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Two new two-dimensional (2D) coordination polymers, [FeII(L)2{PdII(SCN)4}] (L1 = 2-methoxypyrazine, 1; and L2 = (E)-3-(phenyldiazenyl)pyridine, 2), were successfully constructed by using square-planar [Pd(SCN)4]2− building blocks. Complex 1 exhibits complete and one-step spin-crossover (SCO) behavior, while 2 exhibits incomplete and two-step SCO behavior. Further structural insight into this synergy reveals that the flat/flexing [Fe{Pd(SCN)4}]∞ sheets in 1 and 2 are stabilized by interlayered/intralayered supramolecular interactions. [ABSTRACT FROM AUTHOR]

Integrating controllable spin states into single‐molecule magnets (SMMs) enables precise manipulation of magnetic interactions at a molecular level, but remains a synthetic challenge. Herein, we developed a 3d–4f metallacrown (MC) magnet [DyNi5(quinha)5(Clsal)2(py)8](ClO4) ⋅ 4H2O (H2quinha=quinaldichydroxamic acid, HClsal=5‐chlorosalicylaldehyde) wherein a square planar NiII is stabilized by chemical stacking. Thioacetal modification was employed via post‐synthetic ligand substitutions and yielded [DyNi5(quinha)5(Clsaldt)2(py)8](ClO4) ⋅ 3H2O (HClsaldt=4‐chloro‐2‐(1,3‐dithiolan‐2‐yl)phenol). Thanks to the additional ligations of thioacetal onto the NiII site, coordination‐induced spin state switching (CISSS) took place with spin state altering from low‐spin S=0 to high‐spin S=1. The synergy of CISSS effect and magnetic interactions results in distinct energy splitting and magnetic dynamics. Magnetic studies indicate prominent enhancement of reversal barrier from 57 cm−1 to 423 cm−1, along with hysteresis opening and an over 200‐fold increment in coercive field at 2 K. Ab initio calculations provide deeper insights into the exchange models and rationalize the relaxation/tunnelling pathways. These results demonstrate here provide a fire‐new perspective in modulating the magnetization relaxation via the incorporation of controllable spin states and magnetic interactions facilitated by the CISSS approach. [ABSTRACT FROM AUTHOR]

Phase transitions in molecular solids involve synergistic changes in chemical and electronic structures, leading to diversification in physical and chemical properties. Despite the pivotal role of hydrogen bonds (H‐bonds) in many phase‐transition materials, it is rare and challenging to chemically regulate the dynamics and to elucidate the structure‐property relationship. Here, four high‐spin CoII compounds were isolated and systematically investigated by modifying the ligand terminal groups (X=S, Se) and substituents (Y=Cl, Br). S−Cl and Se−Br undergo a reversible structural phase transition near room temperature, triggering the rotation of 15‐crown‐5 guests and the swing between syn‐ and anti‐conformation of NCX− ligands, accompanied by switchable magnetism. Conversely, S−Br and Se−Cl retain stability in ordered and disordered phases, respectively. H‐bonds geometric analysis and ab initio calculations reveal that the electronegativity of X and Y affects the strength of NY‐ap−H⋅⋅⋅X interactions. Entropy‐driven structural phase transitions occur when the H‐bond strength is appropriate; otherwise, the phase stays unchanged if it is too strong or weak. This work highlights a phase transition driven by H‐bond strength complementarity – pairing strong acceptor with weak donor and vice versa, which offers a straightforward and effective approach for designing phase‐transition molecular solids from a chemical perspective. [ABSTRACT FROM AUTHOR]

In this study, we successfully synthesize cationic/neutral/anionic inverse-Hofmann-type spin crossover (SCO) frameworks with 1,1,2,2-tetrakis(4-(pyridine-4-yl)phenyl)-ethene ligand by means of cyanometallic charge engineering strategy. The cationic and neutral frameworks exhibit single-step thermally induced spin transition behaviors, while the SCO capability of anionic framework can be aroused by partial desolvation. This strategy provides a new idea to construct ionic SCO frameworks and extends the toolkit for SCO materials. [ABSTRACT FROM AUTHOR]

