Real-Time In Situ Volatile Organic Compound Sensing by a Dual-Emissive Polynuclear Ln-MOF with Pronounced LnIII Luminescence Response.

Lanthanide metal-organic frameworks (Ln-MOFs) are promising for luminescence detection of volatile organic compound (VOC) vapors, but usually suffer from the silent or quenched Ln3+ emission. Herein, we report a new dual-emissive Eu-MOF composed of the coordinatively unsaturated Eu9 clusters that afford abundant open metal sites to form a confined "binding pocket" to facilitate the preconcentration and recognition of VOCs. Single-crystal structural analyses reveal that specific analytes can replace the OH oscillators in the first coordination sphere of Eu3+ and form a unique hydrogen-bonding second-sphere adduct tying adjacent Eu9 clusters together to minimize their nonradiative vibrational decay. With the promoted Eu3+ luminescence, the MOF realizes real-time in situ visual sensing of THF vapor (<1 s) and shows a quantitative ratiometric response to the vapor pressure with a limit of detection down to 17.33 Pa. Also, it represents a top-performing ratiometric luminescent thermometer.

Dynamic Full-Color Tuning of Organic Chromophore in a Multi-Stimuli-Responsive 2D Flexible MOF.

Developing universal stimuli-responsive materials capable of emitting a broad spectrum of colors is highly desirable. Herein, we deliberately grafted a conformation-adaptable organic chromophore into the established coordination space of a flexible metal-organic framework (MOF). In terms of the coupled structural transformations and the space confinement, the chromophore in the MOF matrix underwent well-regulated conformational changes under physical and chemical stimuli, simultaneously displaying thermo-, piezo-, and solvato-fluoro-chromism with color tunability over the visible range. Owing to the resilient nature and the reduced dimensionality of the selected coordination space, all three color modulations behaved in a sensitive and self-reversible manner, each following a linear correlation of the emission maximum with stimulus. Single-crystal X-ray diffraction of the variable-temperature structures and solvent-inclusion crystals elucidated the intricate color varying mechanisms.

Opening Magnetic Hysteresis by Axial Ferromagnetic Coupling: From Mono-Decker to Double-Decker Metallacrown.

Combining Ising-type magnetic anisotropy with collinear magnetic interactions in single-molecule magnets (SMMs) is a significant synthetic challenge. Herein we report a Dy[15-MCCu -5] (1-Dy) SMM, where a DyIII ion is held in a central pseudo-D5h pocket of a rigid and planar Cu5 metallacrown (MC). Linking two Dy[15-MCCu -5] units with a single hydroxide bridge yields the double-decker {Dy[15-MCCu -5]}2 (2-Dy) SMM where the anisotropy axes of the two DyIII ions are nearly collinear, resulting in magnetic relaxation times for 2-Dy that are approximately 200 000 times slower at 2 K than for 1-Dy in zero external field. Whereas 1-Dy and the YIII -diluted Dy@2-Y analogue do not show remanence in magnetic hysteresis experiments, the hysteresis data for 2-Dy remain open up to 6 K without a sudden drop at zero field. In conjunction with theoretical calculations, these results demonstrate that the axial ferromagnetic Dy-Dy coupling suppresses fast quantum tunneling of magnetization (QTM). The relaxation profiles of both complexes curiously exhibit three distinct exponential regimes, and hold the largest effective energy barriers for any reported d-f SMMs up to 625 cm-1 .

A Giant Dy76 Cluster: A Fused Bi-Nanopillar Structural Model for Lanthanide Clusters.

Although great achievements have been made in the synthesis of giant lanthanide clusters, novel structural models are still scarce. Herein, we report a giant lanthanide cluster Dy76 , constructed from [Dy3 (µ3 -OH)4 ] and [Dy5 (µ4 -O)(µ3 -OH)8 ] building blocks. As the largest known Dy cluster, the structure of Dy76 can be seen as arising from the fusion of two Dy48 clusters; these clusters can be isolated under various synthetic conditions and were characterized by single-crystal X-ray diffraction. This new, fused structural model of the pillar motif has not been found in Ln clusters. Furthermore, the successful conversion of Dy76 back into Dy48 in a retrosynthetic manner supports the proposed fusion formation mechanism of Dy76 . Electrospray ionization mass spectrometry (ESI-MS) analysis suggests that the metal cluster skeleton of Dy76 shows good stability in various solvents. This work not only reveals a new structural type of Ln clusters but also provides insight into the novel fusion assembly process.

Slow magnetic relaxation in a {EuCu5} metallacrown.

