54 K Spin Transition Temperature Shift in a Fe6L4 Octahedral Cage Induced by Optimal Fitted Multiple Guests.

Spin-crossover (SCO) coordination cages are at the forefront of research for their potential in crafting next-generation molecular devices. However, due to the scarcity of SCO hosts and their own limited cavities, the interplay between the SCO host and the multiple guests binding has remained elusive. In this contribution, we present a family of pseudo-octahedral coordination cages (M6L4, M = ZnII, CoII, FeII, and NiII) assembled from a tritopic tridentate ligand L with metal ions. The utilization of FeII ion leads to the successful creation of the Fe6L4-type SCO cage. Host-guest studies of these M6L4 cages reveal their capacity to encapsulate four adamantine-based guests. Notably, the spin transition temperature T1/2 of Fe6L4 is dependent on the multiple guests encapsulated. The inclusion of adamantine yields an unprecedented T1/2 shift of 54 K, a record shift in guest-mediated SCO coordination cages to date. This drastic shift is ascribed to the synergistic effect of multiple guests coupled with their optimal fit within the host. Through a straightforward thermodynamic cycle, the binding affinities of the high-spin (HS) and low-spin (LS) states are separated from their apparent binding constant. This result indicates that the LS state has a stronger binding affinity for the multiple guests than the HS state. Exploring the SCO thermodynamics of host-guest complexes allows us to examine the optimal fit of multiple guests to the host cavity. This study reveals that the T1/2 of the SCO host can be manipulated by the encapsulation of multiple guests, and the SCO cage is an ideal candidate for determining the multiple guest fit.

Coordination-Directed Self-Assembly of Functional Polynuclear Lanthanide Supramolecular Architectures.

Lanthanide supramolecular chemistry is a fast growing and intriguing research field due to the unique photophysical, magnetic, and coordination properties of lanthanide ions (LnIII). Compared with the intensively investigated mononuclear Ln-complexes, polymetallic lanthanide supramolecular assemblies offer more structural superiority and functional advantages. In recent decades, significant progress has been made in polynuclear lanthanide supramolecules, varying from structural evolution to luminescent and magnetic functional materials. This review summarizes the design principles in ligand-induced coordination-driven self-assembly of polynuclear Ln-structures and intends to offer guidance for the construction of more elegant Ln-based architectures and optimization of their functional performances. Design principles concerning the water solubility and chirality of the lanthanide-organic assemblies that are vital in extending their applications are emphasized. The strategies for improving the luminescent properties and the applications in up-conversion, host-guest chemistry, luminescent sensing, and catalysis have been summarized. Magnetic materials based on supramolecular assembled lanthanide architectures are given in an individual section and are classified based on their structural features. Challenges remaining and perspective directions in this field are also briefly discussed.

Combinatorial Coordination Self-Assembly for Organopalladium Cages with Fine-Tuned Structure and Function.

Discrete organopalladium coordination cages have shown great potential in applications ranging from molecular recognition and sensing, drug delivery to enzymatic catalysis. While many of the known organopalladium cages are homoleptic structures with regular polyhedral shapes and symmetric inner cavities, heteroleptic cages with complex architectures and new functions coming from their anisotropic cavities have received an increasing attention recently. In this concept article, we discuss a powerful combinatorial coordination self-assembly strategy toward the construction of a family of organopalladium cages, including both homoleptic and heteroleptic ones, from a given library of ligands. Within such a cage family, the heteroleptic cages often feature systematically fine-tuned structures and emergent properties, distinct from their parent homoleptic counterparts. We hope the concepts and examples provided in this article can offer some rational guidance for the design of new coordination cages toward advanced functions.

A Stable 3d-4f Heterometallic Cluster with Magneto-Optical Activity.

A stable 3d-4f heterometallic cluster, namely, {Dy4Ni5L10(NO3)4(CO3)4(CH3OH)2}·CH3CN (Dy4Ni5, HL = 8-hydroxyquinoline), has been solvothermally synthesized and structurally characterized. The compound exhibits an interesting structure in which a tetrahedron based on 4f ions interpenetrates with a square pyramid based on 3d ions. Besides, a unique intermolecular interaction was found in Dy4Ni5, giving rise to its high stability not only when it is in the solid state but also when it dissolves in organic solvents. In addition, the magnetic behavior of solid Dy4Ni5 and the magneto-optical activity of the Dy4Ni5 solution were also studied.

Controlled Self-Assembly and Multistimuli-Responsive Interconversions of Three Conjoined Twin-Cages.