Spin crossover (SCO) materials with new architectures will expand and enrich the research in the SCO field. Here, we report two metal–organic frameworks (MOFs) containing tetradentate organic ligands and hexatopic linkers [Ag8X8(CN)6]6− (X=Br and I), which represents the first SCO MOF with clusters as building blocks. The silver halide cluster can be further removed after reacting with lithium tetracyanoquinodimethan (LiTCNQ). Such post‐synthetic modification (PSM) is realized via single‐crystal to single‐crystal (SCSC) transformation from urk to nbo topology. Accordingly, the spin state and fluorescence properties are greatly modified by cluster deconstruction. Therefore, these achievements will provide new ideas for the design of new SCO systems and the development of PSM methods. [ABSTRACT FROM AUTHOR]

In the field of molecular magnetism, the lanthanide–radical (Ln–Rad) method has become one of the most appealing tactics for introducing strong magnetic interactions and has spurred on the booming development of heterospin single-molecule magnets (SMMs). The article is a timely retrospect on the research progress of Ln–Rad heterospin systems and special attention is invested on low dimensional Ln–Rad compounds with SMM behavior, primarily concerning with nitrogen-based radicals, semiquinone and nitroxide radicals. Rational design, molecular structures, magnetic behaviors and magneto-structural correlations are highlighted. Meanwhile, particular attention is focused on the influence of exchange couplings on the dynamic magnetic properties, with the purpose of helping to guide the design of prospective radical-based Ln–SMMs. [ABSTRACT FROM AUTHOR]

By employing cyanoborohydride and isomeric tetrapyridyl benzene ligands, a new three-dimensional (3D) [Fe(3-tpb)(NCBH3)2] (1·2H2O, 3-tpb = 1,2,4,5-tetra(pyridin-3-yl)benzene) and a two-dimensional (2D) [Fe(4-tpb)(NCBH3)2] (2·2-NapSMe and 2·H2O·3DMF, 4-tpb = 1,2,4,5-tetra(pyridin-4-yl)benzene, 2-NapSMe = 2-(methylthio)naphthalene) porous coordination polymer (PCP) were synthesized, and exhibited the diamond (dia) and square lattice (sql) topologies, respectively. Complex 1·2H2O shows gradual and incomplete spin crossover (SCO) behavior because of the rigid framework and larger octahedral distortion. In contrast, abrupt SCO and hysteretic two-step SCO behaviors are observed in 2·2-NapSMe and 2·H2O·3DMF, respectively. This work proves that the modulation of host–guest interactions significantly influences the transition temperatures and SCO characteristics in a flexible PCP. More importantly, diverse multidentate ligands can be used to construct PCPs with novel topologies and tunable SCO properties. [ABSTRACT FROM AUTHOR]

We report herein three air, thermal and solvent stable interlocked triacontanuclear giant nanocages, generated using a node and spacer concept. Interestingly, the crystal structures of the cages are not only nano-dimensional but also exist in the nano-dimension range, which was corroborated with microscopic images. The combination of microscopic and crystallographic data, in effect, led us to a unique advantageous situation of generating nanomaterials with hard-to-come-by structural information at the molecular level. [ABSTRACT FROM AUTHOR]

Herein, we reported two didysprosium single-molecule magnets constructed with {Dy(bbpen)(MeOH)} subunits and a π-conjugated tpb or non-conjugated tpcb bridging ligand. The former exhibits extremely weak luminescence that makes it difficult to simulate its emission spectra. However, the later shows obviously enhanced and well-resolved luminescence, which helps us to gain knowledge about the magneto-optical correlation and the relevant magnetic energy levels. [ABSTRACT FROM AUTHOR]

Two new two-dimensional (2D) coordination polymers, [FeII(L)2{PdII(SCN)4}] (L1 = 3-(9-anthracenyl)-pyridine (1) and L2 = 4-(9-anthracenyl)-pyridine (2)), were constructed by employing square-planar [Pd(SCN)4]2− building blocks. Compound 1 exhibits a complete spin-crossover (SCO) behaviour under normal atmospheric pressure, and represents the first SCO example in a 2D system containing [Pd(SCN)4]2− units. In contrast, compound 2 only shows paramagnetic behaviour at measured temperatures. It is clear that the fine-tuning of the monodentate ligand can modulate the ligand field and packing fashions, which sheds light on developing new SCO materials. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