A 3d-4f heterometallic metallacrown with formula of [EuCu5(quinha)5(sal)2(py)5]CF3SO3·py·3H2O (1) (H2quinha = quinaldichydroxamic acid; Hsal = salicylaldehyde) has been synthesized. This complex shows field-induced slow magnetic relaxation via a Raman-like process, where studies of the isostructural {LuCu5} (2) and {YCu5} (3) complexes show that the slow dynamics mainly arise from the {Cu5} S = 1/2 ground state rather than the EuIII ion. However, the EuIII ion enhances the relaxation rates of the {Cu5} unit which likely arises from second-order effects in the formally diamagnetic 7F0 ground state of EuIII.

Humidity Sensitive Structural Dynamics and Solvatomagnetic Effects in a 3D Co(II)-Based Coordination Polymer.

A chiral Co(II)-based coordination polymer, [Co3(pimda)2(H2O)5] (1, H3pimda = 2-propyl-1H-imidazole-4,5-dicarboxylic acid) with 3D hyperkagomé topology is reported. Upon heating/cooling, the water molecules which are coordinated to a pair of crystallographically symmetric Co(II) ions are removed/recovered discretely in two steps, giving [Co3(pimda)2(H2O)4] (2) and [Co3(pimda)2(H2O)3] (3), which is evidenced by the reversible single-crystal-to-single-crystal (SCSC) structural transformations. As the coordination geometry of the two Co(II) ions changes from octahedron to trigonal bipyramid, obvious color change from pink for 1 to dark violet for 2 and 3 is observed. Further magnetic measurements demonstrate the presence of a solvatomagnetic effect from paramagnets for 1 and 2 to weak ferromagnet for 3. Moreover, as revealed by the variable-temperature crystallographic measurements, the first and second dehydration temperatures could be controlled from 298 K (25 °C) and 383 K (110 °C) sealed in a capillary (high humidity) to 255 K (-18 °C) and 307 K (34 °C) in dry N2 (low humidity), indicating the strong humidity sensitivity of the structural dynamics.

A Piezochromic Dysprosium(III) Single-Molecule Magnet Based on an Aggregation-Induced-Emission-Active Tetraphenylethene Derivative Ligand.

A bifunctional dysprosium(III) dimer, [Dy2(HTPEIPOMe)2(OAc)4(NO3)2] (1), comprising an AIE-active (AIE = aggregation-induced emission) ligand of 2-methoxy-6-[[[4-(1,2,2-triphenylvinyl)phenyl]imino]methyl]phenol (HTPEIPOMe), was successfully synthesized. It not only behaves as a single-molecule magnet (SMM) with an energy barrier of 168(15) K at zero field but also exhibits piezochromism during the pressing-fuming cycle with switchable color, photoluminescence, and magnetic response.

Tunable Magnetization Dynamics through Solid-State Ligand Substitution Reaction.

The dimeric molecule [Dy2(acac)6(MeOH)2(bpe)]·bpe·2MeOH (1, acac = acetylacetonate, bpe = 1,2-bis(4-pyridyl)ethylene) undergoes a solid-state ligand substitution reaction upon heating, leading to the one-dimensional chain [Dy(acac)3(bpe)]n (2). This structural transformation takes advantage of the potential coordination of the guest bpe molecules present in 1. In both complexes the Dy(III) ions adopt similar octacoordinated D4d geometries. However, the different arrangement of the negatively charged and neutral ligands alters the direction of magnetic anisotropy axis and the energy states, thus resulting in largely distinct magnetization dynamics, as revealed by the CASSCF/RASSI calculations.

Dynamic Magnetic and Optical Insight into a High Performance Pentagonal Bipyramidal DyIII Single-Ion Magnet.

The pentagonal bipyramidal single-ion magnets (SIMs) are among the most attractive prototypes of high-performance single-molecule magnets (SMMs). Here, a fluorescence-active phosphine oxide ligand CyPh2 PO (=cyclohexyl(diphenyl)phosphine oxide) was introduced into [Dy(CyPh2 PO)2 (H2 O)5 ]Br3 ⋅2 (CyPh2 PO)⋅EtOH⋅3 H2 O, and combined dynamic magnetic measurement, optical characterization, ab initio calculation, and magneto-optical correlation of this high-performance pseudo-D5h DyIII SIM with large Ueff (508(2) K) and high magnetic hysteresis temperature (19 K) were performed. This work provides a deeper insight into the rational design of promising molecular magnets.

Unprecedented hexagonal bipyramidal single-ion magnets based on metallacrowns.