Stimuli-responsive structural transformations between discrete coordination supramolecular architectures not only are essential to construct smart functional materials but also provide a versatile molecular-level platform to mimic the biological transformation process. We report here the controlled self-assembly of three topologically unprecedented conjoined twin-cages, i.e., one stapled interlocked Pd12L6 cage (2) and two helically isomeric Pd6L3 cages (3 and 4) made from the same cis-blocked palladium corners and a new bis-bidentate ligand (1). While cage 2 features three mechanically coupled cavities, cages 3 and 4 are topologically isomeric helicate-based twin-cages based on the same metal/ligand stoichiometry. Sole formation of cage 2 or a dynamic mixture of cages 3 and 4 can be controlled by changing the solvents employed during the self-assembly. Structural conversions between cages 3 and 4 can be triggered by changes in both temperature/solvent and induced-fit guest encapsulations. Well-controlled interconversion between such topologically complex superstructures may lay a solid foundation for achieving a variety of functions within a switchable system.

Coordination-Assembled Molecular Cages with Metal Cluster Nodes.

Molecular cages have attracted great attention because of their fascinating topological structures and well-defined functional cavities. These discrete cages were usually fabricated by coordination assembly approach, a process employing directional metal-ligand coordination bonds due to the nature of the divinable coordination geometry and the required lability to encode dynamic equilibrium/error-correction. Compared to these coordination molecular cages with mononulcear metal-nodes, an increasing number of molecular cages featuring dinuclear and then polynuclear metal-cluster nodes have been synthesized. These metal-cluster-based coordination cages (MCCCs) combine the merits of both metal clusters and the cage structure, and exhibit excellent performances in catalysis, separation, host-guest chemistry and so on. In this review, we highlight the syntheses of MCCCs and their potential functions that is donated by the metal-cluster nodes.

A highly hydrolytically stable lanthanide organic framework as a sensitive luminescent probe for DBP and chlorpyrifos detection.

Organic pollutants have attracted increasing attention due to their strong persistence and extensive diffusivity. Plasticizers (PAEs) and organophosphorus pesticides (OPs), as the vital part of organic pollutants, have made extensive damage to the environment with the rapid development of modern agriculture and industry. Therefore, we have, for the first time, carried out a quantitative analysis of the PAEs and OPs by fluorescence recognition. A series of isostructural lanthanide organic frameworks, [Ln(tftpa)1.5(2,2'-bpy)(H2O)] (Ln = Gd 1, Eu 2 and Tb 3, H2tftpa = tetrafluoroterephthalic acid), were hydrothermally synthesized, of which 3 exhibited excellent hydrolytic resistance to both boiling acidic and basic aqueous solutions. Moreover, luminescence investigations show that 3 can be used as a highly sensitive and recyclable luminescence sensor for the detection of DBP (di-n-butyl phthalate) in simulated seawater and chlorpyrifos in ethanol with the detection limits of 2.07 and 0.14 ppb, respectively.

Magnetic Tuning of an Anionic CoII -MOF through Deionization of the Framework: Spin-Canting, Spin-Flop, and Easy-Plane Magnetic Anisotropy.

An anionic CoII -MOF, (Me2 NH2 )[Co3 (Me2 NH)3 (OH)(SDBA)3 ] (1) (H2 SDBA=4,4'-sulfonyldibenzoic acid) consisting of highly symmetric CoII3 (µ3 -OH) triangles exhibits spin-canting, spin-flop, and easy-plane magnetic anisotropy. Measurement on a single crystal shows that the ab plane of 1 is the easy magnetization plane. After structural modification through simultaneous removal of the coordinated dimethylamine (DMA) molecule at the Co center and the ionic groups DMA+ and OH- , the resulting neutral amorphous framework 2 displays an enhanced spin frustration effect. The deionization of 1 does not result in the collapse of the framework, showing the high stability of the backbone structure.

Designed Assembly of Heterometallic Cluster Organic Frameworks Based on Anderson-Type Polyoxometalate Clusters.

A new approach to prepare heterometallic cluster organic frameworks has been developed. The method was employed to link Anderson-type polyoxometalate (POM) clusters and transition-metal clusters by using a designed rigid tris(alkoxo) ligand containing a pyridyl group to form a three-fold interpenetrated anionic diamondoid structure and a 2D anionic layer, respectively. This technique facilitates the integration of the unique inherent properties of Anderson-type POM clusters and cuprous iodide clusters into one cluster organic framework.

Four new Mn(II) inorganic-organic hybrid frameworks with diverse inorganic magnetic chain's sequences: syntheses, structures, magnetic, NLO, and dielectric properties.

