodecanuclear clusters based on azobenzene derivative ligands of salicylic acid (L1–L4) has been synthesized and characterized in the crystalline phase using X-ray diffraction on single crystal and powder, IR spectroscopy, elemental analysis, and DSC–TGA methods. It was revealed that all obtained clusters exhibit the formation of the similar metallic cluster nodes, as vertex-sharing heterocubanes, obtained from four Dy3+ cations, three bridging hydroxyl groups, and O atoms from the salicylic ligands. The coordination geometry around the Dy(III) centers has been carefully analyzed. Whereas Dy12-L1 and Dy12-L2 with L1 and L2 containing Me and OMe groups in para positions of the phenyl rings, respectively, form similar porous 3D diamond-like molecular networks due to CH−π interactions, for Dy12-L3 with L3 bearing NO2-electron-withdrawing group, the generation of 2D molecular grids assembled by π–π staking is observed, and for Dy12-L4 with L4 bearing phenyl substituent, 3D hexagonal channels have been generated. The complexes Dy12-L1, Dy12-L2, and Dy12-L3 exhibit a zero-field slow magnetic relaxation effect. After UV irradiation of Dy12-L1, a decrease of the magnetic anisotropy energy barrier displaying the possibility of control over magnetic properties by the external stimulus has been observed