Two Ln(iii) (Ln = Ce or Nd) complexes based on [15-MC-6] (MC = metallacrown) and phosphine oxide are reported for the first time with the Ln(iii) ion featuring nearly perfect hexagonal bipyramidal LnO8 geometry, with pseudo-D6h symmetry. Magnetic measurements reveal that both behave as single-ion magnets (SIMs), where the slow relaxation is dominated by the Raman mechanism.

Spin-Crossover Phenomenon in a Pentanuclear Iron(II) Cluster Helicate.

The first spin-crossover cluster helicate [{Fe(II)(µ-bpt)3}2Fe(II)3(µ3-O)][Fe(II)2(µ-Cl)(µ-bpt)(NCS)4(H2O)]·2H2O·C2H5OH [Hbpt = 3,5-bis(pyridin-2-yl)-1,2,4-triazole] was reported, in which one spin-crossover unit and one low-spin triple-stranded [Fe(II)(bpt)3](-) unit wrapped a rare planar [Fe(II)3(µ3-O)](4+) core to form a bis(triple-helical) cation with trigonal-bipyramidal topology. The origin of different magnetic behaviors of two [Fe(II)(bpt)3](-) units could be ascribed to their different intermolecular interactions.

Evolution of Slow Magnetic Relaxation: from Diamagnetic Matrix Y(OH)CO3 to Dy(0.06)Y(0.94)(OH)CO3 with High Spin-Reversal Barrier and Blocking Temperature.

A stable Dy(III)-dispersed compound with single-molecule magnet behavior, Dy(0.06)Y(0.94)(OH)CO3, was isolated by a general strategy targeted at the doping of paramagnetic Dy(3+) into a diamagnetic 3D inorganic network of Y(OH)CO3. The single-ion origin of slow magnetic relaxation was gradually released as variations of the dysprosium/yttrium ratio and finally gave a relatively large spin-reversal barrier around 200 K and high hysteresis temperature of 8 K. This study opens up new opportunities to investigate the slow magnetic relaxation and magnetostructural correlation by choosing a suitable inorganic architecture with strong axial anisotropy.

Symmetry-Supported Magnetic Blocking at 20 K in Pentagonal Bipyramidal Dy(III) Single-Ion Magnets.

Single-molecule magnets (SMMs) that can be trapped in one of the bistable magnetic states separated by an energy barrier are among the most promising candidates for high-density information storage, quantum processing, and spintronics. To date, a considerable series of achievements have been made. However, the presence of fast quantum tunnelling of magnetization (QTM) in most SMMs, especially in single-ion magnets (SIMs), provides a rapid relaxation route and often sets up a limit for the relaxation time. Here, we pursue the pentagonal bipyramidal symmetry to suppress the QTM and present pentagonal bipyramidal Dy(III) SIMs [Dy(Cy3PO)2(H2O)5]Cl3·(Cy3PO)·H2O·EtOH (1) and [Dy(Cy3PO)2(H2O)5]Br3·2(Cy3PO)·2H2O·2EtOH (2), (Cy3PO = tricyclohexyl phosphine oxide). Magnetic characterizations reveal their fascinating SMM properties with high energy barriers as 472(7) K for 1 and 543(2) K for 2, along with a record magnetic hysteresis temperature up to 20 K for 2. These results, combined with the ab initio calculations, offer an illuminating insight into the vast possibility and potential of what the symmetry rules can achieve in molecular magnetism.

Magnetocaloric Properties of Heterometallic 3d-Gd Complexes Based on the [Gd(oda)3 ](3-) Metalloligand.

A series of heterometallic 3d-Gd(3+) complexes based on a lanthanide metalloligand, [M(H2 O)6 ][Gd(oda)3 ]⋅3 H2 O [M=Cr(3+) (1-Cr)] (H2 oda=2,2'-oxydiacetic acid), [M(H2 O)6 ][MGd(oda)3 ]2 ⋅3 H2 O [M=Mn(2+) (2-Mn), Fe(2+) (2-Fe) and Co(2+) (2-Co)], and [M3 Gd2 (oda)6 (H2 O)6 ]⋅12 H2 O [M=Ni(2+) (3-Ni), Cu(2+) (3-Cu), and Zn(2+) (3-Zn)], are reported. Magnetic and heat-capacity studies revealed a significant impact on the magnetocaloric effect depending on the anisotropy of the 3d transition metal ions, as confirmed by comparison of the observed maximum values of -ΔSm between complexes 2-Co and 1-Cr. In these two complexes, the 3d metal ions have the same spin (S=3/2 for Co(2+) and Cr(3+) ions), and the theoretical calculation suggested a larger -ΔSm value for 2-Co (47.8 J K(-1) kg(-1) ) than 1-Cr (37.5 J K(-1) kg(-1) ); however, the significant anisotropy of Co(2+) ions in 2-Co, which can result in smaller effective spins, gives a smaller value of -ΔSm for 2-Co (32.2 J K(-1) kg(-1) ) than for 1-Cr (35.4 J K(-1) kg(-1) ) at ΔH=9 T.