By employing mixed ligands, a new trinuclear dysprosium complex [Dy3(dbm)3(L)4](ClO4)2·CH2Cl2·2MeOH (1, Hdbm = dibenzoylmethane; HL = 2-methoxy-6-((quinolin-8-ylimino)methyl)phenol) was synthesized by a one-pot reaction. According to structural characterization, all the 8-coordinated Dy(III) sites are well arranged with slightly distorted square antiprism (D4d) geometries. Magnetic measurements reveal that 1 exhibits typical single-molecule magnetic behavior at zero magnetic field and shows rarely open hysteresis loops up to 3 K among open-ring {Dy3} SMMs, where the relaxation time remains very stable under the protection from the Dy–Dy magnetic coupling in the open-ring arrangement of Ising spins. [ABSTRACT FROM AUTHOR]

The first spin-crossover (SCO) complex with an organic–inorganic hybrid perovskite structure (PPN)[Fe{Au(CN)2}3] (1) is reported, which displays three-step SCO behaviour. The light-induced excited spin-state trapping measurement gives T0 = 134 K for a three-dimensional FeL3-type (L = bis-monodentate ligand) SCO complex. Moreover, spin-state dependent fluorescence is observed in 1. [ABSTRACT FROM AUTHOR]

Single-molecule magnets (SMMs) with higher nuclearity provide opportunity for understanding the inherent nature of magnetic dynamics that are not limited to mononuclear SMMs. Herein, centrosymmetric [Dy2(L)2(9-AC)4(MeOH)2]·2CH2Cl2·2H2O (1, where 9-AC = anthracene-9-carboxylate) and equilateral triangular [Dy3(OH)(OMe)(L)3(dbm)3](OH)·3CH2Cl2·7H2O (2, where dbm = dibenzoylmethane anion) were isolated using the Schiff-base ligand 4-(anthracen-9-yl)-2-((quinolin-8-ylimino)methyl)phenol (HL). Static and dynamic magnetic measurements reveal that 1 and 2 display slow magnetic relaxation under zero and applied dc field, respectively. The magnetization relaxation for 1 is dominated by a Raman process due to its non-negligible transverse anisotropy. Complex 2 exhibits field-induced SMM behavior with a reversal barrier of 56 cm−1. By means of ab initio calculations and magnetic measurements, the multiple relaxation regime in 2 was investigated. We suggest that Orbach and Raman mechanisms dominate in the high/low temperature domains, respectively. [ABSTRACT FROM AUTHOR]

The dye molecule 1,2,4,5-tetra(4-pyridyl)benzene (bztpy), a tetradentate ligand, can be an excellent candidate for construction of coordination polymers with photoluminescence properties. Here, based on Ag(I) and bztpy, three novel complexes, namely [Ag2(bza)2(μ4-bztpy)] (1), [Ag2(μ-ipa)(μ4-bztpy)]·EtOH·3H2O (2) and [Ag3(pda)(μ-pda)1/2(μ4-bztpy)2]·3EtOH·6H2O (3) (Hbza = benzoic acid, H2ipa = isophthalic acid and H2pda = 2,4-pyridinedicarboxylic acid), have been synthesized with the assistance of auxiliary carboxylates. The choice of carboxylates was found to have a pronounced effect on the framework topology. Structural analysis revealed that there are [Ag2(bztpy)]∞ chains as basic side groups and the change of interconnected auxiliary ligands from Hbza to H2pda leads to the formation of 1D, 2D and 3D structures, respectively. They were further characterized by elemental analysis, IR, single-crystal X-ray diffraction and luminescence study. [ABSTRACT FROM AUTHOR]