Four new inorganic-organic hybrid manganese frameworks, formulated as [Mn(Am-Hip)2]·3H2O (1), [Mn2(ip)2(H2O)]·CH3OH (2), [Mn2(OH-ip)2(DMF)]·DMF (3), and (Me2NH2)[Mn4(sdba)4(Hsdba)(H2O)]·3H2O·2DMF (4) (Am-H2ip = 5-aminoisophthalic acid, H2ip = isophthalic acid, OH-H2ip = 5-hydroxyisophthalic acid, and H2sdba = 4,4'-sulfonyldibenzoic acid), have been prepared by solvothermal reactions of Mn(II) ions with different polycarboxylate acids in the presence of LiNO3 or NH4NO3. Single-crystal X-ray diffraction studies reveal that the frameworks of 1-4 contain diverse Mn(II)-oxygen inorganic magnetic chain's sequences, -J1J1J1J1- for 1, -J1J2J1J2- for 2, -J1J1J2J2- for 3, and -J1J2J3J3- for 4. The sequence in 4 has never been seen for the magnetic chain compounds and is a new type of magnetic alternating sequence. Magnetic investigations indicate that these compounds all show weak antiferromagnetic couplings between the adjacent Mn(II) ions. Magnetostructural analyses based on the data of 1-4 and other related Mn(II) chain compounds imply that the magnitude of the magnetic coupling has some relationship with the Mn-O-Mn angle of the µ2-O bridge and the average Mn-O-C-O torsion angle of the carboxylate bridges. Compounds 2 and 4 crystallize in chiral and acentric space groups, and they both exhibit powder second harmonic generation (SHG) efficiencies approximately 0.6 and 0.9 times, respectively, that of the standard potassium dihydrogen phosphate (KDP) powder. In addition, the dielectric properties of 2 and 4 were also investigated.

Self-Assembly of Triple-Stranded Lanthanide Molecular Quasi-Lantern Containing 2,2'-Bipyridine Receptor: Luminescence Sensing and Magnetic Property.

Ln2L3-type supramolecular architectures have received significant attention recently due to their unique magnetism and optical properties. Herein, we report the triple-stranded Ln2L3-type lanthanide molecular quasi-lanterns, which are fabricated by the deprotonation self-assembly of a linear ligand featuring a ß-diketone chelating claw and 2,2'-bipyridine (bpy) moiety with lanthanide ions (Ln = Eu3+ and Dy3+). The crystal structure analysis indicates that Eu3+ and Dy3+ ions are all coordinated by eight oxygen donors but in different coordination geometries. The eight oxygen donors in Eu2L3 and Dy2L3 are arranged in a square antiprism and triangular dodecahedron geometry, respectively. Taking into account the fact that the bpy moiety has a strong coordination affinity for transition metal ions, luminescence sensing toward Cu2+ ions has been demonstrated with Eu2L3, bearing a detection of limit as low as 2.84 ppb. The luminescence sensing behavior of Eu2L3 is ascribed to the formation host-guest complex between Eu2L3 and Cu2+ ions with a 1:2 binding ratio. Dynamic AC susceptibility measurements for Dy2L3 reveal the relaxation of magnetization in it. This work provides a potential way for design and fabrication of lanthanide-based molecular materials with functions endowed by the ligands.

Hierarchical subcomponent self-assembly of covalent triple-stranded complexes with 3d-4f vertices: luminescence and magnetic properties.

Well-defined 3d-4f heterometallic supramolecular architectures have attracted attention because of their applications in the field of luminescence and magnetism. However, covalent metallo-supramolecular discrete complexes, decorated with hetero-metallic vertices, have never been reported because of the difficulties in design and control. Herein, we report a series of covalent metallo-supramolecular discrete complexes with 3d-4f vertices synthesized by hierarchical subcomponent self-assembly of tris(2-aminoethyl)amine, 2,6-diformyl-p-cresol, and lanthanide ions (Ln) with different amines and transition metal ions. The programmable self-assembly process results in the formation of triple-stranded hetero-metallic covalent organic discrete complexes, namely 3a-3c-(Ln, Zn) (Ln = SmIII, EuIII, DyIII, YbIII and LuIII) and 3a'-(Dy, Co), which are characterized by nuclear magnetic resonance (NMR) analysis, electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS), and single-crystal X-ray analysis. Photophysical investigations disclose that the organic skeleton of 3a-(Ln, Zn) exhibits an excellent sensitizing ability toward SmIII, EuIII, and YbIII ions, displaying characteristic luminescence emission in both the visible and near-infrared (NIR) regions. AC susceptibility measurements of 3a'-(Dy, Co) reveal the frequency-independent performance under zero dc field, suggesting the absence of slow relaxation of magnetization. This work offers a new approach for the fabrication of discrete metallic covalent architectures with 3d-4f vertices.

Cation modulated spin state and near room temperature transition within a family of compounds containing the same [FeL2]2- center.