"Half-sandwich" Yb(III) single-ion magnets with metallacrowns.

The first "half-sandwich" Yb(III) single-ion magnets (SIMs) based on [12-MCZn(ii)-4] are reported, in which the central ytterbium ion is coordinated by YbO8 geometry in D4d symmetry. The anisotropic barrier is extracted from the analysis of static, dynamic magnetism and emission spectrum offering an insight into the magneto-optical correlation.

Efficient enhancement of magnetic anisotropy by optimizing the ligand-field in a typically tetranuclear dysprosium cluster.

The perturbation to the ligand field around the lanthanide ion may significantly contribute to the magnetic dynamics of single molecule magnets. This can be demonstrated by two typical Dy4 cluster-based single molecular magnets (SMMs), [Dy4X2(µ3-OH)2(µ-OH)2(2,2-bpt)4(H2O)4]X2·2H2O·4EtOH (X = Cl and Br for and , respectively), which were constructed by using 3,5-bis(pyridin-2-yl)-1,2,4-triazole (2,2-bptH) as the polynuclear-chelating ligand. Alternating-current (ac) magnetic susceptibility measurements show that the energy barriers in complexes and were immensely enhanced by comparing with our previous work due to the optimization of the ligand field around Dy(III) ions. Remarkably, their high thermal active barriers at 190 K () and 197 K () under a zero applied external dc magnetic field are also among the highest within the reported tetranuclear lanthanide-based SMMs.

Spin frustration in a family of pillared kagomé layers of high-spin cobalt(II) ions.

Based on the analogous kagomé [Co3 (imda)2 ] layers (imda=imidazole-4,5-dicarboxylate), a family of pillar-layered frameworks with the formula of [Co3 (imda)2 (L)3 ]⋅(L)n ⋅xH2 O (1: L=pyrazine, n=0, x=8; 2: L=4,4'-bipyridine, n=1, x=8; 3: L=1,4-di(pyridin-4-yl)benzene, n=1, x=13; 4: L=4,4'-di(pyridin-4-yl)-1,1'-biphenyl, n=1, x=14) have been successfully synthesized by a hydrothermal/solvothermal method. Single-crystal structural analysis shows a significant increase in the interlayer distances synchronized with the extension of the pillar ligands, namely, 7.092(3) (1), 10.921(6) (2), 14.780(5) (3), and 19.165(4) Š(4). Despite the wrinkled kagomé layers in complexes 2-4, comprehensive magnetic characterizations revealed weakening of interlayer magnetic interactions and an increase in the degree of frustration as the pillar ligand becomes longer from 1 to 4; this leads to characteristic magnetic ground states. For compound 4, which has the longest interlayer distance, the interlayer interaction is so weak that the magnetic properties observed within the range of temperature measured would correspond to the frustrated layer.

Fluorescent single-ion magnets: molecular hybrid (HNEt3)[DyxYb1-x(bpyda)2] (x = 0.135-1).

Four single-phase isostructural mononuclear complexes (HNEt3)[DyxYb1-x(bpyda)2]·3H2O (x = 1 (1), 0 (2), 0.367 (3), 0.135 (4), bpyda = 2,2'-bipyridine-6,6'-dicarboxylate) show characteristics of controllable slow relaxation and photoluminescence. The molecular hybrids 3 and 4 exhibit the Orbach process for the DyIII component and a mixture of direct and Raman processes for the YbIII component. The presence of paramagnetic YbIII enhances the relaxation time of the DyIII component, originating from the suppression of the direct process/QTM. The correlation between photoluminescence, static susceptibilities and dynamic magnetic relaxation in the hybrid species was also analysed by comparing the energy gap between the ground and first excited states to the energy barrier.

Two 3d-4f nanomagnets formed via a two-step in situ reaction of picolinaldehyde.

Two 3d-4f nanomagnets, [Dy(III)2Cu(II)7] (1) and [Gd(III)6Cu(II)12] (2), are synthesized under a two-step in situ reaction of picolinaldehyde. Not only the final adduct (hemiacetal), but also the intermediate (gem-diol) are "visualized" by X-ray single crystal diffraction. The Dy complex behaves as a single-molecule magnet, while the Gd complex exhibits a significant magnetocaloric effect. Theoretical calculations are employed to obtain the orientation of the magnetic moments and the magnetic exchange.