Herein we report a stable and high-performance Dy(III) single-ion magnet (SIM) showing an energy barrier of 944 K under zero dc field, with an open hysteresis loop up to 6 K. To the best of our knowledge, this is the highest energy barrier for a square antiprism as well as phosphine oxide based Dy-SIMs, reported so far. [ABSTRACT FROM AUTHOR]

A wheel-shaped Dy(iii) single-molecule magnet (SMM), supported by polyoxotungstates, Cs15K8Na12[K⊂{(AsW9O33)Dy(H2O)2}6]·71H2O (1), is described here. The polyanion of 1 possesses an idealized S6 symmetry. The effective energy barrier (68 K) obtained from magnetic studies is consistent with the deconvolution of the luminescence spectra of 1. [ABSTRACT FROM AUTHOR]

Materials with hysteretic multi-step spin-crossover (SCO) have potential application in high-order data storage. Here, an unprecedented hysteretic four-step SCO behavior with the sequence of LS↔HS0.25LS0.75↔HS0.5LS0.5↔ HS0.75LS0.25↔HS is found in a three-dimensional (3D) Hofmann-type metal-organic framework (MOF), which is evidenced by magnetic, differential scanning calorimetry, and crystal data. Further experiments involving guest exchange leads to the first reversible modulation of four-, two-, and one-stepped SCO behaviors, which provides a new strategy for developing multi-step SCO materials. [ABSTRACT FROM AUTHOR]

An unprecedented two-step spin-crossover behavior with the sequence of γHS=1↔ γHS=3/4↔ γHS=1/4 was observed in two-dimensional Hofmann type coordination polymer [Fe(isoq)2{Ag(CN)2}2] (isoq=isoquinoline), which resulted from three crystallographically inequivalent FeII sites with distinct transition temperatures. [ABSTRACT FROM AUTHOR]

Cluster-based spin crossover (SCO) frameworks are a new class of smart metal-organic frameworks (MOFs) with diverse structures and topologies and unique bistable physicochemical properties. Here, we report a cluster-based SCO framework [Fe3{Ag4(CN)6(H2O)}2(TPBA)3](ClO4)2·7DMF (1) with an extremely rare 3,4,6-T108 topology, in which the tripodal [Ag{Ag(CN)2}3(H2O)]2- clusters axially link the Fe2+ ions to form 2D→3D n-fold Borromean entangled networks. Under the guidance of reticular chemistry, the post-synthetic modification (PSM) from 1 with 3,4,6-T108 topology to [Fe3{Ag8X8(CN)6}(TPBA)3] (2_X, X = Cl, Br, I) with urk topology is firstly achieved via single-crystal to single-crystal (SCSC) transformation. Moreover, the successive SCSC transformations from 2_Cl to 2_Br and then to 2_I are realized for the first time. Their SCO behaviors are also modified by halogen-driven stepwise cluster transformations. Hence, these findings provide new strategies for the development of cluster-based SCO MOFs towards the smart functional porous materials., (© 2024 Wiley‐VCH GmbH.)

Two new two-dimensional (2D) coordination polymers, [Fe II (L) 2 {Pd II (SCN) 4 }] (L 1 = 2-methoxypyrazine, 1; and L 2 = ( E )-3-(phenyldiazenyl)pyridine, 2), were successfully constructed by using square-planar [Pd(SCN) 4 ] 2- building blocks. Complex 1 exhibits complete and one-step spin-crossover (SCO) behavior, while 2 exhibits incomplete and two-step SCO behavior. Further structural insight into this synergy reveals that the flat/flexing [Fe{Pd(SCN) 4 }] ∞ sheets in 1 and 2 are stabilized by interlayered/intralayered supramolecular interactions.