Spin-crossover (SCO) active compounds have received much attention due to their potential application in molecular devices. Herein, a family of solvent-free FeII compounds, formulated as (A)2[FeL2], (H2L = pyridine-2,6-bi-tetrazolate, A = (Me)4N+1, Et2NH2+2, iPr2NH2+3 and iPrNH3+4), were synthesized and characterized. Single-crystal X-ray diffraction studies reveal that 1-4 are all supramolecular frameworks containing the same [FeL2]2- center, which is arranged into two packing modes via inter-molecular interactions, that is, a 3D architecture in 1 and 1D chain in 2-4. The spin states of 1-4 at different temperatures are assigned on the basis of the single-crystal X-ray diffraction data. Solid state magnetic investigations indicate that 1 and 4 exhibit a low spin state (below 350 K) and high spin state (2-400 K), respectively. 2 and 3 display clear SCO behavior in the measured temperature, but with different profiles and critical temperatures. 2 undergoes a complete gradual SCO with a critical temperature of T1/2 = 260 K. 3 has an abrupt near room temperature transition between T1/2 cooling = 278 K and T1/2 warming = 286, centered at 282 K (9 °C). This study reveals the importance of organic cations in the modulation of SCO behavior and offers a new insight for the design of SCO compounds with near room temperature spin transitions.

3d-4f Heterometallic cluster incorporated polyoxoniobates with magnetic properties.

A series of 3d-4f heterometallic cluster incorporated polyoxoniobates (PONbs) with different magnetic properties were first made and characterized. This work not only provides a promising strategy to make new heterometallic cluster incorporated PONbs but also demonstrates an ideal model to probe how transition-metal ions influence the magnetic property of PONbs.

A new approach to fabricate the Mn(ii)-based magnetic refrigerant through incorporation of a diamagnetic {LiO4} spacer.

A new 3D MOF [MnLi2(ip)2(H2O)2] (1) with a 1D heterometallic inorganic Mn(ii)-Li(i) chain is reported. With the assistance of diamagnetic {LiO4} connectors, which separate the paramagnetic Mn(ii) ions and act as magnetic spacers, very weak magnetic interactions were obtained. Remarkably, 1 showed a significant magnetocaloric effect (MCE) with a large entropy change value of 30.4 J kg-1 K-1 for ΔH = 8 T at 2 K.

An unprecedented pentanary chalcohalide with Mn atoms in two chemical environments: unique bonding characteristics and magnetic properties.

Mixed-anion chalcohalides have attracted significant attention lately, attributable to their unique structure compositions and captivating physicochemical properties. Herein, an unprecedented pentanary chalcohalide, Cs2[Mn2Ga3S7Cl] (1), was discovered by solid-state reaction at 1223 K. It is constructed by alternately stacked layers, each of which is made by a 2D [Ga3S9]9- ribbon embedded with 1D [Mn2S8Cl]13- chains. The coexistence of two Mn-coordinated polyhedra ([MnS6] octahedra and hetero-ligand [MnS3Cl] tetrahedra) in one material is surprisingly observed for the first time in the Mn-containing inorganic chalcogenides or chalcohalides. More interestingly, it exhibits ferrimagnetic (FIM) behaviour, which could be correlated to the magnetic sub-lattice sites with different coordination geometries. This work suggests a new route for designing and searching for unique functional chalcohalides with different chemical environments.

A novel alb metalloring organic framework with a {Ni12Gd24} cage exhibiting a significant magnetocaloric effect.

With the aid of a bifunctional 6-mercaptonicotinic acid ligand, a novel {Ni12Gd24} cage-based (6, 12)-c alb-MROF that is assembled from a {Gd4(OH)4(COO)6} trigonal-prism building unit and a {Ni6S12} hexagonal-prism molecular building block has been synthesized for the first time. It exhibits a large MCE value of 29.86 J kg-1 K-1 for ΔH = 8 T at 2 K.

[Pb3Cu2I10(phen)4]n: a novel organic-inorganic hybrid ferromagnetic semiconductor.

An iodoplumbate-based organic-inorganic hybrid ferromagnetic semiconductor, [Pb3Cu2I10(phen)4]n, has been solvothermally synthesized. The ferromagnetic exchange interaction is resulting from the multiple aromatic π-π stacking interactions between the adjacent phen molecules.

Chiral template induced homochiral MOFs built from achiral components: SHG enhancement and enantioselective sensing of chiral alkamines by ion-exchange.

A pair of chiral template induced anionic homochiral frameworks constructed from achiral components has been synthesized. Ion-exchange of counter cations with polar or chiral organic cations enhances the SHG efficiency of the frameworks. The enantioselective sensing of chiral alkamines can be achieved by the SHG response.

An unusual chiral 3D inorganic connectivity featuring a {Pb18} wheel: rapid and highly selective and sensitive sensing of Co(II).

A pair of enantiomorphic frameworks featuring rare chiral 3D inorganic connectivity and a {Pb18} wheel, has been obtained via spontaneous resolution. They exhibit rapid and highly selective and sensitive sensing of Co(2+) ions.