Phase transitions in molecular solids involve synergistic changes in chemical and electronic structures, leading to diversification in physical and chemical properties. Despite the pivotal role of hydrogen bonds (H-bonds) in many phase-transition materials, it is rare and challenging to chemically regulate the dynamics and to elucidate the structure-property relationship. Here, four high-spin Co II compounds were isolated and systematically investigated by modifying the ligand terminal groups (X=S, Se) and substituents (Y=Cl, Br). S-Cl and Se-Br undergo a reversible structural phase transition near room temperature, triggering the rotation of 15-crown-5 guests and the swing between syn- and anti-conformation of NCX - ligands, accompanied by switchable magnetism. Conversely, S-Br and Se-Cl retain stability in ordered and disordered phases, respectively. H-bonds geometric analysis and ab initio calculations reveal that the electronegativity of X and Y affects the strength of N Y-ap -H⋅⋅⋅X interactions. Entropy-driven structural phase transitions occur when the H-bond strength is appropriate; otherwise, the phase stays unchanged if it is too strong or weak. This work highlights a phase transition driven by H-bond strength complementarity - pairing strong acceptor with weak donor and vice versa, which offers a straightforward and effective approach for designing phase-transition molecular solids from a chemical perspective., (© 2024 Wiley-VCH GmbH.)

A series of two-dimensional (2D) spin-crossover coordination polymers (SCO-CPs) [Fe II (TPE)(NCX) 2 ]·solv (1: X = BH 3 , solv = H 2 O·2CH 3 OH·DMF; 2: X = Se, solv = H 2 O·2CH 3 OH·0.5DMF; 3: X = S, solv = H 2 O·2CH 3 OH·0.5DMF) were synthesized by employing 1,1,2,2-tetra(pyridin-4-yl)ethene (TPE) and pseudohalide (NCX - ) coligands. Magnetic measurements indicated that complexes 1-3 exhibited SCO behaviors with diminishing thermal hysteresis (7/4/0 K) upon decreasing the ligand-field strength. The critical temperatures ( T c ) during spin transition were found to be inversely proportional to the coordination ability parameters ( a ™) with a linear correlation. The guest effect was also investigated in the solvent-exchanged phases 1-SE/2-SE/3-SE wherein the DMF molecules were replaced by methanol molecules. Compared with 1-3, 1-SE/2-SE/3-SE displayed more abrupt and complete single-step SCO behaviors but narrower thermal hysteretic loops. The results reported here demonstrate that the T c values of these two families were dominated by the ligand-field strength of the NCX - anions (NCBH 3 > NCSe > NCS), whereas the guest effect only modulated the kinetic factor of the SCO nature in this system.

High-nuclear lanthanide clusters have shown great potential for the administration of high-dose mononuclear gadolinium chelates in magnetic resonance imaging (MRI). The development of high-nuclear lanthanide clusters with excellent solubility and high stability in water or solution has been challenging and is very important for expanding the performance of MRI. We used N -methylbenzimidazole-2-methanol (HL) and LnCl 3 ·6H 2 O to synthesize two spherical lanthanide clusters, Ln 32 (Ln = Ho, Ho 32 ; and Ln = Gd, Gd 32 ), which are highly stable in solution. The 24 ligands L - are all distributed on the periphery of Ln 32 and tightly wrap the cluster core, ensuring that the cluster is stable. Notably, Ho 32 can remain highly stable when bombarded with different ion source energies in HRESI-MS or immersed in an aqueous solution of different pH values for 24 h. The possible formation mechanism of Ho 32 was proposed to be Ho(III), (L) - and H 2 O → Ho 3 (L) 3 /Ho 3 (L) 4 → Ho 4 (L) 4 /Ho 4 (L) 5 → Ho 6 (L) 6 /Ho 6 (L) 7 → Ho 16 (L) 19 → Ho 28 (L) 15 → Ho 32 (L) 24 /Ho 32 (L) 21 /Ho 32 (L) 23 . To the best of our knowledge, this is the first study of the assembly mechanism of spherical high-nuclear lanthanide clusters. Spherical cluster Gd 32 , a form of highly aggregated Gd(III), exhibits a high longitudinal relaxation rate (1 T, r 1 = 265.87 mM -1 ·s -1 ). More notably, compared with the clinically used commercial material Gd-DTPA, Gd 32 has a clearer and higher-contrast T 1 -weighted MRI effect in mice bearing 4T1 tumors. This is the first time that high-nuclear lanthanide clusters with high water stability have been utilized for MRI. High-nuclear Gd clusters containing highly aggregated Gd(III) at the molecular level have higher imaging contrast than traditional Gd chelates; thus, using large doses of traditional gadolinium contrast agents can be avoided., (© The Author(s) 2023. Published by Oxford University Press on behalf of China Science Publishing & Media Ltd.)

Metal-organic frameworks (MOFs) provide versatile platforms to construct multi-responsive materials. Herein, by introducing the neutral tetradentate ligand and the linear dicyanoaurate(I) anion, we reported a rare cationic MOF [Fe II (TPB){Au I (CN) 2 }]I·4H 2 O·4DMF (TPB = 1,2,4,5-tetra(pyridin-4-yl)benzene) with hysteretic spin-crossover (SCO) behavior near room temperature. This hybrid framework with an open metal site (Au I ) exhibits redox-programmable capability toward dihalogen molecules. By means of post-synthetic modification, all the linear [Au I (CN) 2 ] - linkers can be oxidized to square planar [Au III (CN) 2 X 2 ] - units, which results in the hysteretic SCO behaviors switching from one-step to two-step for Br 2 and three-step for I 2 . More importantly, the stepwise SCO behaviors can go back to one-step via the reduction by l-ascorbic acid (AA). Periodic DFT calculations using various SCAN-type exchange-correlation functionals have been employed to rationalize the experimental data. Hence, these results demonstrate for the first time that switchable one-/two-/three-stepped SCO dynamics can be manipulated by chemical redox reactions, which opens a new perspective for multi-responsive molecular switches.

Herein, we reported two didysprosium single-molecule magnets constructed with {Dy(bbpen)(MeOH)} subunits and a π-conjugated tpb or non-conjugated tpcb bridging ligand. The former exhibits extremely weak luminescence that makes it difficult to simulate its emission spectra. However, the later shows obviously enhanced and well-resolved luminescence, which helps us to gain knowledge about the magneto-optical correlation and the relevant magnetic energy levels.

Two new two-dimensional (2D) coordination polymers, [Fe II (L) 2 {Pd II (SCN) 4 }] (L 1 = 3-(9-anthracenyl)-pyridine (1) and L 2 = 4-(9-anthracenyl)-pyridine (2)), were constructed by employing square-planar [Pd(SCN) 4 ] 2- building blocks. Compound 1 exhibits a complete spin-crossover (SCO) behaviour under normal atmospheric pressure, and represents the first SCO example in a 2D system containing [Pd(SCN) 4 ] 2- units. In contrast, compound 2 only shows paramagnetic behaviour at measured temperatures. It is clear that the fine-tuning of the monodentate ligand can modulate the ligand field and packing fashions, which sheds light on developing new SCO materials.

The combination of magnetic interaction with high magnetic anisotropy provides a promising way for modulating/fine-tuning molecular magnetic behaviors. Here, we show the building block approach for the synthesis of a family of dilanthanide single-molecule magnets (SMMs) bridged with a cyanometallate starting from a monolanthanide SMM. Contingent on the central para-/diamagnetic [M(CN) 6 ] 3- (M = Fe, Co) integrated between two highly anisotropic pentagonal-bipyramid Dy(III) subunits, the remanence of magnetization is OFF/ON below 15 K and they respectively display a record reversal barrier of 659 K among d-f SMMs and 975 K among cyano-bridged SMMs.

Two structurally intriguing dysprosium(III)-substituted polyoxometalates, [Dy 6 (ampH) 4 (H 2 O) 23 (ampH 2 )(PW 11 O 39 ) 2 ] (1) and [Dy 9 (CO 3 ) 3 (ampH) 2 (H 2 O) 12 (PW 10 O 37 ) 6 ] 35- (2), are assembled by the same precursor under different pH conditions. The structure of 1 contains an octahedral {Dy 6 (ampH) 4 } core, and a unique windmill-type {Dy 9 (CO 3 ) 3 (ampH) 2 } for 2. Single-molecule magnet behavior is observed for 2 with a thermally activated energy barrier of 56 K and no appreciable quantum tunneling of magnetization under zero field.